Early guenon from the late Miocene Baynunah Formation,Abu Dhabi,with implications for cercopithecoid biogeography and evolution

A newly discovered fossil monkey (AUH 1321) from the Baynunah Formation, Emirate of Abu Dhabi, United Arab Emirates, is important in a number of distinct ways. At ∼6.5–8.0 Ma, it represents the earliest known member of the primate subfamily Cercopithecinae found outside of Africa, and it may also be the earliest cercopithecine in the fossil record. In addition, the fossil appears to represent the earliest member of the cercopithecine tribe Cercopithecini (guenons) to be found anywhere, adding between 2 and 3.5 million y (∼50–70%) to the previous first-appearance datum of the crown guenon clade. It is the only guenon—fossil or extant—known outside the continent of Africa, and it is only the second fossil monkey specimen so far found in the whole of Arabia. This discovery suggests that identifiable crown guenons extend back into the Miocene epoch, thereby refuting hypotheses that they are a recent radiation first appearing in the Pliocene or Pleistocene. Finally, the new monkey is a member of a unique fauna that had dispersed from Africa and southern Asia into Arabia by this time, suggesting that the Arabian Peninsula was a potential filter for cross-continental faunal exchange. Thus, the presence of early cercopithecines on the Arabian Peninsula during the late Miocene reinforces the probability of a cercopithecoid dispersal route out of Africa through southwest Asia before Messinian dispersal routes over the Mediterranean Basin or Straits of Gibraltar.Cercopithecine monkeys (Order Primates, Superfamily Cercopithecoidea, Family Cercopithecidae, Subfamily Cercopithecinae), also known as cheek-pouch monkeys, are the most speciose and widely distributed group of living Old World primates. Recent molecular estimates date the divergence of Cercopithecinae from Colobinae (leaf-eating monkeys) to between 17.6 Ma (range 21.5–13.9 Ma) and 14.5 Ma (range 16.2–12.8 Ma) and the origin of crown Cercopithecinae to around 11.5 Ma (range 13.9–9.2 Ma) (1, 2). However, the earliest known fossil cercopithecines only appear much later, around 7.4 Ma in the Turkana Basin of East Africa (3, 4).Cercopithecine monkeys are divided into two tribes: Cercopithecini, including African guenons (Allenopithecus, Miopithecus, Chlorocebus, Erythrocebus, Allochrocebus, Cercopithecus), and Papionini, which includes African and Eurasian macaques (Macaca) as well as African papionins (Papio, Lophocebus, Rungwecebus, Theropithecus, Mandrillus, Cercocebus). Of the living cercopithecines, only two genera are known outside of the African continent, both of them papionins: Papio (found on the Arabian Peninsula) and Macaca (found throughout Southern and Southeast Asia, and introduced in Gibraltar). The earliest fossil cercopithecines known outside of Africa are attributed to the genus Macaca and appear to be latest Miocene or early Pliocene in age (∼6.0–5.0 Ma) (Fig. 1) (5–9). Until now, no guenons, extant or extinct, have ever been known outside of the African continent.Open in a separate windowFig. 1.Hypothesized cercopithecoid dispersal routes out of Africa in relation to the known late Miocene fossil record. The oldest cercopithecine, Parapapio lothagamensis (light blue circles), is known from ∼7.4–6.1 Ma in the Turkana Basin and Tugen Hills, Kenya (3, 4, 41). An unnamed fossil papionin (purple circle) is known from the late Miocene of Ongoliba, Congo (5, 57). Macaca spp. (dark blue circles) are located throughout North Africa at sites ranging in age from ∼6.5–5.5 Ma (5, 8, 58, 59), and Macaca spp. first appear in Europe ∼6.0–5.3 Ma and in China in the early Pliocene (5–9). The oldest colobine outside of Africa, Mesopithecus (green circles), is known from a number of late Miocene sites securely dated between ∼8.5 and 5.3 Ma in Greece, Macedonia, Italy, Ukraine, Iran, Afghanistan, possibly Pakistan, and China (46–48). Three dispersal routes for cercopithecoids can be hypothesized: route 1 imagines a dispersal event over the Straits of Gibraltar or Mediterranean Basin into Europe and Asia; route 2 postulates a dispersal event through the Arabian Sinai Peninsula; and route 3 suggests a migration over the Arabian Straits of Bab el Mandeb. The discovery of AUH 1321 and AUH 35 in Abu Dhabi at >6.5–8 Ma (red circle), contemporaneous with the first appearance of Mesopithecus sp. in Eurasia and ∼1–2 million y earlier than the appearance of Macaca spp. in Eurasia, suggests scenarios 2 and 3 were possible before scenario 1. None of these scenarios is mutually exclusive and may have occurred in combination or succession.Three possible routes can be reasonably hypothesized for cercopithecine (and cercopithecoid) dispersal out of Africa and into Europe and Asia during the late Miocene: (i) over the Mediterranean Basin or Straits of Gibraltar to the north/northwest, (ii) across the Arabian Sinai Peninsula to the northeast, or (iii) across the Arabian Straits of Bab el Mandeb to the east (Fig. 1). Fossil Macaca specimens from the terminal Miocene of Spain and Italy have been suggested to provide evidence for the use of a route across the Mediterranean Basin or the Straits of Gibraltar via an ephemeral land bridge either immediately before—or perhaps associated with—the drop in Mediterranean sea levels during the Messinian (∼6.0–5.3 Ma) (8–19). Paleontological evidence for an Arabian route has been lacking, but paleogeographic and paleoenvironmental work on circum-Arabia suggests that the region did not present a persistent ecological barrier to some amount of intercontinental exchange during the late Miocene (20). In fact, an established land connection through Sinai was probably present during this time period, and oceanic spreading is not estimated to have begun in the southern Red Sea until around 5 Ma, with progressive development of open marine conditions throughout the Pliocene. Thus, before 6.5 Ma, a southern route in the region of the Straits of Bab el Mandeb was also possible (Fig. 1) (21).Although Arabia is a large area of the earth, fossil monkeys have so far been represented by only a single specimen, an isolated male lower canine (AUH 35), discovered in 1989 by A.H. and Peter Whybrow in the late Miocene Baynunah Formation, Abu Dhabi, United Arab Emirates (22–25). The specimen came from Jebel Dhanna, site JDH-3 (JD-3 in refs. 24 and 26) (Fig. 2), a locality now lost to industrial development. Because male cercopithecid lower canines are not metrically identifiable beyond the Family level of classification (23), AUH 35 was described as a cercopithecid with indeterminate affinities. Here we report the discovery of a second monkey specimen from the Baynunah Formation in Abu Dhabi (AUH 1321), found almost 20 y after the first. AUH 1321 clearly represents a cercopithecine and, because it is dated to between 6.5 and 8.0 Ma, it is the oldest cercopithecine yet known outside of Africa and possibly the oldest cercopithecine in the fossil record. Thus, the discovery of AUH 1321 provides the earliest paleontological evidence of cercopithecine dispersal out of continental Africa and possibly hints at an Arabian cercopithecoid dispersal route into Eurasia during the Late Miocene (Fig. 1). Furthermore, we believe AUH 1321 can be attributed to the Cercopithecini (guenons) and, therefore, it represents the only record of this tribe, living or fossil, yet known outside of Africa.Open in a separate windowFig. 2.Map illustrating the location of the two fossil sites in the Baynunah Formation that have produced fossil monkeys. Top Right Inset shows the location of the SHU 2–2 excavation (kite aerial photography by Nathan Craig).     

Dietary options and behavior suggested by plant biomarker evidence in an early human habitat

