One-electron Transfer Process Research Articles

Exploring the Cooperation of the Redox Non-Innocent Ligand and Di-Cobalt Center for the Water Oxidation Reaction Catalyzed by a Binuclear Complex.

Water oxidation is a crucial reaction in the artificial photosynthesis system. In the present work, density functional calculations were employed to decipher the mechanism of water oxidation catalyzed by a binuclear cobalt complex, which was disclosed to be a homogeneous water oxidation catalyst in pH=7 phosphate buffer. The calculations showed that the catalytic cycle starts from the CoIII,III-OH2 species. Then, a proton-coupled electron transfer followed by a one-electron transfer process leads to the generation of the formal CoIV,IV-OH intermediate. The subsequent PCET produces the active species, namely the formal CoIV,V=O intermediate (4). The oxidation processes mainly occur on the ligand moiety, including the coordinated water moiety, implying a redox non-innocent behavior. Two cobalt centers keep their oxidation states and provide one catalytic center for water activation during the oxidation process. 4 triggers the O-O bond formation via the water nucleophilic attack pathway, in which the phosphate buffer ion functions as the proton acceptor. The O-O bond formation is the rate-limiting step with a calculated total barrier of 17.7 kcal/mol. The last electron oxidation process coupled with an intramolecular electron transfer results in the generation of O2.

Photolysis of Dissolved Organic Matter over Hematite Nanoplatelets.

Solar photoexcitation of chromophoric groups in dissolved organic matter (DOM), when coupled to photoreduction of ubiquitous Fe(III)-oxide nanoparticles, can significantly accelerate DOM degradation in near-surface terrestrial systems, but the mechanisms of these reactions remain elusive. We examined the photolysis of chromophoric soil DOM coated onto hematite nanoplatelets featuring (001) exposed facets using a combination of molecular spectroscopies and density functional theory (DFT) computations. Reactive oxygen species (ROS) probed by electron paramagnetic resonance (EPR) spectroscopy revealed that both singlet oxygen and superoxide are the predominant ROS responsible for DOM degradation. DFT calculations confirmed that Fe(II) on the hematite (001) surface, created by interfacial electron transfer from photoexcited chromophores in DOM, can reduce dioxygen molecules to superoxide radicals (•O2-) through a one-electron transfer process. 1H nuclear magnetic resonance (NMR) and electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) spectroscopies show that the association of DOM with hematite enhances the cleavage of aromatic groups during photodegradation. The findings point to a pivotal role for organic matter at the interface that guides specific ROS generation and the subsequent photodegradation process, as well as the prospect of using ROS signatures as a forensic tool to help interpret more complicated field-relevant systems.

Molecular level interaction, HOMO-LUMO, MEP, UV–Vis, Hirshfeld, topological analysis, and in-vitro of isoflavones from Eremostachys Vicaryi Benth. Ex Hook. f.

Eremostachys vicaryi Benth. Ex Hook. f. (Labiatae), a Pakistani (Baluchistan) herbal medicinal plant commonly known as “Stagh,” which has a sharp taste and smell. It acts as an antiseptic and antimicrobial agent and is used for fish poisoning, treating skin diseases, and holding a cooling effect. Following the assessment of the plant extract's cytotoxic and phytotoxic assays using phytochemical screening, the antioxidant and anti-inflammatory properties of the pure ingredients that were separated from the ethyl acetate soluble fractions have been evaluated. The bioassay-guided fractionation and purification of E. vicaryi B. crude methanol extract yielded two isoflavones (1–2) that showed promising antioxidative activities with DPPH and cytochrome-c-reduction assays. Compounds 1 and 2 have shown considerable anti-inflammatory efficacy, 1 being a good inhibitor of the superoxide within the living system. Initial assumptions on the one-electron transfer process indicated that Compound 1 has a smaller ionization potential value compared to Compound 2 and so has greater antioxidant potential than its predecessor, isoflavone. Moreover, the anti-inflammatory and antioxidant activity of isoflavones was also probed by first-principles calculations. Based on the findings, it has been concluded that the crude extract of E. vicaryi B. and its organic components exhibit noteworthy phytotoxic and cytotoxic properties. The isolated pure isoflavones 1 and 2 showed significant antioxidant and anti-inflammatory activities. Solute-solvent interactions were studied and reported for both compounds. An analysis was conducted on the UV–Vis electronic transition for different solvents. Using a Multiwave function analyzer the topological findings such as ELF, LOL, and RDG were done to comprehend the surface electron density, delocalization, localized orbital, and weak interaction in the compounds. The antioxidant activity is evaluated by radical methods using DPPH, and cytochrome-c-reduction assays using ascorbic acid as a standard. Through cell-based respiratory burst testing, the anti-inflammatory activity of standard indomethacin was examined. The ground state geometries of isoflavones and reference compounds were optimized by Density Functional Theory- (DFT) by computing various electronic properties. In-vitro bioassay results were validated by first-principles calculations.

