共查询到20条相似文献,搜索用时 15 毫秒
1.
Robert A. Lewis Jean-Michel Mencia-Huerta Roy J. Soberman Dennis Hoover Anthony Marfat E. J. Corey K. Frank Austen 《Proceedings of the National Academy of Sciences of the United States of America》1982,79(24):7904-7908
A rabbit immunized with leukotriene B4 [LTB4; (5S,12R)-6, 14-cis-8, 10-trans-icosatetraenoic acid] coupled to bovine serum albumin via the 12-oxy function of the lipid produced antibodies having an average association constant (Ka) for [14,15-3H]LTB4 of 3.2 × 109 M-1 at 37°C and in a concentration of 0.37 μg/ml of the immune plasma. When 10 μl of anti-LTB4 and 3.9 nCi of [14,15-3H]LTB4 (28 Ci/mmol; 1 Ci = 3.7 × 1010 becquerels) were incubated in a volume of 250 μl, 50% inhibition of radioligand binding was achieved with 0.31 ng of LTB4 and with 1.95 ng of (5S,12S)-6-trans-8-cis-LTB4. The sulfidopeptide leukotrienes, LTC4 and LTD4, displaced the radioligand from this antibody with less than 1/100th the activity of LTB4, and the diastereoisomers of 6-trans-LTB4, 5-L-hydroxy-6-trans-8,11,14-cis-icosatetraenoic acid (5-HETE), and three prostaglandins were minimally effective. The specificity of this radioimmunoassay was further shown by assessment of the immunoreactive products generated from calcium ionophore (A23187)-activated rat serosal mast cells and human neutrophils after reversed-phase HPLC. Resolution of the supernatants from each cell type yielded a single immunoreactive peak that coeluted with synthetic LTB4 and quantitatively correlated with the physical measurement by integrated A269 in that peak; UV-absorbing peaks eluting at other retention times were not immunoreactive. The immunoreactive LTB4 generated averaged 4.6 ng per 106 rat mast cells and resolution of the supernatants by reversed-phase HPLC without a prior extraction step gave a recovery of 54%, validating the direct applicability of this sensitive and specific assay for LTB4, a highly potent chemotactic factor, to unfractionated biologic fluids. 相似文献
2.
The catalytic activity of ruthenium(III) acetylacetonate was investigated for the first time in the dehydrogenation of dimethylamine borane. During catalytic reaction, a new ruthenium(II) species is formed in situ from the reduction of ruthenium(III) and characterized using UV-Visible, Fourier transform infrared (FTIR), 1H NMR, and mass spectroscopy. The most likely structure suggested for the ruthenium(II) species is mer-[Ru(N2Me4)3(acac)H]. Mercury poisoning experiment indicates that the catalytic dehydrogenation of dimethylamine-borane is homogeneous catalysis. The kinetics of the catalytic dehydrogenation of dimethylamine borane starting with Ru(acac)3 were studied depending on the catalyst concentration, substrate concentration and temperature. The hydrogen generation was found to be first-order with respect to catalyst concentration and zero-order regarding the substrate concentration. Evaluation of the kinetic data provides the activation parameters for the dehydrogenation reaction: the activation energy Ea = 85 ± 2 kJ·mol−1, the enthalpy of activation ∆H# = 82 ± 2 kJ·mol−1 and the entropy of activation; ∆S# = −85 ± 5 J·mol−1·K−1. The ruthenium(II) catalyst formed from the reduction of ruthenium(III) acetylacetonate provides 1700 turnovers over 100 hours in hydrogen generation from the dehydrogenation of dimethylamine borane before deactivation at 60 °C. 相似文献
3.