The availability of plants and freshwater shapes the diets and social behavior of chimpanzees, our closest living relative. However, limited evidence about the spatial relationships shared between ancestral human (hominin) remains, edible resources, refuge, and freshwater leaves the influence of local resources on our species’ evolution open to debate. Exceptionally well-preserved organic geochemical fossils—biomarkers—preserved in a soil horizon resolve different plant communities at meter scales across a contiguous 25,000 m² archaeological land surface at Olduvai Gorge from about 2 Ma. Biomarkers reveal hominins had access to aquatic plants and protective woods in a patchwork landscape, which included a spring-fed wetland near a woodland that both were surrounded by open grassland. Numerous cut-marked animal bones are located within the wooded area, and within meters of wetland vegetation delineated by biomarkers for ferns and sedges. Taken together, plant biomarkers, clustered bone debris, and hominin remains define a clear spatial pattern that places animal butchery amid the refuge of an isolated forest patch and near freshwater with diverse edible resources.Spatial patterns in archaeological remains provide a glimpse into the lives of our ancestors (1–5). Although many early hominin environments are interpreted as grassy or open woodlands (6–8), fossil bones and plant remains are rarely preserved together in the same settings. As a result, associated landscape reconstructions commonly lack coexisting fossil evidence for hominins and local-scale habitat (microhabitat) that defined the distribution of plant foods, refuge, and water (7). This problem is exacerbated by the discontinuous nature and low time resolution often available across ancient soil (paleosol) horizons, including hominin archaeological localities. One notable exception is well-time-correlated 1.8-million-y-old paleosol horizons exposed at Olduvai Gorge. Associated horizons contain exceptionally preserved plant biomarkers along with many artifacts and fossilized bones. Plant biomarkers, which previously revealed temporal patterns in vegetation and water (8), are well preserved in the paleosol horizon and document plant-type spatial distributions that provide an ecosystem context (9, 10) for resources that likely affected the diets and behavior of hominin inhabitants.Plant biomarkers are delivered by litter to soils and can distinguish plant functional type differences in standing biomass over scales of 1–1,000 m² (11). Trees, grasses, and other terrestrial plants produce leaf waxes that include long-chain n-alkanes such as hentriacontane (nC₃₁), whereas aquatic plants and phytoplankton produce midchain homologs (e.g., nC₂₃) (12, 13). The ratio of shorter- versus long-chain n-alkane abundances distinguish relative organic matter inputs from aquatic versus terrestrial plants to sediments (13):P_aq = (nC₂₃ + nC₂₅)/(nC₂₃ + nC₂₅ + nC₂₉ + nC₃₁).Sedges and ferns are prolific in many tropical ecosystems (14). These plants both have variable and therefore nondiagnostic n-alkane profiles. However, sedges produce distinctive phenolic compounds [e.g., 5-n-tricosylresorcinol (ⁿR₂₃)] and ferns produce distinctive midchain diols [e.g., 1,13-dotriacontanediol (C₃₂-diol)] (SI Discussion).Lignin monomers provide evidence for woody and nonwoody plants. This refractory biopolymer occurs in both leaves and wood, serves as a structural tissue, and accounts for up to half of the total organic carbon in modern vegetation (11). Lignin is composed of three phenolic monomer types that show distinctive distributions in woody and herbaceous plant tissues. Woody tissues from dicotyledonous trees and shrubs contain syringyl (S) and vanillyl (V) phenols (12), whereas cinnamyl (C) phenols are exclusively found in herbaceous tissues (12). The relative abundance of C versus V phenols (C/V) is widely used to distinguish between woody and herbaceous inputs to sedimentary and soil organic matter (15).Plant biomarker ¹³C/¹²C ratios (expressed as δ¹³C values) are sensitive indicators of community composition, ecosystem structure, and climate conditions (8). Most woody plants and forbs in eastern Africa use C₃ photosynthesis (6), whereas arid-adapted grasses use C₄ photosynthesis (8, 14). These two pathways discriminate differently against ¹³C during photosynthesis, resulting in characteristic δ¹³C values for leaf waxes derived from C₃ (about –36.0‰) and C₄ (–21.0‰) plants (16). Carbon isotopic abundances of phenolic monomers of lignin amplify the C₃–C₄ difference and range between ca. –34.0‰ (C₃) and –14.0‰ (C₄) in tropical ecosystems (15). Terrestrial C₃ plant δ¹³C values decrease with increased exposure to water, respired CO₂, and shade (8), with lowest values observed in moist regions with dense canopy (17). Although concentration and δ¹³C values of atmospheric CO₂ can affect C₃ plant δ¹³C values (17), this influence is not relevant to our work here, which focuses on a single time window (SI Discussion). The large differences in leaf-wax δ¹³C values between closed C₃ forest to open C₄ grassland are consistent with soil organic carbon isotope gradients across canopy-shaded ground surfaces (6) and serve as a quantitative proxy for woody cover (f_woody) in savannas (8).As is observed for nonhuman primates, hominin dietary choices were likely shaped by ecosystem characteristics over habitat scales of 1–1,000 m² (3–5). To evaluate plant distributions at this small spatial scale (9), we excavated 71 paleosol samples from close-correlated trenches across a ∼25,000-m² area that included FLK Zinjanthropus Level 22 (FLK Zinj) at Olduvai Gorge (Fig. 1). Recent excavations (18–21) at multiple trenches at four sites (FLK^NN, FLK^N, FLK, and FLK^S, Fig. 1D) exposed a traceable thin (5–50 cm), waxy green to olive-brown clay horizon developed by pedogenic alterations of playa lake margin alluvium (22). Weak stratification and irregular redox stains suggest initial soil development occurred during playa lake regression (18, 22), around 1.848 Ma (ref. 23 and SI Discussion). To date, craniodental remains from at least three hominin individuals (18–20), including preadolescent early Homo and Paranthropus boisei, were recovered from FLK Zinj. Fossils and artifacts embedded in the paleosol horizon often protrude into an overlying airfall tuff (18, 19), which suggests fossil remains were catastrophically buried in situ under volcanic ash. Rapid burial likely fostered the exceptional preservation of both macrofossils (10) and plant biomarkers across the FLK Zinj land surface.Open in a separate windowFig. 1.Location and map of FLK Zinj paleosol excavations. (A and B) Location of FLK Zinj as referenced to reconstructed depositional environments at Olduvai Gorge during the early Pleistocene (18, 22) and the modern gorge walls. The perennial lake contained shallow saline–alkaline waters that frequently flooded the surrounding playa margin (i.e., floodplain) flats. (C) Outline of FLK Zinj paleosol excavation sites used for our spatial biomarker reconstructions. (D) Concentric (5 m) gridded distribution map of FLK Zinj paleosol excavations relative to previous archaeological trenches (18–21). Major aggregate complexes (FLK^NN, FLK^N, FLK, and FLK^S) are color-coded to show excavation-site associations.Plant biomarker signatures reveal distinct types of vegetation juxtaposed across the FLK Zinj land surface (Figs. 2–4 and Fig. S1). In the northwest, FLK^NN trenches show high nC₂₃ δ¹³C values (Fig. 2B) as well as high C/V and P_aq values (Figs. 3 and ​and4A).4A). They indicate floating or submerged aquatic plants (macrophytes) in standing freshwater (13), a finding that is consistent with nearby low-temperature freshwater carbonates (tufa), interpreted to be deposited from spring waters (22). Adjacent FLK^N trenches have lower P_aq values (Fig. 4A) with occurrences of fern-derived C₃₂-diol and sedge-derived ⁿR₂₃ (Fig. 2 C and D). These biomarker distributions indicate an abrupt (around 10 m) transition from aquatic to wetland vegetation. Less than 100 m away (Fig. 1C), low nC₃₁ δ¹³C values (Fig. 2A) and low C/V and very low P_aq values (Figs. 3 and ​and4A)4A) collectively indicate dense woody cover (Fig. 4B). In the farthest southeastern (FLK^S) trenches, high C/V values and high δ¹³C values for C lignin phenols (Fig. 3) indicate open C₄ grassland.Open in a separate windowFig. 2.Spatial distributions and δ¹³C values for plant biomarkers across FLK Zinj. Measured and modeled δ¹³C values (large and smaller circles, respectively) are shown for (A) nC₃₁ from terrestrial plants, (B) nC₂₃ from (semi)aquatic plants, (C) C₃₂-diol from ferns, and (D) ⁿR₂₃ from sedges (see refs. 12 and 13 and SI Discussion). Modeled values [inverse distance-weighted (9)] account for spatial autocorrelation (15-m radius) in standing biomass (35) over scales of soil organic matter accumulation (11). Black dots represent paleosols with insufficient plant biomarker concentrations for isotopic analysis.Open in a separate windowFig. 3.Molecular and isotopic signatures for lignin phenols across FLK Zinj. Bivariate plots are shown for diagnostic lignin compositional parameters (see refs. 12 and 15 and Fig. 1C). Symbols are colored according to respective δ¹³C values for the C lignin phenol, p-coumaric acid. FLK symbols are uncolored due to insufficient p-coumaric acid concentrations for isotopic analysis. Representative lignin compositional parameters (12, 15) are shown for monocotyledonous herbaceous tissues (G), dicotyledonous herbaceous tissues (H), cryptogams (N), and dicotyledonous woody tissues (W).Open in a separate windowFig. 4.Spatial relationships shared between local plant resources and hominin remains. Measured and modeled values (large and smaller circles, respectively) are shown for (A) P_aq (13) and (B) f_woody (8). Modeled values [inverse distance-weighted (9)] account for spatial autocorrelation (15-m radius) in standing biomass (35) over scales of soil organic matter accumulation (11). (C) Kernel density map of cut-marked bones (18–21) across the FLK Zinj land surface (Fig. S4). High estimator values indicate hotspots of hominin butchery (Fig. S5). A shaded rectangle captures the area (ca. 0.68 probability mass) with highest cut-marked bone densities and is shown in A and B for reference.Open in a separate windowFig. S1.Total ion chromatograms for saturated hydrocarbons in representative paleosols at (A) FLK^NN, (B) FLK^N, (C) FLK, and (D) FLK^S. C₂₃, tricosane; C₂₅, pentacosane; C₂₉ nonacosane; C₃₁, hentriacontane.Biomarkers define a heterogeneous landscape at Olduvai and suggest an influence of local resources on hominin diets and behavior. It is recognized (2, 24–26) that early Homo species and P. boisei had similar physiological characteristics. These similarities in physical attributes suggest behavioral differences were what allowed for overlapping ranges and local coexistence (sympatry) of both hominins. For instance, differences in seasonal subsistence strategies or different behavior during periods of drought and limited food could have reduced local hominin competition and fostered diversification via niche specialization (27–29).Physical and isotopic properties of fossil teeth indicate P. boisei was more water-dependent [low enamel δ¹⁸O values (24)] and consumed larger quantities of abrasive, ¹³C-enriched foodstuffs [flat-worn surfaces (25) and high enamel δ¹³C values (26)] than coexisting early Homo species. Although ¹³C-enriched enamel is commonly attributed to consumption of C₄ grasses or meat from grazers (14), this was not likely, because P. boisei craniodental features are inconsistent with contemporary gramnivores (24, 25) or extensive uncooked flesh mastication (26). Numerous scholars have proposed the nutritious underground storage organs (USOs) of C₄ sedges were a staple of hominin diets (14, 24, 26, 27). Consistent with this suggestion, occurrences of ⁿR₂₃ attest to the presence of sedges at FLK^NN and FLK^N (Fig. 2D). However, the low δ¹³C values measured for ⁿR₂₃ at these same sites (Fig. 2D and Fig. S2) indicate C₃ photosynthesis (12, 16), a trait common in modern sedges that grow in alkaline wetlands and lakes (30) (Fig. S3). Thus, biomarker signatures support the presence of C₃ sedges in the wetland area of FLK Zinj.Open in a separate windowFig. S2.Total ion chromatogram [TIC (A)] and selected ion chromatograms for derivatized 5-n-alkylresorcinols [m/z 268 (●)] and midchain diols [m/z 369 (○)] from a representative paleosol at FLK^N. Also shown are δ¹³C values for homologous (B) 5-n-alkylresorcinols and (C) midchain diols. C₃₂-diol, dotriacontanediol; ⁿR₂₃, tricosylresorcinol.Open in a separate windowFig. S3.Summary phyogenetic consensus tree of Cyperaceae (sedges) based on nucleotide (rcbL and ETS1f) sequence data (50–54, 95, 96). Important taxonomic distinctions discussed in SI Discussion, Fern Alkyldiols are shown explicitly. Triangle-enclosed digits represent the number of additional branches at different levels of taxonomic classification. CEFA, Cypereae Eleocharideae Fuireneae Abildgaardieae; CSD, Cariceae Scirpeae Dulichieae.Alternative foodstuffs with abrasive, ¹³C-enriched biomass include seedless vascular plants (cryptogams), such as ferns and lycophytes [e.g., quillworts (27, 30)]. Ferns are widely distributed throughout eastern Africa in moist and shaded microhabitats (31) and are often found near dependable sources of drinking water (32). Today, ferns serve as a dietary resource for humans and nonhuman primates alike (27), and fiddlehead consumption is consistent with the inferred digestive physiology [salivary proteins (33)] and the microwear on molars (34) of P. boisei in eastern Africa (25, 26). Ferns were present at FLK^N, based on measurements of C₃₂-diol (Fig. 2D). Further, the high δ¹³C values measured for these compounds are consistent with significant fern consumption by P. boisei at Olduvai Gorge.Ferns and grasses were not the only plant foods present during the time window documented by FLK Zinj. Further, the exclusive reliance on a couple of dietary resources was improbable for P. boisei, because its fossils occur in diverse localities (24–26). Aquatic plants are an additional candidate substrate, as evidenced by high P_aq values at FLK^NN and FLK^N (Fig. 4A). Floating and submerged plants proliferate in wetlands throughout eastern Africa today (13, 14), and many produce nutritious leaves and rootstock all year long (27, 28). Although C₄ photosynthesis is rare among modern macrophytes (30), they can assimilate bicarbonate under alkaline conditions, which results in C₄-like isotope signatures in their biomass (30). Their leaf waxes, such as nC₂₃ (13), are both present and carry ¹³C-enriched signatures at FLK^NN and FLK^N (Fig. 2B). It is also likely that aquatic macrophytes sustained invertebrates and fish with comparably ¹³C-enriched biomass, as they do in modern systems (14), and we suggest aquatic animal foods could have been important in P. boisei diets (27, 28).Biomarkers across the FLK Zinj soil horizon resolve clear patterns in the distribution of plants and water and suggest critical resources that shaped hominin existence at Olduvai Gorge. The behavioral implications of local conditions require understanding of regional climate and biogeography (3–5, 7), because hominin species likely had home ranges much larger than the extent of excavated sites at FLK Zinj. Lake sediments at Olduvai Gorge include numerous stacked tuffs with precise radiometric age constraints (23). These tephrostratigraphic correlations (21) tie the FLK Zinj landscape horizon to published records of plant biomarkers in lake sediments that record climate cycles and catchment-scale variations in ecology. Correlative lake sediment data indicate the wet and wooded microhabitats of FLK Zinj sat within a catchment dominated by arid C₄ grassland (8). Under similarly arid conditions today, only a small fraction of landscape area (ca. 0.05) occurs within 5 km of either forest or standing freshwater (35). Given a paucity of shaded refuge and potable water in the catchment, the concentration of hominin butchery debris (18–21) exclusively within the forest microhabitat and adjacent to a freshwater wetland (Fig. 4) is notable. We suggest the spatial patterns defined by both macro- and molecular fossils reflect hominins engaged in social transport of resources (1–5), such as bringing animal carcasses and freshwater-sourced foods from surrounding grassy or wetland habitats to a wooded patch that provided both physical protection and access to water.     

Diffusion of a disordered protein on its folded ligand

Intrinsically disordered proteins often form dynamic complexes with their ligands. Yet, the speed and amplitude of these motions are hidden in classical binding kinetics. Here, we directly measure the dynamics in an exceptionally mobile, high-affinity complex. We show that the disordered tail of the cell adhesion protein E-cadherin dynamically samples a large surface area of the protooncogene β-catenin. Single-molecule experiments and molecular simulations resolve these motions with high resolution in space and time. Contacts break and form within hundreds of microseconds without a dissociation of the complex. The energy landscape of this complex is rugged with many small barriers (3 to 4 k_BT) and reconciles specificity, high affinity, and extreme disorder. A few persistent contacts provide specificity, whereas unspecific interactions boost affinity.

Specific molecular interactions orchestrate a multitude of simultaneous cellular processes. The discovery of intrinsically disordered proteins (IDPs) (1, 2) has substantially aided our understanding of such interactions. More than two decades of research revealed a plethora of functions and mechanisms (2–6) that complemented the prevalent structure-based view on protein interactions. Even the idea that IDPs always ought to fold upon binding has largely been dismantled by recent discoveries of high-affine–disordered complexes (7, 8). Classical shape complementary is indeed superfluous in the complex between prothymosin-α and histone H1, in which charge complementary is the main driving force for binding (7). However, complexes between IDPs and folded proteins can also be highly dynamic [e.g., Sic1 and Cdc4 (9), the Na⁺/H⁺ exchanger tail and ERK2 (10), nucleoporin tails, and nuclear transport receptors (11)]. Yet timescales of motions and their spatial amplitudes are often elusive, such that it is unclear how precisely the surfaces of folded proteins alter the dynamics of bound IDPs. Answering this question is a key step in understanding how specificity, affinity, and flexibility can be simultaneously realized in such complexes.To address this question, we focused on the dynamics of the cell adhesion complex between E-cadherin (E-cad) and β-catenin (β-cat), which is involved in growth pathologies and cancer (12). E-cad is a transmembrane protein that mediates cell–cell adhesions by linking actin filaments of adjacent epithelial cells (Fig. 1A). Previous NMR results showed that the cytoplasmic tail of E-cad is intrinsically disordered (13). E-cad binds β-cat, which establishes a connection to the actin-associated protein α-catenin (14–16). β-cat, on the other hand, is a multifunctional repeat protein (17–20) that mediates cadherin-based cell adhesions (21) and governs cell fate decisions during embryogenesis (22). It contains three domains: an N-terminal domain (130 amino acids [aa]), a central repeat domain (550 aa), and a C-terminal domain (100 aa). Whereas the N- and C-terminal domains of β-cat are in large parts unstructured (17), with little effect on the affinity of the E-cad/β-cat complex (23), the 12 repeats of the central domain arrange in a superhelix (24). The X-ray structure showed that the E-cad wraps around this central domain of β-cat (24) (Fig. 1B). However, not only is half of the electron density of E-cad missing, the X-ray unit cell also comprises two structures with different resolved parts of E-cad (Fig. 1B). In fact, only 45% of all resolved E-cad residues are found in both structures (Fig. 1C). Although this ambiguity together with the large portion of missing residues (25) suggests that E-cad is highly dynamic in the complex with β-cat, the timescales and amplitudes of these dynamics are unknown.Open in a separate windowFig. 1.Complex between the cytoplasmic tail of E-cad and β-cat. (A) Schematics of cell–cell junctions mediated by E-cad and β-cat. (B) The two X-ray structures of the complex between the tail of E-cad (red) and the central repeat domain of β-cat (white) resolve different parts of E-cad (Protein Data Bank: 1i7x), indicating the flexibility of E-cad in the complex. (Bottom) Cartoon representation of the resolved E-cad parts. (C) Scheme showing the resolved parts of E-cad (red).Here, we integrated single-molecule Förster resonance energy transfer (smFRET) experiments with molecular simulations to directly measure the dynamics of E-cad on β-cat with high spatial and temporal resolution. In our bottom-up strategy, we first probed intramolecular interactions within E-cad using smFRET to parameterize a coarse-grained (CG) model. In a second step, we monitored E-cad on β-cat, integrated this information into the CG model, and obtained a dynamic picture of the complex. We found that all segments of E-cad diffuse on the surface of β-cat at submillisecond timescales and obtained a residue-resolved understanding of these motions: A small number of persistent interactions provide specificity, whereas many weak multivalent contacts boost affinity, which confirms the idea that regulatory enzymes access their recognition motifs on E-cad and β-cat without requiring the complex to dissociate (24).     