Differential interactions between natural clay minerals and dissolved organic matter affect reactive oxygen species formation

Naturally occurring reactive oxygen species (ROS) are widely involved in many environmental processes. Here we investigated the ROS generation associated with the interaction between complexed natural clay minerals (CMs) and dissolved organic matter (DOM). Our results showed that among the nine chemical-reduced CMs (CR-CMs), the light brown CR-CM (CR-CM 7) generated the highest ROS via oxygenation, relying on the reactive structural Fe(II) (Fe species that can transfer electrons to oxygen) instead of total structural Fe(II) as previously reported. Moreover, DOM affected the oxygenation of CR-CMs differently. The tight interaction between DOM and CR-CM 7 formed DOM-complexed Fe, while the weak interaction between DOM and the dark gold CR-CM (CR-CM 1) and the black CR-CM (CR-CM 5) exhibited decreased efficiencies. Mechanism studies revealed that ROS were generated through three pathways but all followed a similar one-electron transfer process in the presence of DOM. We further developed a three-layer geobattery model system and demonstrated that long electron transfer driven by CR-CMs/DOM could extend ROS generation to several centimetres across the oxic-anoxic interface, even without redox switching. These findings offer new insights into CMs-involved ROS generation and associated organic matter transformation in natural environments.

Dramatically enhanced phenol degradation upon FeS oxygenation by low-molecular-weight organic acids

Oxidizing potential of FeS for organic contaminants degradation due to hydroxyl radicals (•OH) production has been recently documented, but the oxidizing efficiency was limited. Here, we revealed that low-molecular-weight organic acids (LMWOAs) can immensely enhance phenol degradation during FeS oxygenation due to increased utilization efficiency of FeS electron for •OH production. Upon oxygenation of 0.5 g/L FeS, phenol degradation boosted from 7.1% without LMWOAs to 91.5%, 84.6% and 95.0% with the addition of 1 mM oxalate, citrate and EDTA, respectively. Electron utilization efficiency of Fe(II) for •OH production dramatically rose from 0.3% with FeS alone to respective 2.0%, 2.5% and 2.7% in the LMWOAs systems. An increase in oxalate concentrations benefited •OH formation and phenol degradation. Coexisting oxalate led to an additional •OH production pathway from Fe(II)-oxalate oxidation, which expanded the O2 reduction to H2O2 from a two- to one-electron transfer process. Meanwhile, electron transfer from FeS to dissolved Fe(III)-oxalate promoted the redox cycling of Fe(III)/Fe(II), thus supplying the Fe(II) oxidation for •OH production. Moreover, the presence of oxalate decreased the crystallinity and particles size of lepidocrocite generated from FeS oxidation. Consequently, this study shed lights on the LMWOAs-enhanced contaminant degradation in either natural or engineered FeS oxidation systems.

Photocatalytic Cross-Pinacol Coupling Promoted by Carbon Dioxide.

Cross-pinacol coupling of two different carbonyl compounds was achieved through successive one-electron transfer processes under photocatalytic conditions. In the reaction, an umpoled anionic carbinol synthon was generated in situ to react nucleophilically with a second electrophilic carbonyl compound. We revealed that a CO2 additive promoted the photocatalytic generation of the carbinol synthon to suppress undesired radical dimerization. A wide variety of aromatic and aliphatic carbonyl substrates underwent the cross-pinacol coupling to afford the corresponding unsymmetric vicinal 1,2-diols, where even a combination of carbonyl reactants with similar structures such as two aldehydes and two ketones were also well tolerated with high cross-coupling selectivity.

Revisiting the Three Vanadium Sandwich-Type Polyoxometalates: Structures, Solution Behavior, and Redox Properties.

