Mechanism Of Electron Transfer Processes Research Articles

Utilizing MXene-mediated electron transfer pathway to boost peroxymonosulfate activation for water purification

Regulating the performance of manganese oxide catalysts to enhance peroxymonosulfate (PMS) activation for degrading emerging organic pollutants remains a significant challenge. To address this issue, Mn3O4/MXene composites with precisely controlled MXene contents are synthesized by combining hydrothermal and calcining methods, resulting in a significant regulate the pathway of Mn3O4 activation of PMS and a notable enhancement bisphenol A (BPA) degradation efficiency. The normalized first-order rate constant for optimized Mn3O4/MXene composites is 0.0218 g/(m2⋅min), which is 8.4 and 2.0 times higher than those of MXene and Mn3O4, respectively. Moreover, this catalyst exhibits excellent mineralization capacities, achieving up to 88.2 % total organic carbon removal efficiency. Combining with electrochemical and electron paramagnetic resonance analysis, the mechanism of electron transfer processes in this composite is elucidated comprehensively. Moreover, Mn3O4/MXene displays remarkable efficiency in degrading refractory pollutants, including antibiotics, phenols, and dyes. Furthermore, Mn3O4/MXene composites exhibit superior stability, reusability, and resistance to interference, highlighting their versatility in diverse environmental contexts. Notably, the catalyst maintains stable catalytic activity for long-term pollutant removal in a continuous-flow system. This study presents a novel approach for developing composite catalysts, providing new avenues for the treatment of emerging pollutants in wastewater.

Electrochemical Sensor for Choline Based on Iron (III) Oxide and Functionalized Multi-Walled Carbon Nanotube at the Glassy Carbon Electrode Surface

Iron (III) oxide nanoparticle (Fe3O4NP) was synthesized via green route using Callistemon viminalis leaf extract. A composite of Fe3O4NP with functionalized multi-walled carbon nanotube (f-MWCNT) was then applied as glassy carbon electrode modifier to develop a choline sensor. Electrocatalytic oxidation of choline on nanocomposite modified electrode (GCE/f-MWCNT/Fe3O4NP) was studied by cyclic voltammetry while mechanism of electron transfer process during choline electrocatalytic oxidation was monitored by electrochemical impedance spectroscopy at fixed potential 0.5 V with frequencies between 100 kHz and 0.01 Hz. Active surface coverage area of choline, charge transfer coefficient and number of electron transferred were reported. Square wave voltammetry (SWV) was employed for the determination of choline over a linear concentration range of 24.3 - 215.6 μM. A sensitivity of 0.0244 μA/μM and 9.9 μM detection limit was found. The sensor was selective to choline (0.1 mM) in the presence of 100 mM and 0.1 mM ascorbic acid (AA) and dopamine (DA) respectively using SWV and chronoamperometry. The designed electrode was reproducible and stable. The sensor was successfully used for choline detection in choline dietary supplements with resultant good recoveries. The fabrication of the sensor was simple and cost-effective. Figure 1

First-principles study of electron dynamics with explicit treatment of momentum dispersion on Si nanowires along different directions

ABSTRACTIn this research, ground-state electronic structure and optical properties along with photoinduced electron dynamics of Si nanowires oriented in various directions are reviewed. These nanowires are significant functional units of future nano-electronic devices. All observables are computed for a distribution of wave vectors at ambient temperature. Optical properties are computed under the approximation of momentum conservation. The total absorption is composed of partial contributions from fixed values of momentum. The on-the-fly non-adiabatic couplings obtained along the ab initio molecular dynamics nuclear trajectories are used as parameters for Redfield density matrix equation of motion. The main outcomes of this study are transition energies, light absorption spectra, electron and hole relaxation rates, and electron transport properties. The results of these calculations would contribute to the understanding of the mechanism of electron transfer process on the Si nanowires for optoelectronic applications.

