Charge Transfer Rate Constant Research Articles

Synthesis of nanoflakes-covered microparticles of nickel-Application for electrocatalytic oxidation and quantitation of nitrofurazone

Nickel microparticles covered with nanoflakes (NMCN) were hydrothermally synthesized in an alkaline solution of acrylamide dissolved in ethylene glycol/ethylenediamine at 200 °C. Structure and morphology of NMCN were characterized by field-emission scanning electron microscopy and X-ray powder diffraction, respectively. NMCN was applied, as an electrode modifier, with a surface concentration of 5.1 × 10−8 mol cm−2, and a detailed study was performed for the kinetics of charge transfer across the modified electrode/electrolyte interface using cyclic voltammetry. For the redox transition of NMCN in an alkaline solution, electron transfer coefficient and apparent charge-transfer rate constant were acquired as 0.65 and 0.6 s−1, respectively. The modified electrode was then applied for a study on the electrocatalytic oxidation of nitrofurazone (NF) on the NMCN surface through an electrochemical-catalytic (EC') mechanism. The oxidation process was followed by a NF diffusion coefficient of 2.9 × 10−6 cm2 s−1 and a catalytic rate constant of 3.0 × 104 cm3 mol−1 s−1. Also, an electron transfer coefficient of 0.40 was attained. The modified electrode was employed as a novel, time-saving, sensitive and simple amperometric sensor for NF, and quantified the drug with a linear range of 30–570 μmol L−1 and a sensitivity of 0.694 ± 0.002 A L mol−1 cm−2. Also, a detection limit of 4.3 μmol L−1 was attained. The sensor was employed for direct assay of NF in the human serum and ointments.

Biogenic synthesis of CuO/ZnO nanocomposite from Bauhinia variegate flower extract for highly sensitive electrochemical detection of vitamin B2

In this study, we report the preparation of bio-inspired binary CuO/ZnO nanocomposite (bb-CuO/ZnO nanocomposite) via the biological route using Bauhinia variegata flower extract following hydrothermal treatment. The prepared bb-CuO/ZnO nanocomposite was electrophoretically deposited (EPD) on indium tin oxide (ITO) substrate to develop bb-CuO/ZnO/ITO biosensing electrode which is employed for the determination of vitamin B2 (Riboflavin) through electrochemical techniques. Physicochemical assets of the prepared bb-CuO/ZnO nanocomposite have been extensively evaluated and make use of different characterization techniques including powder XRD, FT-IR, AFM, SEM, TEM, EDX, XPS, Raman, and TGA. Electrochemical characteristics of the bb-CuO/ZnO/ITO biosensing electrode have been studied towards vitamin B2 determination. Furthermore, different biosensing parameters such as response time, reusability, stability, interference, and real sample analysis were also estimated. From the linear plot of scan rate, charge transfer rate constant (Ks), surface concentration of electrode (γ), and diffusion coefficient (D) have been calculated, and these are found to be 6.56 × 10−1 s−1, 1.21 × 10−7 mol cm−2, and 6.99 × 10−3 cm2 s−1, respectively. This biosensor exhibits the linear range of vitamin B2 detection from 1 to 40 μM, including sensitivity and limit of detection (LOD) of 1.37 × 10−3 mA/μM cm2 and 0.254 μM, respectively. For higher concentration range detection linearity is 50–100 μM, with sensitivity and the LOD of 1.26 × 10−3 mA/μM cm2 and 0.145 μM, respectively. The results indicate that the bio-inspired nanomaterials are promising sustainable biosensing platforms for various food and health-based biosensing devices.

Engineering Metal Halide Perovskite Nanocrystals with BODIPY Dyes for Photosensitization and Photocatalytic Applications.