Amphitheater-headed canyons formed by megaflooding at Malad Gorge,Idaho

Many bedrock canyons on Earth and Mars were eroded by upstream propagating headwalls, and a prominent goal in geomorphology and planetary science is to determine formation processes from canyon morphology. A diagnostic link between process and form remains highly controversial, however, and field investigations that isolate controls on canyon morphology are needed. Here we investigate the origin of Malad Gorge, Idaho, a canyon system cut into basalt with three remarkably distinct heads: two with amphitheater headwalls and the third housing the active Wood River and ending in a 7% grade knickzone. Scoured rims of the headwalls, relict plunge pools, sediment-transport constraints, and cosmogenic (³He) exposure ages indicate formation of the amphitheater-headed canyons by large-scale flooding ∼46 ka, coeval with formation of Box Canyon 18 km to the south as well as the eruption of McKinney Butte Basalt, suggesting widespread canyon formation following lava-flow diversion of the paleo-Wood River. Exposure ages within the knickzone-headed canyon indicate progressive upstream younging of strath terraces and a knickzone propagation rate of 2.5 cm/y over at least the past 33 ka. Results point to a potential diagnostic link between vertical amphitheater headwalls in basalt and rapid erosion during megaflooding due to the onset of block toppling, rather than previous interpretations of seepage erosion, with implications for quantifying the early hydrosphere of Mars.Landscapes adjust to perturbations in tectonics and base level through upstream propagation of steepened river reaches, or knickzones, thereby communicating environmental signals throughout a drainage basin (e.g., ref. 1). Nowhere are knickzones more important and apparent than in landscapes where canyon heads actively cut into plateaus, such as tributaries of the Grand Canyon, United States, and the basaltic plains of Mars (e.g., refs. 2–4). Here the stark topographic contrast between low-relief uplands and deeply incised canyons sharply delineates canyon rims and planform morphology. Canyon heads can have varied shapes from amphitheaters with vertical headwalls to more pointed planform shapes with lower gradients, and a prominent goal in geomorphology and planetary science is to link canyon morphology to formation processes (e.g., refs. 4–8), with implications for understanding the history of water on Mars.Amphitheater-headed canyons on Mars are most likely cut into layered basalt (9, 10), and canyon-formation interpretations have ranged widely from slow seepage erosion to catastrophic megafloods (4–6, 11, 12). Few studies have been conducted on the formation of amphitheater-headed canyons in basalt on Earth, however, and instead, terrestrial canyons in other substrates are often used as Martian analogs. For example, groundwater sapping is a key process in forming amphitheater-headed canyons in unconsolidated sand (e.g., refs. 8, 13, 14), but its importance is controversial in rock (5, 12, 15). Amphitheater-headed canyons are also common to plateaus with strong-over-weak sedimentary rocks (3, 16); however, here the tendency for undercutting is so strong that canyon-head morphology may bear little information about erosional processes, whether driven by groundwater or overland flow (e.g., refs. 3, 5, 17). Canyons in some basaltic landscapes lack strong-over-weak stratigraphy, contain large boulders that require transport, and show potential for headwall retreat by block toppling (18–21), all of which make extension of process–form relationships in sand and sedimentary rocks to basalt and Mars uncertain.To test the hypothesis of a link between canyon formation and canyon morphology in basalt, we need field measurements that can constrain formation processes for canyons with distinct morphologies, but carved into the same rock type. Here we report on the origin of Malad Gorge, a canyon complex eroded into columnar basalt with markedly different shaped canyon heads. Results point to a potential diagnostic link between canyon-head morphology and formative process by megaflood erosion in basalt.Malad Gorge is a tributary to the Snake River Canyon, Idaho, within the Snake River Plain, a broad depression filled by volcanic flows that erupted between ∼15 Ma and ∼2 ka (22, 23). The gorge sits at the northern extent of Hagerman Valley, a particularly wide (∼7 km) part of the Snake River Canyon (Fig. 1). Malad Gorge is eroded into the Gooding Butte Basalt [⁴⁰Ar/³⁹Ar eruption age: 373 ± 12 ka (25)] which is composed of stacked lava beds, each several meters thick with similar well-defined columns bounded by cooling joints and no apparent differences in strength between beds. The Wood (or Malad) River, a major drainage system from the Sawtooth Range to the north, drains through Malad Gorge before joining the Snake River. The Wood River is thought to have been diverted from an ancestral, now pillow lava-filled canyon into Malad Gorge by McKinney Butte basalt flows (24) [⁴⁰Ar/³⁹Ar eruption age: 52 ± 24 ka (25) (Fig. 1).Open in a separate windowFig. 1.Shaded relief map of the study region (50-m contour interval) showing basalt flows (23), their exposure age sample locations, and the path of the ancestral Wood River following Malde (24) (US Geological Survey).Malad Gorge contains three distinct canyon heads herein referred to as Woody’s Cove, Stubby Canyon, and Pointed Canyon (Fig. 2A). Woody’s Cove and Stubby have amphitheater heads with ∼50-m-high vertical headwalls (Fig. 2C), and talus accumulation at headwall bases indicates long-lived inactive fluvial transport (Fig. 3 A and B). Woody’s Cove, the shortest of the three canyons, lacks major spring flows and has minor, intermittent overland flow partially fed by irrigation runoff that spills over the canyon rim. Stubby has no modern-day overland flow entering the canyon, and springs emanate from a pool near its headwall (Fig. 3B). In contrast, Pointed Canyon is distinctly more acute in planform morphology, contains a 7% grade knickzone composed of multiple steps rather than a vertical headwall (Figs. 2C and ​and3C),3C), and extends the farthest upstream.Open in a separate windowFig. 2.Malad Gorge topography (10-m contour interval) and aerial orthophotography (US Geological Survey). (A) Overview map and (B) close-up for Stubby and Pointed canyons showing mapped bedrock scours (white arrows), exposure age sample locations (red circles) with age results, location of the uppermost active knickpoint (black circle), abandoned bedrock channels (blue dashed lines), and grain-size analysis sites (blue squares). The blue star shows the reconstructed location of the headwall of Pointed Canyon at 46 ka (see Discussion and Fig. 5). (C) Longitudinal profile along Stubby and Pointed canyons from their confluence (shown as white lines in B) with local slope, S, averaged over regions demarked by dashed lines (Fig. 4A shows close-up of profile in Stubby Canyon).Open in a separate windowFig. 3.Photographs of (A) headwall of Woody’s Cove (person for scale, circled), (B) ∼50-m-high headwall of Stubby Canyon, (C) downstream-most waterfall at Pointed Canyon knickzone (12-m-high waterfall with overcrossing highway for scale), (D) fluted and polished notch at the rim of Stubby Canyon (notch relief is 10 m), (E) upstream-most waterfall at Pointed Canyon knickzone (within the southern anabranch of Fig. S2), and (F) upstream-most abandoned channel in Fig. 2B and Fig. S2 (channel relief is ∼10 m). White coloring on the headwalls in A and B is likely residue from irrigation runoff.Early work attributed the amphitheater-headed canyons in this region—Malad Gorge, Box Canyon, located 18 km south of Malad Gorge (Fig. 1), and Blue Lakes Canyon located 42 km to the SE—to formation by seepage erosion because of no modern overland flow and the occurrence of some of the largest springs in the United States in this region (7). Because spring flows (e.g., ∼10 m³/s in Box Canyon; US Geological Survey gauge 13095500) are far deficient to move the boulders that line the canyon floors, Stearns (7) reasoned that the boulders must chemically erode in place. This explanation is improbable, however, given the young age of the Quaternary basalt (25), spring water saturated in dissolved solids (19), and no evidence of rapid chemical weathering (e.g., talus blocks are angular and have little to no weathering rinds). Instead of groundwater sapping, Box Canyon was likely carved by a large-scale flood event that occurred ∼45 ka based on ³He cosmogenic exposure age dating of the scoured rim of the canyon headwall (19, 26). In addition, Blue Lakes Canyon was formed during the Bonneville Flood [∼18–22 ka (27, 28)], one of the world’s largest outburst floods that occurred as a result of catastrophic draining of glacial lake Bonneville (21). In both cases, canyon formation was inferred to have occurred through upstream headwall propagation by waterfall erosion.Herein we aim to test whether the amphitheater-headed canyons at Malad Gorge also owe their origin to catastrophic flooding, whether Pointed Canyon has a different origin, and whether canyon morphology is diagnostic of formation process. To this end we present field observations, sediment-size measurements, hydraulic modeling, and cosmogenic exposure ages of water-scoured rock surfaces and basalt-flow surfaces (Methods and Tables S1 and S2).     

Electrophilic aromatic substitution reactions of compounds with Craig-Möbius aromaticity

Electrophilic aromatic substitution (EAS) reactions are widely regarded as characteristic reactions of aromatic species, but no comparable reaction has been reported for molecules with Craig-Möbius aromaticity. Here, we demonstrate successful EAS reactions of Craig-Möbius aromatics, osmapentalenes, and fused osmapentalenes. The highly reactive nature of osmapentalene makes it susceptible to electrophilic attack by halogens, thus osmapentalene, osmafuran-fused osmapentalene, and osmabenzene-fused osmapentalene can undergo typical EAS reactions. In addition, the selective formation of a series of halogen substituted metalla-aromatics via EAS reactions has revealed an unprecedented approach to otherwise elusive compounds such as the unsaturated cyclic chlorirenium ions. Density functional theory calculations were conducted to study the electronic effect on the regioselectivity of the EAS reactions.

Aromaticity, a core concept in chemistry, was initially introduced to account for the bonding, stability, reactivity, and other properties of many unsaturated organic compounds. There have been many elaborations and extensions of the concept of aromaticity (1, 2). The concepts of Hückel aromaticity and Möbius aromaticity are widely accepted (Fig. 1A). A π-aromatic molecule of the Hückel type is planar and has 4n + 2 conjugated π-electrons (n = 0 or an integer), whereas a Möbius aromatic molecule has one twist of the π-system, similar to that in a Möbius strip, and 4n π-electrons (3, 4). Since the discovery of naphthalene in 1821, aromatic chemistry has developed into a rich field and with a variety of subdisciplines over the course of its 200-y history, and the concept of aromaticity has been extended to other nontraditional structures with “cyclic delocalization of mobile electrons” (5). For example, benzene-like metallacycles—predicted by Hoffmann et al. as metallabenzenes—in which a metal replaces a C–H group in the benzene ring (6), have garnered extensive research interest from both experimentalists and theoreticians (7–12). As paradigms of the metalla-aromatic family, most complexes involving metallabenzene exhibit thermodynamic stability, kinetic persistence, and chemical reactivity associated with the classical aromaticity concept (13–15). Typically, like benzene, metallabenzene can undergo characteristic reactions of aromatics such as electrophilic aromatic substitution (EAS) reactions (16–18) (Fig. 1B, I) and nucleophilic aromatic substitution reactions (19–21).Open in a separate windowFig. 1.Schematic representations of aromaticity classification (A) and EAS reactions (B) of benzene, metallabenzene, and polycyclic metallacycles with Craig-Möbius aromaticity.The incorporation of transition metals has also led to an increase in the variety of the aromatic families (22–25). We have reported that stable and highly unusual bicyclic systems, metallapentalenes (osmapentalenes), benefit from Craig-Möbius aromaticity (26–30). In contrast to other reported Möbius aromatic compounds with twisted topologies, which are known as Heilbronner-Möbius aromatics (31–34), the involvement of transition metal d orbitals in π-conjugation switches the Hückel anti-aromaticity of pentalene into the planar Craig-Möbius aromaticity of metallapentalene (35–38) (Fig. 1A, III). Both the twisted topology and the planar Craig-Möbius aromaticity are well established and have been accepted as reasonable extensions of aromaticity (39–43). There has been no experimental evidence, however, as to whether these Möbius aromatic molecules can undergo classical aromatic substitution reactions, such as EAS reactions, instead of addition reactions. Given the key role of EAS in aromatic chemistry to obtain various derivatives, we sought to extend the understanding of the reactivity paradigm in the metalla-aromatic family.Our recent synthetic efforts associated with the metallapentalene system prompted us to investigate whether typical EAS reactions could proceed in these Craig-Möbius aromatics. If so, how could substitution be achieved in the same way that it is with traditional Hückel aromatics such as benzenes? In this paper, we present EAS reactions, mainly the halogenation of osmapentalene, osmafuran-fused osmapentalene, and osmabenzene-fused osmapentalene, which follow the classic EAS mechanistic scheme (Fig. 1B). With the aid of density functional theory (DFT) calculations, we characterized the effects on EAS reactivity and regioselectivity.     

Electrochemical borylation of carboxylic acids

A simple electrochemically mediated method for the conversion of alkyl carboxylic acids to their borylated congeners is presented. This protocol features an undivided cell setup with inexpensive carbon-based electrodes and exhibits a broad substrate scope and scalability in both flow and batch reactors. The use of this method in challenging contexts is exemplified with a modular formal synthesis of jawsamycin, a natural product harboring five cyclopropane rings.

Boronic acids are among the most malleable functional groups in organic chemistry as they can be converted into almost any other functionality (1–3). Aside from these versatile interconversions, their use in the pharmaceutical industry is gaining traction, resulting in approved drugs such as Velcade, Ninlaro, and Vabomere (4). It has been shown that boronic acids can be rapidly installed from simple alkyl halides (5–19) or alkyl carboxylic acids through the intermediacy of redox-active esters (RAEs) (Fig. 1A) (20–24). Our laboratory has shown that both Ni (20) and Cu (21) can facilitate this reaction. Conversely, Aggarwal and coworkers (22) and Li and coworkers (23) demonstrated photochemical variations of the same transformation. While these state-of-the-art approaches provide complementary access to alkyl boronic acids, each one poses certain challenges. For example, the requirement of excess boron source and pyrophoric MeLi under Ni catalysis is not ideal. Although more cost-effective and operationally simple, Cu-catalyzed borylation conditions can be challenging on scale due to the heterogeneity resulting from the large excess of LiOH•H₂O required. In addition to its limited scope, Li and coworkers’ protocol requires 4 equivalence of B₂pin₂ and an expensive Ir photocatalyst. The simplicity of Aggarwal and coworkers’ approach is appealing in this regard and represents an important precedent for the current study.Open in a separate windowFig. 1.(A) Prior approaches to access alkyl boronic esters from activated acids. (B) Inspiration for initiating SET events electrochemically to achieve borylation. (C) Summary of this work.At the heart of each method described above, the underlying mechanism relies on a single electron transfer (SET) event to promote decarboxylation and form an alkyl radical species. In parallel, the related borylation of aryl halides via a highly reactive aryl radical can also be promoted by SET. While numerous methods have demonstrated that light can trigger this mechanism (Fig. 1B) (16, 25–31), simple electrochemical cathodic reduction can elicit the same outcome (32–35). It was postulated that similar electrochemically driven reactivity could be translated to alkyl RAEs. The development of such a transformation would be highly enabling, as synthetic organic electrochemistry allows the direct addition or removal of electrons to a reaction, representing an incredibly efficient way to forge new bonds (36–40). This disclosure reports a mild, scalable, and operationally simple electrochemical decarboxylative borylation (Fig. 1C) not reliant on transition metals or stoichiometric reductants. In addition to mechanistic studies of this interesting transformation, applications to a variety of alkyl RAEs, comparison to known decarboxylative borylation methods, and a formal synthesis of the polycyclopropane natural product jawsamycin [(–)-FR-900848] are presented.     

