Probability Of Electron Transfer Research Articles

One- and Two- Electron Reductions in MiniSOG and their Implication in Catalysis.

In the last years, the unconventional bioorthogonal catalytic activation of anticancer metal complexes by flavin and flavoproteins photocatalysis has been described. The reactivity is based on a two-electron redox reaction of the photoactivated flavin. Furthermore, when it comes to flavoproteins, we recently reported that site mutagenesis can modulate and improve this catalytic activity in the mini Singlet Oxygen Generator protein (SOG). In this paper, we analyze the reductive half-reaction in the different miniSOG environments by means of density functional theory. We report that the redox properties of the flavin and the resulting reactivity of miniSOG is modulated by specific mutations, in line with the experimental results in the literature. This modulation can be attributed to fundamental physicochemical properties of the system, specifically (i) the competition of single and double reduction of the flavin and (ii) the probability of electron transfer from the protein to the flavin. These factors are ultimately linked to the stability of the electronaccepting orbitals of the flavin in the different coordination modes.

(Digital Presentation) Study of the Intervalence Charge Transfer in a 18NaCl+Na3SmF6 Model System By Quantum Chemical Methods

The frontier orbital method showed a high informativity for the study of electron transfer in the model system 18NaCl+Na3SmF6. Structures having a high probability of electron transfer from the cathode to the samarium complex were observed when varying the transition state parameters. The influence of the full-symmetric oscillations Sm-F bonds and the boundary ion shift on the activation barrier, the frontier molecular orbitals energy and the delocalization character of the lowest unoccupied molecular orbital wave function in the samarium-containing model systems was systematically studied. This analysis allowed to identify the most probable structures of the transition state for the electron transfer process. The application of the method of frontier orbitals made it possible to determine the structure of the transition state of the complex SmF6 3- near the electrode surface with a small costs of machine time, using an agreement of the calculated and experimental values for the activation energy of electron transfer.

Experimental spectroscopic investigations, solute-solvent interactions, topological analysis and biological evaluations of N-(9-Fluorenylmethoxycarbonyloxy)succinimide: An effective agent in anti-breast cancer activity

In this study, the solvation effects, and spectroscopic characterization of the N-(9-Fluorenylmethoxycarbonyloxy)succinimide (Fmoc-OSu) were described using experimental approaches (FT-IR, FT-Raman, and UV–Vis) with quantum computations. The stable optimized structure in various media was evaluated with the structural and topological (AIM, LOL, and ELF) parameters. The vibrational investigation was utilized to determine the structure of the chemical as well as to find the relation between potential energy distribution and molecular structure. FMOs analysis, Electrostatic potential energy map, and Fukui chemical reactivity descriptors were utilized to study the influence of the solvents on the reactivity of the compound. UV–Vis absorptions with vertical excitations are to detect where there is a greater probability of electron transfer in the compound. Furthermore, the Solvent parameters have described the effects of polar and non-polar solvents on the title molecule. The bioactivity of the chemical was further examined via molecular docking with cancer cell proteins. The Fmoc-OSu produces the most non-covalent interactions against the breast cancer cell development protein (PDB code: 1OQA), which has the highest binding energy of −8.08 kcal/mol.

An Ab Initio Molecular Dynamics Study of the Mechanism and Rate of Dye Regeneration by Iodide Ions in Dye-Sensitized Solar Cells

In the ambition to improve the power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs), it will be essential to understand the mechanisms and rates of dye regeneration. Although the mechanism of dye regeneration has been studied by static density functional theory (DFT) and classical molecular dynamics (CMD) simulations, ab initio molecular dynamics simulation (aiMD) has the potential to combine the insights from both methods for a deeper understanding. In this work, a series of aiMD simulations has been performed to study the interaction between an oxidized organic model dye, LEG4, and an electrolyte containing iodide ions as reducing agents. Dynamic Mulliken and natural spin population analyses show that two iodide ions, I–···I–, are required for dye regeneration. It was found that a distance between I–···I– of less than 6.5 Å at site 1 benefits from the electrostatic environment of the triphenylamine group of the LEG4 dye, and a corresponding distance of 4.8 Å at site 2 is essential for the dye regeneration process to take place. The rate constants of the LEG4 regeneration by two iodine ions range from 105 to 1012 s–1, spanning a window in which results from both experimental and static theoretical calculations fall. It is also verified that the probability of electron transfer from a radical I2– to the oxidized LEG4 dye is extremely low due to the rapid electron back-transfer. However, it has been found that the addition of an additional iodide ion at a distance of 5 Å with respect to the radical I2– opens the pathway for the reduction of the oxidized LEG4 dye with an associated formation of I3–. The current results highlight the necessity for a dynamical approach for a full understanding of the regeneration process.