The sensitization of surface-anchored organic dyes on semiconductor nanocrystals through energy transfer mechanisms has received increasing attention owing to their potential applications in photodynamic therapy, photocatalysis, and photon upconversion. Here, we investigate the sensitization mechanisms through visible-light excitation of two nanohybrids based on CsPbBr3 perovskite nanocrystals (NC) functionalized with borondipyrromethene (BODIPY) dyes, specifically 8-(4-carboxyphenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BDP) and 8-(4-carboxyphenyl)-2,6-diiodo-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (I2-BDP), named as NC@BDP and NC@I2-BDP, respectively. The ability of I2-BDP dyes to extract hot hole carriers from the perovskite nanocrystals is comprehensively investigated by combining steady-state and time-resolved fluorescence as well as femtosecond transient absorption spectroscopy with spectroelectrochemistry and quantum chemical theoretical calculations, which together provide a complete overview of the phenomena that take place in the nanohybrid. Förster resonance energy transfer (FRET) dominates (82%) the photosensitization of the singlet excited state of BDP in the NC@BDP nanohybrid with a rate constant of 3.8 ± 0.2 × 1010 s-1, while charge transfer (64%) mediated by an ultrafast charge transfer rate constant of 1.00 ± 0.08 × 1012 s-1 from hot states and hole transfer from the band edge is found to be mainly responsible for the photosensitization of the triplet excited state of I2-BDP in the NC@I2-BDP nanohybrid. These findings suggest that the NC@I2-BDP nanohybrid is a unique energy transfer photocatalyst for oxidizing α-terpinene to ascaridole through singlet oxygen formation.

Electrochemical Behavior of Niobium and Titanium Complexes in Chloride-Fluoride Melts with Addition of Alkaline Earth Metal Cations

The standard rate constants of charge transfer (k s) for the Nb(V)/Nb(IV) redox couple in the NaCl-KCl(equimol.)-NaF(10 wt%)-K2NbF7 melt with addition of alkaline Earth metal cations (Mg2+, Ca2+, Sr2+, Ba2+) were determined. It was found that addition of alkaline Earth metal cations resulted in increasing of k s to the certain ratio of Me2+/Nb(V) for the all alkaline Earth metal cations due to substitution of Na+ and K+ cations by Me2+ in the second coordination sphere of niobium complexes that leads to decreasing of niobium fluoride complexes stability. Further addition brought to some decrease of the standard rate constants because the viscosity of melts increasing, which brings to decrease of the diffusion coefficients. The standard rate constants increase with increasing of the ionic potential and reach maximum values for the complexes with outer-sphere magnesium cations. Comparative analysis of the electrochemical behavior of Nb(V)/Nb(IV) and Ti(IV/Ti(III)) redox couples in the NaCl-KCl(equimol.)-NaF(10 wt%) melt without and with addition of alkaline Earth metal cations has been done. It was determined that mechanism of electron transfer from the cathode to niobium and titanium complexes in melts containing alkaline Earth metal cations is the same and has a bridge nature.

Kinetics of electrochemical Eu3+ to Eu2+ reduction in aqueous media

All lanthanides have a stable trivalent oxidation state, but some of them can also occur in the divalent or tetravalent state. Europium is well-known for its divalent oxidation state, which has been investigated in aqueous, organic, and molten salt media. In contrast to other lanthanides, Eu3+ can be easily reduced (Eo=−0.34 V vs. SHE) via chemical, electrochemical or photochemical routes, and Eu2+ is quite stable in a variety of electrolytes, including nitrate salts. To date, the kinetics of the Eu3+/Eu2+ reduction reaction has been investigated only by polarography and chronopotentiometry, most often in perchlorate medium. In this study, the kinetics of the Eu3+/Eu2+ couple were analysed in nitrate, chloride and perchlorate media by cyclic voltammetry and linear sweep voltammetry with a rotating disk electrode (RDE). The diffusion coefficient, charge transfer coefficient and rate constants were calculated based on the Levich and Koutecký-Levich analysis and Tafel plot to gain insight in the electrochemical process and the influence of the electrolyte type on it. Given the pre-existing characterization of this redox couple in perchlorate medium, it is selected as a reference system to both compare the kinetic parameters and to validate whether the methodology can be applied to other electrolytes. The Eu3+ reduction reaction was found to be quasi-reversible in these electrolytes and the calculated kinetic parameters are in line with the previously reported values.

