New Volatile Perfluorinated Amidine–Carboxylate Copper(II) Complexes as Promising Precursors in CVD and FEBID Methods

In the present study, we have synthesised and characterised newly copper(II) complexes with the general formula [Cu₂(NH₂(NH=)CC₂F₅)₂(µ–O₂CR_F)₄], where R_F = CF₃, C₂F₅, C₃F₇, C₄F₉. Infrared spectroscopy, mass spectrometry with electron ionisation (EI MS), and density-functional theory (DFT) calculations were used to confirm compounds’ composition and structure. The volatility of the compounds was studied using thermal analysis (TGA), EI MS mass spectrometry, variable temperature infrared spectroscopy (VT IR), and sublimation experiments. Research has revealed that these compounds are the source of metal carriers in the gas phase. The thermal decomposition mechanism over reduced pressure was proposed. TGA studies demonstrated that copper transfer to the gaseous phase occurs even at atmospheric pressure. Two selected complexes [Cu₂(NH₂(NH=)CC₂F₅)₂(µ–O₂CC₂F₅)₄] and [Cu₂(NH₂(NH=)CC₂F₅)₂(µ–O₂CC₃F₇)₄] were successful used as chemical vapour deposition precursors. Copper films were deposited with an evaporation temperature of 393 K and 453 K, respectively, and a decomposition temperature in the range of 573–633 K without the use of hydrogen. The microscopic observations made to investigate the interaction of the [Cu₂(NH₂(NH=)CC₂F₅)₂(µ–O₂CC₂F₅)₄] with the electron beam showed that the ligands are completely lost under transmission electron microscopy analysis conditions (200 keV), and the final product is copper(II) fluoride. In contrast, the beam energy in scanning electron microscopy (20 keV) was insufficient to break all coordination bonds. It was shown that the Cu-O bond is more sensitive to the electron beam than the Cu-N bond.     

Magnetic and Electrical Behaviors of the Homo- and Heterometallic 1D and 3D Coordination Polymers Based on the Partial Decomposition of the [Cr(C2O4)3]3− Building Block

One-dimensional (1D) oxalate-bridged homometallic {[Mn(bpy)(C₂O₄)]·1.5H₂O}_n (1) (bpy = 2,2’-bipyridine) and heterodimetallic {[CrCu₃(bpy)₃(CH₃OH)(H₂O)(C₂O₄)₄][Cu(bpy)Cr(C₂O₄)₃]·CH₂Cl₂·CH₃OH·H₂O}_n (2) coordination polymers, as well as the three-dimensional (3D) heterotrimetallic {[CaCr₂Cu₂(phen)₄(C₂O₄)₆]·4CH₃CN·2H₂O}_n (3) (1,10-phenanthroline) network, have been synthesized by a building block approach using a layering technique, and characterized by single-crystal X-ray diffraction, infrared (IR) and impedance spectroscopies and magnetization measurements. During the crystallization process partial decomposition of the tris(oxalato)chromate(III) happened and 1D polymers 1 and 2 were formed. The antiferromagnetic interactions between the manganese(II) ions were mediated by oxalate ligands in the chain [Mn(bpy)(C₂O₄)]_n of 1, with intra-chain super-exchange interaction 𝐽 = (−3.134 ± 0.004) K; magnetic interaction between neighbouring chains is negligible making this system closer than other known Mn-chains to the ideal 1D Heisenberg antiferromagnet. Compound 2 comprises a 1D coordination anion [Cu(bpy)Cr(C₂O₄)₃]_nⁿ⁻ (Cr2–Cu4) with alternating [Cr(C₂O₄)₃]³⁻ and [Cu(bpy)]²⁺ units mutually bridged through the oxalate group. Another chain (Cr1–Cu3) is similar, but involves a homodinuclear unit [Cu(bpy)(H₂O)(µ-C₂O₄)Cu(bpy)(CH₃OH)]²⁺ (Cu1–Cu2) coordinated as a pendant group to a terminal oxalate oxygen. Magnetic measurements showed that the Cu1−Cu2 cationic unit is a strongly coupled antiferromagnetic dimer, independent from the other magnetic ions within ferromagnetic chains Cr1–Cu3 and Cr2–Cu4. A 3D polymer {[CaCr₂Cu₂(phen)₄(C₂O₄)₆]·4CH₃CN·2H₂O}_n (3) comprising three different metal centers (Ca²⁺, Cr³⁺ and Cu²⁺) oxalate-bridged, contains Ca²⁺ atoms as nodes connected with four Cr³⁺ atoms through oxalate ligands. The network thus formed can be reduced to an underlying graph of diamondoid (dia) or (6⁶) topology. Magnetization of 3 shows the ferromagnetic oxalate-bridged dimers [Cu^IICr^III], whose mutual interaction could possibly originate through the spin polarization of Ca²⁺ orbitals. Compounds 1 and 3 exhibit lower electrical conductivity at room temperature (RT) in comparison to compound 2.     