Exploring the effect of attractive and repulsive magnetic field on electricity generation and microbial community in microbial fuel cells

External magnetic field technology enhances microbial electrochemical reactions in biological processes. This study added Neodymium-Iron-Boron magnets to the outside of a double-chamber cubic microbial fuel cell (MFC) to explore the attractive or repulsive magnetic field effects at various intensities (0, 60, and 120 mT) on MFC performance. The results show that an extra 120 mT repulsive magnetic field can generate a peak power density of 144 mW/m2 and a maximum current density of 1558 mA/m2. This value is 45 and 8 times higher, respectively, compared without adding the magnetic field. Moreover, adding 120 mT repulsive magnetic field can increase coulombic efficiency (CE) to 63.0%, which is higher than the CE of 25.9% without magnetic field addition. Taxonomy profiling classification results show that Geobacter and Pseudomonas, which can achieve e-pili and redox mediators, were the domain microorganism community. Magnetic fields enhance the electron movement efficiency through extracellular electron transfer mechanisms, including e-pili and redox mediators provided by the exoelectrogenic microorganism to enlarge the chemical oxygen demand removal efficiency and CE value as well as increase the electron transfer probability to the electrode.

Multiple invivo Effects of Cadmium on Photosynthetic Electron Transport in Pea Plants.

The inhibitory effects of cadmium (CdSO4 ) on the primary photosynthetic processes were studied invivo in Pisum sativum by using Multi-function Plant Efficiency Analyser (M-PEA-2). Photosynthetic parameters related to photosystem (PS) II, PS I and intersystem electron carriers were calculated from the light-induced kinetics of prompt chlorophyll a fluorescence (OJIP transient), delayed chlorophyll a fluorescence (DF), and 820 nm modulated reflection (MR). Low-dose exposure to cadmium (20 μm CdSO4 for 48 h) reduced probability of electron transfer from plastoquinones to the terminal electron acceptors of PSI (δRo ) accompanied by a decrease in the rate of P700 + and PC reduction (Vred ) and the magnitude of the I2 step on the DF kinetics. Electron transport through PSI remained unaltered. The obtained results allowed us to propose existence of the potential site of inhibition of photosynthetic electron flow by cadmium between PSII and PSI. We propose to use parameters δRo , Vred , and I2 /I1 as sensitive indicators of an early contamination by heavy metals.

Dynamics of Collisions and Adsorption in the Stochastic Electrochemistry of Emulsion Microdroplets.

Current-time recordings of emulsified toluene microdroplets containing 20 mM Ferrocene (Fc), show electrochemical oxidation peaks from individual adsorption events on disk microelectrodes (5 μm diameter). The average droplet diameter (∼0.7 μm) determined from peak area integration was close to Dynamic Light Scattering measurements (∼1 μm). Random walk simulations were performed deriving equations for droplet electrolysis using the diffusion and thermal velocity expressions from Einstein. The simulations show that multiple droplet-electrode collisions, lasting ∼0.11 μs each, occur before a droplet wanders away. Updating the Fc-concentration at every collision shows that a droplet only oxidizes ∼0.58% of its content in one collisional journey. In fact, it would take ∼5.45 × 106 collisions and ∼1.26 h to electrolyze the Fc in one droplet with the collision frequency derived from the thermal velocity (∼0.52 cm/s) of a 1 μm-droplet. To simulate adsorption, the droplet was immobilized at first contact with the electrode while the electrolysis current was computed. This approach along with modeling of instrumental filtering, produced the best match of experimental peaks, which were attributed to electrolysis from single adsorption events instead of multiple consecutive collisions. These results point to a heightened sensitivity and speed when relying on adsorption instead of collisions. The electrochemical current for the former is limited by the probability of adsorption per collision, whereas for the latter, the current depends on the collision frequency and the probability of electron transfer per collision (J. Am. Chem. Soc. 2017, 139, 16923-16931).

An All-Atom Theory of Electron Transfer at Nanocrystal/Molecule Interfaces: A Hybrid LCAO/DFT Approach

Interfacial electron transfer (IET) probabilities and rates between CdSe and CdS nanocrystals of diameters 2, 4, and 6 nm, and an anthraquinone dimer (AQ2H+), have been studied. To account for elec...

