Entire Electron Transfer Research Articles

Revealing electron transfer mechanisms of microelectrolysis for pollutant degradation by a dual electrode approach

Microelectrolysis has been proven to be a practical technology for the catalytic elimination of pollutants in wastewater. This study presents a research method focusing on the demonstration of electron transfer in microelectrolysis through a dual-electrode unit. 2,4-Dichlorophenol, sodium isobutyl xanthate and sodium diethyldithiocarbamate were taken as the typical pollutants for degradation. The results of electrochemical tests and quantum chemical calculations indicated that the ΔG among electron transfer steps proceeding on cathodes is the internal factor deciding the electron flow kinetics between the anode and cathode. The electron transfer rate is influenced by the electron transfer step with a ΔGmax in the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) of the cathode process and is restricted by the number of active sites on the cathode surface. Organics that react with intermediates formed in electrochemical chain reactions promote the entire electron transfer process between the poles, while organics that increase cathode electronegativity have the opposite effect. The cathode products of ·OH, ⋅H, ⋅OOH/⋅O2—, and H2O2, which are derived from the ORR and HER processes, are important for pollutant degradation. Catalysts can be selected and designed based on the required active substance and solution chemical environment for the degradation of targeted contaminants. This study elucidates the electrode kinetics of microelectrolysis, which can be the inspirational basis for catalyst design and technology application.

Ultra sensitive determination of Cadmium (II) using Ag-Au BMNPs–aptamer–modified glassy carbon electrodes (GCE)

PurposeThe purpose of this study is determination of cadmium using silver-gold bimetallic nanoparticles (Ag-Au BMNPs) and an aptamer modified glassy carbon electrode.Design/methodology/approachThe maximum response of modified electrode was obtained with, 50 mV pulse amplitude, 20 mV/s scan rate in phosphate buffer of pH 4.0. Ag-Au BMNPs, as the mediators improved electron transmit during the entire electron transfer process and the aptasensor response. Herein, the authors used aptamer as the capture probe to prepare an aptasensor with enhanced stability.FindingsThe proposed aptasensor exhibited a wide linearity to cadmium in the range of 0.001–0.100 µg/L with a low detection limit of 0.005×10−3 µg/L. The glassy carbon electrodes with Ag-Au BMNPs showed a lower detection limit.Originality/valueThis aptasensor has good reproducibility, stability and repeatability and is cost-effective to regenerate. The specificity and selectivity of the novel modified electrode is tested in the presence of other interfering metal ions such as Fe2+, Mn2+, Mg2+, Sb3+ and Bi3+. The aptasensor shows 10 times more sensitivity and selectivity for Cd2+ ions.

Involvement of the chloroplast plastoquinone pool in the Mehler reaction.

Light-dependent oxygen reduction in the photosynthetic electron transfer chain, i.e. the Mehler reaction, has been studied using isolated pea thylakoids. The role of the plastoquinone pool in the Mehler reaction was investigated in the presence of dinitrophenyl ether of 2-iodo-4-nitrothymol (DNP-INT), the inhibitor of plastohydroquinone oxidation by cytochrome b6/f complex. Oxygen reduction rate in the presence of DNP-INT was higher than in the absence of the inhibitor in low light at pH 6.5 and 7.6, showing that the capacity of the plastoquinone pool to reduce molecular oxygen in this case exceeded that of the entire electron transfer chain. In the presence of DNP-INT, appearance of superoxide anion radicals outside thylakoid membrane represented approximately 60% of the total superoxide anion radicals produced. The remaining 40% of the produced superoxide anion radicals was suggested to be trapped by plastohydroquinone molecules within thylakoid membrane, leading to the formation of hydrogen peroxide (H2 O2 ). To validate the reaction of superoxide anion radical with plastohydroquinone, xanthine/xanthine oxidase system was integrated with thylakoid membrane in order to generate superoxide anion radical in close vicinity of plastohydroquinone. Addition of xanthine/xanthine oxidase to the thylakoid suspension resulted in a decrease in the reduction level of the plastoquinone pool in the light. The obtained data provide additional clarification of the aspects that the plastoquinone pool is involved in both reduction of oxygen to superoxide anion radicals and reduction of superoxide anion radicals to H2 O2 . Significance of the plastoquinone pool involvement in the Mehler reaction for the acclimation of plants to light conditions is discussed.

