Electron Transfer Reduction Research Articles

HYSCORE and QM/MM Studies of Second Sphere Variants of the Type 1 Copper Site in Azurin: Influence of Mutations on the Hyperfine Couplings of Remote Nitrogens.

Secondary coordination sphere (SCS) interactions have been shown to play important roles in tuning reduction potentials and electron transfer (ET) properties of the Type 1 copper proteins, but the precise roles of these interactions are not fully understood. In this work, we examined the influence of F114P, F114N, and N47S mutations in the SCS on the electronic structure of the T1 copper center in azurin (Az) by studying the hyperfine couplings of (i) histidine remote Nε nitrogens and (ii) the amide Np using the two-dimensional (2D) pulsed electron paramagnetic resonance (EPR) technique HYSCORE (hyperfine sublevel correlation) combined with quantum mechanics/molecular mechanics (QM/MM) and DLPNO-CCSD calculations. Our data show that some components of hyperfine tensor and isotropic coupling in N47SAz and F114PAz (but not F114NAz) deviate by up to ∼±20% from WTAz, indicating that these mutations significantly influence the spin density distribution between the CuII site and coordinating ligands. Furthermore, our calculations support the assignment of Np to the backbone amide of residue 47 (both in Asn and Ser variants). Since the spin density distributions play an important role in tuning the covalency of the Cu-Scys bond of Type 1 copper center that has been shown to be crucial in controlling the reduction potentials, this study provides additional insights into the electron spin factor in tuning the reduction potentials and ET properties.

A novel LDHs-VB3- inhibitor for rebar corrosion in simulated concrete pore solution: Synthesis, performance and mechanism

Developing novel chloride-trapping inhibitors is of great significance for enhancing the durability of marine concrete structures. In this study, a novel LDHs-VB3- inhibitor was synthesized through the ion exchange method. Then, the corrosion inhibition mechanism of LDHs-VB3- inhibitor for rebar in the whole process of release - capture - adsorption - retardation was studied using experiments and density functional theory (DFT) simulations. The chloride ion exchange test demonstrates that the LDHs-VB3- inhibitor has a chloride trapping capacity of 35.5 mg/g in the saturated Ca(OH)2 solution containing 0.14 M NaCl, implying that it could capture Cl- in concrete pore solution. According to the electrochemical tests, the critical chloride concentration of rebar in the simulated concrete solution containing LDHs-VB3- falls within a range of 0.22 M–0.28 M, which is much higher than that in the solution without LDHs-VB3- (0.10 M–0.14 M). DFT simulations indicate that LDHs-VB3- exhibits more positive binding energy and uneven binding forces in contrast to LDHs-Cl-. Consequently, VB3- could be easily replaced by Cl- and then released into the pore solution of concrete. Moreover, the released VB3- could adsorb on the α-Fe2O3 surface in a concrete environment via the interaction of surface Fe atoms with N and O atoms of VB3-. The preadsorbed VB3- could diminish the interaction of Cl- with the α-Fe2O3 surface by reducing electron transfer, thereby mitigating the risk of passive film breakdown and retarding the chloride-induced corrosion of rebars.

Harmonizing Enzyme-like Cofactors to Boost Nanozyme Catalysis.

Engineering isolated metal sites resembling the primary coordination sphere of metallocofactors enables atomically dispersed materials as promising nanozymes. However, most existing nanozymes primarily focus on replicating specific metallocofactors while neglecting other supporting cofactors within active pockets, leading to reduced electron transfer (ET) efficiency and thus inferior catalytic performances. Herein, we report a metal-organic framework UiO-67 nanozyme with atomically dispersed iron sites, which involves multiple tailored enzyme-like nanocofactors that synergistically drive the ET process for enhanced peroxidase-like catalysis. Among them, the linker-coupled atomic iron site plays a critical role in substrate activation, while bare linkers and zirconia nodes facilitate the ET efficiency of intermediates. The synergy of three nanocofactors results in a 4.29-fold enhancement compared with the single effort of isolated metal site-based nanocofactor, holding promise in immunoassay for sensitive detection of chlorpyrifos. This finding opens a new way for designing high-performance nanozymes by harmonizing various nanocofactors at the atomic and molecular scale.

