Electron Transfer System Research Articles

Multiple electron transfer systems in oxygen reducing biocathodes revealed by different conditions of aeration/agitation

Oxygen reducing biocathodes were formed at −0.2V/SCE (+0.04V/SHE) from compost leachate. Depending on whether aeration was implemented or not, two different redox systems responsible for the electrocatalysis of oxygen reduction were evidenced. System I was observed at low potential (−0.03V/SHE) on cyclic voltammetries (CVs). It appeared during the early formation of the biocathode (few hours) and resisted the hydrodynamic conditions induced by the aeration. System II was observed at higher potential on CV (+0.46V/SHE); it required a longer lag time (up to 10days) and quiescent conditions to produce an electrochemical signal. The hydrodynamic effects produced by the forced aeration led to its extinction. From their different behaviors and examples in the literature, system I was identified as being a membrane-bound cytochrome-related molecule, while system II was identified as a soluble redox mediator excreted by the biofilm. This study highlighted the importance of controlling the local hydrodynamics to design efficient oxygen reducing biocathodes able to operate at high potential.

Heterologous expression of fungal cytochromes P450 (CYP5136A1 and CYP5136A3) from the white-rot basidiomycete Phanerochaete chrysosporium: Functionalization with cytochrome b5 in Escherichia coli.

Cytochromes P450 from the white-rot basidiomycete Phanerochaete chrysosporium, CYP5136A1 and CYP5136A3, are capable of catalyzing oxygenation reactions of a wide variety of exogenous compounds, implying their significant roles in the metabolism of xenobiotics by the fungus. It is therefore interesting to explore their biochemistry to better understand fungal biology and to enable the use of fungal enzymes in the biotechnology sector. In the present study, we developed heterologous expression systems for CYP5136A1 and CYP5136A3 using the T7 RNA polymerase/promoter system in Escherichia coli. Expression levels of recombinant P450s were dramatically improved by modifications and optimization of their N-terminal amino acid sequences. A CYP5136A1 reaction system was reconstructed in E. coli whole cells by coexpression of CYP5136A1 and a redox partner, NADPH-dependent P450 reductase (CPR). The catalytic activity of CYP5136A1 was significantly increased when cytochrome b5 (Cyt-b5) was further coexpressed with CPR, indicating that Cyt-b5 supports electron transfer reactions from NAD(P)H to CYP5136A1. Notably, P450 reaction occurred in E. coli cells that harbored CYP5136A1 and Cyt-b5 but not CPR, implying that the reducing equivalents required for the P450 catalytic cycle were transferred via a CPR-independent pathway. Such an "alternative" electron transfer system in CYP5136A1 reaction was also demonstrated using purified enzymes in vitro. The fungal P450 reaction system may be associated with sophisticated electron transfer pathways.

Heterogeneous Asymmetric Oxidation Catalysis Using Hemophore HasApf. Application in the Chemoenzymatic Deracemization of sec-Alcohols with Sodium Borohydride

This study aims to demonstrate the coordination of oxygen regarding the hemophore HasApf expressed by Escherichia coli cells, which appears to create an unlikely oxygen-activating system in HasA due to the already-coordinated iron. In the asymmetric oxidation of rac-1-(6-methoxynaphthalen-2-yl)ethanol (rac-1) using dissolved oxygen, the signals at g-values of 2.8, 2.22, and 1.72 in the electron spin resonance (ESR) spectra disappeared in conjunction with the promotion of oxoferric (FeIII−O–O−) species in the distal site. These results suggest that the iron of porphyrin/Fe may be oxidized in water, leading to exhibition of greater asymmetric oxidation activity in the promotion of oxoferryl (FeIV=O) species. A ketone (~50% chemical yield) produced from (R)-(−)-sec-alcohol can be desymmetrized by NaBH4 in aqueous medium at 40 °C (>99% enantiomer excess, ee, >90% chemical yield) in the absence of NAD(P). Therefore, HasA can be regenerated via successive asymmetric catalytic events through an incorporated iron electron-transfer system in the presence of oxygen: FeII + O2 → FeIII−O–O− → FeIV=O (oxidizing rac-1) → FeII + H2O. This process is similar to a Fenton reaction. The use of a HasA-catalytic system with an incorporated redox cofactor for asymmetric oxidation overcomes the apparent difficulties in working with pure dehydrogenase enzyme/redox cofactor systems for biotransformations.

Self and directed assembly: people and molecules.