Ultrasensitive detection of ornidazole–antibiotic drug residues in water using NiMOFs functionalized MWCNT modified electrode

Nitroimidazole-based drugs are widely used as an antibiotic for the treatment of anaerobic bacterial and parasite illnesses. The widespread use of these drugs in animal feed and the consequent environmental pollution have become significant concerns in recent years. Simple, sensitive, and rapid detection of the antibody in various real samples is demanding research interest. Herein, we report a Nickel-metal organic framework functionalized Multiwalled Carbon nanotubes modified glassy carbon electrode (MWCNT@NiMOFs) as an ultrasensitive and rapid voltammetric sensor for the detection of ornidazole (ORDZ) in a neutral pH solution. The MWCNT@NiMOFs were prepared using a microwave-assisted solvothermal technique accompanied by an ultrasonication method. The designed MWCNT@NiMOFs offered a low charge transfer resistance (Rct) of 141 Ω along with excellent electrocatalytic activity, and high current density at the lowered cathodic peak potential (-0.62 V vs Ag/AgCl) for ORDZ detection. The surface adsorption capacity (Γs) in terms of surface excess and heterogeneous charge transfer rate constant (k0) of the MWCNT@NiMOFs were calculated to be 3.29 × 10-9 mol cm−2 and 5.33 × 10-3 cm s−1, respectively. Under an optimal working condition, differential pulse voltammetry measurements of ORDZ have shown concentration linearity in a window, 100 nm to 10 µM range with excellent sensitivity, 5.69 × 10-5A µM−1 cm−2, and detection limit, 26 nM (3.3/s). The designed MWCNT@NiMOFs offered appreciable reproducibility, and repeatability up to 30 days of storage time. The real-time quantitative evaluation of ORDZ in human urine and tap water specimens was done along with ∼ 100 % recovery values. Since the new approach is simple, selective, and separation-free, it can be extendable to a variety of real-time practical applications.

Theoretical Study on Functionalizing A–D–A Type Non‐Fullerene Acceptor by Fused Rings and Side Chains for Organic Solar Cells

AbstractThe modification of fused rings in the central backbone, side chains, and end groups of the non‐fullerene acceptor (NFA) for organic solar cells (OSCs) can modulate properties and photovoltaic performance. In order to investigate the effect of fused rings and side chains on photovoltaic performance, PBDB‐T is selected as electron donor and IDTIC, IDIC, IDIC‐PhC6, IDIC‐C4Ph, 4TIC, ITIC‐OE, IDTTIC, ITC6‐IC, ITIC, and C8‐ITIC are selected as NFAs. Based on quantum chemistry calculations, the geometries, electronic structures, excitation properties, excited‐state lifetimes, and electrostatic potentials (ESPs) of the monomer and the PBDB‐T:NFA complexes are studied, and the rate constants of charge transfer (CT), exciton dissociation (ED) and charge recombination (CR) processes are analyzed. The results show that the increase of fused‐ring in NFA's backbone by substituting phenyl or thienyl with bithiophene can elevate the highest occupied molecular orbital energies, reduce the gap of frontier molecular orbital energies, induce red‐shift of absorption spectrum, increase CT energy, improve CT and ED rates. This work provides a detailed understanding of tuning optoelectronic properties and photovoltaic performance by modifying NFA's side chains and extending backbones.

Enhancing solar energy conversion with nickel/iron oxyhydroxide-modified hematite photoanodes: The role of Fe species in alkaline electrolyte

Hematite photoanodes have shown potential for use in practical applications of photoelectrochemical (PEC) water splitting cells due to their abundance and stability, yet their efficiency needs to be improved. To optimize photoanode performance, co-catalysts such as amorphous nickel/iron oxyhydroxide layers are often deposited on the surface of hematite to enhance activity by catalyzing oxygen evolution. Recent studies have shown that the role of oxyhydroxide layers in changing PEC activity can vary depending on factors such as film morphology, co-catalyst layer thickness, and electrolyte composition. In this study, we investigate the effect of NiOOH and (Ni,Fe)OOH layers on the PEC activity of electrodeposited nanostructured hematite films. Our analysis of charge transfer and recombination rate constants determined from chronoamperometry and electrochemical impedance data suggests that the coatings' role is purely passivating, which is crucial for discontinuous electrodeposited films. Importantly, we show that the passivating properties of these coatings are enhanced by the presence of ppm concentrations of Fe in the electrolyte. We believe that our findings will be useful for further development of hematite photoanodes.