First-Principles Study of Charge Carrier Dynamics with Explicit Treatment of Momentum Dispersion on Si Nanowires along <211> crystallographic Directions

ABSTRACTThe ground state structure, optical properties and charge carrier dynamics of silicon nanowire (SiNW) grown in <211> crystallographic direction is studied as a function of wavevector using density functional theory. This nanowire can be used as fundamental unit of nanoelectronic devices. The optical properties are computed under assumption of momentum conservation$\Delta \vec{k} = 0$. The on-the-fly non-adiabatic couplings for electronic degrees of freedom are obtained along the ab initio molecular dynamics nuclear trajectories, which are used as parameters for Redfield density matrix equation of motion. By investigating the photo-induced process on this nanowire, it is shown that high-energy photoexcitation relaxes to the band gap edge within 75 ps. The results of these calculations help to understand the mechanism of electron transfer process on the Si nanowire.

Photochemical Reaction Between 1,2‐Naphthoquinone and Adenine in Binary Water‐Acetonitrile Solutions

The photochemical reaction between 1,2-naphthoquinone (NQ) and adenine was investigated using nanosecond time-resolved laser flash photolysis. With photolysis at 355nm, the lowest triplet state T1 of NQ was produced via intersystem crossing from its singlet excited state. The triplet-triplet absorption of the state contributes three bands of transient spectra at 374, 596 and 650nm, respectively, in pure acetonitrile and binary water-acetonitrile solutions. In the presence of adenine, the observation of A·+ (at 363nm) and NQ+H· radical (at 343 and 485nm) indicates a multistep mechanism of electron transfer process followed by a proton transfer between 3 NQ* and adenine. By fitting with the Stern-Volmer relationship, the quenching rate constant kq of 3 NQ* by adenine in binary water-acetonitrile solutions (4/1, volume ratio, v/v) is determined as 1.66×109 m-1 s-1 . Additionally, no spectral evidence confirms the existence of electron transfer between 3 NQ* with thymine, cytosine and uracil.

Electron dynamics in charged wet TiO2 anatase (001) surface functionalised by ruthenium ions

The surface of charged wet TiO2 anatase (001) functionalised by ruthenium ion at ambient temperatures is studied by computational modelling. Response of this model to photoexcitations at ambient temperatures is explored with the Redfield density matrix equation of motion on the basis of Kohn–Sham orbitals. The parameters of the Redfield equation are on-the-fly non-adiabatic couplings for electronic degrees of freedom obtained along the ab initio molecular dynamics nuclear trajectories. The main results in this study are the following: (1) optical properties of the doped models such as light absorption intensity and transition energies can be tuned by modifying total charge; (2) electron and hole relaxation rates depend on the initial excitation; and (3) in the doped model, excitations of lower energy provide quicker relaxation. Results of computational modelling would benefit understanding of the mechanism of electron transfer processes on the surface of ruthenium-doped TiO2.

Mechanism of electron transfer processes photoinduced by lumazine

UV-A (320-400 nm) and UV-B (280-320 nm) radiation causes damage to DNA and other biomolecules through reactions induced by different endogenous or exogenous photosensitizers. Lumazines are heterocyclic compounds present in biological systems as biosynthetic precursors and/or products of metabolic degradation. The parent and unsubstituted compound called lumazine (pteridine-2,4(1,3H)-dione; Lum) is able to act as photosensitizer through electron transfer-initiated oxidations. To get further insight into the mechanisms involved, we have studied in detail the oxidation of 2'-deoxyadenosine 5'-monophosphate (dAMP) photosensitized by Lum in aqueous solution. After UV-A or UV-B excitation of Lum and formation of its triplet excited state ((3)Lum*), three reaction pathways compete for the deactivation of the latter: intersystem crossing to singlet ground state, energy transfer to O(2), and electron transfer between dAMP and (3)Lum* yielding the corresponding pair of radical ions (Lum˙(-) and dAMP˙(+)). In the following step, the electron transfer from Lum˙(-) to O(2) regenerates Lum and forms the superoxide anion (O(2)˙(-)), which undergoes disproportionation into H(2)O(2) and O(2). Finally dAMP˙(+) participates in subsequent reactions to yield products.