Surface structural-chemical characterization of a single-site d0 heterogeneous arene hydrogenation catalyst having 100% active sites

Structural characterization of the catalytically significant sites on solid catalyst surfaces is frequently tenuous because their fraction, among all sites, typically is quite low. Here we report the combined application of solid-state ¹³C-cross-polarization magic angle spinning nuclear magnetic resonance (¹³C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η⁵-C₅H₅)₂ZrR₂ (R = H, CH₃) and [η⁵-C₅(CH₃)₅]Zr(CH₃)₃ adsorbed on Brønsted superacidic sulfated alumina (AlS). The latter complex is exceptionally active for benzene hydrogenation, with ∼100% of the Zr sites catalytically significant as determined by kinetic poisoning experiments. The ¹³C-CPMAS-NMR, DFT, and XAS data indicate formation of organozirconium cations having a largely electrostatic [η⁵-C₅(CH₃)₅]Zr(CH₃)₂⁺···AlS⁻ interaction with greatly elongated Zr···O_AlS distances of ∼2.35(2) Å. The catalytic benzene hydrogenation cycle is stepwise understandable by DFT, and proceeds via turnover-limiting H₂ delivery to surface [η⁵-C₅(CH₃)₅]ZrH₂(benzene)⁺···AlS⁻ species, observable by solid-state NMR and XAS.     

Copper-Doped Biphasic Calcium Phosphate Powders: Dopant Release,Cytotoxicity and Antibacterial Properties

Cytotoxicity and antibacterial properties associated with the dopant release of Cu-doped Biphasic Calcium Phosphate (BCP) powders, mainly composed of hydroxyapatite mixed with β-tricalcium phosphate powders, were investigated. Twelve BCP ceramics were synthesized at three different sintering temperatures (600 °C, 900 °C and 1200 °C) and four copper doping rates (x = 0.0, 0.05, 0.10 and 0.20, corresponding to the stoichiometric amount of copper in Ca₁₀Cu_x(PO₄)₆(OH)_2-2xO_2x). Cytotoxicity assessments of Cu-doped BCP powders, using MTT assay with human-Mesenchymal Stem Cells (h-MSCs), indicated no cytotoxicity and the release of less than 12 ppm of copper into the biological medium. The antibacterial activity of the powders was determined against both Gram-positive (methicillin-sensitive (MS) and methicillin resistant (MR) Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. The Cu-doped biomaterials exhibited a strong antibacterial activity against MSSA, MRSA and E. coli, releasing approximatively 2.5 ppm after 24 h, whereas 10 ppm were required to induce an antibacterial effect against P. aeruginosa. This study also demonstrated that the culture medium used during experiments can directly impact the antibacterial effect observed; only 4 ppm of Cu²⁺ were effective for killing all the bacteria in a 1:500 diluted TS medium, whereas 20 ppm were necessary to achieve the same result in a rich, non-diluted standard marrow cell culture medium.     