Harmonizing Enzyme‐like Cofactors to Boost Nanozyme Catalysis

AbstractEngineering isolated metal sites resembling the primary coordination sphere of metallocofactors enables atomically dispersed materials as promising nanozymes. However, most existing nanozymes primarily focus on replicating specific metallocofactors while neglecting other supporting cofactors within active pockets, leading to reduced electron transfer (ET) efficiency and thus inferior catalytic performances. Herein, we report a metal–organic framework UiO‐67 nanozyme with atomically dispersed iron sites, which involves multiple tailored enzyme‐like nanocofactors that synergistically drive the ET process for enhanced peroxidase‐like catalysis. Among them, the linker‐coupled atomic iron site plays a critical role in substrate activation, while bare linkers and zirconia nodes facilitate the ET efficiency of intermediates. The synergy of three nanocofactors results in a 4.29‐fold enhancement compared with the single effort of isolated metal site‐based nanocofactor, holding promise in immunoassay for sensitive detection of chlorpyrifos. This finding opens a new way for designing high‐performance nanozymes by harmonizing various nanocofactors at the atomic and molecular scale.

Effect of bath temperature on the efficiency and properties of Cu2O/ZnS/ZnO heterojunctions thin film prepared by electrodeposition and chemical bath deposition methods

A novel p-n type Cu2O/ZnS/ZnO heterojunction thin film was successfully fabricated by a combination of electrodeposition and chemical bath deposition techniques. The effect of bath temperature (T = 75, 80, 85, 90 °C) on the growth of ZnS layers was investigated. The influence of ZnS buffer layers on the properties and efficiency of the prepared heterojunction thin films were examined using XRD, FE-SEM, AFM, EDS, UV–Vis, and electrochemical measurements. The analysis of prepared films revealed that the Cu2O/ZnS/ZnO heterojunction exhibits a unique combination of hexagonal structure of ZnO and the cubic structure of Cu2O. It was found that all the heterojunction films exhibit the growth of composed pyramids and corner grains with a homogenous distribution. The optical band-gap of the deposited ZnS buffer layers decreased from 3.46 eV to 3.35 eV with an increase of bath temperature from 75 °C to 90 °C. Moreover, the obtained results revealed that the thicknesses and the surface roughness of ZnS buffer layers increased when bath temperature increased. Mott-Schottky results of the heterojunctions indicate a p-type semiconductor behavior for the Cu2O, while it was observed an n-type semiconductor behavior for the ZnO and ZnS layers. As a result, the photocurrent response of Cu2O/ZnO heterojunctions with ZnS layer insertion was enhanced from 0.175 to 0.730 mA, which can be attributed to the reduced electron transfer resistance, enlarged photo-generated (e−/h+) carrier separation efficiency, and enhanced light absorption due to the presence of ZnS buffer layers. These results highlight the advantages of the bath temperature on the deposition of ZnS for photoelectrochemical and solar cells applications.

Unleashing the power of directed electron transfer: unraveling the potential of {PV4}2 in heterogeneous photocatalysis

{PV4}2 unleash the power of directed electron transfer in heterogeneous photocatalysis reduction.

The role of an intramolecular hydrogen bond in the redox properties of carboxylic acid naphthoquinones.

A bioinspired naphthoquinone model of the quinones in photosynthetic reaction centers but bearing an intramolecular hydrogen-bonded carboxylic acid has been synthesized and characterized electrochemically, spectroscopically, and computationally to provide mechanistic insight into the role of proton-coupled electron transfer (PCET) of quinone reduction in photosynthesis. The reduction potential of this construct is 370 mV more positive than the unsubstituted naphthoquinone. In addition to the reversible cyclic voltammetry, infrared spectroelectrochemistry confirms that the naphthoquinone/naphthoquinone radical anion couple is fully reversible. Calculated redox potentials agree with the experimental trends arising from the intramolecular hydrogen bond. Molecular electrostatic potentials illustrate the reversible proton transfer driving forces, and analysis of the computed vibrational spectra supports the possibility of a combination of electron transfer and PCET processes. The significance of PCET, reversibility, and redox potential management relevant to the design of artificial photosynthetic assemblies involving PCET processes is discussed.

Synthesis of Ru(II) and Os(II) photosensitizers bearing one 9,10-diamino-1,4,5,8-tetraazaphenanthrene scaffold.