Archean komatiite volcanism controlled by the evolution of early continents

The generation and evolution of Earth’s continental crust has played a fundamental role in the development of the planet. Its formation modified the composition of the mantle, contributed to the establishment of the atmosphere, and led to the creation of ecological niches important for early life. Here we show that in the Archean, the formation and stabilization of continents also controlled the location, geochemistry, and volcanology of the hottest preserved lavas on Earth: komatiites. These magmas typically represent 50–30% partial melting of the mantle and subsequently record important information on the thermal and chemical evolution of the Archean–Proterozoic Earth. As a result, it is vital to constrain and understand the processes that govern their localization and emplacement. Here, we combined Lu-Hf isotopes and U-Pb geochronology to map the four-dimensional evolution of the Yilgarn Craton, Western Australia, and reveal the progressive development of an Archean microcontinent. Our results show that in the early Earth, relatively small crustal blocks, analogous to modern microplates, progressively amalgamated to form larger continental masses, and eventually the first cratons. This cratonization process drove the hottest and most voluminous komatiite eruptions to the edge of established continental blocks. The dynamic evolution of the early continents thus directly influenced the addition of deep mantle material to the Archean crust, oceans, and atmosphere, while also providing a fundamental control on the distribution of major magmatic ore deposits.Volcanism on Earth is the dynamic surface expression of our planet’s thermal cycle, with heat created from radioactive decay and lost through mantle convection (1). In the Archean eon (>2.5 bya), Earth’s heat flux was significantly higher than that observed today (1, 2) due to the combined effects of a more radioactive mantle (1, 3) and residual heat from planetary accretion (4). This resulted in the eruption of komatiites: ultra-high temperature, low-viscosity lavas with MgO >18% and eruption temperatures >1,600 °C (5) formed from mantle plumes (1, 2, 6). These rare, ancient magmas are dominantly restricted to the early history of the planet (3.5–1.5 Ga; ref. 7) and represent the remnants of huge volcanic flow fields (8) consisting of the hottest lavas preserved on Earth (5, 9, 10). These now-extinct volcanic systems and flow complexes had the potential to cover significant portions of the early continents, and were likely analogous to large igneous provinces in size and magma volume (11, 12). Komatiites are vital to our understanding of Earth’s thermal evolution (1–3, 7, 13–16), and represent a window into the dynamic secular development of the mantle throughout the early history of our planet (5). Subsequently, understanding the physical and chemical processes that govern their localization, volcanology, and geochemistry is vital in deciphering this information.In the Yilgarn Craton of Western Australia (Fig. 1), two major pulses of komatiite activity occurred at ∼2.9 Ga (southern Youanmi Terrane; refs. 17–19) and 2.7 Ga (Kalgoorlie Terrane, Eastern Goldfields Superterrane; refs. 5, 10). These represent two separate plume events that impinged onto preexisting continental crust (20–23), with the resulting magmas heterogeneously distributed across the craton (8, 10, 17–19, 23, 24). In this study, we provide the first evidence of a fundamental relationship between the spatiotemporal variation in komatiite abundance, geochemistry, and volcanology and the evolution of an Archean microcontinent, reflected in the changing isotopic composition of the crust.Open in a separate windowFig. 1.Map of the Archean Yilgarn Craton showing the basic granite-greenstone bedrock geology and location of the ∼2.9 and 2.7 Ga komatiite localities. Individual terranes/domains (39, 40) are labeled. Greenstone belts are labeled as follows: MD, Marda–Diemals; SC, Southern Cross; FO, Forrestania; LJ, Lake Johnston; RAV, Ravensthorpe; AW, Agnew–Wiluna; and KAL, Kalgoorlie/Kambalda. Komatiite localities are from Barnes and Fiorentini (10) (Table S4).We used Lu-Hf and U-Pb isotopic techniques on multiple magmatic and inherited zircon populations from granitoid rocks and felsic volcanic units, which represent the exposed Archean crust of the Yilgarn Craton. All zircon grains were dated using the sensitive high-resolution ion microprobe (SHRIMP), before in situ laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS) analysis for Lu-Hf isotopes. The Lu-Hf isotopic data are expressed as εHf, which denotes the derivation of the ¹⁷⁶Hf/¹⁷⁷Hf ratio of the sample from the contemporaneous ratio of the chondritic uniform reservoir (CHUR), multiplied by 10⁴. The term “juvenile” refers to crustal material that plots on or close to the depleted mantle evolution line, suggesting derivation from a depleted mantle source. In contrast, “reworked” refers to the remobilization of preexisting crust by partial melting and/or erosion and sedimentation (25, 26). Complete sample information, methodology, and geochemical datasets (U-Pb, Lu-Hf, and komatiite) are available in the Supporting Information, Figs. S1–S3, and Tables S1–S4.The Lu-Hf data are displayed as a series of time-slice contour maps, which show “snapshots” of the changing source and age of the crust at 3,050–2,820; 2,820–2,720; and 2,720–2,600 Ma [Figs. 2–4; intervals based on the work of Mole et al. (21); full Hf dataset displayed in Fig. S4]. In these maps, point data representing the median εHf value of granites and felsic volcanics are plotted as contour maps that show the spatial extent of “blocks” of specific Lu-Hf isotopic character and their evolution through time. This method is based on previous isotopic mapping of the Yilgarn Craton using the analogous Sm-Nd system (27). Importantly, the Lu-Hf data presented here replicate the features of the Sm-Nd work (27, 28), with the added ability to look further back in time due to the in situ analysis of abundant inherited zircons (21).Open in a separate windowFig. 2.Lu-Hf (εHf) map of the Yilgarn Craton at 3,050–2,820 Ma. (A) Hf isotope map with the location of sample sites and komatiite localities. (B) Interpretive map of the area, showing the individual crustal blocks identified from the Hf isotope map and corresponding probability density plots. The blue curve represents the median εHf for discrete temporal groups (n_g), whereas the red curve represents all of the individual grain analyses (n_a). Dark gray polygons shown in the background of all maps represent supracrustal belts (Fig. 1).Open in a separate windowFig. 4.Lu-Hf (εHf) map of the Yilgarn Craton at 2,720–2,600 Ma. (A) Hf isotope map with the location of sample sites and komatiite localities. (B) Interpretive map of the area, showing the individual crustal blocks identified from the Hf isotope map and corresponding probability density plots. The blue curve represents the median εHf for discrete temporal groups (n_g), whereas the red curve represents all of the individual grain analyses (n_a). Dark gray polygons shown in the background of all maps represent supracrustal belts (Fig. 1).The variable isotopic signatures of the crust (Figs. 2–4) can be interpreted as proxies for lithospheric thickness (Figs. 5 and ​and6;6; ref. 29), where young, juvenile εHf values (εHf > 0) indicate relatively thin lithosphere and old, reworked values (εHf < 0) reflect thicker lithosphere (29, 30); a pattern observed in the modern-day western United States (29–32). Here, this information is combined to document the four-dimensional lithospheric architecture of the Yilgarn Craton and development of an Archean microcontinent.Open in a separate windowFig. 5.Isotopic cross-section and interpreted lithospheric architecture during the emplacement of ∼2.9 Ga komatiites in the southern Youanmi Terrane. (A) εHf map showing the isotopic architecture at the time of the ∼2.9 Ga plume emplacement, with the approximate extent of the plume head (red) and tail (yellow) shown for scale; (B) isotopic cross-section (A–A′) documenting the changing εHf of the crust from east to west (circles represent median; squares represent individual analyses) together with the occurrence and MgO content (Table S4) of ultramafic–mafic magmatism; and (C) interpreted lithospheric architecture based on the changing isotopic properties of the crust. The white ellipses represent the types of magma available in a particular area and the dashed lines show the approximate limits of their source regions. TiO₂ vs. Al₂O₃ data (17, 19) are shown for komatiites of the relevant greenstone belts, demonstrating the progressive eastward homogenization of Barberton-type melts. The location of the continent core and continent edge are shown based on the Lu-Hf data. The eruption of komatiite would likely have been facilitated by plume-related extension at this interface. Approximate thickness values for developed Archean lithosphere (∼250–150 km) were taken from Boyd et al. (41), Artemieva and Mooney (42), and Begg et al. (43). The approximate scale of the plume head (∼1,600 km), tail (200–100 km), and thickness (∼150–100 km) were taken from Campbell et al. (15). Note that the plume-tail material moves above the plume head, despite impacting the lithosphere later, as it is hotter, more buoyant, and subsequently emplaced at higher flux (15).Open in a separate windowFig. 6.Isotopic cross-sections and interpreted lithospheric architecture during the emplacement of the ∼2.7 Ga komatiites in the Eastern Goldfields (Kalgoorlie Terrane). (A) εHf map showing the isotopic architecture at the time of the ∼2.7 Ga plume emplacement, with the approximate extent of the plume head (red) and tail (yellow) shown for scale; (B) isotopic cross-section (B–B′) documenting the changing εHf of the crust from east to west (circles represent median; squares represent individual analyses) together with the occurrence and MgO content (Table S4) of ultramafic–mafic magmatism; and (C) interpreted lithospheric architecture based on the changing isotopic properties of the crust. The white ellipses represent the types of magma available in a particular area and the dashed lines show the approximate limits of their source regions. TiO₂ vs. Al₂O₃ data (9) are shown for komatiites of the Eastern Goldfields, demonstrating the eastward dilution and removal of Barberton-type melts. The location of the continent core and continent edge are shown based on the Lu-Hf dataset. The eruption of komatiite would likely have been facilitated by plume-related extension at this interface. The dashed red lines shown in C account for the potential variation in lithospheric architecture within the Lake Johnston block based on the Lu-Hf data. External data used to construct these diagrams are the same as for Fig. 5. Note that the plume-tail material moves above the plume head, despite impacting the lithosphere later, as it is hotter, more buoyant, and subsequently emplaced at higher flux (15).     

A nitroaromatic cathode with an ultrahigh energy density based on six-electron reaction per nitro group for lithium batteries

Organic electrode materials have emerged as promising alternatives to conventional inorganic materials because of their structural diversity and environmental friendliness feature. However, their low energy densities, limited by the single-electron reaction per active group, have plagued the practical applications. Here, we report a nitroaromatic cathode that performs a six-electron reaction per nitro group, drastically improving the specific capacity and energy density compared with the organic electrodes based on single-electron reactions. Based on such a reaction mechanism, the organic cathode of 1,5-dinitronaphthalene demonstrates an ultrahigh specific capacity of 1,338 mAh⋅g⁻¹ and energy density of 3,273 Wh⋅kg⁻¹, which surpass all existing organic cathodes. The reaction path was verified as a conversion from nitro to amino groups. Our findings open up a pathway, in terms of battery chemistry, for ultrahigh-energy-density Li-organic batteries.

With the rapid development of social economy, the demand for high-energy-density storage systems is ever increasing, particularly in the fields of military, aerospace, medical, and civilian applications. Lithium-ion batteries (LIBs) have been extensively explored as high-energy-density storage devices (1–4). Commercial LIBs use crystalline transition metal oxide cathodes, such as LiCoO₂, LiMnO₂, and LiNi_xMn_yCo_1-x-yO₂ (5–12). They store energy via insertion/extraction of Li ions, which highly depends on the crystal structure and limits their capacities and energy densities (<300 mAh⋅g⁻¹ with energy density of <1,000 Wh⋅kg⁻¹). Some new battery systems with conversion reaction cathodes, such as Li-S (2,600 Wh⋅kg⁻¹) and Li-O₂ (3,450 Wh⋅kg⁻¹) batteries (13–19), have been extensively investigated due to their high theoretical energy densities. However, they suffer from serious dissolution, interfacial stability, and/or side reaction issues, and the practical energy densities are much lower than their theoretical values.Compared with the aforementioned rechargeable batteries, lithium primary batteries can provide remarkably higher energy densities. For example, lithium-fluorinated carbon (Li-CF_x) batteries use a CF_x cathode that has a high theoretical energy density of 2,180 Wh⋅kg⁻¹, which is the highest value among all commercial cathode materials in lithium batteries (20–22). Recently, it is reported that, different from the formation of crystal LiF in liquid electrolytes, amorphous LiF was produced and uniformly distributed on the carbon matrix when a solid-state electrolyte was used (23). This may enable a reversible electrochemical reactivity of CF_x with lithium and provide a possibility for high-energy-density batteries. Nevertheless, CF_x must be synthesized in harsh conditions with precise control, leading to high cost and hindering the wide application (20). Some liquid and gas cathodes, such as SO₂, SOCl₂, and SF₆ (24–27), can also offer high energy densities, but they tend to be volatile and induce severe safety hazards, especially on the occasion of thermal runaway. Therefore, it is highly desired to develop feasible and reliable battery systems with high energy density.Organic electrode materials offer many merits compared with inorganic electrode materials, including structure diversity and designability, abundance of raw materials, relatively easy synthesis, and environmental friendliness (28–35). Their energy storage processes rely on the uptake of cations or anions on the active groups, such as carbonyl group, quaternary nitrogen, and nitroxyl radical (36–40). Most of them undergo one electron reaction, leading to limited specific capacity and energy density (Fig. 1). For example, one carbonyl group (C=O) can be converted into C-OLi structure via accepting one electron and one lithium ion (36), providing a theoretical specific capacity of 957 mAh⋅g⁻¹ (based on the mass of functional group as marked by dashed circle in Fig. 1). If considering the inactive components, insulating property, and high solubility of organic molecules, most organic electrode materials exhibit inferior specific capacities. Although a high specific capacity of 902 mAh⋅g⁻¹ was gained for cyclohexanehexone in LIBs, its high solubility induces significant challenges in practical applications (41). Recently, a Li-containing organic compound, dilithium 1,4-phenylenebis ((methylsulfonyl) amide) (Li₂-p-PDSA) was synthesized, offering a new design for organic electrode materials, while it still follows the single-electron reaction path per electroactive group and shows a low specific capacity of 194 mAh⋅g⁻¹ (42). Therefore, new battery system needs to be developed to take full advantage of organic electrode materials for high-energy-density LIBs.Open in a separate windowFig. 1.Reaction mechanisms of organic groups in batteries.In this work, we report a battery chemistry of six-electron reduction on nitro group (−NO₂) of nitroaromatic cathode. Based on such a reaction, 1,5-dinitronaphthalene (1,5-DNN; Fig. 2A) as a cathode in LIBs achieves an ultrahigh specific capacity of 1,338 mAh⋅g⁻¹ and energy density of 3,273 Wh⋅kg⁻¹. This is a record for organic electrode materials, even higher than inorganic electrode materials. It is identified that nitro groups are reduced to amino groups through a six-electron transfer reaction via multiple characterization techniques. Our findings provide a path for achieving high-energy-density Li-organic batteries.Open in a separate windowFig. 2.Electrochemical performance of 1,5-DNN. (A) Chemical structure of 1,5-DNN. (B and C) Galvanostatic charge/discharge profiles of 1,5-DNN. (D) Performance comparison of 1,5-DNN with reported organic/inorganic electrode materials in terms of energy density, specific capacity and voltage. Cathodes for comparison (references): 1, p-DNB (43); 2, Li₂C₆O₆ (49); 3, P14AQ (50); 4, PTO (51); 5, 3Q (31); 6, AQ (44); 7, C₆O₆ (41); 8, o-DNB (43); 9, m-DNB (43); 10, 4,5-PhenQ (51); 11, C4Q (52); 12, LiCoO₂ (53); 13, LiFePO₄ (54); 14, NCA (55); 15, NCM-811 (56); 16, Li-rich (57); 17, CF_x (21); 18, MnO₂ (58); 19 SOCl₂ (59), 20 SO₂ (24); 21, S (60).     

Continental crust beneath southeast Iceland

The magmatic activity (0–16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland—and especially the Öræfajökull volcano—is characterized by a unique enriched-mantle component (EM2-like) with elevated ⁸⁷Sr/⁸⁶Sr and ²⁰⁷Pb/²⁰⁴Pb. Here, we demonstrate through modeling of Sr–Nd–Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2–6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume.The North Atlantic Igneous Province covers vast areas in Baffin Island, Greenland, United Kingdom, Ireland, the Faroe Islands, and offshore regions (Fig. 1). Volcanic activity commenced ∼62 Mya (1) and is attributed to the impingement of a mantle plume head on the lithosphere (2). Enriched and depleted geochemical signatures in the Paleogene to Recent basalts from Iceland reflect a combination of plume-derived and shallow asthenospheric material, representing a classic case of plume–ridge interaction. The volcanic products of the Iceland plume have signatures of recycled oceanic crust and primordial-like material with high ³He/⁴He ratios (up to 50 R_A, where R_A is the ³He/⁴He ratio of air), spanning a range of refractory to fertile compositions (3, 4). Additional shallow-level contributions include the depleted mid-ocean ridge basalt–type asthenosphere, variably mixed with subcontinental lithospheric mantle material (5–8). The proximity of Iceland to the Jan Mayen Microcontinent (JMM) (Fig. 1) raises the question of whether Iceland includes underlying fragments of continental crust (9, 10). There are unconfirmed reports of both Precambrian and Mesozoic zircons in young basalts from Iceland, but only in abstract form (9, 11). The recovery of a 1.8-Ga-old grain from the most primitive Öræfajökull basalts (9) in southeast Iceland (Figs. 1 and ​and2A)2A) is potentially very interesting, although two Jurassic zircon grains (160 Ma) uncovered in the same separation are now suspected to be due to laboratory contamination.Open in a separate windowFig. 1.Crustal thickness map based on gravity inversion and revised location of the Iceland plume (white star symbols in 10-My intervals) relative to Greenland back to 60 Ma (see Fig. 6A for details). Transition between continental and oceanic crust (COB, black lines), plate boundaries (blue lines), site locations for dated North Atlantic Igneous Province magmatism (yellow circles with black fill), and the estimated size of the “classic” Jan Mayen Microcontinent (JMM) and the extended JMM (JMM-E) are also shown. The classic JMM is ∼500 km long (200 km at its widest and shown with four continental basement ridges), and crustal thicknesses are about 18–20 km (scale at Upper Left), which suggests considerable continental stretching before drifting off Greenland. We extend JMM 350 km southwestward (∼70 km wide) beneath southeast Iceland where we calculate maximum crustal thicknesses of ∼32 km (Fig. 2B). The size of JMM-E is a conservative estimate and could be as large as the white-stippled area. Öræfajökull location is shown as a yellow star.Open in a separate windowFig. 2.(A) Simplified geological map of Iceland outlining the major rift zones (RZ), rift zone central volcanoes (black outline), flank zone central volcanoes (colored outlines), the location of the Öræfajökull central volcano, and the position of the current plume axis of Shorttle et al. (25). Yellow areas are fissure swarms. WRZ, ERZ, NRZ, and MIB: Western, Eastern, and Northern Rift Zone and Mid-Iceland Belt, respectively. The stippled west-northwest–trending line through the plume axis depicts the position of the cross sections in Fig. 9. (B) Enlarged crustal thickness map (Fig. 1) with superimposed earthquake locations (earthquake.usgs.gov/earthquakes) and contour intervals (in meters) showing that the anomalously thick crust under southeast Iceland extends offshore to the northeast suggesting that it is a southerly fragment of the Jan Mayen Microcontinent (JMM) rather than an extension of the southeast-northwest–orientated Iceland-Faroes Ridge.     

