Kinetic regulation of a corrinoid‐reducing metallo‐ATPase by its substrates

Corrinoid cofactors play a crucial role as methyl group carriers in the C1 metabolism of anaerobes, e.g. in the cleavage of phenyl methyl ethers by O‐demethylases. For the methylation, the protein‐bound corrinoid has to be in the super‐reduced [Co^I]‐state, which is highly sensitive to autoxidation. The reduction of inadvertently oxidized corrinoids ([Co^II]‐state) is catalysed in an ATP‐dependent reaction by RACE proteins, the r eductive a ctivators of c orrinoid‐dependent e nzymes. In this study, a reductive activator of O‐demethylase corrinoid proteins was characterized with respect to its ATPase and corrinoid reduction activity. The reduction of the corrinoid cofactor was dependent on the presence of potassium or ammonium ions. In the absence of the corrinoid protein, a basal slow ATP hydrolysis was observed which was obviously not coupled to corrinoid reduction. ATP hydrolysis was significantly stimulated by the corrinoid protein in the [Co^II]‐state of the corrinoid cofactor. The stoichiometry of ATP hydrolysed per mol corrinoid reduced was near 1:1. Site‐directed mutagenesis was applied to study the impact of a highly conserved region possibly involved in nucleotide binding of RACE proteins, indicating that an aspartate and a glycine residue may play an essential role for the function of the enzyme.     

Veratrol-<Emphasis Type="Italic">O</Emphasis>-demethylase of <Emphasis Type="Italic">Acetobacterium dehalogenans</Emphasis>: ATP-dependent reduction of the corrinoid protein

The anaerobic veratrol O-demethylase mediates the transfer of the methyl group of the phenyl methyl ether veratrol to tetrahydrofolate. The primary methyl group acceptor is the cobalt of a corrinoid protein, which has to be in the +1 oxidation state to bind the methyl group. Due to the negative redox potential of the cob(II)/cob(I)alamin couple, autoxidation of the cobalt may accidentally occur. In this study, the reduction of the corrinoid to the superreduced [Co^I] state was investigated. The ATP-dependent reduction of the corrinoid protein of the veratrol O-demethylase was shown to be dependent on titanium(III) citrate as electron donor and on an activating enzyme. In the presence of ATP, activating enzyme, and Ti(III), the redox potential versus the standard hydrogen electrode (E _SHE) of the cob(II)alamin/cob(I)alamin couple in the corrinoid protein was determined to be −290 mV (pH 7.5), whereas E _SHE at pH 7.5 was lower than −450 mV in the absence of either activating enzyme or ATP. ADP, AMP, or GTP could not replace ATP in the activation reaction. The ATP analogue adenosine-5′-(β,γ-imido)triphosphate (AMP-PNP, 2–4 mM) completely inhibited the corrinoid reduction in the presence of ATP (2 mM).     

Reductive activation of the corrinoid-containing enzyme involved in methyl group transfer between methyl-tetrahydromethanopterin and coenzyme M inMethanosarcina barkeri

The conversion of methyl-tetrahydromethanopterin to methylcoenzyme M inMethanosarcina barkeri is catalyzed by two enzymes: an enzyme with a bound corrinoid, which becomes methylated during the reaction and an enzyme which tranfers the methyl group from this corrinoid to coenzyme M. As in the similar methyltransfer reaction inMethanobacterium thermoautotrophicum the corrinoid enzyme inM. barkeri needs to be activated by H₂ and ATP. ATP can be replaced by Ti(III)citrate or CO.     

14.2% Efficiency Dye‐Sensitized Solar Cells by Co‐sensitizing Novel Thieno[3,2‐b]indole‐Based Organic Dyes with a Promising Porphyrin Sensitizer