The synthesis of eight Ru(II) and Os(II) photosensitizers bearing a common 9,10-disubstituted-1,4,5,8-tetraazaphenanthrene backbone is reported. With Os(II) photosensitizers, the 9,10-diNH2-1,4,5,8-tetraazaphenanthrene could be directly chelated onto the metal center via the heteroaromatic moiety, whereas similar conditions using Ru(II) resulted in the formation of an o-quinonediimine derivative. Hence, an alternative route, proceeding via the chelation of 9-NH2-10-NO2-1,4,5,8-tetraazaphenanthrene and subsequent ligand reduction of the corresponding photosensitizers was developed. Photosensitizers chelated via the polypyridyl-type moiety exhibited classical photophysical properties whereas the o-quinonediimine chelated Ru(II) analogues exhibited red-shifted absorption (520 nm) and no photoluminescence at room temperature in acetonitrile. The most promising photosensitizers were investigated for excited-state quenching with guanosine-5'-monophosphate in aqueous buffered conditions where reductive excited-state electron transfer was observed by nanosecond transient absorption spectroscopy.

Photocatalytic oxidative coupling of terminal alkynes with p-benzoquinone to diaryl ketones by the Cu(I)-PS-POM assembling system through synergistic effect

Photocatalytic C–C bonds formation is an effective approach to synthesize the significant drug intermediates diaryl ketones. Herein, a new polyoxometalate-based metal–organic framework (POMOF), CuW6–TPT, was synthesized by assembling an oxidation catalyst [W6O19]2− into photoactive MOF constructed by photosensitizer (PS) 4,6-tri(4-pyridyl)-1,3,5-triazine (TPT) and binuclear Cu(I) units. CuW6–TPT exhibits excellent light absorption ability and unique conductivity due to the coordination bond, strong π∙∙∙π interactions and H-bonding among Cu(I) ions, TPT moieties and [W6O19]2− in the defined spatial. The abundant exposed Cu(I) catalytic centres are conductive to activate phenylacetylene in situ formation Cu(I)-phenylacetylide, which then undergoes a reductive single electron transfer (SET) process to obtain the key intermediate Cu(II)-phenylactetylide for the Paterno-Buchi (2+2) cycloaddition with benzoquinone to form the labile Cu(II)-oxetane ring. It is a direct route to synthesize diaryl ketones with a hydroxyl group from simple starting materials such as terminal alkynes with p-benzoquinone.

Synergistic behavior of organic and inorganic constituents in improving the charge transfer ability of Polyoxometalate-Based ionic liquids

The electron transfer kinetics and electronic properties of (3-sulfonic acid) propyl bipyridine-12tungstophosphoric acid (BPyPS-PW) as a novel organic–inorganic ionic liquid have been investigated. Cyclic voltammetry (CV) revealed that BPyPS enhanced the oxidation peak currents of tungstophosphoric acid (PW) by 1.4-fold. According to linear sweep voltammetry (LSV), BPyPS-PW exhibited significantly lower tafel slope (96 mV) than BPyPS and PW (144 and 119 mV, respectively). This indicates that the current density increases more rapidly with overpotential, pointing the superior electron transfer ability of BPyPS-PW. Further, it showed about 1.5- and 1.2-fold higher charge transfer coefficient than BPyPS and PW. Differential pulse voltammetry (DPV) and square wave voltammetry (SWV) showed increased peak current intensities for the hybrid compared to both constituents. Electrochemical impedance spectroscopy (EIS) indicated that BPyPS-PW has the lowest charge transfer resistance (RCT, 685 Ω), Warburg impedance (ZW, 1.87 Ω), electrolyte solution resistance (RS, 86 Ω), and double-layer capacitance resistance (ZC, 38.73 Ω) among the studied compounds, indicative of its reduced electron transfer resistance at the electrode/electrolyte interface. According to chronoamperometry (CA), BPyPS-PW exhibited higher electrostability, with only 21.48 % current decay after 120 s, while BPyPS and PW experienced a stronger decay (50.09 % and 24.57 %, respectively), attributed to a synergistic behavior of the constituents that results in a larger charge transfer network and more electron active centers. These findings are crucial for the design of new ionic liquid electrolytes to be used in electrochemical applications.