North American tree migration paced by climate in the West,lagging in the East

Tree fecundity and recruitment have not yet been quantified at scales needed to anticipate biogeographic shifts in response to climate change. By separating their responses, this study shows coherence across species and communities, offering the strongest support to date that migration is in progress with regional limitations on rates. The southeastern continent emerges as a fecundity hotspot, but it is situated south of population centers where high seed production could contribute to poleward population spread. By contrast, seedling success is highest in the West and North, serving to partially offset limited seed production near poleward frontiers. The evidence of fecundity and recruitment control on tree migration can inform conservation planning for the expected long-term disequilibrium between climate and forest distribution.

Effective planning for the redistribution of habitats from climate change will depend on understanding demographic rates that control population spread at continental scales. Mobile species are moving, some migrating poleward (1, 2) and/or upward in elevation (3, 4). Species redistribution is also predicted for sessile, long-lived trees that provide the resource and structural foundation for global forest biodiversity (5–7), but their movement is harder to study. Contemporary range shifts are recognized primarily where contractions have followed extensive die-backs (8) or where local changes occur along compact climate gradients in steep terrain (9, 10). Whether migration capacity can pace habitat shifts of hundreds of kilometers on decade time scales depends on seed production and juvenile recruitment (Fig. 1A), which have not been fitted to data in ways that can be incorporated in models to anticipate biogeographic change (11–13). For example, do the regions of rapid warming coincide with locations where species can produce abundant seed (Fig. 1B)? If so, does seed production translate to juvenile recruitment? Here, we combine continent-wide fecundity estimates from the Masting Inference and Forecasting (MASTIF) network (13) with tree inventories to identify North American hotspots for recruitment and find that species are well-positioned to track warming in the West and North, but not in parts of the East.Open in a separate windowFig. 1.Transitions, hypothesized effects on spread, and sites. (A) Population spread from trees (BA) to new recruits is controlled by fecundity (seed mass per BA) followed by recruitment (recruits per seed mass). (B) The CTH that warming has stimulated fecundity ahead of the center of adult distributions, which reflect climate changes of recent decades. Arrows indicate how centroids from trees to fecundity to recruitment could be displaced poleward with warming climate. (C) The RSH that cold-sensitive fecundity is optimal where minimum temperatures are warmer than for adult trees and, thus, may slow northward migration. The two hypotheses are not mutually exclusive. B and C refer to the probability densities of the different life stages. (D) MASTIF sites are summarized in SI Appendix, Table S2.2 by eco-regions: mixed forest (greens), montane (blues), grass/shrub/desert (browns), and taiga (blue-green).Suitable habitats for many species are projected to shift hundreds of kilometers in a matter of decades (14, 15). While climate effects on tree mortality are increasingly apparent (16–19), advances into new habitats are not (20–23). For example, natural populations of Pinus taeda may be sustained only if the Northeast can be occupied as habitats are lost in the South (Fig. 2). Current estimates of tree migration inferred from geographic comparisons of juvenile and adult trees have been inconclusive (2, 7, 21, 24, 25). Ambiguous results are to be expected if fecundity and juvenile success do not respond to change in the same ways (20, 26–29). Moreover, seedling abundances (7, 30) do not provide estimates of recruitment rates because seedlings may reside in seedling banks for decades, or they may turn over annually (31–33). Another method based on geographic shifts in population centers calculated from tree inventories (3, 34) does not separate the effects of mortality from recruitment, i.e., the balance of losses in some regions against gains in others. The example in Fig. 2 is consistent with an emerging consensus that suitable habitats are moving fast (2, 14, 15), even if population frontiers are not, highlighting the need for methods that can identify recruitment limitation on population spread. Management for forest products and conservation goals under transient conditions can benefit from an understanding of recruitment limitation that comes from seed supply, as opposed to seedling survival (35).Open in a separate windowFig. 2.Suitable habitats redistribute with decade-scale climate change for P. taeda (BA units m² /ha). (Suitability is not a prediction of abundance, but rather, it is defined for climate and habitat variables included in a model, to be modified by management and disturbance [e.g., fire]. By providing habitat suitability in units of BA, it can be related it to the observation scale for the data.) Predictive distributions for suitability under current (A) and change expected from mid-21^st-century climate scenario Representative Concentration Pathway 4.5 (B) showing habitat declines in the Southwest and East. Specific climate changes important for this example include net increases in aridity in the southeast (especially summer) and western frontier and warming to the North. Occupation of improving habitats depends on fecundity in northern parts of the range and how it is responding. Obtained with Generalized Joint Attribute Modeling (see Materials and Methods for more information).We hypothesized two ways in which fecundity and recruitment could slow or accelerate population spread. Contemporary forests were established under climates that prevailed decades to centuries ago. These climate changes combine with habitat variables to affect seeds, seedlings, and adults in different ways (36, 37). The “climate-tracking hypothesis” (CTH) proposes that, after decades of warming and changing moisture availability (Fig. 3 A and B), seed production for many species has shifted toward the northern frontiers of the range, thus primed for poleward spread. “Fecundity,” the transition from tree basal area (BA) to seed density on the landscape (Fig. 1A), is taken on a mass basis (kg/m² BA) as a more accurate index of reproductive effort than seed number (38, 39). “Recruitment,” the transition from seed density to recruit density (recruits per kg seed), may have also shifted poleward, amplifying the impact of poleward shifts in fecundity on the capacity for poleward spread (Fig. 1B). Under CTH, the centers for adult abundance, fecundity, and recruitment are ordered from south to north in Fig. 1B as might be expected if each life-history stage leads the previous stage in a poleward migration.Open in a separate windowFig. 3.Climate change and tracking. (A) Mean annual temperatures since 1990 have increased rapidly in the Southwest and much of the North. (Zero-change contour line is in red.) (B) Moisture deficit index (monthly potential evapotranspiration minus P summed over 12 mo) has increased in much of the West. (Climate sources are listed in SI Appendix.) (C) Fecundity (kg seed per BA summed over species) is high in the Southeast. (D) Recruits per kg seed (square-root transformed) is highest in the Northeast. (E and F) Geographic displacement of 81 species show transitions in Fig. 1A, as arrows from centroids for adult BA to fecundity (E) and from fecundity to recruitment (F). Blue arrows point north; red arrows point south. Consistent with the RSH (Fig. 1B), most species centered in the East and Northwest have fecundity centroids south of adult distributions (red arrows in E). Consistent with the CTH, species of the interior West have fecundity centroids northwest of adults (blue arrows). Recruitment is shifted north of fecundity for most species (blue arrows in F). SI Appendix, Fig. S2 shows that uncertainty in vectors is low.The “reproductive-sensitivity hypothesis” (RSH) proposes that recruitment may limit population growth in cold parts of the range (Fig. 1C), where fecundity and/or seedling survival is already low. Cold-sensitive reproduction in plants includes late frost that can disrupt flowering, pollination, and/or seed development, suggesting that poleward population frontiers tend to be seed-limited (40–44). While climate warming could reduce the negative impacts of low temperatures, especially at northern frontiers, these regions still experience the lowest temperatures. The view of cold-sensitive fecundity as a continuing rate-limiting step, i.e., that has not responded to warming in Fig. 1C, is intended to contrast with the case where warming has alleviated temperature limitation in Fig. 1B. Lags can result if cold-sensitive recruitment naturally limits growth at high-latitude/high-altitude population frontiers (Fig. 1C). In this case, reproductive sensitivity may delay the pace of migration to an extent that depends on fecundity, recruitment, or both at poleward frontiers. The arrows in Fig. 1C depict a case where optimal fecundity is equator-ward of optimal growth and recruitment. The precise location of recruitment relative to fecundity in Fig. 1C will depend on all of the direct and indirect effects of climate, including through seed and seedling predators and disturbances like fire. Fig. 1C depicts one of many hypothetical examples to show that climate variables might have opposing effects on fecundity and recruitment.Both CTH and RSH can apply to both temperature and moisture; the latter is here quantified as cumulative moisture deficit between potential evapotranspiration and precipitation, D=∑m=112(PETm−Pm) for month m, derived from the widely used Standardized Precipitation Evapotranspiration Index (45). Whereas latitude dominates temperature gradients and longitude is important for moisture in the East, gradients are complicated by steep terrain in the West, with temperature tending to decline and moisture increase with elevation.We quantified the transitions that control population spread, from adult trees (BA) to fecundity (seeds per BA) to recruitment (recruits per kg seed) (Fig. 1A–C). Fecundity observations are needed to establish the link between trees and recruits in the migration process. They must be available at the tree scale across the continent because seed production depends on tree species and size, local habitat, and climate for all of the dominant species and size classes (13, 46). These estimates are not sufficient in themselves, because migration depends on seed production per area, not per tree. The per-area estimates come from individual seed production and dispersal from trees on inventory plots that monitor all trees that occupy a fixed sample area. Fecundity estimates were obtained in the MASTIF project (13) from 211,000 (211K) individual trees and 2.5 million (2.5M) tree-years from 81 species. We used a model that accommodates individual tree size, species, and environment and the codependence between trees and over time (Fig. 1C). In other words, it allows valid inference on fecundity, the quasisynchronous, quasiperiodic seed production typical of many species (47). The fitted model was then used to generate a predictive distribution of fecundity for each of 7.6M trees on 170K forest inventory plots across the United States and Canada. Because trees are modeled together, we obtain fecundity estimates per plot and, thus, per area. BA (m² /ha) of adult trees and new recruits into the smallest diameter class allowed us to determine fecundity as kg seed per m² BA and recruitment per kg seed, i.e., each of the transitions in Fig. 1A.Recruitment rates, rather than juvenile abundances, come from the transitions from seedlings to sapling stages. The lag between seed production and recruitment does not allow for comparisons on an annual basis; again, residence times in a seedling bank can span decades. Instead, we focus on geographic variation in mean rates of fecundity and recruitment.We summarized the geographic distributions for each transition as 1) the mean transition rates across all species and 2) the geographic centroids (central tendency) for each species as weighted-average locations, where weights are the demographic transitions (BA to fecundity, fecundity to recruitment, and BA to recruitment). We analyzed central tendency, or centroids (e.g., refs. 3 and 34) because range limits cannot be accurately identified on the basis of small inventory plots (21). If fecundity is not limiting poleward spread (CTH of Fig. 1B), then fecundity centroids are expected to be displaced poleward from the adult population. If reproductive sensitivity dominates population spread (RSH of Fig. 1C), then fecundity and/or recruitment centroids will be displaced equator-ward from adult BA. The same comparisons between fecundity and recruitment determine the contribution of recruitment to spread.     

Studies on enmetazobactam clarify mechanisms of widely used β-lactamase inhibitors

β-Lactams are the most important class of antibacterials, but their use is increasingly compromised by resistance, most importantly via serine β-lactamase (SBL)-catalyzed hydrolysis. The scope of β-lactam antibacterial activity can be substantially extended by coadministration with a penicillin-derived SBL inhibitor (SBLi), i.e., the penam sulfones tazobactam and sulbactam, which are mechanism-based inhibitors working by acylation of the nucleophilic serine. The new SBLi enmetazobactam, an N-methylated tazobactam derivative, has recently completed clinical trials. Biophysical studies on the mechanism of SBL inhibition by enmetazobactam reveal that it inhibits representatives of all SBL classes without undergoing substantial scaffold fragmentation, a finding that contrasts with previous reports on SBL inhibition by tazobactam and sulbactam. We therefore reinvestigated the mechanisms of tazobactam and sulbactam using mass spectrometry under denaturing and nondenaturing conditions, X-ray crystallography, and NMR spectroscopy. The results imply that the reported extensive fragmentation of penam sulfone–derived acyl–enzyme complexes does not substantially contribute to SBL inhibition. In addition to observation of previously identified inhibitor-induced SBL modifications, the results reveal that prolonged reaction of penam sulfones with SBLs can induce dehydration of the nucleophilic serine to give a dehydroalanine residue that undergoes reaction to give a previously unobserved lysinoalanine cross-link. The results clarify the mechanisms of action of widely clinically used SBLi, reveal limitations on the interpretation of mass spectrometry studies concerning mechanisms of SBLi, and will inform the development of new SBLi working by reaction to form hydrolytically stable acyl–enzyme complexes.