Spin Selectivity in Electron Transfer in Photosystem I

Photosystem I (PSI) is one of the most studied electron transfer (ET) systems in nature; it is found in plants, algae, and bacteria. The effect of the system structure and its electronic properties on the electron transfer rate and yield was investigated for years in details. In this work we show that not only those system properties affect the ET efficiency, but also the electrons’ spin. Using a newly developed spintronic device and a technique which enables control over the orientation of the PSI monolayer relative to the device (silver) surface, it was possible to evaluate the degree and direction of the spin polarization in ET in PSI. We find high-spin selectivity throughout the entire ET path and establish that the spins of the electrons being transferred are aligned parallel to their momenta. The spin selectivity peaks at 300 K and vanishes at temperatures below about 150 K. A mechanism is suggested in which the chiral structure of the protein complex plays an important role in determining the high-spin selectivity and its temperature dependence. Our observation of high light induced spin dependent ET in PSI introduces the possibility that spin may play an important role in ET in biology.

Spin selectivity in electron transfer in photosystem I.

Photosystem I (PSI) is one of the most studied electron transfer (ET) systems in nature; it is found in plants, algae, and bacteria. The effect of the system structure and its electronic properties on the electron transfer rate and yield was investigated for years in details. In this work we show that not only those system properties affect the ET efficiency, but also the electrons' spin. Using a newly developed spintronic device and a technique which enables control over the orientation of the PSI monolayer relative to the device (silver) surface, it was possible to evaluate the degree and direction of the spin polarization in ET in PSI. We find high-spin selectivity throughout the entire ET path and establish that the spins of the electrons being transferred are aligned parallel to their momenta. The spin selectivity peaks at 300 K and vanishes at temperatures below about 150 K. A mechanism is suggested in which the chiral structure of the protein complex plays an important role in determining the high-spin selectivity and its temperature dependence. Our observation of high light induced spin dependent ET in PSI introduces the possibility that spin may play an important role in ET in biology.

Spin Selectivity in Electron Transfer in Photosystem I

AbstractPhotosystem I (PSI) is one of the most studied electron transfer (ET) systems in nature; it is found in plants, algae, and bacteria. The effect of the system structure and its electronic properties on the electron transfer rate and yield was investigated for years in details. In this work we show that not only those system properties affect the ET efficiency, but also the electrons’ spin. Using a newly developed spintronic device and a technique which enables control over the orientation of the PSI monolayer relative to the device (silver) surface, it was possible to evaluate the degree and direction of the spin polarization in ET in PSI. We find high‐spin selectivity throughout the entire ET path and establish that the spins of the electrons being transferred are aligned parallel to their momenta. The spin selectivity peaks at 300 K and vanishes at temperatures below about 150 K. A mechanism is suggested in which the chiral structure of the protein complex plays an important role in determining the high‐spin selectivity and its temperature dependence. Our observation of high light induced spin dependent ET in PSI introduces the possibility that spin may play an important role in ET in biology.

Aptasensor based on the synergistic contributions of chitosan–gold nanoparticles, graphene–gold nanoparticles and multi-walled carbon nanotubes-cobalt phthalocyanine nanocomposites for kanamycin detection

An electrochemical aptasensor was developed for the detection of kanamycin based on the synergistic contributions of chitosan-gold nanoparticles (CS-AuNPs), graphene-gold nanoparticles (GR-AuNPs) and multi-walled carbon nanotubes-cobalt phthalocyanine (MWCNTs-CoPc) nanocomposites. The aptasensor was prepared by sequentially dripping CS-AuNPs, GR-AuNPs and MWCNTs-CoPc nanocomposites onto a gold electrode (GE) surface. During the above process, these nanomaterials showed a remarkable synergistic effect towards the aptasensor. CS-AuNPs, GR-AuNPs and MWCNTs-CoPc as the nanocomposites mediator improved electron relay during the entire electron transfer process and the aptasensor response speed. The electrochemical properties of the modified processes were characterized by cyclic voltammetry (CV). The morphologies of the nanocomposites were characterized by scanning electron microscopy (SEM). The experimental conditions such as the concentration of the aptamer, the time, temperature and the pH were optimized. Based on the synergistic contributions of CS-AuNPs, GR-AuNPs and MWCNTs-CoPc nanocomposites, the proposed aptasensor displayed high sensitivity, high specificity, a low detection limit (5.8 × 10(-9) M) (S/N = 3) and excellent stability. It was successfully applied to the detection of kanamycin in real milk spiked samples.