One-Pot Self-Assembly of Dinuclear,Tetranuclear, and H-Bonding-Directed Polynuclear Cobalt(II), Cobalt(III), and Mixed-Valence Co(II)/Co(III) Complexes of Schiff Base Ligands with Incomplete Double Cubane Core

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 Co^IICo^III: [Co₂^III(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), [Co₂^IICo₂^III(HL⁻²)₂(µ-CH₃CO₂)₂(µ₃-OH)₂](NO₃)₂·2CH₃CH₂OH (3), and [Co₂^IICo₂^III (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 [Co₂^IICo₂^III(HL⁻²)₂(µ-CH₃CO₂)₂(µ_3-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 [Co₂^IICo₂^III (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.     

Increasing Cu bioavailability inhibits Aβ oligomers and tau phosphorylation

Cognitive decline in Alzheimer's disease (AD) involves pathological accumulation of synaptotoxic amyloid-β (Aβ) oligomers and hyperphosphorylated tau. Because recent evidence indicates that glycogen synthase kinase 3β (GSK3β) activity regulates these neurotoxic pathways, we developed an AD therapeutic strategy to target GSK3β. The strategy involves the use of copper-bis(thiosemicarbazonoto) complexes to increase intracellular copper bioavailability and inhibit GSK3β through activation of an Akt signaling pathway. Our lead compound Cu^II(gtsm) significantly inhibited GSK3β in the brains of APP/PS1 transgenic AD model mice. Cu^II(gtsm) also decreased the abundance of Aβ trimers and phosphorylated tau, and restored performance of AD mice in the Y-maze test to levels expected for cognitively normal animals. Improvement in the Y-maze correlated directly with decreased Aβ trimer levels. This study demonstrates that increasing intracellular copper bioavailability can restore cognitive function by inhibiting the accumulation of neurotoxic Aβ trimers and phosphorylated tau.     

Molecular and Polymer Ln2M2 (Ln = Eu,Gd, Tb,Dy; M = Zn,Cd) Complexes with Pentafluorobenzoate Anions: The Role of Temperature and Stacking Effects in the Structure; Magnetic and Luminescent Properties

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.     

Magnetic Properties and Morphology Copper-Substituted Barium Hexaferrites from Sol-Gel Auto-Combustion Synthesis

The copper (Cu) substitution in barium hexaferrite (BaFe₁₂O₁₉) crystals from the sol-gel auto-combustion synthesis is demonstrated as a cost-effective pathway to achieve alterable magnetic properties. Subsequent heat treatments at 450 °C and 1050 °C result in irregularly shaped nanoparticles characterized as the M-type BaFe₁₂O₁₉ with the secondary phase of hematite (α-Fe₂O₃). Despite the mixed phase, the substantial coercivity of 2626 Oe and magnetization as high as 74.8 emu/g are obtained in this undoped ferrite. The copper (Cu) doing strongly affects morphology and magnetic properties of BaFe_12−xCu_xO₁₉ (x = 0.1, 0.3, and 0.5). The majority of particles become microrods for x = 0.1 and microplates in the case of x = 0.3 and 0.5. The coercivity and magnetization tend to reduce as Cu²⁺ increasingly substitutes Fe³⁺. From these findings, magnetic properties for various applications in microwave absorbers, recording media, electrodes, and permanent magnets can be tailored by the partial substitution in hexaferrite crystals.     

Similarities of artificial photosystems by ruthenium oxo complexes and native water splitting systems

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.     

Maximal functions: Homogeneous curves

Let t → γ(t) be a homogeneous curve in Rⁿ. For suitable f, define [unk](f)(x) = sup_{h > 0}|(1/h) [unk]₀^hf(x - γ(t)) dt|. Then [unk](f)_p ≤ A_p f_p, 1 < p ≤ ∞.     

Maximal functions associated to smooth curves

Let t → γ(t), 0 ≤ t ≤ 1, be a smooth curve in IRⁿ. Define the maximal function [unk](f) by [unk](f)(x) = sup_0<h≤1 (1/h) ʃ₀^h | f(x - γ(t))| dt. We state conditions under which [unk](f)_p ≤ A_p f_p, for 1 < p ≤ ∞.     