Electron transfer in fast proton-helium collisions

We have measured the electron-transfer process in fast collisions (630--1200 keV/u) of protons with helium, which is dependent on the projectile scattering angle and the final electronic state. The fully differential data accompanied by theoretical second-order perturbation theory allow a detailed insight into the mechanism of electron-transfer processes.

Kinetics and mechanism of electron transfer processes in a hydrogen peroxide—trispicolinatoruthenate(II) system

Oxidation of trispicolinatoruthenate(II) complex by hydrogen peroxide leads to the formation of mer-trispicolinatoruthenium(III) in acidic or neutral solutions. Kinetics of the reaction were studied under a large excess of H2O2 at constant pH. The initial rate method gives a rate expression of the form: $$ - \hbox{d}[{\text{Ru}}({\text{II}})]/{\text{d}}t = k^{II} [{\text{H}}_{2} {\text{O}}_{2} ][{\text{Ru}}({\text{II}})] $$ but the overall process examined till completion is far more complex. The rate of the reaction decreases with increasing pH to be practically completely retarded in alkaline media. The key step in the proposed reaction mechanism is the picolinato chelate ring opening followed by the substitution of the coordinated water by H2O2 and two-electron intramolecular ruthenium(II) oxidation. Formation of the final ruthenium(III) complex is assigned rather to the ruthenium(IV) reduction by H2O2 than ruthenium(II)–ruthenium(IV) comproportionation. The obtained results show the much slower rate of the trispicolinatoruthenate(II) oxidation by hydrogen peroxide or dioxygen than the mer-trispicolinatoruthenium(III) reduction by such bioreductants as cytochrome cII or some cobalt(II) reductants.

Study of the Recombination Process of Light-Induced Charge Separation in Reaction Centers of Purple Bacteria Under Long-Term Exposition

Experimental results, which confirm the nonlinear dynamic behavior of bacterial photosynthetic reaction centers under light-activated conditions, are presented. Different light-adapted conformational states of the reaction centers can be obtained by varying the exposition time. It is shown that the fast and slow equilibration kinetics of the reaction centers reflect the mechanisms of electron transfer processes. The reaction centers possessing light-induced structural changes, which have not relaxed completely before a flash, produce the pronounced slow relaxation component. This slow component splits into two separate components with increase in the exposition time. The amplitudes of the resulting components depend on the light adaptation time.

Probing Biomolecular Interactions at Conductive and Semiconductive Surfaces by Impedance Spectroscopy: Routes to Impedimetric Immunosensors, DNA‐Sensors, and Enzyme Biosensors

AbstractImpedance spectroscopy is a rapidly developing electrochemical technique for the characterization of biomaterial‐functionalized electrodes and biocatalytic transformations at electrode surfaces, and specifically for the transduction of biosensing events at electrodes or field‐effect transistor devices. The immobilization of biomaterials, e.g., enzymes, antigens/antibodies or DNA on electrodes or semiconductor surfaces alters the capacitance and interfacial electron transfer resistance of the conductive or semiconductive electrodes. Impedance spectroscopy allows analysis of interfacial changes originating from biorecognition events at electrode surfaces. Kinetics and mechanisms of electron transfer processes corresponding to biocatalytic reactions occurring at modified electrodes can be also derived from Faradaic impedance spectroscopy. Different immunosensors that use impedance measurements for the transduction of antigen‐antibody complex formation on electronic transducers were developed. Similarly, DNA biosensors using impedance measurements as readout signals were developed. Amplified detection of the analyte DNA using Faradaic impedance spectroscopy was accomplished by the coupling of functionalized liposomes or by the association of biocatalytic conjugates to the sensing interface providing biocatalyzed precipitation of an insoluble product on the electrodes. The amplified detections of viral DNA and single‐base mismatches in DNA were accomplished by similar methods. The changes of interfacial features of gate surfaces of field‐effect transistors (FET) upon the formation of antigen‐antibody complexes or assembly of protein arrays were probed by impedance measurements and specifically by transconductance measurements. Impedance spectroscopy was also applied to characterize enzyme‐based biosensors. The reconstitution of apo‐enzymes on cofactor‐functionalized electrodes and the formation of cofactor‐enzyme affinity complexes on electrodes were probed by Faradaic impedance spectroscopy. Also biocatalyzed reactions occurring on electrode surfaces were analyzed by impedance spectroscopy. The theoretical background of the different methods and their practical applications in analytical procedures were outlined in this article.