It is well known that the trivacant anions α-B-[XW9O33]9- react with vanadyl ions to give the sandwich-type polyoxometalates [(VIVO)3(XW9O33)2]12- with X = AsIII or SbIII. Nevertheless, the oxidized derivatives have been obtained selectively by electrochemical oxidation from the fully reduced derivatives [(VIVO)3(XW9O33)2]12- allowing full characterization both in solution using UV-vis and multinuclear (17O, 51V, and 183W) NMR spectroscopies and in the solid state by single-crystal X-ray diffraction. Structural analysis of the oxidized [(VVO)3(XW9O33)2]9- polyanions is consistent with the idealized D3h symmetry, while solution studies reveal a fair hydrolytic stability in a wide pH range from 0 to 6. Besides, the D3h polyanions either as reduced or oxidized forms [(VO)3(AsW9O33)2]9/12- have been identified as the thermodynamic product that results from the conversion of the C2v polyanion [(H2O)(VO)3(AsW9O33)2]9/12- through moderate heating. Conversely, the SbIII-containing derivative gives exclusively the D3h polyanion, probably either due to the extended lone pair of the trigonal SbIII heterogroup that prevents the formation of the C2v arrangement or the lability of the oxo-metalate bonds that favor chemical exchange. The electrochemical studies of sandwich-type polyoxometalates revealed that each {V═O} group gives rise to a one-electron transfer process. At last, the redox properties appear strongly altered in the 0.3-5 pH range, consistent with proton-coupled electron transfers.

Ferrocene appended 1,8-naphthalimide chromophores: Synthesis, theoretical, the effect of phenyl substitution on aggregation-induced enhanced emission and second-order nonlinear optical studies

A new ferrocene appended linear donor-π-acceptor (D-π-A) type 1,8-naphthalimide chromophores [FcPhNap-n-butyl (1) and Fc(Ph)2Nap-n-butyl (2)] have been synthesized and characterized using various analytical and spectroscopic techniques. The chromophores 1 and 2 show the one-electron transfer process, which was examined through cyclic voltammetric (CV) method. The solvatochromic studies show red shift by increasing the solvent polarity from non-polar to polar for both the chromophores 1 and 2, due to the better stabilization of the more polarized excited state than the ground state in the polar solvent. The fluorescence studies show low fluorescence emission, which was enhanced by aggregation in THF/water mixture when the water ratio is increased upto 60%, due to the restricted intramolecular rotation (RIR) process in the aggregated state. Also, the quantum yield increases 3.4 (1) and 6.8 (2) times in the aggregation induced enhanced emission (AIEE) state than THF solution for both the chromophores [THF/AIEE = 0.05/0.17 for 1 and 0.03/0.22 for 2]. The second-order non-linear optical properties of the chromophores 1 and 2 were studied using Kurtz and Perry powder technique, chromophore 2 shows 1.2 times higher SHG efficiency than 1, owing to the presence of additional phenyl group in 2, which further supports the effective charge transfer process from donor to acceptor. Furthermore, optical and non-linear optical properties of chromophores 1 and 2 were analyzed by DFT/TD-DFT calculations using different functionals (B3LYP, long-range corrected CAM-B3LYP and LC-BLYP) with 6–31+G** level of theory. The B3LYP functional shows higher hyperpolarizability values [β0 = 109.2 × 10-30 esu (1), 299.7 × 10-30 esu (2)], due to the overestimation of the dipole moment, polarizability and hyperpolarizabilities between the donor–π–acceptor systems in B3LYP-hybrid functional, which leads to incorrect long-range charge transfer.

Synthesis, Characterization and Bio-Potential Activities of Co(II) and Ni(II) Complexes with O and N Donor Mixed Ligands

The synthesis and characterization of Co(II) and Ni(II) mixed ligand complexes are derived from isoniazid, 9-fluorenoneandoxalate. The metal complexes were characterized on the basis of elemental analysis, IR, UV-visible, CV, PXRD, and molar conductance analytical data, viz., all the metal complexes were suggested in an octahedral geometry, respectively. The mixed ligand complexes are formed in the 1:1:2:1 (M:L1:L2:L3) ratios, as found from the elemental analyses, and originate to have the formula [M(L1)(L2)2(L3)]. Where M = Co(II), Ni(II), L1 = isoniazid, L2 = 9-fluorenone, and L3 = oxalate. The molar conductance data reveals that the complexes are non-electrolytes. The cyclic voltammogram of the Co(II) complex revealed that the quasi-reversible single electron transfer process and Ni(II) complex corresponding to a one-electron transfer process were observed during controlled potential electrolysis. IR spectra show that the ligands are coordinated to the metal ions through N and O donor sites of isoniazid-N, 9-fluorenone-O and oxalate-O. Magnetic moment values and UV-visible spectra were used to infer the coordinating of the geometrics of these complexes found to be octahedral. The PXRD patterns suggest that all the complexes are crystalline phases. The metal chelates have been screened for antimicrobial, antioxidant and anti-inflammatory activities, and our findings have been reported, explained and compared with some known antibiotics.