Studying the optoelectronic properties and emission quenching dynamics of poly‐TPD by incorporating ZnO nanoparticles and multiwalled carbon nanotubes

AbstractIn this study, the optoelectronic properties and emission dynamic quenching of poly‐TPD were investigated upon incorporating ZnO nanoparticles and multiwalled carbon nanotubes (MWCNTs). A solution blending method was utilized to successfully prepare poly‐TPD incorporated with various contents of ZnO/MWCNT nanocomposites. The optoelectronic properties of the nanocomposites were analyzed using UV–Vis and photoluminescence spectrophotometry. The incorporation of the nanocomposites resulted in a decrease in transmittance, reflectance, and absorption edge, indicating a reduction in the poly‐TPD's bandgap. Parameters such as extinction coefficient, Urbach energy, and charge carrier density also decreased with addition of the nanocomposites, suggesting increased scattering, disorder, and the presence of defect states. The decrease in bandgap from 2.970 to 2.852 eV with increasing the nanocomposite content confirmed the emergence of new electronic states. Furthermore, the nature of the transitions changed from direct allowed for pure poly‐TPD to direct forbidden upon incorporation of the nanocomposites. The inclusion of the nanocomposites also led to a decrease in refractive index and fluorescence intensity. The observed fluorescence quenching primarily exhibited dynamic characteristics, with a Stern–Volmer constant of 5.14 L/g and quenching rate constants surpassing the minimum threshold for efficient quenching. The increase in charge transfer rate constants with the nanocomposite content indicated enhanced quenching efficiency and charge transfer, likely due to the increased surface area and presence of defects. These findings suggest that poly‐TPD incorporated with ZnO/MWCNT nanocomposites displays promising properties for applications in optoelectronic devices.

Spin-dependent charge transmission through chiral 2T3N self-assembled monolayer on Au.

A gold surface is functionalized by chemisorption of the enantiopure N,N'-bis-[2,2';5',2″]tert-thiophene-5-yl methylcyclohexane-1,2-diamine (2T3N), a chiral oligothiophene derivative, via overnight incubation in a 2T3N ethanol solution. The Au|2T3N interface is characterized by x-ray photoelectron circular dichroism and comparing x-ray photoemission spectroscopy and electro-desorption results. Charge transmission at the Au|2T3N| solution interface is characterized by recording the cyclic voltammetry of the Fe(III)/Fe(II) reversible redox couple, finding a charge transfer rate constant, k°, variation from 1 × 10-1 to 3.3 × 10-2 cm s-1, when comparing the bare Au and the Au|2T3N interfaces, respectively. The "anomalous" high value of k° found for the chiral Au|2T3N interface can be rationalized on the basis of the chiral-induced spin selectivity effect, as further proved by magnetic-conductive atomic force microscopy measurements at room temperature. A spin polarization of about 30% is found.

Bulk embedding of Ti-defected TiO2 nano-heterointerfaces in hematite photoanode for boosted photoelectrochemical water splitting

The practical application of the most promising α-Fe2O3 photoanode in solar hydrogen generation is facing an awkward challenge arising from its poor bulk carrier transport. Present work demonstrates the acceleration of the carrier transport via embedding the p-type Ti-defected TiO2 (TiO2-VTi) nanocrystals in the n-type Fe2O3 photoanode matrix, which results in significantly improved photoelectrochemical performance. By embedding sub-5 nm TiO2-VTi nanocrystals in the bulk of α-Fe2O3 photoanode, numerous p-n nano-heterointerfaces were constructed for the first time in Fe2O3 photoanode matrix. The formed p-n nano-heterointerfaces lead to 10 times enhancement of charge transfer rate constant (ktran), and 1.5 times reduction of the charge recombination rate constant (krec), which is due to the formation of the built-in electric fields and effective carrier transport and separation at the p-n nano-heterointerfaces of TiO2-VTi/Fe2O3. Such strategy leads to the Fe2O3 photoanode with a reduction of photogenerated carrier transport time by 3 times, resulting in an excellent photocurrent density as high as 1.45 mA cm−2 at 1.23 VRHE, 5 times higher than that of pristine hematite (0.27 mA cm−2). We thus believe that our study opens up a route to regulate hematite or even metal-oxide semiconductor chemical/physical features via p-n nano-heterostructure embedding.