Fragment-based Quantum Mechanical/Molecular Mechanical Simulations of Thermodynamic and Kinetic Process of the Ru2+-Ru3+ Self-Exchange Electron Transfer.

A fragment-based fractional number of electron (FNE) approach, is developed to study entire electron transfer (ET) processes from the electron donor region to the acceptor region in condensed phase. Both regions are described by the density-fragment interaction (DFI) method while FNE as an efficient ET order parameter is applied to simulate the electron transfer process. In association with the QM/MM energy expression, the DFI-FNE method is demonstrated to describe ET processes robustly with the Ru2+-Ru3+ self-exchange ET as a proof-of-concept example. This method allows for systematic calculations of redox free energies, reorganization energies, and electronic couplings, and the absolute ET rate constants within the Marcus regime.

Investigation of the apparent inefficiency of the coupling between Photosystem II electron transfer and ATP formation

The maximum phosphorylation efficiency achieved with synchronous turnovers of Photosystem II (PS II) in spinach chloroplast lamellae is 0.3 molecules of ATP per pair of electrons transferred. This is the same as the efficiency observed for PS II operating alone in continuous light and would seem to indicate less than 50% coupling efficiency. Flash-induced ATP synthesis associated with both photosystems acting in unison closely approaches twice the flash-induced ATP synthesis associated with the Photosystem-I-dependent oxidation of duroquinol (itself 0.6) and comes close to equalling the highest efficiency observed in steady-state PS I + PS II electron transport. The anomalously low coupling efficiency seen when PS II is operating alone can be overcome by a ΔpH of two units imposed before flash illumination, or by a prior flash series involving the entire electron transfer chain. In contrast, prior electron transport through PS II alone is only slightly effective in enhancing the coupling efficiency of subsequent PS II turnovers. (It should be noted that in all cases where supplementary energy was provided, either by a proton gradient or by prior illumination, this supplementary energy was always below the energetic threshold for phosphorylation. Furthermore, the enhancement of PS II coupling efficiency by supplementary energy persisted even after a large number of subsequent PS II-inducing flashes). The efficiency of flash-induced ATP synthesis associated with whole-chain electron transfer or with PS-I-dependent duroquinol oxidation is also enhanced by the supplementary energy, but only during the first few inefficient flashes, suggesting that in this case the supplementary energy may simply be contributing to the initial build-up of an energetic threshold for ATP synthesis. This cannot be the case when the same supplementary energy contributes to the efficiency of the PS II reaction, since the enhancement then persists for a long time and contributes to an essentially constant flash yield of ATP. Our results imply that during electron transfer involving both photosystems, PS II participates in generating about half of the total ATP, whereas it operates inefficiently only when operating alone. Since hydrogen ions produced by PS I are able to raise the efficiency of subsequent PS-II-dependent phosphorylation, at least some cooperation between the two photosystems takes place and this suggests some donation of protons from PS I to PS II. However, the inability of PS II alone to achieve high efficiency, even with prolonged pre-illumination, would seem to indicate some functional distinction of protons from the two photosystems.

Functional Organization of the Chlorophyll-Containing Complexes of Chlamydomonas reinhardi

The stepwise synthesis and assembly of photosynthetic membrane components in the y-1 mutant of Chlamydomonas reinhardi have been previously demonstrated (Ohad 1975 In Membrane Biogenesis, Mitochondria, Chloroplasts and Bacteria, Plenum, pp 279-350). This experimental system was used here in order to investigate the process of formation and interconnection of the energy collecting chlorophylls with the reaction centers of both photosystems I and II. The following measurements were carried out: photosynthetic electron flow at various light intensities, including parts or the entire electron transfer chain; analysis of the kinetics of fluorescence emission at room temperature and fluorescence emission spectra at 77 K, and electrophoretic separation of membrane polypeptides and chlorophyll protein complexes. Based on the data obtained it is concluded that: (a) each photosystem (PSI and PSII) contains, in addition to the reaction center, an interconnecting antenna and a main or light harvesting antenna complex; (b) the formation of the light harvesting complex, interconnecting antenna, and reaction centers for each photosystem can occur independently. (c) the interconnecting antennae link the light harvesting complexes with the respective reaction centers. In their absence, energy transfer between the light harvesting chlorophylls and the reaction centers is inefficient. The formation of the interconnecting antennae and efficient assembly of photosystem components occur simultaneously with the de novo synthesis of chlorophyll and at least three polypeptides, one translated in the cytoplasm and two translated in the chloroplast. The synthesis of these polypeptides was found to be light dependent.