Equipartition of energy for higher-order hyperbolic equations

Let A₀, A₁,...,A_2^N-1 be commuting skew-adjoint operators on a Hilbert space [unk]. Then the equation Π_j=0^2N-1 (d/dt - A_j)v(t) = 0 (t real) admits equipartition of energy [in the sense that the jth partial energy E_j(t) of any solution at time t satisfies lim_t→±∞E_j(t) = 2^-N·(total energy) for each of the 2^N values of j] if and only if the closure B_jk of A_j - A_k satisfies weak-operator-limit exp(tB_jk) = 0 as t → ±∞ whenever j ≠ k.     

Model of effectively neutral mutations in which selective constraint is incorporated

Based on the idea that selective neutrality is the limit when the selective disadvantage becomes indefinitely small, a model of neutral (and nearly neutral) mutations is proposed that assumes that the selection coefficient (s′) against the mutant at various sites within a cistron (gene) follows a Γ distribution; f(s′) = α^βe^-αs′s′^β-1/Γ(β), in which α = β/¯s′ and ¯s′ is the mean selection coefficient against the mutants (¯s′ > 0; 1 [unk] β > 0). The mutation rate for alleles whose selection coefficients s′ lie in the range between 0 and 1/(2N_e), in which N_e is the effective population size, is termed the effectively neutral mutation rate (denoted by v_e). Using the model of “infinite sites” in population genetics, formulas are derived giving the average heterozygosity (¯h_e) and evolutionary rate per generation (k_g) in terms of mutant substitutions. It is shown that, with parameter values such as β = 0.5 and ¯s′ = 0.001, the average heterozygosity increases much more slowly as N_e increases, compared with the case in which a constant fraction of mutations are neutral. Furthermore, the rate of evolution per year (k₁) becomes constant among various organisms, if the generation span (g) in years is inversely proportional to √N_e among them and if the mutation rate per generation is constant. Also, it is shown that we have roughly k_g = v_e. The situation becomes quite different if slightly advantageous mutations occur at a constant rate independent of environmental conditions. In this case, the evolutionary rate can become enormously higher in a species with a very large population size than in a species with a small population size, contrary to the observed pattern of evolution at the molecular level.     

Superionic Solid Electrolyte Li7La3Zr2O12 Synthesis and Thermodynamics for Application in All-Solid-State Lithium-Ion Batteries

Solid-state reaction was used for Li₇La₃Zr₂O₁₂ material synthesis from Li₂CO₃, La₂O₃ and ZrO₂ powders. Phase investigation of Li₇La₃Zr₂O₁₂ was carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS) methods. The thermodynamic characteristics were investigated by calorimetry measurements. The molar heat capacity (C_p,m), the standard enthalpy of formation from binary compounds (Δ_oxH_LLZO) and from elements (Δ_fH_LLZO), entropy (S⁰₂₉₈), the Gibbs free energy of the Li₇La₃Zr₂O₁₂ formation (∆_f G⁰₂₉₈) and the Gibbs free energy of the LLZO reaction with metallic Li (∆_rG_LLZO/Li) were determined. The corresponding values are C_p,m = 518.135 + 0.599 × T − 8.339 × T⁻², (temperature range is 298–800 K), Δ_oxH_LLZO = −186.4 kJ·mol⁻¹, Δ_fH_LLZO = −9327.65 ± 7.9 kJ·mol⁻¹, S⁰₂₉₈ = 362.3 J·mol⁻¹·K⁻¹, ∆_f G⁰₂₉₈ = −9435.6 kJ·mol⁻¹, and ∆_rG_LLZO/Li = 8.2 kJ·mol⁻¹, respectively. Thermodynamic performance shows the possibility of Li₇La₃Zr₂O₁₂ usage in lithium-ion batteries.     