β-Lactamases are a major mechanism of resistance to the clinically vital β-lactam antibiotics, with >2,000 different β-lactamases reported (1). β-Lactamases are grouped into classes A, C, and D, which employ a nucleophilic serine in catalysis (serine β-lactamases, SBLs), and class B, which employ metal ions in catalysis (2). Presently, SBLs are the most important β-lactamases from a clinical perspective. SBL inhibitors (SBLi) have been developed for use in combination with a β-lactam antibiotic, with tazobactam (3), sulbactam (4), and clavulanic acid (5) being the most widely used SBLi. These SBLi all contain a β-lactam ring which reacts with SBLs to produce an acyl–enzyme complex (AEC) intermediate, as is also the case for efficient SBL substrates (Fig. 1A). With efficient substrates the β-lactam–derived AEC is readily hydrolyzed. With SBLi the reaction bifurcates at the AEC stage; in addition to hydrolysis, reaction of the AEC via opening of the β-lactam fused five-membered ring occurs to give one or more relatively hydrolytically stable species (Figs. 1B and ​and2).2). The nature of these species is central to SBLi inhibition and has been studied by crystallography (6–11) and ultraviolet-visible (UV/Vis) (10, 12) and Raman (6, 7, 9, 12–15) spectroscopy, as well as different types of mass spectrometry (MS) (10, 16–22).Open in a separate windowFig. 1.Sulfone derivatives of penicillins are potent clinically used mechanism-based inhibitors of SBLs. (A) Outline mechanism for penicillin hydrolysis as catalyzed by SBLs; reaction proceeds via an AEC, which is efficiently hydrolyzed. (B) Sulfone derivatives of penicillins are SBLi that react to give one or more hydrolytically stable complex(es), the nature of which was the focus of our work.Open in a separate windowFig. 2.Pathways for reactions of penam sulfones with SBLs. Following initial acyl–enzyme 2 formation the main transient inactivation pathway occurs via thiazolidine ring opening to give species 3-5 which are relatively stable to hydrolysis. Fragmentation of 3-5 can occur in rare cases and is promoted by acid to give 6-8 or heat to give 11. In rare cases fragmentation of 2-5 can result in irreversible inactivation of the SBL to give 9 and 10. Efficient hydrolysis of the β-lactam occurs to give a β-amino acid product 12, which in solution fragments to give 13-16. Our results imply biologically relevant inhibition involves 3-5, or equivalent mass species.The structures of tazobactam and sulbactam are closely related to those of the penicillins; they differ by lack of a C-6 side chain, functionalization of the pro-S methyl group (in case of tazobactam), and by oxidation of the thiazolidine to a sulfone. These differences result in a loss of useful antibacterial activity but a gain of potent SBL inhibition. Although the presence of sulfur in drugs is common [e.g., sulfonamide antibiotics (23)] and there is growing interest in covalently acting drugs (24, 25), sulfones are rare in drugs and, as far as we are aware, sulbactam and tazobactam are the only clinically approved sulfone-containing drugs working by covalent reaction with their targets (26–28).Since the clinical introduction of the pioneering SBLi, β-lactamases have evolved and SBLi use is increasingly compromised by extended spectrum β-lactamases (ESBLs) and inhibitor-resistant SBLs (29). Efforts have been made to develop new SBLi, including those with and without a β-lactam. The latter include diazabicyclooctanes (30) and cyclic boronates (31, 32). However, β-lactam–containing SBLi remain of most clinical importance. Among SBLi in clinical development, enmetazobactam (formerly AAI-101; Fig. 1) is of particular interest because it is a “simple” N-methylated derivative of the triazole ring of tazobactam (33). In combination with cefepime, enmetazobactam is reported to manifest substantially better antimicrobial properties against class A ESBL-producing strains than the commonly used piperacillin/tazobactam combination (20, 33, 34).We report studies on the mechanism of SBL inhibition by enmetazobactam using denaturing and nondenaturing (native) MS methods, NMR spectroscopy, and crystallography. The results led us to reevaluate the mechanisms of SBL inhibition by the clinically important sulfone-containing SBLi, i.e., tazobactam and sulbactam, and reveal limitations on the interpretation of MS studies concerning SBL inhibition.     

Spatiotemporal evolution of the Jehol Biota: Responses to the North China craton destruction in the Early Cretaceous

The Early Cretaceous Jehol Biota is a terrestrial lagerstätte that contains exceptionally well-preserved fossils indicating the origin and early evolution of Mesozoic life, such as birds, dinosaurs, pterosaurs, mammals, insects, and flowering plants. New geochronologic studies have further constrained the ages of the fossil-bearing beds, and recent investigations on Early Cretaceous tectonic settings have provided much new information for understanding the spatiotemporal distribution of the biota and dispersal pattern of its members. Notably, the occurrence of the Jehol Biota coincides with the initial and peak stages of the North China craton destruction in the Early Cretaceous, and thus the biotic evolution is related to the North China craton destruction. However, it remains largely unknown how the tectonic activities impacted the development of the Jehol Biota in northeast China and other contemporaneous biotas in neighboring areas in East and Central Asia. It is proposed that the Early Cretaceous rift basins migrated eastward in the northern margin of the North China craton and the Great Xing’an Range, and the migration is regarded to have resulted from eastward retreat of the subducting paleo-Pacific plate. The diachronous development of the rift basins led to the lateral variations of stratigraphic sequences and depositional environments, which in turn influenced the spatiotemporal evolution of the Jehol Biota. This study represents an effort to explore the linkage between terrestrial biota evolution and regional tectonics and how plate tectonics constrained the evolution of a terrestrial biota through various surface geological processes.

The Early Cretaceous Jehol Biota has been well known for producing hundreds of exceptionally preserved fossils, including feathered dinosaurs, birds, mammals, pterosaurs, lizards, turtles, choristoderes, amphibians, fishes, as well as abundant insects and flowering plants (1–5). Many vertebrate fossils are preserved as completely articulated skeletons, and some are even associated with gut contents, showing direct evidence of their diets (6, 7). It is most notable that the Jehol fossils often preserve soft tissues in great fidelity, such as skins, feathers, hairs, wing membranes, ovarian follicle, lung, and foot webs (8–10). Micro- or even nanoscale structures, including melanosomes and even beta keratins, have been reported (11–14). These fossils with superb quality have made them feasible to address a number of important issues on vertebrate evolution, e.g., the origin and early evolution of birds and their flight, origin of feathers, and origin and early evolution of mammals and their middle ear bones (15–17). The Jehol fossils also preserve much information about paleoecology of terrestrial biota, and thus can be used to investigate the Early Cretaceous terrestrial ecosystem (1, 18–20).The Jehol Biota has been extensively studied. Understanding of its composition and distribution depends on how the Jehol Biota is defined. Traditionally, the Jehol Biota is defined by three typical elements: the conchostracan Eosetheria, the insect Ephemeropsis, and the fish Lycoptera. The Jehol Biota sensu stricto is normally considered in the literature to have a limited paleogeographic distribution in northeast China, whereas the Jehol Biota sensu lato is distributed across the whole of northern China and neighboring regions in eastern and central Asia (21). The recent paleoecology-based definition of the biota is similar to the Jehol Biota sensu stricto (22) and is followed here. According to the new definition, the Jehol Biota only occurs, in ascending order, in the Huajiying, Yixian, and Jiufotang formations in northern Hebei, western Liaoning, and southeast Inner Mongolia (22), in which volcanic and volcaniclastic beds are commonplace (23, 24). The growing geochronologic data now put a tight constraint on the ages of the fossil-bearing units, which indicate that the Jehol Biota spanned from approximately 135 to 120 Ma (25–28).The North China craton (NCC) is one of the key elements of eastern Asian continental geology and usually divided into the eastern and western blocks, which were welded by the Trans-North China Orogen in the Paleoproterozoic orogeny (∼1.90 to 1.85 Ga) (29) (Fig. 1). The NCC had remained tectonically stable until the late Mesozoic when decratonization took place. The decratonization is accompanied by vigorous magmatism, rifting, strike-slip faulting, and transformation of lithospheric nature (30). It is generally regarded that the destruction of the NCC was triggered by the combined tectonic processes, including high-angle subduction, trench retreat, and rollback of the paleo-Pacific plate during the late Mesozoic (30–33).Open in a separate windowFig. 1.Spaciotemporal distribution of the Jehol Biota and its contemporaneous or nearly contemporaneous biotas in East and Central Asia. The Jehol Biota and its contemporaneous biotas are largely north-southerly distributed during the first evolving stage, along the western margin of the east block of the North China craton (NCC) (dotted line), and expanded eastward, westward, and southward during the second (dash line) and third stages (solid line). The Inset shows the distribution of the major vertebrate-bearing horizons of the Jehol Biota in northern Hebei, western Liaoning, and southeast Inner Mongolia in the northern margin of central and eastern blocks of the NCC, with red, green, and blue circles denoting localities from the first, second, and third stages, respectively. 1, Sichakou; 2, Senjitu; 3, Lujiatun; 4, Boluochi; 5, Meileyingzi; 6, Shangheshou; 7, Sihetun; 8, Jinggangshan; 9, Daxinfangzi; 10, Fengshan; 11, Dawangzhangzi; 12, Dapingfang; 13, Xiaotaizi; 14, Shifo; 15, Liutiaogou; 16, Shixia; 17, Sihedang; 18, Wutun; 19, Dawujiazi; and 20, Baicaigou.It is worth noting that the Jehol Biota evolution is in accord with the NCC destruction in time and space (19, 20, 31, 33), with its flourishing period of around 125 Ma coincident with the peak of the NCC destruction. Also noticeable is that the Jehol Biota is mostly distributed in the northern margin of the eastern NCC, where the destruction is most severe (19, 33). It is also shown that magmatism, sedimentation, and biota migrated toward the east with time during the Early Cretaceous, as indicated by the east-younging trends of volcanic eruption, basin initiation, and beginning of the Jehol elements in northeastern China (32). All the spatiotemporal changes in magmatism, stratigraphy, basin tectonics, and biota were possibly linked to the various subduction processes of the western paleo-Pacific plate, such as the trench retreat and slab rollback. This study aims to review the latest development in the study of the western paleo-Pacific plate subduction and its possible controls of the evolution and distribution of the Jehol Biota through various surface processes, such as basin development. The focus is on the spatiotemporal evolution of the Jehol Biota and contemporaneous biotas in East and Central Asia, exploring their possible relationship with coeval destruction processes of the NCC.Spatiotemporal Distribution of the Jehol Biota.Recent discoveries of fossils and newly obtained isotopic ages of the Jehol fossil-bearing stratigraphic units have significantly refined our understanding of the temporal (chronological) and spatial (geographic) distribution of the Jehol and contemporaneous biotas in East and Central Asia. The Jehol Biota is generally divided into three evolving stages, i.e., Jehol Biota stages I to III (JBS I to III), as represented by fossil assemblages from the Huajiying, Yixian, and Jiufotang formations, respectively (18, 20, 22). More fossils are discovered in recent years not only from the Jehol Biota in northern China but also from contemporaneous deposits in Mongolia, Japan, Korea, and Transbaikalia of Russia (18). An updated chronological framework has been built for more precise regional stratigraphic and biotal correlations. All the results help to elaborate the origin, evolution, and spatiotemporal distribution of various biological groups in the Jehol Biota during the Early Cretaceous (28).The earliest occurrence of the Jehol Biota (JBS I) was best recorded in the Huajiying Formation in Fengning (equivalent to the Dabeigou Formation in Luanping), northern Hebei Province (Fig. 1). The unit is composed mainly of thin-bedded mudstones with abundant tuff interlayers, and the fossils are exceptionally well preserved. Soft tissues can be recognized and are often associated with completely articulated vertebrate skeletons. In addition, there occur conchostracan (clam shrimp) assemblage Nestoria-Keratestheria and the ostrocod assemblage Darwinula-Luanpingella-Eoparacypris (Fig. 2 A and B) (21), which are of significance in stratigraphic correlation. The vertebrate assemblages are also very common. The fossil birds Protopteryx, Eoconfuciusornis, and Eopengornis document the earliest and lowermost member of the Enantiornithes, Confuciusornithidae, and Pengornithidae, respectively (34–36). Other important vertebrate assemblages include acipenseriform fishes, a compsognathid dinosaur, and a newly discovered mammal. A recently described bird in the Huajiying Formation in Weichang, northern Hebei can also be an early-stage representative of the Jehol Biota (37). The first stage (JBS I) spans from ∼135 to 127 Ma (38) based on new geochronologic data, thereby recording the earliest avian radiation in the Early Cretaceous.Open in a separate windowFig. 2.Photographs of selected fossils of the Jehol Biota with biostratigraphic and paleogeographic significance. (A and B) Typical and common fossils of JBS I: Nestoria (A; Diplostraca: Spinicaudata), and Darwinula (B; Crustacea: Ostracoda), both mainly distributed in northern Hebei and the Great Xing’an Range of China and Transbaikalia of Russia. (C–F) Common fossils from JBS II and III: Eosestheria (C; Arthropoda: Conchostraca), and Lycoptera davidi (D; Osteichthyes: Osteoglossomorpha), both extensively distributed in northern and northeast China, Mongolia, Korea, and Transbaikalia of Russia; (E) Monjurosuchus (Reptilia: Choristodera), found in northern China and Japan; (F) Psittacosaurus (Dinosauria: Ornithischia), found in northern China, Mongolia, and Transbaikalia of Russia. (Scale bars: 5 mm [A], 100 μm [B], 10 mm [C, D], 20 mm [E], 50 mm [F].)JBS II is represented by fossil assemblages in the Yixian Formation in western Liaoning and similar deposits in northern Hebei and southern Inner Mongolia (18, 20). The fossils are present in two different types of sedimentary facies. The first type of sedimentary facies is shales and thin-bedded mudstones with many tuff interlayers, making up the Jianshangou Bed of the lower Yixian Formation. This type of facies archives many well-preserved two-dimensional articulated skeletons often with soft tissues. The second type of sedimentary facies is characterized by massive, tuffaceous, pebbly sandstones, as represented by the Lujiatun Bed at the base of the Yixian Formation. Articulated vertebrate skeletons in this type of facies are usually three-dimensional and have no trace of soft tissues (18, 24). The Yixian Formation records the first great species diversification of the Jehol Biota. The second stage of the Jehol Biota (JBS II) spans only 2 Ma from ∼126 Ma to ∼124 Ma (39). This short period, however, witnesses the second great species diversification, as indicated by the fossil assemblage containing diverse birds, dinosaurs, pterosaurs, mammals, lizards, turtles, choristoderes, amphibians, fishes, as well as insects and plants like angiosperms (18).JBS III is best represented by fossil assemblages that primarily occur in the Jiufotang Formation in western Liaoning and in coeval stratigraphic units in northern Hebei and southern Inner Mongolia (18, 20). The units are mainly composed of interbedded mudstone, siltstone, and fine-grained sandstone, and tuffs are also common in the sequences. The fossils are mostly two-dimensional, but soft tissues are less well preserved compared with the fossils in the Huajiying and Yixian formations. JBS III is roughly represented by fossils from 124 Ma to 120 Ma in western Liaoning (26). The fossil assemblage in the Jiufotang Formation also displays a remarkable differentiation of vertebrates, including birds, dinosaurs, pterosaurs, mammals, lizards, turtles, choristoderes, amphibians, and fishes (18).The fossils of biostratigraphic significance (e.g., conchosracans and ostracods) in JBS II and III are hardly distinguishable but distinct from JBS I fossils that are characterized by the appearance of Eosetheria (Fig. 2C) in the conchostracan assemblage and Cypridea in the ostrocod assemblage, respectively. Although JBS I is only distributed in northern Hebei Province, the contemporaneous units in Inner Mongolia, Heilongjiang, Mongolia, and Siberia contain some fossil elements (e.g., conchostracan Nestoria and Keratestheria) that are correlatable with JBS I. It is important to note that JBS I and contemporaneous biotas are distributed in many rift basins that develop in a NE- or NNE-oriented zone west of the Great Xing’an Range (38, 40). The earliest Cretaceous biotas are also found in the Transbaikalia in Siberia (41). JBS I contains several early birds, as discovered in the Huajiying Formation in Hebei Province. However, there is yet no documentation of bird fossils in the contemporaneous strata in other areas of East Asia. Hence, the Jehol Biota and its contemporaneous biotas in eastern and central Asia exhibit a limited paleogeographic distribution in northeast Asia and Siberia during the earliest Cretaceous (Fig. 1). The JBS I vertebrate assemblage, particularly the bird assemblage that is mainly composed of stem members, is basically less diverse than those of the two younger stages (Fig. 3), confirming that northern Hebei might be the center of the initiation, early differentiation, and evolution of the Jehol Biota.Open in a separate windowFig. 3.Chronological distribution of Jehol birds. Time-scaled phylogeny of Mesozoic birds is modified with permission from ref. 54. Data from refs. 26–28. The purple arrowheads denote that taxa from the Huajiying Formation often emerge as the basalmost phylogenetic position of corresponding clades, with two exceptions (yellow arrowheads). A simple count of avian species unearthed from the three formations (Huajiying: 6 taxa; Yixian: 21 taxa; Jiufotang: 36 taxa) of the Jehol Biota shows that the youngest Jiufotang Formation yielded more species than the others (^aref. 28; ^bref. 27; and ^cref. 26).Jehol Biota stages II and III start from the middle Early Cretaceous and the fossil assemblages are best preserved in western Liaoning. The contemporaneous or subcontemporaneous biotas occur in many other areas in NE Asia, such as Hebei, Inner Mongolia, Shandong, Jilin, and Heilongjiang provinces of China, Japan, Korea, and Transbaikalia of Russia, and share with the Jehol Biota more or less typical Jehol fossils. In addition to some biostratigraphically important invertebrates like Eoestheria and Cypridea, several other vertebrate taxa have also been reported in these regions, including the fishes Acipenseriformes, Osteoglossomorphs (e.g., Lycoptera) (Fig. 2D), the aquatic or semiaquatic reptilian Choristoderes (e.g., Monjurosuchus) (Fig. 2E) (42–44), the Squamates, the dinosaurian Psittacosauridae (e.g., Psittacosaurus) (Fig. 2F), and the avians Confuciusornithidae (9, 45), Enantiornithes, and Ornithuromorpha, etc. (46). Obviously, the Jehol Biota and its contemporaneous biotas have significantly expanded laterally in East and Central Asia during the middle Early Cretaceous. Compared with the early Early Cretaceous fossil assemblages, some elements of the Jehol Biota have expanded toward the east, west, and south (Fig. 1). The study of biotic composition and phylogenetic relationships will help reveal the paleogeographic history of the biota.Spatiotemporal Evolution of Rift Basins in Response to the NCC Destruction. It is generally accepted that the destruction of the NCC was triggered by the paleo-Pacific plate subduction (31–33). Trench retreat and slab rollback are considered as the main mechanisms for late Mesozoic lithospheric stretching of the NCC, as manifested by widespread magmatism and occurrences of rift basins and metamorphic core complexes (32, 33). It is hypothesized that the Jehol Biota evolution might have been born on these tectonic processes (19, 31, 33). The NCC experienced diachronous destruction in the late Mesozoic, as indicated by time-space variations of magmatism and rifting (33). The Middle Jurassic magmatism mainly occurred in the easternmost NCC and then migrated westward in the Late Jurassic. In contrast, the Early Cretaceous magmatism shows a younging trend from west to east across the eastern NCC (32, 33).The eastern NCC destruction involves the thinning of the lithosphere from ∼200 km in the Paleozoic to ∼80 km in the Cenozoic. As a result, the NCC lithosphere displays rapid thickness change across the boundary between the eastern and western blocks of the NCC. The eastern block has been greatly attenuated and decratonized in the late Mesozoic, contrasting strikingly with the western block that has remained stable throughout the Mesozoic. Rift basins developed in the period from the Middle Jurassic to Early Cretaceous in the eastern NCC, and basin successions are well preserved in the northern margin of the NCC (29, 32). Three phases of crustal shortening, which are usually called phases A–C of the Yanshanian Movement in the literature. The three contractional events interrupted the rift basin development and resulted in three regional unconformities within Late Mesozoic strata. The first unconformity is between the Middle and Upper Jurassic, registering the phase A contraction from 170 to 165 Ma (32, 47). The second unconformity displays the marked change in timing and duration from west to east (Fig. 4). The Lower Cretaceous volcanics above the second unconformity are dated at 143 Ma in the west of the northern NCC and then gradually get younger to the east, spanning 136 to 123 Ma (Fig. 4). The third unconformity separates Lower from Upper Cretaceous strata. The three unconformities divide Late Mesozoic successions into three distinct sequences, which record three stages of rift basins in the northern NCC. In other words, Late Mesozoic rift basin development was punctuated by three phases of crustal shortening, leading to the sequential inversion of the Middle Jurassic, Late Jurassic, and Early Cretaceous rift basins, respectively (33). This study is mainly concerned with the development of rift basins after the phase B contractile event or the Early Cretaceous basins where the Jehol Biota dwelled. As indicated by the ages of basal volcanics of the Lower Cretaceous sequences, the rift basins in the northern NCC did not initiate simultaneously but occurred early in the west. The Jingxi basin initiated around 145 Ma, whereas the basins in eastern Liaoning had not started until ∼125 Ma (Figs. 1 and ​and44).Open in a separate windowFig. 4.Spatiotemporal distribution of the Early Cretaceous fossil-bearing volcaniclastic deposits and corresponding biotas in northeastern China, showing the progressive eastward younging trend.Paleogeographic study suggested that from the Late Jurassic to early Early Cretaceous, the NNE-trending Great Xing’an Range-Yanshan Mountain area contrasts with the North China Highland (which had remained until the middle Early Cretaceous) on the east (40). By the late Early Cretaceous, the North China Highland disappeared and it was replaced by the Great Xing’an Range Highland on the west. It is also notable that during the Early Triassic, the Central Asian Orogenic Belt was formed with the closure of the paleo-Asian Ocean between the NCC and Siberian craton (29). The Great Xing’an Range, as part of the Xing’an Mongolian Orogenic Belt, which is the eastern part of the Central Asian Orogenic Belt, merged with the northern margin of the NCC and the southern margin of the Siberian craton. Therefore, the subduction of the paleo-Pacific Ocean had not only resulted in the destruction of the NCC, but also had greatly controlled tectonic activity, basin development, and biotal evolution of the Great Xing’an Range and the Transbaikalia since the early Early Cretaceous.     