Charge Transfer Kinetics of the Ti(IV)/Ti(III) Redox Couple in the Cesium Chloride-Cesium Fluoride Melt with Addition of Alkaline Earth Metal Cations

The electrochemical behavior of the Ti(IV)/Ti(III) redox couple in the CsCl-CsF(10 wt%)-K2TiF6 melt was studied by cyclic voltammetry. The diffusion coefficients of the Ti(IV) complexes were calculated using the Randles-Sevcik equation. The standard rate constants of charge transfer for the Ti(IV)/Ti(III) redox couple in the CsCl-CsF(10 wt%)-K2TiF6 melt without and with additions of alkaline Earth metal cations (Mg2+, Ca2+, Sr2+, Ba2+) were determined. It was found that the rate constants of charge transfer increase with increasing ionic potential of the addition, reaching a maximum value for complexes with outer-sphere cations of magnesium, and this dependence is rectilinear. The activation energies of the charge transfer process in melts with additions of alkaline Earth metal cations were calculated and these values are significantly lower than the activation energy of the initial system CsCl-CsF(10 wt%)-K2TiF6. The kinetic parameters of the Ti(IV)/Ti(III) redox couple in chloride-fluoride melts with different second coordination sphere composition of the complexes were compared.

Electrochemistry of Neodymium in an Equimolar NaCl-KCl Melt without and with Addition of Fluoride Ions

Abstract The paper presents the results of neodymium electrochemical behavior in chloride and chloride-fluoride melts. It was shown that the process of neodymium electroreduction in the NaCl-KCl-NdCl3 melt proceeds in two stages. By diagnostic criteria of voltammetry it was established that the discharge process of Nd(III) to Nd(II) at a sweep rate in the range of 0.6 ≤  ≤ 1.0 V s-1 is not complicated by disproportionation reaction. In this study diffusion coefficients, activation energy of diffusion for Nd(III) chloride complexes and standard rate constants of charge transfer for the Nd(III)/Nd(II) redox couple in the NaCl-KCl melt were determined. The nature of the working electrode on the standard rate constants of charge transfer for the Nd(III)/Nd(II) redox couple has been studied by cyclic voltammetry and electrochemical impedance spectroscopy. The formal redox potentials E*Nd(III)/Nd(II) in the NaCl-KCl melt were obtained from the cyclic voltammetry data. It was shown that the addition of fluorine anions into the NaCl-KCl-NdCl3 melt leads to stabilization of the higher oxidation state of neodymium in chloride-fluoride melts and the intermediate oxidation state Nd(II) does not exist in these melts.

Effect of external electric fields in the charge transfer rates of donor-acceptor dyads: A straightforward computational evaluation.

We present a straightforward and low-cost computational protocol to estimate the variation of the charge transfer rate constant, kCT, in a molecular donor-acceptor caused by an external electric field. The proposed protocol also allows for determining the strength and direction of the field that maximize the kCT. The application of this external electric field results in up to a >4000-fold increase in the kCT for one of the systems studied. Our method allows the identification of field-induced charge-transfer processes that would not occur without the perturbation caused by an external electric field. In addition, the proposed protocol can be used to predict the effect on the kCT due to the presence of charged functional groups, which may allow for the rational design of more efficient donor-acceptor dyads.

Kinetic and Thermodynamic Properties of Ytterbium Chloride and Fluoride Complexes in Chloride Melts

The electrochemical behavior of trichloride ytterbium in NaCl-KCl, KCl, and CsCl melts was studied in the temperature range 973–1173 K by different electrochemical methods. The diffusion coefficients (D) of Yb(III) and Yb(II) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods. The standard rate constants of charge transfer (k s) for the Yb(III)/Yb(II) redox couple were calculated on the basis of cyclic voltammetry data using Nicholson’s equation. The formal redox potentials E * Yb(III)/Yb(II) in alkali chloride melts were obtained by the cyclic voltammetry and the Gibbs free energy for the reaction: YbCl2(sol.) + 1/2 Cl2(g.) ↔YbCl3(sol.) in alkali chloride melts was calculated. The electrochemical behavior of the Yb(III)/Yb(II) redox couple in the NaCl-KCl- NaF (5 wt%) melt was studied. A comparative analysis of electrochemical behavior of ytterbium chloride complexes in the NaCl-KCl melt and ytterbium fluoride complexes in the NaCl-KCl- NaF (5 wt%) melt was performed. It was shown that the formation of the stronger fluoride complexes reduced diffusion coefficients, standard rate constants of charge transfer for the Yb(III)/Yb(II) redox couple, and shifted the formal standard redox potentials to more electronegative values.