A new series of 4‐hexyl‐4H‐thieno[3,2‐b]indole (HxTI) based organic chromophores is developed by structural engineering of the electron donor (D) group in the D–HxTI–benzothiadiazole‐phenyl‐acceptor platform with different fluorenyl moieties, such as unsubstituted fluorenyl (SGT‐146) and hexyloxy (SGT‐147), decyloxy (SGT‐148) and hexyloxy‐phenyl substituted (SGT‐149) fluorenyl moieties. In comparison to a reference dye SGT‐137 with a biphenyl‐based donor, the effects of the donating ability and bulkiness of the fluorenyl based donor in this D–π–A‐structured platform on molecular properties and photovoltaic performance are investigated to establish the structure–property relationship. The photovoltaic performance of dye‐sensitized solar cells (DSSCs) is improved according to the bulkiness of the donor groups. As a result, the DSSCs based on SGT‐149 show high power conversion efficiencies (PCEs) of 11.7% and 10.0% with a [Co(bpy)₃]^2+/3+ (bpy = 2,2′‐bipyridine) and an I^?/I₃^? redox electrolyte, respectively. Notably, the co‐sensitization of SGT‐149 with a SGT‐021 porphyrin dye by utilizing a simple “cocktail” method, exhibit state‐of‐the‐art PCEs of 14.2% and 11.6% with a [Co(bpy)₃]^2+/3+ and an I^?/I₃^? redox electrolyte, respectively.     

Controlled Oxygen Redox for Excellent Power Capability in Layered Sodium‐Based Compounds

A high‐rate of oxygen redox assisted by cobalt in layered sodium‐based compounds is achieved. The rationally designed Na_0.6[Mg_0.2Mn_0.6Co_0.2]O₂ exhibits outstanding electrode performance, delivering a discharge capacity of 214 mAh g^?1 (26 mA g^?1) with capacity retention of 87% after 100 cycles. High rate performance is also achieved at 7C (1.82 A g^?1) with a capacity of 107 mAh g^?1. Surprisingly, the Na_0.6[Mg_0.2Mn_0.6Co_0.2]O₂ compound is able to deliver capacity for 1000 cycles at 5C (at 1.3 A g^?1), retaining 72% of its initial capacity of 108 mAh g^?1. X‐ray absorption spectroscopy analysis of the O K‐edge indicates the oxygen‐redox species (O^2?/1?) is active during cycling. First‐principles calculations show that the addition of Co reduces the bandgap energy from ≈2.65 to ≈0.61 eV and that overlapping of the Co 3d and O 2p orbitals facilitates facile electron transfer, enabling the long‐term reversibility of the oxygen redox, even at high rates. To the best of the authors' knowledge, this is the first report on high‐rate oxygen redox in sodium‐based cathode materials, and it is believed that the findings will open a new pathway for the use of oxygen‐redox‐based materials for sodium‐ion batteries.     

Stabilized Co3+/Co4+ Redox Pair in In Situ Produced CoSe2−x‐Derived Cobalt Oxides for Alkaline Zn Batteries with 10 000‐Cycle Lifespan and 1.9‐V Voltage Plateau

In aqueous alkaline Zn batteries (AZBs), the Co³⁺/Co⁴⁺ redox pair offers a higher voltage plateau than its Co²⁺/Co³⁺ counterpart. However, related studies are scarce, due to two challenges: the Co³⁺/Co⁴⁺ redox pair is more difficult to activate than Co²⁺/Co³⁺; once activated, the Co³⁺/Co⁴⁺ redox pair is unstable, owing to the rapid reduction of surplus Co³⁺ to Co²⁺. Herein, CoSe_2?x is employed as a cathode material in AZBs. Electrochemical analysis recognizes the principal contributions of the Co³⁺/Co⁴⁺ redox pair to the capacity and voltage plateau. Mechanistic studies reveal that CoSe_2?x initially undergoes a phase transformation to derived Co_xO_ySe_z, which has not been observed in other Zn//cobalt oxide batteries. The Se doping effect is conducive to sustaining abundant and stable Co³⁺ species in Co_xO_ySe_z. As a result, the battery achieves a 10 000‐cycle ultralong lifespan with 0.02% cycle^?1 capacity decay, a 1.9‐V voltage plateau, and an immense areal specific capacity compared to its low‐valence oxide counterparts. When used in a quasi‐solid‐state electrolyte, as‐assembled AZB delivers 4200 cycles and excellent tailorability, a promising result for wearable applications. The presented effective strategy for obtaining long‐cyclability cathodes via a phase transformation‐induced heteroatom doping effect may promote high‐valence metal species mediation toward highly stable electrodes.     