Investigation on the electroreduction azo coupling mechanism of 1,4-dinitrobenzene in aprotic media containing CO2

The electrochemical behavior of 1,4-dinitrobenzene (PNB) in the aprotic solvent containing CO2 was investigated by using CO2 instead of proton donor to eliminate the interference of hydrogenation reaction. In the absence of CO2, the electrochemical behavior of PNB was a chemical reversible two-steps one-electron transfer process, but with the introduction of CO2, it was transformed into an irreversible 7-electrons transfer process. In the potential range between −0.3 V and −1.7 V, three reduction peaks were observed, and minutely studied by cyclic voltammetry, chronoamperometry, and in situ FT-IR spectroelectrochemistry methods, respectively. The results show that CO2 is involved in five steps reaction during the electroreduction process of PNB, which plays a key role in PNB electroreduction azo coupling. The electroreduction azo coupling mechanism of PNB in the presence of CO2 is exposed, which will provide a theoretical basis for precise control of the electroreduction degradation of dinitrobenzene. The product obtained by potentiostatic electrolysis is confirmed as 4,4′-dinitrosoazobenzene by 13C NMR, 1H NMR, MS and FTIR because of the instability of the final product, which is consistent with the mechanism inference. It has been well-proved that in situ FT-IR spectroelectrochemistry is an applicable method to study the wide range of complex electrochemical process.

Structural Features of Cytochrome b5-Cytochrome b5 Reductase Complex Formation and Implications for the Intramolecular Dynamics of Cytochrome b5 Reductase.

Membrane cytochrome b5 reductase is a pleiotropic oxidoreductase that uses primarily soluble reduced nicotinamide adenine dinucleotide (NADH) as an electron donor to reduce multiple biological acceptors localized in cellular membranes. Some of the biological acceptors of the reductase and coupled redox proteins might eventually transfer electrons to oxygen to form reactive oxygen species. Additionally, an inefficient electron transfer to redox acceptors can lead to electron uncoupling and superoxide anion formation by the reductase. Many efforts have been made to characterize the involved catalytic domains in the electron transfer from the reduced flavoprotein to its electron acceptors, such as cytochrome b5, through a detailed description of the flavin and NADH-binding sites. This information might help to understand better the processes and modifications involved in reactive oxygen formation by the cytochrome b5 reductase. Nevertheless, more than half a century since this enzyme was first purified, the one-electron transfer process toward potential electron acceptors of the reductase is still only partially understood. New advances in computational analysis of protein structures allow predicting the intramolecular protein dynamics, identifying potential functional sites, or evaluating the effects of microenvironment changes in protein structure and dynamics. We applied this approach to characterize further the roles of amino acid domains within cytochrome b5 reductase structure, part of the catalytic domain, and several sensors and structural domains involved in the interactions with cytochrome b5 and other electron acceptors. The computational analysis results allowed us to rationalize some of the available spectroscopic data regarding ligand-induced conformational changes leading to an increase in the flavin adenine dinucleotide (FAD) solvent-exposed surface, which has been previously correlated with the formation of complexes with electron acceptors.

Elucidating the Mechanistic Origin of a Spin State-Dependent FeNx-C Catalyst toward Organic Contaminant Oxidation via Peroxymonosulfate Activation.