Photo-driven interfacial electron transfer reduction of cis-[Co(phen)2Cl2]Cl complexes with heterojunction CeO2/SnO2 nanocomposite and functional insights into supercapacitance

Photo-driven interfacial electron transfer reduction of cis-[Co(phen)2Cl2]Cl complexes with heterojunction CeO2/SnO2 nanocomposite and functional insights into supercapacitance

Electron Transfer Reduction by Hydrogen Creates Porosity in Tantalate Crystals and Produce Multifunctionality.

Contrary to partially substituted systems, WO3 molecular sieves that exclusively comprise a d0 transition metal ion and do not possess template ions in the cavity are a new class of materials for photocatalysis owing to their framework structure. Because WO3 thermodynamically lacks proton-reduction capability, exploring diverse synthetic approaches of other materials is desirable for facilitating utilization as H2 evolution and water splitting systems. Herein, we report an efficient approach for the protonation of Ag2Ta4O11 to afford H2Ta4O11 for application as a H2 molecular sieve. Hydrogen reduction of Ag2Ta4O11 at 300 °C and post-treatment using HNO3 afforded H2Ta4O11. Characterizations of H2Ta4O11, coupled with density functional theory (DFT) calculations, reveal that the intrinsic structure of Ag2Ta4O11 is maintained. Moreover, H+ is generated from H2 oxidation and forms OH, and the orientation of OH is parallel to that of the ab plane. Desorption and adsorption of H2 within H2Ta4O11 were achieved by heating H2Ta4O11 to above 90 °C. This is attributed to positive thermal expansion, as confirmed by high-temperature X-ray diffraction. H2Ta4O11 is an active heterogeneous photocatalyst for the half-reactions of water splitting. Moreover, deuteration experiments of H2Ta4O11 in D2O suggest its capability as a H2-D2 conversion catalyst. Furthermore, H2Ta4O11 functions as an active synthetic precursor for new tantalate materials, the direct synthesis of which is challenging.

Spatial confinement-regulated peroxymonosulfate activation to boost the generation of high-valent cobalt and radical species for achieving rapid removal of organic pollutants

It is of great significance to establish simple and effective methods to tackle water pollution problems. Herein, Co-loaded hollow carbon sphere (namely Co-HCS-1) served as PMS activation mediator was synthesized. The construction of hollow structure can improve specific surface areas and offer more active sites, thereby reducing electron transfer resistance and increasing contact among PMS, pollutant and catalyst. Hence, the Co-HCS-1-mediated direct electron-transfer oxidation between PMS and pollutant was enhanced. After embedding Co-based catalyst in the shell of hollow carbon sphere, hollow carbon shell will provide spatial confinement for Co-based catalyst, which shortened mass transfer process. Thus, spatial confinement effect originating from carbon sphere can accelerate the charge transfer between PMS and active sites of Co-HCS-1, thereby promoting O-O bond cleavage of PMS. As a result, the generations of radicals and high-valent metal complexes (namely Co-HCS-1≡Co4+) were boosted. Under the combined effects of electron-transfer oxidation, reactive oxygen species and Co-HCS-1≡Co4+, more than 90 % of typical organic pollutants can be removed from simulated wastewater within 5 min by Co-HCS-1/PMS system, and a high removal efficiency of total organic carbon can also be realized. To sum up, current work provided a valuable reference for the preparation and application of catalyst with high activity in PMS activation.

Genotype‐dependent Strategies to “Overcome” Excessive Light: Insights into Non‐Photochemical Quenching under High Light Intensity

AbstractHigh light (HL) intensities have a significant impact on energy flux and distribution within photosynthetic apparatus. To understand the effect of high light intensity (HL) on the HL tolerance mechanisms in tomatoes, we examined the response of the photosynthesis apparatus of 12 tomato genotypes to HL. A reduced electron transfer per reaction center (ET0/RC), an increased energy dissipation (DI0/RC) and non‐photochemical quenching (NPQ), along with a reduced maximum quantum yield of photosystem II (FV/FM), and performance index per absorbed photon (PIABS) were common HL‐induced responses among genotypes; however, the magnitude of those responses was highly genotype‐dependent. Tolerant and sensitive genotypes were distinguished based on chlorophyll fluorescence and energy‐quenching responses to HL. Tolerant genotypes alleviated excess light through energy‐dependent quenching (qE), resulting in smaller photoinhibitory quenching (qI) compared to sensitive genotypes. Quantum yield components also shifted under HL, favoring the quantum yield of NPQ (ՓNPQ) and the quantum yield of basal energy loss (ՓN0), while reducing the efficient quantum yield of PSII (ՓPSII). The impact of HL on tolerant genotypes was less pronounced. While the energy partitioning ratio did not differ significantly between sensitive and tolerant genotypes, the ratio of NPQ components, especially qI, affected plant resilience against HL. These findings provide insights into different patterns of HL‐induced NPQ components in tolerant and sensitive genotypes, aiding the development of resilient crops for heterogeneous light conditions.