Simona Zarini Miguel A. Gijón Aaron E. Ransome Robert C. Murphy Angelo Sala 《Proceedings of the National Academy of Sciences of the United States of America》2009,106(20):8296-8301
Leukotrienes (LTs) are lipid mediators of inflammation formed by enzymatic oxidation of arachidonic acid. One intriguing aspect of LT production is transcellular biosynthesis: cells expressing 5-lipoxygenase (5LO) form LTA4 and transfer it to cells expressing LTA4 hydrolase (LTA4H) or LTC4 synthase (LTC4S) to produce LTB4 or LTC4. This process has been demonstrated in vivo for LTB4, but not for cysteinyl LTs (cysLTs). We examined transcellular cysLT synthesis during zymosan-induced peritonitis, using bone marrow transplants with transgenic mice deficient in key enzymes of LT synthesis and analyzing all eicosanoids by liquid chromatography/tandem mass spectrometry. WT mice time-dependently produced LTB4 and cysLTs (LTC4, LTD4, and LTE4). 5LO−/− mice were incapable of producing LTs. WT bone marrow cells restored this biosynthetic ability, but 5LO−/− bone marrow did not rescue LT synthesis in irradiated WT mice, demonstrating that bone marrow-derived cells are the ultimate source of all LTs in this model. Total levels of 5LO-derived products were comparable in LTA4H−/− and WT mice, but were reduced in LTC4S−/− animals. No differences in prostaglandin production were observed between these transgenic or chimeric mice. Bone marrow cells from LTA4H−/− or LTC4S−/− mice injected into 5LO−/− mice restored the ability to synthesize LTB4 and cysLTs, providing unequivocal evidence of efficient transcellular biosynthesis of cysLTs. These results highlight the potential relevance of transcellular exchange of LTA4 for the synthesis of LTs mediating biological activities during inflammatory events in vivo. 相似文献
4.
Interaction between the intermediary electron acceptor (pheophytin) and a possible plastoquinone-iron complex in photosystem II reaction centers
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Klimov VV Dolan E Shaw ER Ke B 《Proceedings of the National Academy of Sciences of the United States of America》1980,77(12):7227-7231
Photoreduction of the intermediary electron acceptor, pheophytin (Pheo), in photosystem II reaction centers of spinach chloroplasts or subchloroplast particles (TSF-II and TSF-IIa) at 220 K and redox potential Eh = -450 mV produces an EPR doublet centered at g = 2.00 with a splitting of 52 G at 7 K in addition to a narrow signal attributed to Pheo[unk] (g = 2.0033, ΔH ≈ 13 G). The doublet is eliminated after extraction of lyophilized TSF-II with hexane containing 0.13-0.16% methanol but is restored by reconstitution with plastoquinone A (alone or with β-carotene) although not with vitamin K1. TSF-II and TSF-IIa are found to contain ≈2 nonheme Fe atoms per reaction center. Incubation with 0.55 M LiClO4 plus 2.5 mM o-phenanthroline (but not with 0.55 M LiClO4 alone) decreases this value to ≈0.6 and completely eliminates the EPR doublet, but photoreduction of Pheo is not significantly affected. Partial restoration of the doublet (about 25%) was achieved by subsequent incubation with 0.2 mM Fe2+, but not with either Mn2+ or Mg2+. The Fe removal results in the development of a photoinduced EPR signal (g = 2.0044 ± 0.0003, ΔH = 9.2 ± 0.5 G) at Eh = 50 mV, which is not observed after extraction with 0.16% methanol in hexane. It is ascribed to plastosemiquinone no longer coupled to Fe in photosystem II reaction centers. The results show that a complex of plastoquinone and Fe can act as the stable “primary” electron acceptor in photosystem II reaction centers and that the interaction of its singly reduced form with the reduced intermediary acceptor, Pheo[unk], is responsible for the EPR doublet. 相似文献
5.
Low Temperature Electronic Absorption Spectra of Oxidized and Reduced Spinach Ferredoxins. Evidence for Nonequivalent Iron(III) Sites
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Rawlings J Siiman O Gray HB 《Proceedings of the National Academy of Sciences of the United States of America》1974,71(1):125-127
The electronic absorption spectra of oxidized and reduced spinach ferredoxins have been measured between 1200 and 600 nm at low temperature in D2O/ethylene glycol glasses. Relatively weak absorption bands are observed at 720, 820, and 920 nm in oxidized ferredoxin, and at 652, 820, and 920 nm in reduced ferredoxin. The spectral results show that the two Fe(III) centers in oxidized ferredoxin are not equivalent, and that the 820- and 920-nm bands are associated with the nonreducible site. Assignment of the reducible site as tetrahedral Fe(III) is indicated. The 720-nm (13.9 kcm-1) band in oxidized ferredoxin is attributed to an intensity-enhanced 6A1 → 4T1d-d transition, whereas the 652-nm (15.3 kcm-1) feature of reduced ferredoxin could be due either to 5E → 3T1 in tetrahedral Fe(II)S4 or an Fe(II) → Fe(III) intervalence excitation. 相似文献
6.