Self-assembly and directed-assembly are two very important aspects of supramolecular chemistry. As a young postgraduate student working in Canada with Tom Fyles my introduction to Supramolecular Chemistry was through the self-assembly of phospholipid membranes to form vesicles for which we were developing unimolecular and self-assembling transporter molecules. The next stage of my development as a scientist was in Japan with Seiji Shinkai where in a “Eureka” moment, the boronic acid templating unit (directed-assembly) of Wulff was combined with photoinduced electron transfer systems pioneered by De Silva. The result was a turn-on fluorescence sensor for saccharides; this simple result has continued to fuel my research to the present day. Throughout my career as well as assembling molecules, I have enjoyed bringing together researchers in order to develop collaborative networks. This is where molecules meet people resulting in assemblies worth more than the individual “molecule” or “researcher”. My role in developing networks with Japan was rewarded by the award of a Daiwa-Adrian Prize in 2013 and I was recently rewarded for developing networks with China with an Inaugural CASE Prize in 2015.

ChemInform Abstract: Self and Directed Assembly: People and Molecules

AbstractReview: [124 refs.

Multistep Electron Transfer Systems Containing [2.2]- or [3.3]Paracyclophane.

Paracyclophanes (PCPs), which exhibit interesting properties due to their transannular interactions, have been employed as a spacer in various electron transfer (ET) systems. In the present work, we investigated ET processes in dyads and triads containing [2.2]PCP or [3.3]PCP as donors to study their properties in multistep ET processes. The dyad molecules of PCP and 1,8-naphthalimide (NI) as a photosensitizing electron acceptor exhibited charge separation (CS) upon excitation of NI. In addition, triads of NI, PCP, and carbazole showed charge shift after an initial CS, thus confirming multistep ET. In this study, we demonstrated that use of [3.3]PCP in place of [2.2]PCP enhanced the initial CS rate. Lower oxidation potentials and a smaller reorganization energy for [3.3]PCP are shown to be key factors for this enhanced CS rate. Both of these properties are closely related to the strained structure of PCP; hence, the present results demonstrate the importance of strain in ET chemistry.

Geobacter sulfurreducens adapts to low electrode potential for extracellular electron transfer

Microbial extracellular electron transfer (EET) occurring in natural and engineering processes is attracting increasing interests. While a meaningful question for bioenergetics, microbial physiology and microbial electrochemical systems; less is known about the lower limit of electron acceptor reduction potential for EET. It is also unclear how microbes adapt to weak electron acceptors. This study evaluated Geobacter sulfurreducens biofilms grown with an electrode poised at −0.25V vs. SHE. This potential was found to be sufficient for microbial metabolism and proliferation. The turnover cyclic voltammetries found that these biofilms had a half-saturation potential of −0.242±0.004V, in contrast to −0.151±0.003V for that of the biofilms grown under 0.2V. For the biofilms grown under 0.2V, differential pulse voltammetry showed that the metabolic current was mediated by interfacial cofactors with mid-point potential around −0.16V performing single-electron electron transfer (ET). The major electron conduits for the biofilms respiring under −0.25V had mid-point potentials of −0.22V or −0.26V, which appeared to perform two-electron ET. Under the non-turnover condition, both biofilms showed similar patterns in voltammograms and the low-potential conduits largely disappeared for the biofilms grown under −0.25V. Transcriptome analysis identified 17 cytochrome-c genes significantly up-regulated for the biofilms grown under −0.25V, together with many other genes linked to the ET system. It was also noted that, lowering the poised potential from −0.25V to −0.28V (the fuel standard oxidation potential) did not fully inhibit microbial respiration.

Proton-coupled electron hopping in Ru-modified P. aeruginosa azurin.

We constructed two artificial multiple-step electron transfer (hopping) systems based on Pseudomonas aeruginosa azurin where a tyrosine (YOH) is situated between Ru(2,2'-bipyridine)2(imidazole)(histidine) and the native copper site: RuH107YOH109 and RuH124-YOH122. We investigated the rates of Cu(I) oxidation by flash-quench generated Ru(III) over a range of conditions that probed the role of proton-coupled oxidation/reduction of YOH in the reaction. Rates of Cu(I) oxidation were enhanced over single-step electron transfer by factors between 3 and 80, depending on specific scaffold and buffer conditions.

On the regulative role of the glutamate receptor in mitochondria.

The purpose of this work was to study the regulative role of the glutamate receptor found earlier in the brain mitochondria. In the present work a glutamate-dependent signaling system with similar features was detected in mitochondria of the heart. The glutamate-dependent signaling system in the heart mitochondria was shown to be suppressed by γ-aminobutyric acid (GABA). The GABA receptor presence in the heart mitochondria was shown by golding with the use of antibodies to α- and β-subunits of the receptor. The activity of glutamate receptor was assessed according to the rate of synthesis of hydrogen peroxide. The glutamate receptor in mitochondria could be activated only under conditions of hypoxic stress, which in model experiments was imitated by blocking Complex I by rotenone or fatty acids. The glutamate signal in mitochondria was shown to be calcium- and potential-dependent and the activation of the glutamate cascade was shown to be accompanied by production of hydrogen peroxide. It was discovered that H2O2 synthesis involves two complexes of the mitochondrial electron transfer system - succinate dehydrogenase (SDH) and fatty acid dehydrogenase (ETF:QO). Thus, functions of the glutamate signaling system are associated with the system of respiration-glycolysis switching (the Pasteur-Crabtree) under conditions of hypoxia.