Charge separation and singlet fission in covalently linked diketopyrrolopyrrole derivatives and triphenylamine triad in solution

A covalently linked push-pull type triad containing two unsymmetrical electron donors, triphenylamine (TPA) and benzothiophene (BT), and diketopyrrolopyrrole (DPP), an electron acceptor, through thiophene spacer has been synthesized (BT-DPP-TPA(7)) and ultrafast relaxation dynamics of the triad has been explored in solution phase by various spectroscopic methods. Steady-state and time-resolved emission studies show the efficient fluorescence quenching of the DPP entity of as prepared BT-DPP-TPA(7) triad. The negative free energy values comprising the redox potentials and singlet state energy of BT-DPP-TPA(7) revealed the probability of electron transfer from the singlet ground state of TPA to the excited singlet state of DPP. Femtosecond transient absorption (fsTA) spectroscopic studies confirmed the formation of charge separation state by detecting triphenylamine radical cation as electron-transfer transients. The rate of charge separation, kCS, is (109−108 s−1) observed to be increasing from nonpolar to polar solvents and the rate of charge recombination, kCR, was found to be slower (μs time scale) in polar solvents like DMF and chloroform, than that in hexane, non-polar solvent (ns time scale). This novel aspect could be due to asymmetrically designed push-pull type triad, a feature that was not evident in push-pull triad constructed using symmetric TPA as electron donors. Furthermore, fsTA studies also demonstrate, for the first time, that the DPP derivatives, TDPP(4) and BT-DPP-TPA(7), both undergo singlet fission (SF) event (S→TT) in 100−200 ps time scale in solution phase for the solution of concentration above ∼100 μM. These results may pave the new avenue for device design comprising DPP derivatives.

Configuration mixing upon reorganization of dihedral angle induces rapid intersystem crossing in organic photoredox catalyst.

A long excited state lifetime is a desirable quality of photocatalysts because it enables a higher probability of energy or electron transfer from the photocatalyst to a substrate. However, achieving a long lifetime in organic (metal-free) catalysts is challenged by competing rapid nonradiative relaxation from excited states and relatively slow intersystem crossing into long-lived states with different spin multiplicity. In this work, we propose an intersystem crossing mechanism in heavy-metal free photocatalyst that results from reorganization of a dihedral angle between moieties. The relaxation of orthogonality of the dihedral angle and increasing the orbital overlap between the two components of the molecule changes the coupling between the configurations of singlet and triplet states, which in turn results in larger spin orbit coupling between the two manifolds as the molecule twists. We predict that this enables intersystem crossing to outcompete the singlet state lifetime.

Nonspecific magnetic biological effects: A model assuming the spin-orbit coupling.

The magnetic response of a particle that tunnels in a double-well potential is considered. The Hamiltonian of the model includes the Zeeman, spin-orbit, and other interactions. The spin state changes due to the motion of electrons in the electric field rather than the action of the magnetic field of nucleus on the electrons. At realistic values of the model parameters, the spin-orbit interaction leads to magnetic effects that resemble those in the well-known radical pair mechanism (RPM) model. In particular, the probability of electron transfer depends on the direction of the magnetic field. At the same time, the model under consideration has distinctions that make it reasonable when searching for a mechanism of nonspecific magnetic biological effects. In particular, unlike in the RPM, the magnitude of the magnetic effect is not limited to a narrow range of the hyperfine interaction. The model enables molecular rotations. This could explain an asymmetry in response to the inversion of the magnetic field vector, which has been observed in experiments.

Theoretical investigation of the ion-induced polarization-charge influence on resonant charge transfer

This work addresses the modeling of the resonant neutralization of positive alkali-metal ions near metal surfaces. Usually the charge, induced by a positive ion, is taken into account by means of point image charge, located symmetrically to the image plane. Such an approach describes the ion level shift near the metal surfaces and gives reasonable values of the alkali-metal ion neutralization probability on the surfaces with a projected band gap, e.g., Au(111), Cu(111), and Ag(111). In this paper, we show that the induced charge is better described by means of a negatively charged plane located near the surface. This charged plane forms a potential barrier, the inclusion of which in the numerical model significantly reduces the calculated electron transfer probability and allows us to reach quantitative agreement with experimental data for free-electron surfaces, e.g., Cu(110). This repulsive potential barrier generates ion-induced states, by means of which the resonant neutralization of positive alkali-metal ions on free-electron surfaces occurs. Ion-induced states are not so important for surfaces with a projected band gap, because in this case ion neutralization occurs via well-known surface states.