Chlorination of arenes via the degradation of toxic chlorophenols

Aryl chlorides are among the most versatile synthetic precursors, and yet inexpensive and benign chlorination techniques to produce them are underdeveloped. We propose a process to generate aryl chlorides by chloro-group transfer from chlorophenol pollutants to arenes during their mineralization, catalyzed by Cu(NO₃)₂/NaNO₃ under aerobic conditions. A wide range of arene substrates have been chlorinated using this process. Mechanistic studies show that the Cu catalyst acts in cooperation with NO_x species generated from the decomposition of NaNO₃ to regulate the formation of chlorine radicals that mediate the chlorination of arenes together with the mineralization of chlorophenol. The selective formation of aryl chlorides with the concomitant degradation of toxic chlorophenol pollutants represents a new approach in environmental pollutant detoxication. A reduction in the use of traditional chlorination reagents provides another (indirect) benefit of this procedure.

Chlorophenols are widely encountered moieties present in herbicides, drugs, and pesticides (1). Owing to the high dissociation energies of carbon‒chloride bonds, chlorophenols biodegrade very slowly, and their prolonged exposure leads to severe ecological and environmental problems (Fig. 1A) (2–4). Several well-established technologies have been developed for the treating of chlorophenols, including catalytic oxidation (5–11), biodegradation (12–15), solvent extraction (16, 17), and adsorption (18–20) Among these methods, adsorption is the most versatile and widely used method due to its high removal efficiency and simple operation, but the resulting products are of no value, and consequently, these processes are not viable.Open in a separate windowFig. 1.Background and reaction design. (A) Examples of chlorophenol pollutants. (B) Examples of aryl chlorides. (C) The chlorination process reported herein was based on chloro-group transfer from chlorophenol pollutants.With the extensive application of substitution reactions (21, 22), transfunctionalizations (23, 24), and cross-coupling reactions (25, 26), aryl chlorides are regarded as one of the most important building blocks widely used in the manufacture of polymers, pharmaceuticals, and other types of chemicals and materials (Fig. 1B) (27–31). Chlorination of arenes is usually carried out with toxic and corrosive reagents (32–34). Less toxic and more selective chlorination reagents tend to be expensive [e.g., chloroamides (35, 36)] and are not atom economic (37–39). Consequently, from the perspective of sustainability, the ability to transfer a chloro group from unwanted chlorophenols to other substrates would be advantageous.Catalytic isofunctional reactions, including transfer hydrogenation and alkene metathesis, have been widely exploited in organic synthesis. We hypothesized that chlorination of arenes also could be achieved by chloro-group transfer, and since stockpiles of chlorophenols tend to be destroyed by mineralization and chlorophenol pollutants may be concentrated by adsorption (18–20), they could be valorized as chlorination reagents via transfer of the chloro group to arene substrates during their mineralization, thereby adding value to the destruction process (Fig. 1C). Although chlorophenol pollutants are not benign, their application as chlorination reagents, with their concomitant destruction to harmless compounds, may be considered as not only meeting the criteria of green chemistry but also potentially surpassing it. Herein, we describe a robust strategy to realize chloro-group transfer from chlorophenol pollutants to arenes and afford a wide range of value-added aryl chlorides.     

Taxodione and arenarone inhibit farnesyl diphosphate synthase by binding to the isopentenyl diphosphate site

We used in silico methods to screen a library of 1,013 compounds for possible binding to the allosteric site in farnesyl diphosphate synthase (FPPS). Two of the 50 predicted hits had activity against either human FPPS (HsFPPS) or Trypanosoma brucei FPPS (TbFPPS), the most active being the quinone methide celastrol (IC₅₀ versus TbFPPS ∼20 µM). Two rounds of similarity searching and activity testing then resulted in three leads that were active against HsFPPS with IC₅₀ values in the range of ∼1–3 µM (as compared with ∼0.5 µM for the bisphosphonate inhibitor, zoledronate). The three leads were the quinone methides taxodone and taxodione and the quinone arenarone, compounds with known antibacterial and/or antitumor activity. We then obtained X-ray crystal structures of HsFPPS with taxodione+zoledronate, arenarone+zoledronate, and taxodione alone. In the zoledronate-containing structures, taxodione and arenarone bound solely to the homoallylic (isopentenyl diphosphate, IPP) site, not to the allosteric site, whereas zoledronate bound via Mg²⁺ to the same site as seen in other bisphosphonate-containing structures. In the taxodione-alone structure, one taxodione bound to the same site as seen in the taxodione+zoledronate structure, but the second located to a more surface-exposed site. In differential scanning calorimetry experiments, taxodione and arenarone broadened the native-to-unfolded thermal transition (T_m), quite different to the large increases in ΔT_m seen with biphosphonate inhibitors. The results identify new classes of FPPS inhibitors, diterpenoids and sesquiterpenoids, that bind to the IPP site and may be of interest as anticancer and antiinfective drug leads.Farnesyl diphosphate synthase (FPPS) catalyzes the condensation of isopentenyl diphosphate (IPP; compound 1 in Fig. 1) with dimethylallyl diphosphate (DMAPP; compound 2 in Fig. 1) to form the C₁₀ isoprenoid geranyl diphosphate (GPP; compound 3 in Fig. 1), which then condenses with a second IPP to form the C₁₅ isoprenoid, farnesyl diphosphate (FPP; compound 4 in Fig. 1). FPP then is used in a wide range of reactions including the formation of geranylgeranyl diphosphate (GGPP) (1), squalene (involved in cholesterol and ergosterol biosynthesis), dehydrosqualene (used in formation of the Staphylococcus aureus virulence factor staphyloxanthin) (2), undecaprenyl diphosphate (used in bacterial cell wall biosynthesis), and quinone and in heme a/o biosynthesis. FPP and GGPP also are used in protein (e.g., Ras, Rho, Rac) prenylation, and FPPS is an important target for the bisphosphonate class of drugs (used to treat bone resorption diseases) such as zoledronate (compound 5 in Fig. 1) (3). Bisphosphonates targeting FPPS have activity as antiparasitics (4), act as immunomodulators (activating γδ T cells containing the Vγ2Vδ2 T-cell receptor) (5), and switch macrophages from an M2 (tumor-promoting) to an M1 (tumor-killing) phenotype (6). They also kill tumor cells (7) and inhibit angiogenesis (8). However, the bisphosphonates in clinical use (zoledronate, alendronate, risedronate, ibandronate, etidronate, and clodronate) are very hydrophilic and bind avidly to bone mineral (9). Therefore, there is interest in developing less hydrophilic species (10) that might have better activity against tumors in soft tissues and better antibacterial (11) and antiparasitic activity.Open in a separate windowFig. 1.Chemical structures of FPPS substrates, products, and inhibitors.The structure of FPPS (from chickens) was first reported by Tarshis et al. (12) and revealed a highly α-helical fold. The structures of bacterial and Homo sapiens FPPS (HsFPPS) are very similar; HsFPPS structure (13, 14) is shown in Fig. 2A. There are two substrate-binding sites, called here “S1” and “S2.” S1 is the allylic (DMAPP, GPP) binding site to which bisphosphonates such as zoledronate bind via a [Mg²⁺]₃ cluster (15) (Fig. 2B). S2 is the homoallylic site to which IPP binds, Fig. 2B. Recently, Jahnke et al. (10) and Salcius et al. (16) discovered a third ligand-binding site called the “allosteric site” (hereafter the “A site”). A representative zoledronate+A-site inhibitor structure [Protein Data Bank (PDB) ID code 3N46] (Nov_980; compound 6 in Fig. 1) showing zoledronate in S1 and Nov_980 (compound 6) in the A site is shown in a stereo close-up view in Fig. 2B, superimposed on a zoledronate+IPP structure (PDB ID code 2F8Z) in S2. Whether the allosteric site serves a biological function (e.g., in feedback regulation) has not been reported. Nevertheless, highly potent inhibitors (IC₅₀ ∼80 nM) have been developed (10), and the best of these newly developed inhibitors are far more hydrophobic than are typical bisphosphonates (∼2.4–3.3 for cLogP vs. ∼−3.3 for zoledronate) and are expected to have better direct antitumor effects in soft tissues (10).Open in a separate windowFig. 2.Structures of human FPPS. (A) Structure of HsFPPS showing zoledronate (compound 5) and IPP (compound 1) bound to the S1 (allylic) and S2 (homoallylic) ligand-binding sites (PDB ID code 2F8Z). (B) Superposition of the IPP-zoledronate structure (PDB ID code 2F8Z) on the zoledronate-Nov_980 A-site inhibitor structure (PDB ID code 3N46). Zoledronate binds to the allylic site S1, IPP binds to the homoallylic site S2, and the allosteric site inhibitor binds to the A site. Active-site “DDXXD” residues are indicated, as are Mg²⁺ molecules (green and yellow spheres, respectively). The views are in stereo.In our group we also have developed more lipophilic compounds (e.g., compound 7 in Fig. 1) (17, 18) as antiparasitic (19) and anticancer drug leads (18) and, using computational methods, have discovered other novel nonbisphosphonate FPPS inhibitors (e.g., compound 8 in Fig. 1) that have micromolar activity against FPPS (20). In this study, we extended our computational work and tried to discover other FPPS inhibitors that target the A site. Such compounds would be of interest because they might potentiate the effects of zoledronate and other bisphosphonates, as reported for other FPPS inhibitors (21), and have better tissue distribution properties in general.     