The Influence of Spirodi(Iminohydantoin) on Charge Transfer through ds-DNA Containing 8-OXO-dG: A Theoretical Approach.

Genetic information stored in a DNA base sequence is continuously exposed to harmful factors. It has been determined that 9 × 104 different DNA damage events occur in a single human cell every 24 h. Of these, 7,8-dihydro-8-oxo-guanosine (OXOG) is one of the most abundant and can undergo further transformations towards spirodi(iminohydantoin) (Sp). Sp is highly mutagenic in comparison to its precursor if not repaired. In this paper, the influence of both Sp diastereomers 4R and 4S as well as their anti and syn conformers on charge transfer through the double helix was taken into theoretical consideration. In addition, the electronic properties of four modelled double-stranded oligonucleotides (ds-oligos) were also discussed, i.e., d[A1Sp2A3oxoG4A5] * [T5C4T3C2T1]. Throughout the study, the M06-2X/6-31++G** level theory was used. Solvent-solute non-equilibrated and equilibrated interactions were also considered. The subsequent results elucidated that the 7,8-dihydro-8-oxo-guanosine:cytidine (OXOGC) base pair is the settled point of a migrated radical cation in each of the discussed cases, due to its low adiabatic ionization potential, i.e., ~5.55 [eV]. The opposite was noted for excess electron transfer through ds-oligos containing anti (R)-Sp or anti (S)-Sp. The radical anion was found on the OXOGC moiety, whereas in the presence of syn (S)-Sp or syn (R)-Sp, an excess electron was found on the distal A1T5 or A5T1 base pair, respectively. Furthermore, a spatial geometry analysis of the discussed ds-oligos revealed that the presence of syn (R)-Sp in the ds-oligo caused only a slight deformation to the double helix, while syn (S)-Sp formed an almost ideal base pair with a complementary dC. The above results are in strong agreement with the final charge transfer rate constant, as calculated according to Marcus' theory. In conclusion, DNA damage such as spirodi(iminohydantoin), especially when becoming part of clustered DNA damage, can affect the effectiveness of other lesion recognition and repair processes. This can lead to the acceleration of undesired and deleterious processes such as carcinogenesis or aging. However, in terms of anticancer radio-/chemo- or combined therapy, the slowing down of the repair machinery can result in increased effectiveness. With this in mind, the influence of clustered damage on charge transfer and its subsequent effect on single-damage recognition by glycosylases justifies future investigation.

Dark Current Water Splitting Employing Ni3TeO6 as a Photocharged Photoelectrocatalyst

Herein, the photoelectrocatalytic and photocharging activity of a Ni3TeO6 (NTO‐700) photoelectrocatalyst for water oxidation in alkaline medium is demonstrated and calcined at 700 °C. The photoelectrocatalytic (PEC) activity of the sample is increased upon an increase in the illumination time. With a twofold increase in photocurrent density at 1.8 V, the PEC 150 sample (having been illuminated for 150 min) attained the highest PEC activity. The synthesized material has displayed an excellent charge storage capacity in KOH and Na2SO4 electrolyte solutions (both 0.1 m). The chrono‐amperometry measurement, subsequent to light interruption, has sustained almost 44% higher current density (even after 200 min) compared to the pure electrocatalytic baseline in a Na2SO4 electrolyte. The charge transfer resistance, Rct, decreases from 633.40 to 170.40 Ω, while the charge transfer rate constant, kct, increases from 7.93 to 27.03 s−1, as a function of illumination time. This points to fast separation of electron–hole (e−–h+) pairs and a slower recombination rate. The lower values of the charge transfer resistance and the time constant recorded for the light interrupted samples, as compared to the electrochemical sample, are attributed to the stored charge that drives water oxidation at a higher rate.