Sensitive Determination of Acetaminophen in the Presence of Dopamine and Pyridoxine Facilitated by their Extent of Interaction with Single‐walled Carbon Nanotubes

AbstractSingle‐walled carbon nanotubes (SWCNTs) were immobilized on glassy carbon (GC) electrode by drop casting The resulting modified electrode (represented as GC/SWCNTs) efficiently oxidizes acetaminophen (AC), dopamine (DA) and pyridoxine (PY) by decreasing the respective oxidation potentials and increasing peak currents in comparison to bare GC electrode. The extent of lowering of overpotentials is in the order of AC>PY>DA, in agreement with the order of decrease in the HOMO‐LUMO energy gap (ΔE) of these analytes, as determined from Density Functional Theory (DFT) calculations. DFT calculations further reveal that due to the interaction of the analytes on the SWCNT(10,10) there is a negative charge density transfer (higher probability of electron transfer, lower ΔE value) to the frontier molecular orbitals of the analytes, which eases their oxidation. Since AC, DA and PY oxidize distinctly at distinct potential values, the present SWCNTs modified electrodes could be used to simultaneously determine them. Cyclic voltammetry, differential pulse voltammetry and amperometry techniques are utilized to understand the electrochemical characteristics of the analytes (AC, DA and PY) and subsequent sensing of them at the GC/SWCNTs electrode. The electrode is then applied to the determination of AC as a case study. Sensitivity, detection limit and linear calibration range for the AC are found to be 7.9 μA μM−1 cm−2, 1.1 μM and 2.0–100.0 μM, respectively. The increased electroactive surface area of the GC/SWCNTs increases the oxidation peak currents and hence increases the sensitivity of the determination.

Effects of surface hydration on the electron injection rate from graphene to anatase and rutile TiO2 surfaces

The effect of hydration of anatase (0 0 1), and rutile (0 0 1), (1 0 1) and (1 1 0) surfaces of TiO2 on the rate of electron capture from an adsorbed graphene sheet is elucidated by means of computation at a level of tight-binding density functional theory. Initially, the clean surfaces are allowed to interact with bulk water. Following an equilibration period, the first solvation shell is exposed to vacuum at 300 K for a sufficiently long period of time to allow any weakly bound water molecules to evaporate or be displaced from the surface. The resultant hydroxylated and originally clean surfaces are used for studying the interaction with a graphene sheet. Comparison of the calculated surface-graphene interaction energies and electron transfer probabilities of a cold electron to clean and hydroxylated surfaces shows that the water-sourced OH layer of these surfaces acts as an insulator in interfacial charge transport of the cold electron.

Effect of Vibrational Transitions on the Nonthermal Charge Transfer Probability

In the framework of the stochastic approach, the effect of transitions between the vibrational sublevels of products on the ultrafast dynamics of “hot” (non-thermal) electron transfer in donor — acceptor complexes dissolved in a polar medium has been investigated. An analytical expression has been obtained for the probability of electron transfer, which takes into account the transition between the vibrational states of products and the mutual influence of sinks. Quantitative estimates of the scale of the mutual influence of sinks on the probability of electron transfer are made.

Low energy secondary electron induced damage of condensed nucleotides.

Radiation damage and stimulated desorption of nucleotides 2'-deoxyadenosine 5'-monophosphate (dAMP), adenosine 5'-monophosphate (rAMP), 2'-deoxycytidine 5'-monophosphate (dCMP), and cytidine 5'-monophosphate (rCMP) deposited on Au have been measured using x-rays as both the probe and source of low energy secondary electrons. The fluence dependent behavior of the O-1s, C-1s, and N-1s photoelectron transitions was analyzed to obtain phosphate, sugar, and nucleobase damage cross sections. Although x-ray induced reactions in nucleotides involve both direct ionization and excitation, the observed bonding changes were likely dominated by the inelastic energy-loss channels associated with secondary electron capture and transient negative ion decay. Growth of the integrated peak area for the O-1s component at 531.3 eV, corresponding to cleavage of the C-O-P phosphodiester bond, yielded effective damage cross sections of about 23 Mb and 32 Mb (1 Mb = 10-18 cm2) for AMP and CMP molecules, respectively. The cross sections for sugar damage, as determined from the decay of the C-1s component at 286.4 eV and the glycosidic carbon at 289.0 eV, were slightly lower (about 20 Mb) and statistically similar for the r- and d- forms of the nucleotides. The C-1s component at 287.6 eV, corresponding to carbons in the nucleobase ring, showed a small initial increase and then decayed slowly, yielding a low damage cross section (∼5 Mb). Although there is no statistical difference between the sugar forms, changing the nucleobase from adenine to cytidine has a slight effect on the damage cross section, possibly due to differing electron capture and transfer probabilities.