Atomically dispersed metals on nitrogen-doped carbon matrices have attracted extensive interest in the removal of refractory organic pollutants. However, a thorough exploration of the particular structure for each active site and specific effects of these sites still remains elusive. Herein, an Fe-pyridinic N4 structure in a single-atom catalyst (FeNx-C) was constructed using a facile pyrolysis strategy, and it exhibited superior catalytic activity in peroxymonosulfate (PMS) activation toward organic contaminant oxidation. The various Fe species and relative amounts of each Fe site in the FeNx-C catalyst were validated using X-ray absorption spectroscopy and 57Fe Mössbauer spectroscopy, which showed critical dependencies on the precursor ratio and calcination temperature. The positive correlations between relative content of high-spin state species (FeII and FeIII) and catalytic performance were found to determine the reactive species generation and electron transfer pathway in the FeNx-C/PMS system. Moreover, catalytic performance and theoretical calculation results revealed that FeII-N4 in the high-spin state (S = 2) tends to activate PMS to form sulfate and hydroxyl radicals via a one-electron transfer process, while the FeIII-N4 moiety (S = 5/2) is prone to high-valent iron species generation with lower free energy. Benefiting from finely tuned active sites, a single-atom FeNx-C catalyst achieved favorable applicability in actual wastewater treatment with efficient resistance of the common water matrix. The present work advances the mechanistic understanding of spin state-dependent persulfate activation in single-atom catalysts and provides guidance to design a superior catalyst based on spin state descriptions.

Synthesis and Characterization of Mixed Ligand Complexes of Copper(II) with Adenine and Dicarboxylic Acids

Three mixed ligand complexes of copper(II) with adenine and dicarboxylic acids have been synthesized. The resulting complexes were characterized by their melting point, solubility, metal content analysis, FT-IR and UV-visible spectroscopy, magnetic measurement, thermal analysis, cyclic voltammetric measurement and X-ray powder diffraction study. The products are microcrystalline powder, slightly soluble in water and decompose at high temperature. Under experimental condition, the ligands adenine (Ade) behaves as a neutral ligand, whereas oxalic acid (OxH2), succinic acid (SucH2) and tartaric acid (TarH2) are doubly deprotonated to form dianionic ligands that are coordinated to the Cu(II) ion. The Cu(II) content analysis of the complexes confine to their stoichiometry [Cu(Ade)(L)(H2O)] (L = Ox, Suc, or Tar dianion). Electrochemical redox behavior of the complexes in their reaction medium was also examined. They exhibit quasi-reversible one-electron transfer processes. Dhaka Univ. J. Sci. 69(2): 76-81, 2021 (July)

Ferrocene/non-ferrocene conjugated linear eight-membered borasiloxanes: Structural, theoretical, optical and non-linear optical studies

A linear donor-π-acceptor-π-donor (D-π-A-π-D) type 4-methoxyphenyl 1 and 4-ferrocenylphenyl 2 conjugated borasiloxanes were synthesized and characterized by various spectroscopic techniques (FT-IR, NMR and HRMS). Further, the molecular structure of 4-methoxyphenyl borasiloxane 1 was confirmed by the single-crystal X-ray diffraction method, shows a monoclinic crystal system in the centrosymmetric space group (P21/c) with various non-covalent interactions in the crystal packing. The intramolecular charge transfer (ICT) process of both the borasiloxanes were studied using the solvatochromic technique, which shows negative solvatochromism for 1 and 2, due to the high ground state dipole moment than the excited states. The second-order nonlinear optical (NLO) properties of the borasiloxanes were studied using Kurtz and Perry powder method. Compound 1 was crystallized in a centrosymmetric crystal system, and it exhibits second-order NLO response, because of the distorted silicon environment in an eight-membered borasiloxane ring with various C–H...π interactions in the crystal packing. The 4-ferrocenylphenyl borasiloxane 2 shows 1.5 times higher SHG efficiency than 1, due to the ferrocene moiety is conjugated in the para position of the borasiloxane ring, which involves an effective one-electron transfer process (FeII ↔ FeIII). Furthermore, the experimental results of optical and nonlinear optical properties of the borasiloxanes 1 and 2 were supported by the DFT and TD-DFT calculations using the B3LYP/6-31+G** level of theory.

A poly-(L-serine)/reduced graphene oxide-Nafion supported on glassy carbon (PLS/rGO-Nafion/GCE) electrode for the detection of naproxen in aqueous solutions.