One‐Step Controllable Synthesis of Catalytic Ni4Mo/MoOx/Cu Nanointerfaces for Highly Efficient Water Reduction

Currently, in addition to the electroactive non‐noble metal water‐splitting electrocatalysts, a scalable synthetic route and simple activity enhancement strategy is also urgently needed. In particular, the well‐controlled synthesis of the well‐recognized metal–metal nanointer face in a single step remains a key challenge. Here, the synthesis of Cu‐supported Ni₄Mo nanodots on MoO_x nanosheets (Ni₄Mo/MoO_x) with controllable Ni₄Mo particle size and d‐band structure is reported via a facile one‐step electrodeposition process. Density functional theory (DFT) calculations reveal that the active open‐shell effect from Ni‐3d‐band optimizes the electronic configuration. The Cu‐substrate enables the surface Ni–Mo alloy dots to be more electron‐rich, forming a local connected electron‐rich network, which boosts the charge transfer for effective binding of O‐related species and proton–electron charge exchange in the hydrogen evolution reaction. The Cu‐supported Ni₄Mo/MoO_x shows an ultralow overpotential of 16 mV at a current density of 10 mA cm^?2 in 1 m KOH, demonstrating the smallest overpotential, at loadings as low as 0.27 mg cm^?2, among all non‐noble metal catalysts reported to date. Moreover, an overpotential of 105 mV allows it to achieve a current density of 250 mA cm^?2 in 70 °C 30% KOH, a remarkable performance for alkaline hydrogen evolution with competitive potential for applications.     

Thieno[3,2‐b][1]benzothiophene Derivative as a New π‐Bridge Unit in D–π–A Structural Organic Sensitizers with Over 10.47% Efficiency for Dye‐Sensitized Solar Cells

Three new thieno[3,2‐b][1]benzothiophene ( TBT )‐based donor–π–acceptor (D–π–A) sensitizers, coded as SGT ‐ 121 , SGT ‐ 129 , and SGT ‐ 130 , have been designed and synthesized for dye‐sensitized solar cells (DSSCs), for the first time. The TBT , prepared by fusing thiophene unit with the phenyl unit of triphenylamine donor, is utilized as the π‐bridge for all sensitizers with good planarity. They have been molecularly engineered to regulate the highest occupied molecular orbital (HOMO)‐lowest unoccupied molecular orbital (LUMO) energy levels and extend absorption range as well as to control the electron‐transfer process that can ensure efficient dye regeneration and prevent undesired electron recombination. The photovoltaic performance of SGT‐sensitizer‐based DSSCs employing Co(bpy)₃^2+/3+ (bpy = 2,2′‐bipyridine) redox couple is systematically evaluated in a thorough comparison with Y123 as a reference sensitizer. Among them, SGT ‐ 130 with benzothiadiazole‐phenyl ( BTD ‐ P ) unit as an auxiliary acceptor exhibits the highest power‐conversion efficiency (PCE) of 10.47% with J_sc = 16.77 mA cm^?2, V_oc = 851 mV, and FF = 73.34%, whose PCE is much higher than that of Y123 (9.5%). It is demonstrated that the molecular combination of each fragment in D–π–A organic sensitizers can be a pivotal factor for achieving the higher PCEs and an innovative strategy for strengthening the drawbacks of the π‐bridge.     

Cooperative interaction of high-potential hemes in the cytochrome subunit of the photosynthetic reaction center of bacterium <Emphasis Type="Italic">Ectothiorhodospira shaposhnikovii</Emphasis>

Cooperative interaction of the high-potential hemes (C_h) in the cytochrome subunit of the photosynthesizing bacterium Ectothiorhodospira shaposhnikovii was studied by comparing redox titration curves of the hemes under the conditions of pulse photoactivation inducing single turnover of electron-transport chain and steady-state photoactivation, as well as by analysis of the kinetics of laser-induced oxidation of cytochromes by reaction center (RC). A mathematical model of the processes of electron transfer in cytochrome-containing RC was considered. Theoretical analysis revealed that the reduction of one heme C_h facilitated the reduction of the other heme, which was equivalent to a 60 mV positive shift of the midpoint potential. In addition, reduction of the second heme C_h caused a three-to four-fold acceleration of the electron transfer from the cytochrome subunit to RC. Published in Russian in Biokhimiya, 2007, Vol. 72, No. 11, pp. 1540–1547.     