Ceric ammonium nitrate on silica gel for efficient and selective removal of trityl and silyl groups

Silica gel-supported ceric ammonium nitrate (CAN-SiO2) was found effective for rapid and selective cleavage of trityl (Tr), monomethoxytrityl (MMTr), and dimethoxytrityl (DMTr) groups from protected nucleosides and nucleotides under mild conditions. Efficiency of deprotections depended upon the stability of the resultant carbocationic species: DMTr+ > MMTr+ > Tr+. Use of a catalytic amount of this solid-supported reagent can also efficiently and selectively remove the tert-butyldimethylsilyl or the triisopropylsilyl group from a primary hydroxyl functionality in di- or trisilyl ethers of ribonucleosides. A comparative study of deprotection reactions by utilization of CAN alone or CAN-SiO2 indicates a remarkable increase in the rate of the reactions involving a solid support. The mechanism of electron-transfer processes is proposed for the use of CAN-SiO2 in the removal of these protective groups from organic molecules.

Flavocytochrome b 2-cytochrome c interactions: The electron transfer reaction revisited

This review is concerned with the kinetics and mechanism of electron transfer processes which occur intermolecularly between reduced flavocytochrome b 2 and cytochrome c molecules within an encounter complex. Analyses are given of previous reports which aimed at describing the formation of stable complexes obtained at low ionic strength in solution and in the crystalline state with a binding stoichiometry of 1 to 1 heme ratio. Relevant data allow to define the respective role of flavin and heme b 2 in the electron transfer towards cytochrome c and give a description of the recognition areas on the two redox partners. The paper also refers to a recent computer model of their postulated interactions as based on the three-dimensional structure of the Saccharomyces cerevisiae single molecules. Special emphasis is given to rapid kinetic investigations of the electron transfer reaction between Hansenula anomala flavocytochrome b 2 and cytochrome c studied as a function of concentration, ionic strength and temperature. Data showed that reaction rates were modulated by ionic strength, reaching a saturation behaviour at low ionic strength. In the present paper the temperature effects on K d and k ET have been re-examined. Thermodynamic analysis of the dissociation constant points out the importance of hydrophobic interactions in the complex formation. Analysis of the variations of rate constants in terms of semiclassical theory of electron-transfer reaction yields values of 1.12 eV for the reorganization energy and 0.05 cm −1 for the electronic coupling factor. Interpretation of the electronic coupling in terms of through-bond and/or through-space pathways takes into account the hypothetical model proposed for the binary complex. The functional implications of this model in the electron transfer reaction are discussed. Finally the existence of a conformational equilibrium between the initial binding complex and the complex from which electron transfer occurs is considered.