Michael M. Mbughuni Mrinmoy Chakrabarti Joshua A. Hayden Emile L. Bominaar Michael P. Hendrich Eckard Münck John D. Lipscomb 《Proceedings of the National Academy of Sciences of the United States of America》2010,107(39):16788-16793
intermediates are well known in heme enzymes, but none have been characterized in the nonheme mononuclear FeII enzyme family. Many steps in the O2 activation and reaction cycle of FeII-containing homoprotocatechuate 2,3-dioxygenase are made detectable by using the alternative substrate 4-nitrocatechol (4NC) and mutation of the active site His200 to Asn (H200N). Here, the first intermediate (Int-1) observed after adding O2 to the H200N-4NC complex is trapped and characterized using EPR and Mössbauer (MB) spectroscopies. Int-1 is a high-spin (S1 = 5/2) FeIII antiferromagnetically (AF) coupled to an S2 = 1/2 radical (J ≈ 6 cm-1 in ). It exhibits parallel-mode EPR signals at g = 8.17 from the S = 2 multiplet, and g = 8.8 and 11.6 from the S = 3 multiplet. These signals are broadened significantly by hyperfine interactions (A17O ≈ 180 MHz). Thus, Int-1 is an AF-coupled species. The experimental observations are supported by density functional theory calculations that show nearly complete transfer of spin density to the bound O2. Int-1 decays to form a second intermediate (Int-2). MB spectra show that it is also an AF-coupled FeIII-radical complex. Int-2 exhibits an EPR signal at g = 8.05 arising from an S = 2 state. The signal is only slightly broadened by (< 3% spin delocalization), suggesting that Int-2 is a peroxo-FeIII-4NC semiquinone radical species. Our results demonstrate facile electron transfer between FeII, O2, and the organic ligand, thereby supporting the proposed wild-type enzyme mechanism. 相似文献
7.
Picosecond photochemistry of a cofacial diporphyrin containing iron(III) and zinc(II): Mimicking electron transfer between cytochrome c and the primary electron donor in reaction centers of photosynthetic bacteria
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Fujita I Netzel TL Chang CK Wang CB 《Proceedings of the National Academy of Sciences of the United States of America》1982,79(2):413-417
Comparison of picosecond kinetic and spectroscopic data for Zn octaethylporphine and Fe(III)Cl octaethylporphine with that for Zn—Fe(III)Cl, a cofacial diporphyrin composed of a Zn porphyrin covalently bound to an Fe(III)Cl porphyrin with two chains of five atoms each, supports the assignment of a light-driven electron transfer (k > 1011s-1) within Zn—Fe(III)Cl to form [Zn+·—Fe(II)]Cl. The kinetics (k ≈ 1010s-1) and thermodynamics of the reverse electron transfer are compared to those of a similar electron transfer in bacterial photosynthesis, the reduction of an oxidized bacteriochlorophyll dimer, (BChl)2+·, by Fe(II) cytochrome c. 相似文献
8.
André Klauss Michael Haumann Holger Dau 《Proceedings of the National Academy of Sciences of the United States of America》2012,109(40):16035-16040
Water oxidation by cyanobacteria, algae, and plants is pivotal in oxygenic photosynthesis, the process that powers life on Earth, and is the paradigm for engineering solar fuel–production systems. Each complete reaction cycle of photosynthetic water oxidation requires the removal of four electrons and four protons from the catalytic site, a manganese–calcium complex and its protein environment in photosystem II. In time-resolved photothermal beam deflection experiments, we monitored apparent volume changes of the photosystem II protein associated with charge creation by light-induced electron transfer (contraction) and charge-compensating proton relocation (expansion). Two previously invisible proton removal steps were detected, thereby filling two gaps in the basic reaction-cycle model of photosynthetic water oxidation. In the S2 → S3 transition of the classical S-state cycle, an intermediate is formed by deprotonation clearly before electron transfer to the oxidant (). The rate-determining elementary step (τ, approximately 30 µs at 20 °C) in the long-distance proton relocation toward the protein–water interface is characterized by a high activation energy (Ea = 0.46 ± 0.05 eV) and strong H/D kinetic isotope effect (approximately 6). The characteristics of a proton transfer step during the S0 → S1 transition are similar (τ, approximately 100 µs; Ea = 0.34 ± 0.08 eV; kinetic isotope effect, approximately 3); however, the proton removal from the Mn complex proceeds after electron transfer to . By discovery of the transient formation of two further intermediate states in the reaction cycle of photosynthetic water oxidation, a temporal sequence of strictly alternating removal of electrons and protons from the catalytic site is established. 相似文献
9.