Synthesis and Biophysical Studies of Bis‐Macrocyclic Cobalt/Copper(II) Complexes Having a Pyridine Spacer with CT DNA and 5′‐GMP

New bis‐macrocyclic complexes of Co^III, 1 , Ni^II, 2 , and Cu^II, 3 , containing pyridyl bridges between 13‐membered macrocyclic subunits, have been synthesized via an in situ one‐pot template condensation reaction (IOPTCR). The proposed structures of these new dinuclear complexes are consistent with the data obtained from elemental analysis, molar conductance, IR, EPR, UV/VIS, ¹H‐ and ¹³C‐NMR, and ESI‐MS. The complexes 2 and 3 possess square‐planar geometry with four secondary N‐atoms coordinated to the metal ion, while complex 1 reveals octahedral geometry in solution due to coordinated H₂O molecules. DNA‐Binding properties of the complexes 1 and 3 were investigated by absorption and emission titrations, cyclic voltammetry, and viscosity measurements. Complexes 1 and 3 are strong DNA binders with binding constants, K_b, of 1.64×10⁵ and 2.05×10⁵ M ^?1, respectively. Hyperchromism, decrease in emission intensity of DNA‐bound ethidium bromide (EB), and changes observed in the viscosity and cyclic voltammograms in the presence of added metal complexes reveals that the complexes bind to DNA predominantly by electrostatic attraction, substantiated by absorption titration with 5′‐GMP.     

Determination of reduction potential of an engineered Cu<Subscript>A</Subscript> azurin by cyclic voltammetry and spectrochemical titrations

The reduction potentials of an engineered Cu_A azurin in its native and thermally denatured states have been determined using cyclic voltammetry and spectrochemical titrations. Using a 4,4-dipyridyl disulfide modified gold electrode, the reduction potentials of native and thermally denatured Cu_A azurin are the same within the experimental error (422±5 and 425±5 mV vs. NHE, respectively, in 50 mM ammonium acetate buffer, pH 5.1, 300 mM NaCl, 25 °C), indicating that the potential is that of a nonnative state. In contrast, using a didodecyldimethylammonium bromide (DDAB) film-pyrolytic graphite edge (PGE) electrode, the reduction potentials of native and thermally denatured Cu_A azurin have been determined to be 271±7 mV (50 mM ammonium acetate buffer, pH 5.1, 4 °C) and 420±1 mV (50 mM ammonium acetate buffer, pH 5.1, 25 °C), respectively. Spectroscopic redox titration using [Ru(NH₃)₅Py]²⁺ resulted in a reduction potential (254±4 mV) (50 mM ammonium acetate buffer, pH 5.1, 4 °C) similar to the value obtained using the DDAB film-PGE electrochemical method. Complete reoxidation of [Ru(NH₃)₅Py]²⁺-reduced Cu_A azurin is also consistent with the conclusion that this spectrochemical titration method using [Ru(NH₃)₅Py]²⁺ measures the reduction potential of native Cu_A azurin.Abbreviations CcO cytochrome c oxidase - N₂OR nitrous oxide reductase - ET electron transfer - CV cyclic voltammetry - NHE normal hydrogen electrode - DDAB didodecyldimethylammonium bromide - PGE pyrolytic graphite edge     

The photosynthetic apparatus and photoinduced electron transfer in the aerobic phototrophic bacteria <Emphasis Type="Italic">Roseicyclus mahoneyensis</Emphasis> and <Emphasis Type="Italic">Porphyrobacter meromictius</Emphasis>

Photosynthetic electron transfer has been examined in whole cells, isolated membranes and in partially purified reaction centers (RCs) of Roseicyclus mahoneyensis, strain ML6 and Porphyrobacter meromictius, strain ML31, two species of obligate aerobic anoxygenic phototrophic bacteria. Photochemical activity in strain ML31 was observed aerobically, but the photosynthetic apparatus was not functional under anaerobic conditions. In strain ML6 low levels of photochemistry were measured anaerobically, possibly due to incomplete reduction of the primary electron acceptor (Q_A) prior to light excitation, however, electron transfer occurred optimally under low oxygen conditions. Photoinduced electron transfer involves a soluble cytochrome c in both strains, and an additional reaction center (RC)-bound cytochrome c in ML6. The redox properties of the primary electron donor (P) and Q_A of ML31 are similar to those previously determined for other aerobic phototrophs, with midpoint redox potentials of +463 mV and −25 mV, respectively. Strain ML6 showed a very narrow range of ambient redox potentials appropriate for photosynthesis, with midpoint redox potentials of +415 mV for P and +94 mV for Q_A. Cytoplasm soluble and photosynthetic complex bound cytochromes were characterized in terms of apparent molecular mass. Fluorescence excitation spectra revealed that abundant carotenoids not intimately associated with the RC are not involved in photosynthetic energy conservation.     