Photosynthetic reaction center variants made via genetic code expansion show Tyr at M210 tunes the initial electron transfer mechanism

Photosynthetic reaction centers (RCs) from Rhodobacter sphaeroides were engineered to vary the electronic properties of a key tyrosine (M210) close to an essential electron transfer component via its replacement with site-specific, genetically encoded noncanonical amino acid tyrosine analogs. High fidelity of noncanonical amino acid incorporation was verified with mass spectrometry and X-ray crystallography and demonstrated that RC variants exhibit no significant structural alterations relative to wild type (WT). Ultrafast transient absorption spectroscopy indicates the excited primary electron donor, P*, decays via a ∼4-ps and a ∼20-ps population to produce the charge-separated state P⁺H_A⁻ in all variants. Global analysis indicates that in the ∼4-ps population, P⁺H_A⁻ forms through a two-step process, P*→ P⁺B_A⁻→ P⁺H_A⁻, while in the ∼20-ps population, it forms via a one-step P* → P⁺H_A⁻ superexchange mechanism. The percentage of the P* population that decays via the superexchange route varies from ∼25 to ∼45% among variants, while in WT, this percentage is ∼15%. Increases in the P* population that decays via superexchange correlate with increases in the free energy of the P⁺B_A⁻ intermediate caused by a given M210 tyrosine analog. This was experimentally estimated through resonance Stark spectroscopy, redox titrations, and near-infrared absorption measurements. As the most energetically perturbative variant, 3-nitrotyrosine at M210 creates an ∼110-meV increase in the free energy of P⁺B_A⁻ along with a dramatic diminution of the 1,030-nm transient absorption band indicative of P⁺B_A^– formation. Collectively, this work indicates the tyrosine at M210 tunes the mechanism of primary electron transfer in the RC.

Photosynthetic reaction centers (RCs) are the integral membrane protein assemblies responsible for nearly all the solar energy conversion maintaining our biosphere. In this study, we focus on the initial electron transfer (ET) steps in bacterial RCs from Rhodobacter sphaeroides, a three-subunit (H, L, and M) ∼100-kDa integral membrane protein complex. RCs in R. sphaeroides possess two branches of chromophores, the A and B (or L and M) branches (Fig. 1A), and each possesses nearly identical chromophore composition, orientation, and distances. The protein secondary structure is pseudo-C2 symmetric, and the symmetry-related amino acids that differ are often structurally similar (Fig. 1A) (1). Despite this high structural symmetry, ET proceeds rapidly down only the A branch of chromophores with near-unity quantum yield (2, 3). Additionally, RC ET is remarkably robust, as few structurally verified single mutations that maintain RC chromophore composition and positioning significantly impact ET kinetics or yield (1, 4–11).Open in a separate windowFig. 1.RC chromophore arrangement and energetics. (A) Chromophore arrangement in WT RCs (PDB ID: 2J8C; accessory carotenoid, chromophore phytyl tails, and quinone isoprenoid tails are removed here for clarity). Tyr at M210, the target in this work, and its symmetry-related residue Phe at L181 are shown in purple. The blue arrow indicates unidirectionality of ET down the A branch. (B) Schematic free-energy diagram of different charge-separated states in WT RCs, where P* is 1.40 eV above ground state and P⁺H_A^– is 0.25 eV below P*. The dashed magenta line and double-headed arrow next to P⁺B_A^– indicates the expected major effect of ncAA incorporation at M210 on the free energy of this state.To understand RC ET asymmetry or unidirectionality and factors underlying its robust nature, a thorough understanding of the mechanism of ET is required. In the model largely accepted in the current literature (1, 12–14), ET is initiated by excitation of the excitonically coupled bacteriochlorophyll pair P. The lowest singlet excited state P* transfers an electron to the bacteriochlorophyll B_A with a time constant of ∼3 ps to form P⁺B_A^–. B_A^– subsequently transfers an electron to the bacteriopheophytin H_A with a time constant of 1 ps, thus forming P⁺H_A^– in a two-step primary ET process, P* → P⁺B_A^– → P⁺H_A^– (1, 12, 13). An alternative model for ET has been proposed in which P* transfers an electron to H_A directly through a superexchange mechanism, as defined by Parson et al. (1). Here, the B_A chromophore mediates the electronic coupling between P* and H_A, and experimental evidence for superexchange ET must be inferred spectroscopically from the absence of P⁺B_A^– formation during transient absorption (TA) measurements and generally slower ET. In wild-type (WT) RCs, evidence favors two-step ET at room temperature (1, 12, 13, 15, 16). It has been previously proposed that minor degrees of superexchange occur in WT RCs, likely arising from or enhanced by the inherent distribution in the energies of P*, P⁺B_A^–, and P⁺H_A^– caused by protein populations with slight variations in amino acid nuclear coordinates around chromophores (5, 17–19), but this has been difficult to study experimentally (1, 12).The ET mechanisms in RCs likely have their origins in the different energies of the various charge-separated states for the two branches relative to P* and each other (Fig. 1B) (20–22), but it is difficult to determine these energetics either experimentally or theoretically (1, 23). Contributions of individual symmetry-breaking amino acid have been thoroughly studied (1, 15, 24–28), and while the importance of certain amino acids has been ascertained, the roles of local protein–chromophore interactions are not always fully understood (8, 24, 25). One highly examined residue has been the tyrosine at site M210 (RC residue numbers are preceded by the protein subunit designation: H, L, or M) because it is a clear deviation in symmetry between A and B branches (Fig. 1A), it is close to B_A, and it is the only one of 27 tyrosines that lacks a hydrogen bond acceptor. Theoretical studies indicate that the magnitude and orientation of the hydroxyl dipole of tyrosine M210 may play an important role in energetically stabilizing P⁺B_A^– (29, 30). Indeed, previous efforts to change the orientation of this tyrosine’s hydroxyl dipole significantly slowed ET (31). It is difficult, however, to subtly vary the electrostatic nature of this tyrosine using canonical mutagenesis without entirely removing the phenolic hydroxyl.To perturb the effects of the tyrosine at M210 in WT protein, we used amber stop codon suppression (32–34) to site-specifically replace it with five noncanonical amino acids (ncAAs), each a tyrosine with a single electron-donating or electron-withdrawing meta-substituent (at the 3 position). We will refer to RC protein variants by acronyms for the amino acid incorporated at M210: 3-methyltyrosine (MeY), 3-nitrotyrosine (NO₂Y), 3-chlorotyrosine (ClY), 3-bromotyrosine (BrY), and 3-iodotyrosine (IY) (Fig. 2 and SI Appendix, Fig. S1 and Table S1). In this way, we engineered a series of RC variants with more systematic electrostatic ET perturbation at this important tyrosine while minimally affecting other RC features.Open in a separate windowFig. 2.RC variants made and structurally characterized in this study, in which truncated P_A and B_A chromophores are depicted for each variant (in teal and magenta, respectively) and electron density maps from solved X-ray structures are shown (2F_o-F_c contoured at 1 σ) for tyrosine analogs at M210. Halogen variants required two different tyrosine ring conformers to model halogen substituent orientations with the contribution of each indicated, one with the halogen oriented toward P (only P_A depicted above) and the other with halogen toward B_A. The resolution for each crystal structure is denoted in black next to the P_A of each RC variant (PDB IDs for NO₂Y, MeY, ClY, BrY, and IY RCs are 7MH9, 7MH8, 7MH3, 7MH4, and 7MH5, respectively; SI Appendix, Table S2).     

Little evidence for enhanced phenotypic evolution in early teleosts relative to their living fossil sister group

Since Darwin, biologists have been struck by the extraordinary diversity of teleost fishes, particularly in contrast to their closest “living fossil” holostean relatives. Hypothesized drivers of teleost success include innovations in jaw mechanics, reproductive biology and, particularly at present, genomic architecture, yet all scenarios presuppose enhanced phenotypic diversification in teleosts. We test this key assumption by quantifying evolutionary rate and capacity for innovation in size and shape for the first 160 million y (Permian–Early Cretaceous) of evolution in neopterygian fishes (the more extensive clade containing teleosts and holosteans). We find that early teleosts do not show enhanced phenotypic evolution relative to holosteans. Instead, holostean rates and innovation often match or can even exceed those of stem-, crown-, and total-group teleosts, belying the living fossil reputation of their extant representatives. In addition, we find some evidence for heterogeneity within the teleost lineage. Although stem teleosts excel at discovering new body shapes, early crown-group taxa commonly display higher rates of shape evolution. However, the latter reflects low rates of shape evolution in stem teleosts relative to all other neopterygian taxa, rather than an exceptional feature of early crown teleosts. These results complement those emerging from studies of both extant teleosts as a whole and their sublineages, which generally fail to detect an association between genome duplication and significant shifts in rates of lineage diversification.Numbering ∼29,000 species, teleost fishes account for half of modern vertebrate richness. In contrast, their holostean sister group, consisting of gars and the bowfin, represents a mere eight species restricted to the freshwaters of eastern North America (1). This stark contrast between teleosts and Darwin''s original “living fossils” (2) provides the basis for assertions of teleost evolutionary superiority that are central to textbook scenarios (3, 4). Classic explanations for teleost success include key innovations in feeding (3, 5) (e.g., protrusible jaws and pharyngeal jaws) and reproduction (6, 7). More recent work implicates the duplicate genomes of teleosts (8–10) as the driver of their prolific phenotypic diversification (8, 11–13), concordant with the more general hypothesis that increased morphological complexity and innovation is an expected consequence of genome duplication (14, 15).Most arguments for enhanced phenotypic evolution in teleosts have been asserted rather than demonstrated (8, 11, 12, 15, 16; but see ref. 17), and draw heavily on the snapshot of taxonomic and phenotypic imbalance apparent between living holosteans and teleosts. The fossil record challenges this neontological narrative by revealing the remarkable taxonomic richness and morphological diversity of extinct holosteans (Fig. 1) (18, 19) and highlights geological intervals when holostean taxonomic richness exceeded that of teleosts (20). This paleontological view has an extensive pedigree. Darwin (2) invoked a long interval of cryptic teleost evolution preceding the late Mesozoic diversification of the modern radiation, a view subsequently supported by the implicit (18) or explicit (19) association of Triassic–Jurassic species previously recognized as “holostean ganoids” with the base of teleost phylogeny. This perspective became enshrined in mid-20th century treatments of actinopterygian evolution, which recognized an early-mid Mesozoic phase dominated by holosteans sensu lato and a later interval, extending to the modern day, dominated by teleosts (4, 20, 21). Contemporary paleontological accounts echo the classic interpretation of modest teleost origins (22–24), despite a systematic framework that substantially revises the classifications upon which older scenarios were based (22–25). Identification of explosive lineage diversification in nested teleost subclades like otophysans and percomorphs, rather than across the group as a whole, provides some circumstantial neontological support for this narrative (26).Open in a separate windowFig. 1.Phenotypic variation in early crown neopterygians. (A) Total-group holosteans. (B) Stem-group teleosts. (C) Crown-group teleosts. Taxa illustrated to scale.In contrast to quantified taxonomic patterns (20, 23, 24, 27), phenotypic evolution in early neopterygians has only been discussed in qualitative terms. The implicit paleontological model of morphological conservatism among early teleosts contrasts with the observation that clades aligned with the teleost stem lineage include some of the most divergent early neopterygians in terms of both size and shape (Fig. 1) (see, for example, refs. 28 and 29). These discrepancies point to considerable ambiguity in initial patterns of phenotypic diversification that lead to a striking contrast in the vertebrate tree of life, and underpins one of the most successful radiations of backboned animals.Here we tackle this uncertainty by quantifying rates of phenotypic evolution and capacity for evolutionary innovation for the first 160 million y of the crown neopterygian radiation. This late Permian (Wuchiapingian, ca. 260 Ma) to Cretaceous (Albian, ca. 100 Ma) sampling interval permits incorporation of diverse fossil holosteans and stem teleosts alongside early diverging crown teleost taxa (Figs. 1 and ​and2A2A and Figs. S1 and ​andS2),S2), resulting in a dataset of 483 nominal species-level lineages roughly divided between the holostean and teleost total groups (Fig. 2B and Fig. S2). Although genera are widely used as the currency in paleobiological studies of fossil fishes (30; but see ref. 31), we sampled at the species level to circumvent problems associated with representing geological age and morphology for multiple congeneric lineages. We gathered size [both log-transformed standard length (SL) and centroid size (CS); results from both are highly comparable (Figs. S3 and ​andS4);S4); SL results are reported in the main text] and shape data (the first three morphospace axes arising from a geometric morphometric analysis) (Fig. 2A and Figs. S1) from species where possible. To place these data within a phylogenetic context, we assembled a supertree based on published hypotheses of relationships. We assigned branch durations to a collection of trees under two scenarios for the timescale of neopterygian diversification based on molecular clock and paleontological estimates. Together, these scenarios bracket a range of plausible evolutionary timelines for this radiation (Fig. 2B). We used the samples of trees in conjunction with our morphological datasets to test for contrasts in rates of, and capacity for, phenotypic change between different partitions of the neopterygian Tree of Life (crown-, total-, and stem-group teleosts, total-group holosteans, and neopterygians minus crown-group teleosts), and the sensitivity of these conclusions to uncertainty in both relationships and evolutionary timescale. Critically, these include comparisons of phenotypic evolution in early crown-group teleosts—those species that are known with certainty to possess duplicate genomes—with rates in taxa characterized largely (neopterygians minus crown teleosts) or exclusively (holosteans) by unduplicated genomes. By restricting our scope to early diverging crown teleost lineages, we avoid potentially confounding signals from highly nested radiations that substantially postdate both genome duplication and the origin of crown teleosts (26, 32). This approach provides a test of widely held assumptions about the nature of morphological evolution in teleosts and their holostean sister lineage.Open in a separate windowFig. 2.(A) Morphospace of Permian–Early Cretaceous crown Neopterygii. (B) One supertree subjected to our paleontological (Upper) and molecular (Lower) timescaling procedures to illustrate contrasts in the range of evolutionary timescales considered. Colors of points (A) and branches (B) indicate membership in major partitions of neopterygian phylogeny. Topologies are given in Datasets S4 and S5. See Dataset S6 for source trees.Open in a separate windowFig. S1.Morphospace of 398 Permian–Early Cretaceous Neopterygii. Three major axes of shape variation are presented. Silhouettes and accompanying arrows illustrate the main anatomical correlates of these principal axes, as described in Open in a separate windowFig. S2.Morphospace of 398 Permian–Early Cretaceous Neopterygii, illustrating the major clades of (A) teleosts and (B) holosteans.Open in a separate windowFig. S3.Comparisons of size rates between (A) holosteans and teleosts, (B) crown teleosts and all other neopterygians, (C) crown teleosts and stem teleosts, (D) crown teleosts and holosteans, and (E) stem teleosts and holosteans. Comparisons were made using the full-size SL dataset, a CS dataset, and a smaller SL dataset pruned to exactly match the taxon sampling of the CS dataset. Identical taxon sampling leads the CS and pruned SL datasets to yield near identical results. Although the larger SL dataset results often differ slightly, the overall conclusion from each pairwise comparison (i.e., which outcome is the most likely in an overall majority of trees) is identical in all but one comparison (E, under molecular timescales).Open in a separate windowFig. S4.Comparisons of size innovation between (A) holosteans and teleosts, (B) crown teleosts and all other neopterygians, (C) crown teleosts and stem teleosts, (D) crown teleosts and holosteans, and (E) stem teleosts and holosteans. Comparisons were made using the full-size SL dataset, a CS dataset, and a smaller SL dataset pruned to exactly match the taxon sampling of the CS dataset. Comparisons of size innovation are presented for K value distributions of the three datasets resemble each other closely.