ЭЛЕКТРОХИМИЧЕСКОЕ ПОВЕДЕНИЕ ТИТАНА В ХЛОРИДНО-ФТОРИДНЫХ РАСПЛАВАХ РАЗЛИЧНОГО СОСТАВА В ПРИСУТСТВИИ КАТИОНОВ ЩЕЛОЧНОЗЕМЕЛЬНЫХ МЕТАЛЛОВ

The electrochemical behavior of titanium and the influence of alkali earth metal cations (Mg2+, Ca2+, Sr2+ and Ва2+) on the charge transfer kinetics of the Ti(IV)/Ti(III) redox couple were studied by cyclic voltammetry method in chloride-fluoride melts of different composition. Standard rate constants of charge transfer and the activation energies of the charge transfer process were calculated.

The Influence of 5',8-Cyclo-2'-Deoxyguanosine on ds-DNA Charge Transfer Depends on Its Diastereomeric Form: A Theoretical Study.

The genetic information stored in the nucleobase sequence is continuously exposed to harmful extra- and intra-cellular factors, which can lead to different types of DNA damage, with more than 70 lesion types identified so far. In this article, the influence of a multi-damage site containing (5'R/S) 5',8-cyclo-2'-deoxyguanosine (cdG) and 7,8-dihydro-8-oxo-2'-deoxyguanosine (OXOdG) on charge transfer through ds-DNA was taken into consideration. The spatial geometries of oligo-RcdG: d[A1(5'R)cG2A3OXOG4A5]*d[T5C4T3C2T1] and oligo-ScdG: d[A1(5'S)cG2A3OXOG4A5]*d[T5C4T3C2T1] were optimized at the M06-2X/6-D95**//M06-2X/sto-3G level of theory in the aqueous phase using ONIOM methodology. For all the electronic property energies under discussion, the M06-2X/6-31++G** level of theory was used. Additionally, the non-equilibrated and equilibrated solvent-solute interactions were into consideration. The obtained results confirm the predisposition of OXOdG to radical cation formation regardless of the presence of other lesions in a ds-DNA structure. In the case of electron transfer, however, the situation is different. An excess electron migration towards (5'S)cdG was found to be preferred in the case of oligo-ScdG, while in the case of oligo-RcdG, OXOdG was favored. The above observation was confirmed by the charge transfer rate constant, vertical/adiabatic ionization potential, and electron affinity energy values, as well as the charge and spin distribution analysis. The obtained results indicate that 5',8-cyclo-2'-deoxyguanosine, depending on the C5' atom chirality, can significantly influence the charge migration process through the double helix. The above can be manifested by the slowdown of DNA lesion recognition and removal processes, which can increase the probability of mutagenesis and subsequent pathological processes. With regard to anticancer therapy (radio/chemo), the presence of (5'S)cdG in the structure of formed clustered DNA damage can lead to improvements in cancer treatment.

Revealing the enhanced photoelectrochemical water oxidation activity of Fe-based metal-organic polymer-modified BiVO4 photoanode

Metal-organic polymers (MOPs) can enhance the photoelectrochemical (PEC) water oxidation performance of BiVO4 photoanodes, but their PEC mechanisms have yet to be comprehended. In this work, we constructed an active and stable composite photoelectrode by overlaying a uniform MOP on the BiVO4 surface using Fe2+ as the metal ions and 2,5-dihydroxyterephthalic acid (DHTA) as ligand. Such modification on the BiVO4 surface yielded a core-shell structure that could effectively enhance the PEC water oxidation activity of the BiVO4 photoanode. Our intensity-modulated photocurrent spectroscopy analysis revealed that the MOP overlayer could concurrently reduce the surface charge recombination rate constant (ksr) and enhance the charge transfer rate constant (ktr), thus accelerating water oxidation activity. These phenomena can be ascribed to the passivation of the surface that inhibits the recombination of the charge carrier and the MOP catalytic layer that improves the hole transfer. Our rate law analysis also demonstrated that the MOP coverage shifted the reaction order of the BiVO4 photoanode from the third-order to the first-order, resulting in a more favorable rate-determining step where only one hole accumulation is required to overcome water oxidation. This work provides new insights into the reaction mechanism of MOP-modified semiconductor photoanodes.