Picosecond kinetics of fluorescence and absorbance changes in photosystem II particles excited at low photon density 总被引:3,自引:3,他引:3
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Schatz GH Brock H Holzwarth AR 《Proceedings of the National Academy of Sciences of the United States of America》1987,84(23):8414-8418
Oxygen-evolving photosystem II particles (from Synechococcus) with about 80 chlorophyll molecules per primary electron donor (P680) were used for a correlated study of picosecond kinetics of fluorescence and absorbance changes, detected by the single-photon-timing technique and by a pump-probe apparatus, respectively. Chlorophyll fluorescence decays were biexponential with lifetimes τ1 = 80 ± 20 ps and τ2 = 520 ± 120 ps in open reaction centers and τ1 = 220 ± 30 ps and τ2 = 1.3 ± 0.15 ns in closed reaction centers. The corresponding fluorescence yield ratio Fmax/Fo was 3-4. Absorbance changes were monitored in the spectral range of 620-700 nm after excitation at 675 nm with 10-ps pulses sufficiently weak (<7 × 1012 photons/cm2 per pulse) to avoid singlet-singlet annihilation. With open reaction centers, the absorbance changes could be fit to the sum of three exponentials. The associated absorbance difference spectra were attributed to (i) exciton trapping and charge separation (τ = 100 ± 20 ps), (ii) the electron-transfer step P680+ I- QA → P680+ I QA- (where I is the primary electron acceptor and QA is the first quinone acceptor) (τ = 510 ± 50 ps), and (iii) the reduction of P680+ by the intact donor side (τ > 10 ns). With closed reaction centers, the absorbance changes were biexponential with lifetimes τ1 = 170-260 ps and τ2 = 1.6-1.75 ns. The results are explained in terms of a kinetic model that assumes P680 to constitute a shallow trap. The results show that QA reduction in these photosystem II particles decreases both the apparent rate and the yield of the primary charge separation by a factor of 2-3 and increases the mean lifetime of excitons in the antenna by a factor of 3-4. Thus, we conclude that the long-lived, nanosecond chlorophyll fluorescence is not charge-recombination luminescence but rather emission from equilibrated excited states of antenna chlorophylls. 相似文献
10.
Maxim A. Shmelev Mikhail A. Kiskin Julia K. Voronina Konstantin A. Babeshkin Nikolay N. Efimov Evgenia A. Varaksina Vladislav M. Korshunov Ilya V. Taydakov Natalia V. Gogoleva Alexey A. Sidorov Igor L. Eremenko 《Materials》2020,13(24)
Varying the temperature of the reaction of [{Cd(pfb)(H2O)4}+n·n(pfb)−], [Ln2(pfb)6(H2O)8]·H2O (Hpfb = pentafluorobenzoic acid), and 1,10-phenanthroline (phen) in MeCN followed by crystallization resulted in the isolation of two type of products: 1D-polymers [LnCd(pfb)5(phen)]n·1.5nMeCN (Ln = Eu (I), Gd (II), Tb (III), Dy (IV)) which were isolated at 25 °C, and molecular compounds [Tb2Cd2(pfb)10(phen)2] (V) formed at 75 °C. The transition from a molecular to a polymer structure becomes possible because of intra- and intermolecular interactions between the aromatic cycles of phen and pfb from neighboring tetranuclear Ln2Cd2 fragments. Replacement of cadmium with zinc in the reaction resulted in molecular compounds Ln2Zn2 [Ln2Zn2(pfb)10(phen)2]·4MeCN (Ln = Eu (VI), Tb (VIII), Dy (IX)) and [Gd2Zn2(pfb)10(H2O)2(phen)2]·4MeCN (VII). A new molecular EuCd complex [Eu2Cd2(pfb)10(phen)4]·4MeCN (X)] was isolated from a mixture of cadmium, zinc, and europium pentafluorobenzoates (Cd:Zn:Ln = 1:1:2). Complexes II-IV, VII and IX exhibit magnetic relaxation at liquid helium temperatures in nonzero magnetic fields. Luminescent studies revealed a bright luminescence of complexes with europium(III) and terbium(III) ions. 相似文献
11.