Bioelectrocatalytic CO2 Reduction by Mo-Dependent Formylmethanofuran Dehydrogenase.

Massive efforts are invested in developing innovative CO2 -sequestration strategies to counter climate change and transform CO2 into higher-value products. CO2 -capture by reduction is a chemical challenge, and attention is turned toward biological systems that selectively and efficiently catalyse this reaction under mild conditions and in aqueous solvents. While a few reports have evaluated the effectiveness of isolated bacterial formate dehydrogenases as catalysts for the reversible electrochemical reduction of CO2 , it is imperative to explore other enzymes among the natural reservoir of potential models that might exhibit higher turnover rates or preferential directionality for the reductive reaction. Here, we present electroenzymatic catalysis of formylmethanofuran dehydrogenase, a CO2 -reducing-and-fixing biomachinery isolated from a thermophilic methanogen, which was deposited on a graphite rod electrode to enable direct electron transfer for electroenzymatic CO2 reduction. The gas is reduced with a high Faradaic efficiency (109±1 %), where a low affinity for formate prevents its electrochemical reoxidation and favours formate accumulation. These properties make the enzyme an excellent tool for electroenzymatic CO2 -fixation and inspiration for protein engineering that would be beneficial for biotechnological purposes to convert the greenhouse gas into stable formate that can subsequently be safely stored, transported, and used for power generation without energy loss.

Bioelectrocatalytic CO2 Reduction by Mo‐Dependent Formylmethanofuran Dehydrogenase

AbstractMassive efforts are invested in developing innovative CO2‐sequestration strategies to counter climate change and transform CO2 into higher‐value products. CO2‐capture by reduction is a chemical challenge, and attention is turned toward biological systems that selectively and efficiently catalyse this reaction under mild conditions and in aqueous solvents. While a few reports have evaluated the effectiveness of isolated bacterial formate dehydrogenases as catalysts for the reversible electrochemical reduction of CO2, it is imperative to explore other enzymes among the natural reservoir of potential models that might exhibit higher turnover rates or preferential directionality for the reductive reaction. Here, we present electroenzymatic catalysis of formylmethanofuran dehydrogenase, a CO2‐reducing‐and‐fixing biomachinery isolated from a thermophilic methanogen, which was deposited on a graphite rod electrode to enable direct electron transfer for electroenzymatic CO2 reduction. The gas is reduced with a high Faradaic efficiency (109±1 %), where a low affinity for formate prevents its electrochemical reoxidation and favours formate accumulation. These properties make the enzyme an excellent tool for electroenzymatic CO2‐fixation and inspiration for protein engineering that would be beneficial for biotechnological purposes to convert the greenhouse gas into stable formate that can subsequently be safely stored, transported, and used for power generation without energy loss.

Chloride, Bromide, and Iodide Photooxidation in Acetonitrile/Water Mixtures Using Binuclear Iridium(III) Photosensitizers.

Two iridium(III) binuclear photosensitizers, [Ir(dFCF3ppy)2(N-N)Ir(dFCF3ppy)2]2+, where N-N is tetrapyrido[3,2-a:2',3'-c:3″,2″-h:2‴,3‴-j]phenazine (Ir-TPPHZ) and 1,4,5,8-tetraazaphenanthrene[9,10-b]-1,4,5,8,9,12-hexaazatriphenylene (Ir-TAPHAT) are reported for iodide, bromide, and chloride photooxidation in acetonitrile and acetonitrile/water mixtures using blue-light irradiation. Excited-state reduction potentials Ered* of +2.02 and +2.09 V vs NHE were determined for Ir-TPPHZ and Ir-TAPHAT, respectively. Both photosensitizers' excited states were efficiently quenched by iodide, bromide, and chloride with quenching rate constants in the (3.5-9.2) × 1010 and (0.0036-2.9) × 1010 M-1 s-1 ranges in neat acetonitrile and acetonitrile/water mixtures, respectively. Nanosecond transient absorption spectroscopy provided unambiguous evidence of reductive excited-state electron transfer, with all halides in the solvent mixtures containing up to 50% water. Cage-escape yields were large (55-96%) in acetonitrile and dropped below 32% in 50:50 acetonitrile/water mixtures.