Structure of a Fe4O6-Heteraadamantane-Type Hexacation Stabilized by Chelating Organophosphine Oxide Ligands

Metal-containing heteraadamantanes are compounds of interest due to their spectroscopic and magnetic properties, which make them promising materials for non-linear optics and semiconductors. Herein we report the comprehensive structural characterization of a new coordination compound of the formula [(µ-OH′)₂(µ-OH″)₄(O = P(Ph₂)CH₂CH₂(Ph₂)P = O)₄{Fe(t-BuOH)}₄](PF₆)₄(Cl)₂ with the chelating ligand Ph₂P(O)-CH₂CH₂-P(O)Ph₂. The compound crystallizes as a polynuclear metal complex with the adamantane-like core [Fe₄O₆] in the space group I-43d of a cubic system. The single-crystal XRD analysis showed that the crystal contains one symmetrically independent octahedrally coordinated Fe atom in the oxidation state +3. The adamantine-like scaffold of the Fe complex is formed by hydroxy bridging oxygen atoms only. Hirshfeld surface analysis of the bridging oxygen atoms revealed two types of µ-OH groups, which differ in the degree of exposure and participation in long-range interactions. Additionally, the Hirshfeld surface analysis supported by the enrichment ratio calculations demonstrated the high propensity of the title complex to form C-H^…Cl, C-H^…F and C-H^…O interactions.     

Extended x-ray absorption fine structure of copper in cytochrome c oxidase: Direct evidence for copper-sulfur ligation

The copper x-ray fluorescence excitation spectrum of cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) has been recorded in the 245—270 K range. The beat pattern observed in the extended x-ray absorption fine structure can be accounted for only by postulating a combination of sulfur and nitrogen (or oxygen) ligands to the copper. The average Cu—S distance is 2.27 ± 0.02 Å and the average Cu—N (or Cu—O) distance is 1.97 ± 0.02 Å. The amplitudes require ca, 1-1.5 sulfurs and 2 nitrogens (or oxygens) per copper. The distribution of sulfur ligands between Cu_A and Cu_B sites is not known, although there is some evidence that two sulfur atoms are bound to Cu_A.     

Reactive and nonreactive quenching of O(1D) by the potent greenhouse gases SO2F2, NF3, and SF5CF3

A laser flash photolysis–resonance fluorescence technique has been employed to measure rate coefficients and physical vs. reactive quenching branching ratios for O(¹D) deactivation by three potent greenhouse gases, SO₂F₂(k₁), NF₃(k₂), and SF₅CF₃(k₃). In excellent agreement with one published study, we find that k₁(T) = 9.0 × 10^-11 exp(+98/T) cm³ molecule^-1 s^-1 and that the reactive quenching rate coefficient is k_1b = (5.8 ± 2.3) × 10^-11 cm³ molecule^-1 s^-1 independent of temperature. We find that k₂(T) = 2.0 × 10^-11 exp(+52/T) cm³ molecule^-1 s^-1 with reaction proceeding almost entirely (∼99%) by reactive quenching. Reactive quenching of O(¹D) by NF₃ is more than a factor of two faster than reported in one published study, a result that will significantly lower the model-derived atmospheric lifetime and global warming potential of NF₃. Deactivation of O(¹D) by SF₅CF₃ is slow enough (k₃ < 2.0 × 10^-13 cm³ molecule^-1 s^-1 at 298 K) that reaction with O(¹D) is unimportant as an atmospheric removal mechanism for SF₅CF₃. The kinetics of O(¹D) reactions with SO₂ (k₄) and CS₂ (k₅) have also been investigated at 298 K. We find that k₄ = (2.2 ± 0.3) × 10^-10 and k₅ = (4.6 ± 0.6) × 10^-10 cm³ molecule^-1 s^-1; branching ratios for reactive quenching are 0.76 ± 0.12 and 0.94 ± 0.06 for the SO₂ and CS₂ reactions, respectively. All uncertainties reported above are estimates of accuracy (2σ) and rate coefficients k_i(T) (i = 1,2) calculated from the above Arrhenius expressions have estimated accuracies of ± 15% (2σ).     