Determination of the primary charge separation rate in isolated photosystem II reaction centers with 500-fs time resolution 总被引:1,自引:5,他引:1
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Wasielewski MR Johnson DG Seibert M Govindjee 《Proceedings of the National Academy of Sciences of the United States of America》1989,86(2):524-528
We have measured directly the rate of formation of the oxidized chlorophyll a electron donor (P680+) and the reduced electron acceptor pheophytin a- (Pheoa-) following excitation of isolated spinach photosystem II reaction centers at 4°C. The reaction-center complex consists of D1, D2, and cytochrome b-559 proteins and was prepared by a procedure that stabilizes the protein complex. Transient absorption difference spectra were measured from 440 to 850 nm as a function of time with 500-fs resolution following 610-nm laser excitation. The formation of P680+-Pheoa- is indicated by the appearance of a band due to P680+ at 820 nm and corresponding absorbance changes at 505 and 540 nm due to formation of Pheoa-. The appearance of the 820-nm band is monoexponential with τ = 3.0 ± 0.6 ps. The time constant for decay of 1*P680, the lowest excited singlet state of P680, monitored at 650 nm, is τ = 2.6 ± 0.6 ps and agrees with that of the appearance of P680+ within experimental error. Treatment of the photosystem II reaction centers with sodium dithionite and methyl viologen followed by exposure to laser excitation, conditions known to result in accumulation of Pheoa-, results in formation of a transient absorption spectrum due to 1*P680. We find no evidence for an electron acceptor that precedes the formation of Pheoa-. 相似文献
12.
Yasuhiro Ohki Kazunari Yasumura Masaru Ando Satoko Shimokata Kazuyuki Tatsumi 《Proceedings of the National Academy of Sciences of the United States of America》2010,107(9):3994-3997
A [NiFe] hydrogenase model compound having a distorted trigonal-pyramidal nickel center, (CO)3Fe(μ-StBu)3Ni(SDmp), 1 (Dmp = C6H3-2,6-(mesityl)2), was synthesized from the reaction of the tetranuclear Fe-Ni-Ni-Fe complex [(CO)3Fe(μ-StBu)3Ni]2(μ-Br)2, 2 with NaSDmp at -40 °C. The nickel site of complex 1 was found to add CO or CNtBu at -40 °C to give (CO)3Fe(StBu)(μ-StBu)2Ni(CO)(SDmp), 3, or (CO)3Fe(StBu)(μ-StBu)2Ni(CNtBu)(SDmp), 4, respectively. One of the CO bands of 3, appearing at 2055 cm-1 in the infrared spectrum, was assigned as the Ni-CO band, and this frequency is comparable to those observed for the CO-inhibited forms of [NiFe] hydrogenase. Like the CO-inhibited forms of [NiFe] hydrogenase, the coordination of CO at the nickel site of 1 is reversible, while the CNtBu adduct 4 is more robust. 相似文献
13.
A new complex [Mg(L)2(phen)(H2O)2](phen)(H2O)2 [L= N-benzenesulphonyl-L-leucine] was synthesized by the reaction of magnesium chloride hexahydrate with N-benzenesulphonyl-L-leucine and 1,10-phenanthroline in the CH3CH2OH/H2O (v:v = 5:1). It was characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The crystal of the title complex [Mg(L)2(phen)(H2O)2](phen)(H2O)2 belongs to triclinic, space group P-1 with a = 0.72772(15) nm, b = 1.4279(3) nm, c = 1.4418(3) nm, α = 63.53(3)°, β = 79.75(3)°, γ = 81.83(3)°, V = 1.3163(5) nm3, Z =1, Dc= 1.258 μg·m−3, μ = 0.177 mm−1, F(000) = 526, and final R1 = 0.0506, ωR2 = 0.1328. The complex comprises a six-coordinated magnesium(II) center, with a N2O4 distorted octahedron coordination environment. The molecules are connected by hydrogen bonds and π-π stacking to form one dimensional chain structure. The luminescent property of the Mg(II) complex has been investigated in solid. 相似文献
14.