Use of laser flash photolysis time-resolved spectrophotometry to investigate interprotein and intraprotein electron transfer mechanisms

A description is given of the methodology developed in our laboratory for the application of laser flash photolysis to the elucidation of the kinetics and mechanism of electron transfer processes which occur intermolecularly between two protein molecules within a collisional complex, or intramolecularly between two redox centers within a single multisubunit or multidomain protein. This involves the use of flavin analogs, excited to their lowest triplet state by a laser flash, to initiate electron transfer, either by oxidation of a sacrificial donor followed by redox protein reduction via the flavin semiquinone, or by direct oxidation of a reduced redox protein by the flavin triplet. Time-resolved spectrophotometry is used to follow the course of the sequence of electron transfer events initiated by the laser flash. The application of this methodology to the following systems is described: cytochrome c/cytochrome c peroxidase; ferredoxin/ferredoxin NADP + reductase; cytochrome c/plastocyanin; flavocytochrome b 2; and sulfite oxidase.

Organization and dynamics of pyrene and pyrene lipids in intact lipid bilayers. Photo-induced charge transfer processes

The dynamics of fluorescence quenching and the organization of a series of pyrene derivatives anchored in various depths in bilayers of phosphatidylcholine small unilamellar vesicles was studied and compared with their behavior in homogeneous solvent systems. The studies include characterization of the environmental polarity of the pyrene fluorophore based on its vibronic peaks, as well as the interaction with three collisional quenchers: the two membrane-soluble quenchers, diethylaniline and bromobenzene, and the water soluble quencher potassium iodide. The system of diethylaniline-pyrene derivatives in the membrane of phosphatidylcholine vesicles was characterized in detail. The diethylaniline partition coefficient between the lipid bilayers and the buffer is approximately 5,800. Up to a diethylaniline/phospholipid mole ratio of 1:3 the perturbation to membrane structure is minimal so that all photophysical studies were performed below this mole ratio. The quenching reaction, in all cases, was shown to take place in the lipid bilayer interior and the relative quenching efficiencies of the various probe molecules was used to provide information on the distribution of both fluorescent probes and quencher molecules in the lipid bilayer. The quenching efficiency by diethylaniline in the lipid bilayer was found to be essentially independent on the length of the methylene chain of the pyrene moiety. These findings suggest that the quenching process, being a diffusion controlled reaction, is determined by the mobility of the diethylaniline quencher (with an effective diffusion coefficient D approximately 10(-7) cm2 s-1) which appears to be homogeneously distributed throughout the lipid bilayer. The pulsed laser photolysis products of the charge-transfer quenching reaction were examined. No exciplex (excited-complex) formation was observed and the yield of the separated radical ions was shown to be tenfold smaller than in homogenous polar solutions. The decay of the radical ions is considerably faster than the corresponding process in homogenous solutions. Relatively high intersystem crossing yields are observed. The results are explained on the basis of the intrinsic properties of a lipid bilayer, primarily, its rigid spatial organization. It is suggested that such properties favor ion-pair formation over exciplex generation. They also enhance primary geminate recombination of initially formed (solvent-shared) ion pairs. Triplet states are generated via secondary geminate recombination of ion pairs in the membrane interior. The results bear on the general mechanism of electron transfer processes in biomembranes.

Photoelectrochemically‐Induced Gold Deposition on p ‐ GaAs Electrodes: Part I . Nucleation and Growth

This paper reports on the deposition of Au on cathodically biased electrodes from alkaline solutions in the dark or under illumination. Nucleation and growth of Au have been studied by potentiodynamic and potentiostatic current measurements in combination with scanning and transmission electron microscopy. Au deposition is characterized by progressive nucleation and three‐dimensional growth followed by coalescence of Au particles. Different mechanisms of electron transfer processes occurring during nucleation and growth are discussed. Au nucleation in the dark occurs readily at relatively high‐doped electrodes, both in the absence and presence of excess CN−ions. Selective photoinduced nucleation is possible on low‐doped electrodes in a solution with excess CN−ions. It is observed that the critical size of Au nuclei is smaller than 1 nm. Growth of previously formed Au nuclei can proceed in the dark and is initially controlled both by kinetic factors and diffusion of ions. Our results indicate that only a small potential barrier exists between and deposited Au particles.