Enhanced rate of intramolecular electron transfer in an engineered purple CuA azurin

The recent expression of an azurin mutant where the blue type 1 copper site is replaced by the purple Cu_A site of Paracoccus denitrificans cytochrome c oxidase has yielded an optimal system for examining the unique electron mediation properties of the binuclear Cu_A center, because both type 1 and Cu_A centers are placed in the same location in the protein while all other structural elements remain the same. Long-range electron transfer is induced between the disulfide radical anion, produced pulse radiolytically, and the oxidized binuclear Cu_A center in the purple azurin mutant. The rate constant of this intramolecular process, k_ET = 650 ± 60 s⁻¹ at 298 K and pH 5.1, is almost 3-fold faster than for the same process in the wild-type single blue copper azurin from Pseudomonas aeruginosa (250 ± 20 s⁻¹), in spite of a smaller driving force (0.69 eV for purple Cu_A azurin vs. 0.76 eV for blue copper azurin). The reorganization energy of the Cu_A center is calculated to be 0.4 eV, which is only 50% of that found for the wild-type azurin. These results represent a direct comparison of electron transfer properties of the blue and purple Cu_A sites in the same protein framework and provide support for the notion that the binuclear purple Cu_A center is a more efficient electron transfer agent than the blue single copper center because reactivity of the former involves a lower reorganization energy.     

Highly efficient and robust molecular ruthenium catalysts for water oxidation

Water oxidation catalysts are essential components of light-driven water splitting systems, which could convert water to H₂ driven by solar radiation (H₂O + hν → 1/2O₂ + H₂). The oxidation of water (H₂O → 1/2O₂ + 2H⁺ + 2e^-) provides protons and electrons for the production of dihydrogen (2H⁺ + 2e^- → H₂), a clean-burning and high-capacity energy carrier. One of the obstacles now is the lack of effective and robust water oxidation catalysts. Aiming at developing robust molecular Ru-bda (H₂bda = 2,2^′-bipyridine-6,6′-dicarboxylic acid) water oxidation catalysts, we carried out density functional theory studies, correlated the robustness of catalysts against hydration with the highest occupied molecular orbital levels of a set of ligands, and successfully directed the synthesis of robust Ru-bda water oxidation catalysts. A series of mononuclear ruthenium complexes [Ru(bda)L₂] (L = pyridazine, pyrimidine, and phthalazine) were subsequently synthesized and shown to effectively catalyze Ce^IV-driven [Ce^IV = Ce(NH₄)₂(NO₃)₆] water oxidation with high oxygen production rates up to 286 s^-1 and high turnover numbers up to 55,400.     

Novel H-Bonded Synthons in Copper Supramolecular Frameworks with Aminoethylpiperazine-Based Ligands. Synthesis,Structure and Catalytic Activity

New Schiff base complexes [Cu₂(HL¹)(L¹)(N₃)₃]∙2H₂O (1) and [Cu₂L²(N₃)₂]∙H₂O (2) were synthesized. The crystal structures of 1 and 2 were determined by single-crystal X-ray diffraction analysis. The HL¹ ligand results from the condensation of salicylaldehyde and 1-(2-aminoethyl)piperazine, while a new organic ligand, H₂L², was formed by the dimerization of HL¹ via a coupling of two piperazine rings of HL¹ on a carbon atom coming from DMF solvent. The dinuclear building units in 1 and 2 are linked into complex supramolecular networks through hydrogen and coordination bondings, resulting in 2D and 1D architectures, respectively. Single-point and broken-symmetry DFT calculations disclosed negligible singlet–triplet splittings within the dinuclear copper fragments in 1 and 2. Catalytic studies showed a remarkable activity of 1 and 2 towards cyclohexane oxidation with H₂O₂ in the presence of nitric acid and pyridine as promoters and under mild conditions (yield of products up to 21%). Coordination compound 1 also acts as an active catalyst in the intermolecular coupling of cyclohexane with benzamide using di-tert-butyl peroxide (^tBuOO^tBu) as a terminal oxidant. Conversion of benzamide at 55% was observed after 24 h reaction time. By-product patterns and plausible reaction mechanisms are discussed.