A new trinuclear Cd (II) complex [Cd3(L)6(2,2-bipyridine)3] [L = N-phenylsulfonyl-L-leucinato] has been synthesized and characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The results show that the complex belongs to the orthorhombic, space group P212121 with a = 16.877(3) Å, b = 22.875(5) Å, c = 29.495(6) Å, α = β = γ = 90°, V = 11387(4) Å3, Z = 4, Dc= 1.416 μg·m−3, μ = 0.737 mm−1, F (000) = 4992, and final R1 = 0.0390, ωR2 = 0.0989. The complex comprises two seven-coordinated Cd (II) atoms, with a N2O5 distorted pengonal bipyramidal coordination environment and a six-coordinated Cd (II) atom, with a N2O4 distorted octahedral coordination environment. The molecules form one dimensional chain structure by the interaction of bridged carboxylato groups, hydrogen bonds and π-π interaction of 2,2-bipyridine. The luminescent properties of the Cd (II) complex and N-Benzenesulphonyl-L-leucine in solid and in CH3OH solution also have been investigated. 相似文献
15.
Yasuhiro Ohki Kazuki Tanifuji Norihiro Yamada Motosuke Imada Tomoyuki Tajima Kazuyuki Tatsumi 《Proceedings of the National Academy of Sciences of the United States of America》2011,108(31):12635-12640
The all-ferric [Fe4S4]4+ cluster [Fe4S4{N(SiMe3)2}4] 1 and its one-electron reduced form [1]- serve as convenient precursors for the synthesis of 3∶1-site differentiated [Fe4S4] clusters and high-potential iron-sulfur protein (HiPIP) model clusters. The reaction of 1 with four equivalents (equiv) of the bulky thiol HSDmp (Dmp = 2,6-(mesityl)2C6H3, mesityl = 2,4,6-Me3C6H2) followed by treatment with tetrahydrofuran (THF) resulted in the isolation of [Fe4S4(SDmp)3(THF)3] 2. Cluster 2 contains an octahedral iron atom with three THF ligands, and its Fe(S)3(O)3 coordination environment is relevant to that in the active site of substrate-bound aconitase. An analogous reaction of [1]- with four equiv of HSDmp gave [Fe4S4(SDmp)4]- 3, which models the oxidized form of HiPIP. The THF ligands in 2 can be replaced by tetramethyl-imidazole (Me4Im) to give [Fe4S4(SDmp)3(Me4Im)] 4 modeling the [Fe4S4(Cys)3(His)] cluster in hydrogenases, and its one-electron reduced form [4]- was synthesized from the reaction of 3 with Me4Im. The reversible redox couple between 3 and [3]- was observed at E1/2 = -820 mV vs. Ag/Ag+, and the corresponding reversible couple for 4 and [4]- is positively shifted by +440 mV. The cyclic voltammogram of 3 also exhibited a reversible oxidation couple, which indicates generation of the all-ferric [Fe4S4]4+ cluster, [Fe4S4(SDmp)4]. 相似文献
16.
Lithium dodecyl sulfate/polyacrylamide gel electrophoresis of thylakoid membranes at 4 degrees C: Characterizations of two additional chlorophyll a-protein complexes
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Delepelaire P Chua NH 《Proceedings of the National Academy of Sciences of the United States of America》1979,76(1):111-115
Lithium dodecyl sulfate/polyacrylamide gel electrophoresis of Chlamydomonas reinhardtii thylakoid membranes at room temperature gave two chlorophyll-protein complexes, CP I and CP II, as had been reported previously. However, when the electrophoresis was performed at 4°C, there was an increase in the amount of chlorophyll associated with CP I and CP II, and in addition, three other chlorophyll-protein complexes appeared. Two of these complexes, designated CP III and CP IV, were characterized and found to be similar in their compositions. Each complex contains four to five molecules of chlorophyll a, one molecule of β-carotene, and one polypeptide chain. The apoprotein of CP III is polypeptide 5 (Mr 50,000) and that of CP IV is polypeptide 6 (Mr 47,000); the two polypeptides are structurally unrelated. Chlorophyll-protein complexes similar to C. reinhardtii CP III and CP IV were also detected in higher plants (e.g., Pisum sativum). The apoproteins of the higher plant complexes are immunochemically related to those of the C. reinhardtii complexes, as shown by crossed immunoelectrophoresis. Absorption spectra of CP III and CP IV at -196°C revealed a component at 682 nm. This observation, together with the previous results on photosystem II mutants [Chua, N.-H. & Bennoun, P. (1975) Proc. Natl. Acad. Sci. USA 72, 2175-2179], provides indirect evidence that CP III and CP IV may be involved in the primary photochemistry of photosystem II. 相似文献
17.