Photoelectric Properties of Film Composites Based on Poly(Vinyl Butyral) and Heterometallic Complexes

Photosensitive polymeric film composites based on nonphotoconducting poly(vinyl butyral) doped with heterometallic Cu/M complexes (M = Ca, Sr) were synthesized and investigated. These composites possessed photoconducting and photovoltaic properties and electron-type photoconductivity. The greater photocurrent for composites with complexes having shorter distances between the nearest Cu metal centers was attributed to the greater probability of electron transfer between these centers.

Pushing SmI2 Reactions towards the Limit‐ Entropy Driven Reduction of a Benzene Ring

AbstractIn order to reduce a benzene ring, alkali metals or similar strong reducing agents are needed. We have found that SmI2, which is considered to be a relatively mild reagent, can also perform this task. This is achieved by attaching a side arm of either ethanolamine or ethylenediamine to a benzene ring. These side arms strongly coordinate to SmI2, holding it in close vicinity to the benzene ring. As a result, the probability of electron transfer from the SmI2 to the benzene ring is significantly increased. However, at the same time, this proximity also enhances the rate of the back electron transfer. In order to slow the rate of this step, small amounts of water and Et3N were added to the reaction mixture. The two typical products of the classical Birch reduction of benzene were obtained with a yield as high as 95 %. This method was also applied to the corresponding chlorobenzene and methylbenzoate where the reactions were much enhanced but functionality reduction prevailed over ring reduction. It is remarkable that going from a termolecular to a unimolecular reaction is more effective than excitation of the SmI2 around 600 nm which is equivalent to ca. 47 kcal/mol.

Light intensity dependent photosynthetic electron transport in eelgrass (Zostera marina L.)

Responses of electron transport to three levels of irradiation (20, 200, and 1200 μmol photons m−2 s−1 PAR; exposures called LL, ML and HL, respectively) were investigated in eelgrass (Zostera marina L.) utilizing the chlorophyll a fluorescence technique. Exposure to ML and HL reduced the maximum quantum yield of photosystem II (PSII) (Fv/Fm) and the maximum slope decrease of MR/MRO (VPSI), indicating the occurrence of photoinhibition of both PSII and photosystem I (PSI). A comparatively slow recovery rate of Fv/Fm due to longer half-life recovery time of PSII and 40% lower descending amplitude compared to other higher plants implied the poor resilience of the PSII. Comparatively, PSI demonstrated high resilience and cyclic electron transport (CEF) around PSI maintained high activity. With sustained exposure, the amplitudes of the kinetic components (L1 and L2), the probability of electron transfer from PSII to plastoquinone pool (ψET2o), and the connectivity among PSII units decreased, accompanied by an enhancement of energy dissipation. Principle component analysis revealed that both VPSI and Fv/Fm contributed to the same component, which was consistent with high connectivity between PSII and PSI, suggesting close coordination between both photosystems. Such coordination was likely beneficial for the adaption of high light. Exposure to LL significantly increased the activity of both PSI and CEF, which could lead to increased light harvesting. Moreover, smooth electron transport as indicated by the enhancement of L1, L2, ψET2o and the probability of electron transport to the final PSI acceptor sides, could contribute to an increase in light utilization efficiency.

Confinement effects on the electron transfer cross section: a study of He2+ colliding on atomic H

In this work, the role of pressure produced by the surrounding conditions of neighboring atoms on the charge transfer cross section in the interaction of ions with atoms is studied. The effect of pressure on the target is simulated by a spherical confinement cavity model with the target atom at its center. The electron transfer probability is obtained by a time-dependent solution to the Schrödinger equation by means of a finite-difference approach and the Crank–Nicolson propagation method. Results are presented for the benchmark system HeH() under different confinement conditions. Within this first-order approach to pressure effects, it is found that the radial region of the electron capture probability is affected by the cavity, meanwhile the rotational part of the interaction is only slightly modified. Furthermore, Stückelberg oscillations are preserved as a function of the impact parameter and only its intensity is reduced with a slight shift towards low impact parameters as pressure is increased. The pressure effect is larger when the electron interaction on the target is restricted to within the cavity than when it acts also outside the cavity. In addition, the larger the pressure, the smaller the electron capture cross section. The numerical results are interpreted by an analytic two-state model that supports the numerical findings.