A new electrode was constructed via the anodic electropolymerization of poly-(L-serine) (PLS) on an rGO-Nafion-modified glassy carbon electrode (GCE) for the detection of the emerging organic contaminant naproxen (NPX). The morphology, crystal phase, and surface elements of the electrode were investigated with SEM, TEM, XRD, Raman, ATR-FTIR, zeta potential, C-H-O, and XPS analyses. Results of the surface analysis showed a porous structure resembling graphene sheets inside the Nafion/GCE architecture. Various electrochemical parameters, including scan rate, pH, and NPX concentration, were studied to evaluate the performance of the electrode. The synergistic effect of PLS and rGO-Nafion greatly facilitated the catalytic oxidation of NPX on PLS/rGO-Nafion/GCE. Electrochemical NPX oxidation was a one-electron transfer and adsorption limited process. The optimal working potential was 0.92 V vs. Ag/AgCl. The oxidation current of NPX increased with the increase in the concentration of analyte and scan rate but decreased with pH. The modified electrode exhibited excellent linearity with respect to NPX concentration in the range of 4.3 to 87 μM and limit of detection of 0.23 μM (S/N = 3). The PLS/rGO-Nafion/GCE is a fast, sensitive, reliable, and economical electrode for the detection of NPX in water.

Models to study photoinduced multiple proton coupled electron transfer processes

In water-oxidizing photosynthetic organisms, excitation of the reaction-center chlorophylls (P680) triggers a cascade of electron and proton transfer reactions that establish charge separation across the membrane and proton-motive force. An early oxidation step in this process involves proton-coupled electron transfer (PCET) via a tyrosine-histidine redox relay (Yz-H190). Herein, we report the synthesis and structural characterization of two isomeric dyads designed to model this PCET process. Both are based on the same high potential fluorinated porphyrin (model for P680), linked to isomeric pyridylbenzimidazole-phenols (models for Yz-H190). The two isomeric dyads have different hydrogen bond frameworks, which is expected to change the PCET photooxidation mechanism. In these dyads, 1H NMR evidence indicates that in one dyad the hydrogen bond network would support a Grotthuss-type proton transfer process, whereas in the other the hydrogen bond network is interrupted. Photoinduced one-electron, two-proton transfer is expected to occur in the fully hydrogen-bonded dyad upon oxidation of the phenol by the excited state of the porphyrin. In contrast for the isomer with the interrupted hydrogen bond network, an ultrafast photoinduced one-electron one-proton transfer process is anticipated, followed by a much slower proton transfer to the terminal proton acceptor. Understanding the nature of photoinduced PCET mechanisms in these biomimetic models will provide insights into the design of future generations of artificial constructs involved in energy conversion schemes.

Mechanistic Diversity of Low-Valent Chromium Catalysis: Cross-Coupling and Hydrofunctionalization

ConspectusTransition-metal catalysis has traditionally been dominated by precious metals because of their high reactivity toward chemical transformations. As a cost-effective alternative, catalysis by earth-abundant group 6 metal chromium is underdeveloped, and its reactivity remains largely unexplored, although the industrially important Phillips catalyst, which is composed of Cr as the active metal, is currently used to supply almost 40% of the total world demand for high-density polyethylene. Cr has traditionally served in organoreagents with high-valent states (≥2+), which are typified by reactions involving Nozaki-Hiyama-Kishi (NHK) and Takai-Utimoto one-electron transfer processes. Given that low-valent metals usually facilitate the process of oxidative addition (OA), studying the catalysis of Cr in the low-valent state provides the opportunity to develop new transformations. However, probably because of the low stability of reactive low-valent Cr or the lack of catalytic activity of structurally stable complexes, there has been limited success with respect to developing catalysis promoted by low-valent Cr. In recent years, our group has probed the reactivity of low-valent Cr in catalysis by adopting a strategy of forming reactive Cr in situ. In this Account, we detail our efforts to study the catalytic behavior and mechanism of low-valent Cr in challenging transformations, such as the cleavage of chemically inert bonds for the cross-coupling and hydrofunctionalization of arenes and nitro motifs, by developing strategies to address the prominent selectivity issues. We highlight the finding that low-valent Cr, being formed in situ, possesses the intriguing ability to promote the catalytic cleavage of unactivated C-O, C-N, and C-H bonds to achieve the Kumada couplings and even to enable challenging cross-coupling between two unactivated C(aryl)-O/C(aryl)-N bonds. During these catalytic processes, Cr usually adopts a high-spin state to interact with chemicals, allowing for insertion into unactivated σ-bonds. The OA catalytic model involving a two-electron process for the cleavage of unactivated bonds has rarely been considered for Cr. We highlight the finding that Cr allows for the breakage of two chemically inert bonds in one catalytic cycle. This ability is intriguing because most transition metals are suitable only for the cleavage of one unactivated bond in catalysis. Mechanisms involving two-electron OA for Cr are unusual, with processes involving one-electron transfer more often proposed, as exemplified in the NHK reactions. These reactions provide efficient strategies for forming functionalized benzaldehydes, amides, anilines, and amines, usually with high levels of selectivity. We hope that this account will extend the scope of cognition to Cr catalysis.