Weixue Wang Jikun Li Ke Wang Cancan Huang Yong Zhang Eric Oldfield 《Proceedings of the National Academy of Sciences of the United States of America》2010,107(25):11189-11193
We report the results of a series of chemical, EPR, ENDOR, and HYSCORE spectroscopic investigations of the mechanism of action (and inhibition) of GcpE, E-1-hydroxy-2-methyl-but-2-enyl-4-diphosphate (HMBPP) synthase, also known as IspG, an Fe4S4 cluster-containing protein. We find that the epoxide of HMBPP when reduced by GcpE generates the same transient EPR species as observed on addition of the substrate, 2-C-methyl-D-erythritol-2, 4-cyclo-diphosphate. ENDOR and HYSCORE spectra of these transient species (using 2H, 13C and 17O labeled samples) indicate formation of an Fe-C-H containing organometallic intermediate, most likely a ferraoxetane. This is then rapidly reduced to a ferracyclopropane in which the HMBPP product forms an η2-alkenyl π- (or π/σ) complex with the 4th Fe in the Fe4S4 cluster, and a similar “metallacycle” also forms between isopentenyl diphosphate (IPP) and GcpE. Based on this metallacycle concept, we show that an alkyne (propargyl) diphosphate is a good (Ki ∼ 300 nM) GcpE inhibitor, and supported again by EPR and ENDOR results (a 13C hyperfine coupling of ∼7 MHz), as well as literature precedent, we propose that the alkyne forms another π/σ metallacycle, an η2-alkynyl, or ferracyclopropene. Overall, the results are of broad general interest because they provide new mechanistic insights into GcpE catalysis and inhibition, with organometallic bond formation playing, in both cases, a key role. 相似文献
18.
Koji Tanaka Hiroshi Isobe Shusuke Yamanaka Kizashi Yamaguchi 《Proceedings of the National Academy of Sciences of the United States of America》2012,109(39):15600-15605
The nature of chemical bonds of ruthenium(Ru)–quinine(Q) complexes, mononuclear [Ru(trpy)(3,5-t-Bu2Q)(OH2)](ClO4)2 (trpy = 2,2′:6′,2′′-terpyridine, 3,5-di-tert-butyl-1,2-benzoquinone) (1), and binuclear [Ru2(btpyan)(3,6-di-Bu2Q)2(OH2)]2+ (btpyan = 1,8-bis(2,2′:6′,2′′-terpyrid-4′-yl)anthracene, 3,6-t-Bu2Q = 3,6-di-tert-butyl-1,2-benzoquinone) (2), has been investigated by broken-symmetry (BS) hybrid density functional (DFT) methods. BS DFT computations for the Ru complexes have elucidated that the closed-shell structure (2b) Ru(II)–Q complex is less stable than the open-shell structure (2bb) consisting of Ru(III) and semiquinone (SQ) radical fragments. These computations have also elucidated eight different electronic and spin structures of tetraradical intermediates that may be generated in the course of water splitting reaction. The Heisenberg spin Hamiltonian model for these species has been derived to elucidate six different effective exchange interactions (J) for four spin systems. Six J values have been determined using total energies of the eight (or seven) BS solutions for different spin configurations. The natural orbital analyses of these BS DFT solutions have also been performed in order to obtain natural orbitals and their occupation numbers, which are useful for the lucid understanding of the nature of chemical bonds of the Ru complexes. Implications of the computational results are discussed in relation to the proposed reaction mechanisms of water splitting reaction in artificial photosynthesis systems and the similarity between artificial and native water splitting systems. 相似文献
19.