A novel mode of lactate metabolism in strictly anaerobic bacteria

Lactate is a common substrate for major groups of strictly anaerobic bacteria, but the biochemistry and bioenergetics of lactate oxidation is obscure. The high redox potential of the pyruvate/lactate pair of E₀′ = ?190 mV excludes direct NAD⁺ reduction (E₀′ = ?320 mV). To identify the hitherto unknown electron acceptor, we have purified the lactate dehydrogenase (LDH) from the strictly anaerobic, acetogenic bacterium Acetobacterium woodii. The LDH forms a stable complex with an electron‐transferring flavoprotein (Etf) that exhibited NAD⁺ reduction only when reduced ferredoxin (Fd^2?) was present. Biochemical analyses revealed that the LDH/Etf complex of A. woodii uses flavin‐based electron confurcation to drive endergonic lactate oxidation with NAD⁺ as oxidant at the expense of simultaneous exergonic electron flow from reduced ferredoxin (E₀′ ≈ –500 mV) to NAD⁺ according to: lactate + Fd^2? + 2 NAD⁺ → pyruvate + Fd + 2 NADH. The reduced Fd^2? is regenerated from NADH by a sequence of events that involves conversion of chemical (ATP) to electrochemical and finally redox energy (Fd^2? from NADH) via reversed electron transport catalysed by the Rnf complex. Inspection of genomes revealed that this metabolic scenario for lactate oxidation may also apply to many other anaerobes.     

Interpenetrating Triphase Cobalt‐Based Nanocomposites as Efficient Bifunctional Oxygen Electrocatalysts for Long‐Lasting Rechargeable Zn–Air Batteries

Rational construction of atomic‐scale interfaces in multiphase nanocomposites is an intriguing and challenging approach to developing advanced catalysts for both oxygen reduction (ORR) and evolution reactions (OER). Herein, a hybrid of interpenetrating metallic Co and spinel Co₃O₄ “Janus” nanoparticles stitched in porous graphitized shells (Co/Co₃O₄@PGS) is synthesized via ionic exchange and redox between Co²⁺ and 2D metal–organic‐framework nanosheets. This strategy is proven to effectively establish highways for the transfer of electrons and reactants within the hybrid through interfacial engineering. Specifically, the phase interpenetration of mixed Co species and encapsulating porous graphitized shells provides an optimal charge/mass transport environment. Furthermore, the defect‐rich interfaces act as atomic‐traps to achieve exceptional adsorption capability for oxygen reactants. Finally, robust coupling between Co and N through intimate covalent bonds prohibits the detachment of nanoparticles. As a result, Co/Co₃O₄@PGS outperforms state‐of‐the‐art noble‐metal catalysts with a positive half‐wave potential of 0.89 V for ORR and a low potential of 1.58 V at 10 mA cm^?2 for OER. In a practical demonstration, ultrastable cyclability with a record lifetime of over 800 h at 10 mA cm^?2 is achieved by Zn–air batteries with Co/Co₃O₄@PGS within the rechargeable air electrode.     

Transforming Benzophenoxazine Laser Dyes into Chromophores for Dye‐Sensitized Solar Cells: A Molecular Engineering Approach

The refunctionalization of a series of four well‐known industrial laser dyes, based on benzophenoxazine, is explored with the prospect of molecularly engineering new chromophores for dye‐sensitized solar cell (DSC) applications. Such engineering is important since a lack of suitable dyes is stifling the progress of DSC technology. The conceptual idea involves making laser dyes DSC‐active by chemical modification, while maintaining their key property attributes that are attractive to DSC applications. This molecular engineering follows a stepwise approach. First, molecular structures and optical absorption properties are determined for the parent laser dyes: Cresyl Violet ( 1 ), Oxazine 170 ( 2 ), Nile Blue A ( 3 ), Oxazine 750 ( 4 ). These reveal structure‐property relationships which define the prerequisites for computational molecular design of DSC dyes; the nature of their molecular architecture (D‐π‐A) and intramolecular charge transfer. Second, new DSC dyes are computationally designed by the in silico addition of a carboxylic acid anchor at various chemical substitution points in the parent laser dyes. A comparison of the resulting frontier molecular orbital energy levels with the conduction band edge of a TiO₂ DSC photoanode and the redox potential of two electrolyte options I^?/I₃^? and Co^(II/III)tris(bipyridyl) suggests promise for these computationally designed dyes as co‐sensitizers for DSC applications.     