Sulphur vacancy derived anaerobic hydroxyl radical generation at the pyrite-water interface: Pollutants removal and pyrite self-oxidation behavior

We demonstrate that FeS2 possessing sulfur vacancies (SVs), under anaerobic water environment, can stabilize the H2O adsorption with a strong exothermic effect to compensate the apparent energy barrier of H2O oxidation on pyrite surface. Adsorbed H2O dissociates at SV site via π-back donation of localized electron, and thus breaks through thermodynamic restriction of H2O oxidation to generate bound hydroxyl radical through a one-electron transfer process of localized holes (Vs+). Meanwhile, the synergistic effect of surface Fe3+ and circumjacent H2O molecule can also promote the oxidation of H2O adsorbed at Fe3+ site to produce free hydroxyl radical via oxidation reaction. The generated hydroxyl radical on pyrite surface can induce the oxidation of different pollutants, and also contribute to the pyrite self-oxidation process. These findings clarify the in-depth mechanism of anaerobic hydroxyl radical generation at pyrite-water interface, and shed light on anaerobic environmental effect of pyrite and other natural iron sulfide minerals.

Viologen-Decorated TEMPO for Neutral Aqueous Organic Redox Flow Batteries

A novel electroactive organic molecule, viz., 1-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-1 ′ -(3-(trimethylammonio)propyl)-4,4 ′ -bipyridinium trichloride ((TPABPy)Cl 3 ), is synthesized by decorating 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) with viologen, which is used as the positive electrolyte in neutral aqueous redox flow battery (ARFB). Extensive characterizations are performed to investigate the composition/structure and the electrochemical behavior, revealing the favorable effect of introducing the cationic viologen group on the electroactive TEMPO. Salient findings are as follows. First, the redox potential is elevated from +0.745 V for TEMPO to +0.967 V for decorated TEMPO, favoring its use as the positive electrolyte. Such an elevation originates from the electron-withdrawing effect of the viologen unit, as evidenced by the nuclear magnetic resonance and single crystal structure analysis. Second, linear sweep voltammetry reveals that the diffusion coefficient is 2.97 × 10 − 6 c m 2 s − 1 , and the rate constant of the one-electron transfer process is 7.50 × 10 − 2 cm s − 1 . The two values are sufficiently high as to ensure low concentration and kinetics polarization losses during the battery operation. Third, the permeability through anion-exchange membrane is as low as 1.80 × 10 − 11 c m 2 s − 1 . It is understandable as the positive-charged viologen unit prevents the molecule from permeating through the anion exchange membrane by the Donnan effect. Fourth, the ionic nature features a decent conductivity and thus eliminates the use of additional supporting electrolyte. Finally, a flow battery is operated with 1.50 M (TPABPy)Cl 3 as the positive electrolyte, which affords a high energy density of 19.0 Wh L -1 and a stable cycling performance with capacity retention of 99.98% per cycle.

Spectral and cyclic voltammetry studies of chloro-salicyliden aniline and some of its complexes with Co(II) and Mn(II)

The qualitative information about the interaction between 2-{[p-chlorophenylimino]methyl}phenol as attracting chelating Schiff base ligand (HL) with cobalt(II) and manganese(II) ions have been discussed by using the data of spectroscopy (IR, UV-Visible) and 1H NMR resonance techniques. The electrochemical properties of these species have been carried out by using cyclic voltammetry studies to see the differences in the potential and activity behavior during and after the electron transfer process. The cyclic voltammetry behavior of ligand exhibited an irreversible one-electron transfer and redox diffusion-controlled process due to the linearity relationship between redox peaks current and square root of scan rates. The cyclic sweep for CoL and CoL2 complexes appeared two irreversible oxidation peaks but with different values and positions, while the cyclic sweep of MnL and MnL2 complexes appeared several redox peaks, which related to the formation of various manganese redox species. All complexes had a deviation of current and potential to more anodic values when the cyclic sweep was applied at different scan rates. A positive shift was observed for CoL2 and MnL2 complexes may be to the electron-donating and electron-withdrawing properties of phenyl substituted group.