Santokh S. Tandon Neil Patel Scott D. Bunge Esther C. Wang Rachel Thompson Laurence K. Thompson 《Materials》2020,13(23)
The reaction of 2,6-diformyl-4-methylphenol (DFMF) with 1-amino-2-propanol (AP) and tris(hydroxymethyl)aminomethane (THMAM) was investigated in the presence of Cobalt(II) salts, (X = ClO4−, CH3CO2−, Cl−, NO3−), sodium azide (NaN3), and triethylamine (TEA). In one pot, the variation in Cobalt(II) salt results in the self-assembly of dinuclear, tetranuclear, and H-bonding-directed polynuclear coordination complexes of Cobalt(III), Cobalt(II), and mixed-valence CoIICoIII: [Co2III(H2L−1)2(AP−1)(N3)](ClO4)2 (1), [Co4(H2L−1)2(µ3-1,1,1-N3)2(µ-1,1-N3)2Cl2(CH3OH)2]·4CH3OH (2), [Co2IICo2III(HL−2)2(µ-CH3CO2)2(µ3-OH)2](NO3)2·2CH3CH2OH (3), and [Co2IICo2III (H2L12−)2(THMAM−1)2](NO3)4 (4). In 1, two cobalt(III) ions are connected via three single atom bridges; two from deprotonated ethanolic oxygen atoms in the side arms of the ligands and one from the1-amino-2-propanol moiety forming a dinuclear unit with a very short (2.5430(11) Å) Co-Co intermetallic separation with a coordination number of 7, a rare feature for cobalt(III). In 2, two cobalt(II) ions in a dinuclear unit are bridged through phenoxide O and μ3-1,1,1-N3 azido bridges, and the two dinuclear units are interconnected by two μ-1,1-N3 and two μ3-1,1,1-N3 azido bridges generating tetranuclear cationic [Co4(H2L−1)2(µ3-1,1,1-N3)2(µ-1,1-N3)2Cl2(CH3OH)2]2+ units with an incomplete double cubane core, which grow into polynuclear 1D-single chains along the a-axis through H-bonding. In 3, HL2− holds mixed-valent Co(II)/Co(III) ions in a dinuclear unit bridged via phenoxide O, μ-1,3-CH3CO2−, and μ3-OH− bridges, and the dinuclear units are interconnected through two deprotonated ethanolic O in the side arms of the ligands and two μ3-OH− bridges generating cationic tetranuclear [Co2IICo2III(HL−2)2(µ-CH3CO2)2(µ3-OH)2]2+ units with an incomplete double cubane core. In 4, H2L1−2 holds mixed-valent Co(II)/Co(III) ions in dinuclear units which dimerize through two ethanolic O (μ-RO−) in the side arms of the ligands and two ethanolic O (μ3-RO−) of THMAM bridges producing centrosymmetric cationic tetranuclear [Co2IICo2III (H2L1−2)2(THMAM−1)2]4+ units which grow into 2D-sheets along the bc-axis through a network of H-bonding. Bulk magnetization measurements on 2 demonstrate that the magnetic interactions are completely dominated by an overall ferromagnetic coupling occurring between Co(II) ions. 相似文献
20.
Francisco Arturo Lpez Cota Jos Alonso Díaz-Guilln Oscar Juan Dura Marco Antonio Lpez de la Torre Joelis Rodríguez-Hernndez Antonio Fernndez Fuentes 《Materials》2021,14(13)
This contribution deals with the mechanochemical synthesis, characterization, and thermoelectric properties of tetrahedrite-based materials, Cu12-xMxSb4S13 (M = Fe2+, Zn2+, Cd2+; x = 0, 1.5, 2). High-energy mechanical milling allows obtaining pristine and substituted tetrahedrites, after short milling under ambient conditions, of stoichiometric mixtures of the corresponding commercially available binary sulfides, i.e., Cu2S, CuS, Sb2S3, and MS (M = Fe2+, Zn2+, Cd2+). All the target materials but those containing Cd were obtained as single-phase products; some admixture of a hydrated cadmium sulfate was also identified by XRD as a by-product when synthesizing Cu10Cd2Sb4S13. The as-obtained products were thermally stable when firing in argon up to a temperature of 350–400 °C. Overall, the substitution of Cu(II) by Fe(II), Zn(II), or Cd(II) reduces tetrahedrites’ thermal and electrical conductivities but increases the Seebeck coefficient. Unfortunately, the values of the thermoelectric figure of merit obtained in this study are in general lower than those found in the literature for similar samples obtained by other powder processing methods; slight compositional changes, undetected secondary phases, and/or deficient sintering might account for some of these discrepancies. 相似文献