Biogenic Melanin-Modified Graphene as a Cathode Catalyst Yields Greater Bioelectrochemical Performances by Stimulating Oxygen–Reduction and Microbial Electron Transfer

Biogenic Melanin-Modified Graphene as a Cathode Catalyst Yields Greater Bioelectrochemical Performances by Stimulating Oxygen–Reduction and Microbial Electron Transfer

Carbon source priority and availability limit bidirectional electron transfer in freshwater mixed culture electrochemically active bacterial biofilms

This study investigated, if a mixed electroactive bacterial (EAB) culture cultivated heterotrophically at a positive applied potential could be adapted from oxidative to reductive or bidirectional extracellular electron transfer (EET). To this end, a periodic potential reversal regime between − 0.5 and 0.2 V vs. Ag/AgCl was applied. This yielded biofilm detachment and mediated electroautotrophic EET in combination with carbonate, i.e., dissolved CO2, as the sole carbon source, whereby the emerged mixed culture (S1) contained previously unknown EAB. Using acetate (S2) as well as a mixture of acetate and carbonate (S3) as the main carbon sources yielded primarily alternating electrogenic organoheterotropic metabolism with the higher maximum oxidation current densities recorded for mixed carbon media, exceeding on average 1 mA cm−2. More frequent periodic polarization reversal resulted in the increase of maximum oxidative current densities by about 50% for S2-BES and 80% for S3-BES, in comparison to half-batch polarization. The EAB mixed cultures developed accordingly, with S1 represented by mostly aerobes (84.8%) and being very different in composition to S2 and S3, dominated by anaerobes (96.9 and 96.5%, respectively). S2 and S3 biofilms remained attached to the electrodes. There was only minor evidence of fully reversible bidirectional EET. In conclusion the three triplicates fed with organic and/or inorganic carbon sources demonstrated two forms of diauxie: Firstly, S1-BES showed a preference for the electrode as the electron donor via mediated EET. Secondly, S2-BES and S3-BES showed a preference for acetate as electron donor and c-source, as long as this was available, switching to CO2 reduction, when acetate was depleted.Graphical

Marcus Cross-Relationship Probed by Time-Resolved CIDNP.

The time-resolved CIDNP method can provide information about degenerate exchange reactions (DEEs) involving short-lived radicals. In the temperature range from 8 to 65 °C, the DEE reactions of the guanosine-5'-monophosphate anion GMP(-H)- with the neutral radical GMP(-H)•, of the N-acetyl tyrosine anion N-AcTyrO- with a neutral radical N-AcTyrO•, and of the tyrosine anion TyrO- with a neutral radical TyrO• were studied. In all the studied cases, the radicals were formed in the reaction of quenching triplet 2,2'-dipyridyl. The reorganization energies were obtained from Arrhenius plots. The rate constant of the reductive electron transfer reaction in the pair GMP(-H)•/TyrO- was determined at T = 25 °C. Rate constants of the GMP(-H)• radical reduction reactions with TyrO- and N-AcTyrO- anions calculated by the Marcus cross-relation differ from the experimental ones by two orders of magnitude. The rate constants of several other electron transfer reactions involving GMP(-H)-/GMP(-H)•, N-AcTyrO-/N-AcTyrO•, and TyrO-/TyrO• pairs calculated by cross-relation agree well with the experimental values. The rate of nuclear paramagnetic relaxation was found for the 3,5 and β-protons of TyrO• and N-AcTyrO•, the 8-proton of GMP(-H)•, and the 3,4-protons of DPH• at each temperature. In all cases, the dependences of the rate of nuclear paramagnetic relaxation on temperature are described by the Arrhenius dependence.