The interaction of the reaction center secondary quinone with the ubiquinone-cytochrome c2 oxidoreductase in Rhodopseudomonas sphaeroides chromatophores

(1) Two populations of reaction centers in the chromatophore membrane can be distinguished under some conditions of initial redox poise (300 mV < E_h < 400 mV): those which transfer a reducing equivalent after the first flash from the secondary quinone (Q_II) of the reaction center to cytochrome b of the ubiquinone-cytochrome c₂ oxidoreductase; and those which retain the reducing equivalent on Q^?_II until a second flash is given. These two populations do not exchange on a time scale of tens of seconds. (2) At redox potentials higher than 400 mV, Q^?_II generated after the first flash is no longer able to reduce cytochrome b-560 even in those reaction centers associated with an oxidoreductase. Under these conditions, doubly reduced Q_II generated by a second flash is required for cytochrome b reduction, so that the Q_II effectively functions as a two-electron gate into the oxidoreductase at these high potentials. (3) At redox potentials below 300 mV, although the two populations of Q_II are no longer distinguishable, cytochrome b reduction is still dependent on only part of the reaction center population. (4) Proton binding does not oscillate under any condition tested.     

Anion–Cation Double Substitution in Transition Metal Dichalcogenide to Accelerate Water Dissociation Kinetic for Electrocatalysis

Until now, many works have shown that the hydrogen evolution reaction (HER) performance can be improved by anion or cation substitution into the crystal lattice of pyrite‐structure materials. However, the synergistic effects of anion–cation double substitution for overall enhancement of the catalytic activity remains questionable. Here, the simultaneous incorporation of vanadium and phosphorus into the CoS₂ moiety for preparing 3D mesoporous cubic pyrite‐metal Co_1‐xV_xSP is presented. It is demonstrated that the higher catalytic activity of CoS₂ after V incorporation can be primarily attributed to abundance active sites, whereas P substitution is responsible for improving HER kinetics and intrinsic catalyst. Interestingly, due to the synergistic effect of P–V double substitution, the 3D Co_1‐xV_xSP shows superior electrocatalysis toward the HER with a very small overpotential of 55 mV at 10 mA cm^?2, a small Tafel slope of 50 mV dec^?1, and a high turnover frequency of 0.45 H₂ s^?1 at 10 mA cm^?2, which is very close to commercial 20% Pt/C. Density functional theory calculation reveals that the superior catalytic activity of the 3D Co_1‐xV_xSP is contributed by the reduced kinetic energy barrier of rate‐determining HER step as well as the promotion of the desorption H₂ gas process.     

In situ characterisation of photosynthetic electron transport in Rhodopseudomonas capsulata

1. The effects of varying the ambient oxidation/reduction potential on the redox changes of cytochromes c, cytochromes b and P605 induced by a laser flash in chromatophores from Rhodopseudomonas capsulata Ala Pho⁺ have been investigated.2. The appearance and attenuation of the changes with varying ambient redox potential show that, of the cytochromes present, cytochromes c with Em₇ = 340 mV and 0 mV, and cytochrome b, Em₇ = 60 mV were concerned with photosynthetic electron flow.3. The site of action of antimycin was shown to be between cytochrome b₆₀ and a component, as yet unidentified, called Z.4. The appearance or attenuation of laser-induced changes of cytochromes c₀ and b₆₀ on redox titration was dependent on pH, but no effect of pH on the cytochrome c₃₄₀ titration was observed.5. The dependence on ambient redox potential of the laser-induced bleaching at 605 nm enabled identification of the mid-point potentials of the primary electron donor (Em₇ = 440 mV) and acceptor (Em₇ = ?25 mV).6. The interrelationship of these electron carriers is discussed with respect to the pathway of cyclic electron flow.     

Structural and redox properties in thioether-based (N/S) copper(II/I) complexes: Experimental and theoretical investigations

The complexes [Cu^IN₂(SMe)₂](ClO₄) (1) and [Cu^IIN₂(SMe)₂(CF₃SO₃)₂] (2) in both Cu^I and Cu^II redox states from N₂(SMe)₂ ligand (N,N-(2-pyridylmethyl)bis(2-methyl-thiobenzyl)amine) have been synthesized and structurally characterized by X-ray crystallography. Electrochemical studies show that the two complexes interconvert during the one electron transfer. Comparison with another complex with tBu instead Me groups on the thioether ligand shows detectable changes in X-ray structures and in redox properties. Theoretical calculations on the different steps of the redox process have been performed. Values underline steric constraints induced by the substitutions on thioether alkyl groups.