A perturbation theoretic approach to the Riccati equation for the Floquet energies, spectral intensities, and cutoff energy of harmonic generation in photon emission from nonadiabatic electron-transfer dynamics driven by infrared CW laser fields

A complicated yet interesting induced photon emission can take place by a nonadiabatic intramolecular electron transfer system like LiF under an intense CW laser [Y. Arasaki, S. Scheit, and K. Takatsuka, J. Chem. Phys. 138, 161103 (2013)]. Behind this phenomena, the crossing point between two potential energy curves of covalent and ionic natures in diabatic representation is forced to oscillate, since only the ionic potential curve is shifted significantly up and down repeatedly (called the Dynamical Stark effect). The wavepacket pumped initially to the excited covalent potential curve frequently encounters such a dynamically moving crossing point and thereby undergoes very complicated dynamics including wavepacket bifurcation and deformation. Intramolecular electron transfer thus driven by the coupling between nonadiabatic state-mixing and laser fields induces irregular photon emission. Here in this report we discuss the complicated spectral features of this kind of photon emission induced by infrared laser. In the low frequency domain, the photon emission is much more involved than those of ultraviolet/visible driving fields, since many field-dressed states are created on the ionic potential, which have their own classical turning points and crossing points with the covalent counterpart. To analyze the physics behind the phenomena, we develop a perturbation theoretic approach to the Riccati equation that is transformed from coupled first-order linear differential equations with periodic coefficients, which are supposed to produce the so-called Floquet states. We give mathematical expressions for the Floquet energies, frequencies, and intensities of the photon emission spectra, and the cutoff energy of their harmonic generation. Agreement between these approximate quantities and those estimated with full quantum calculations is found to be excellent. Furthermore, the present analysis provides with notions to facilitate deeper understanding for the physical and mathematical mechanisms of the present photon emission.

Actovegin, a non-prohibited drug increases oxidative capacity in human skeletal muscle

Actovegin, a deproteinized haemodialysate of calf blood, is suggested to have ergogenic properties, but this potential effect has never been investigated in human skeletal muscle. To investigate this purported ergogenic effect, we measured the mitochondrial respiratory capacity in permeabilized human skeletal muscle fibres acutely exposed to Actovegin in a low and in a high dose. We found that Actovegin, in the presence of complex I-linked substrates increased the oxidative phosphorylation (OXPHOS) capacity significantly in a concentration-dependent manner (19 ± 3, 31 ± 4 and 45 ± 4 pmol/mg/s). Maximal OXPHOS capacity with complex I and II-linked substrate was increased when the fibres were exposed to the high dose of Actovegin (62 ± 6 and 77 ± 6 pmol/mg/s) (p < .05). The respiratory capacity of the electron transfer system as well as Vmax and Km were also increased in a concentration-dependent manner after Actovegin exposure (70 ± 6, 79 ± 6 and 88 ± 7 pmol/mg/s; 13 ± 2, 25 ± 3 and 37 ± 4 pmol/mg/s; 0.08 ± 0.02, 0.21 ± 0.03 and 0.36 ± 0.03 mM, respectively) (p < .05). In summary, we report for the first time that Actovegin has a marked effect on mitochondrial oxidative function in human skeletal muscle. Mitochondrial adaptations like this are also seen after a training program in human subjects. Whether this improvement translates into an ergogenic effect in athletes and thus reiterates the need to include Actovegin on the World Anti-Doping Agency's active list remains to be investigated.

Availability of Farmers’ Markets and Supplemental Nutrition Assistance Program/Electronic Benefit Transfer Systems and Associations With Rurality, Poverty, Race/Ethnicity, and Obesity Among North Carolina Counties

Increasing the number of farmers’ markets and implementing Electronic Benefit Transfer (EBT) systems for the Supplemental Nutrition Assistance Program (SNAP) at more farmers’ markets have been suggested as strategies to overcome food access issues, but little is known about their availability in the rural South. This study examines differences in availability of farmers’ markets and SNAP/EBT at markets by county-level rural/urban classification, percentage poverty, percentage racial/ethnic minority, and percentage obese residents in North Carolina counties. Data were collected using a cross-sectional survey. Though results related to rurality and economic status are mixed, regression analyses indicate that the percentage of African American residents is inversely associated with the number of markets and number of markets that accept EBT. Results suggest that access to farmers’ markets varies in North Carolina, and additional research is needed to determine whether this impacts obesity.

Assessment of Use of Diversification Strategy in Enhancing Competitive Performance at Equity Bank, Kenya

Banks and other financial institutions operate in a dynamic environment where opportunities and challenges arise in equal measure. A critical factor that presents challenges and opportunities for the banks and other financial institutions is competition. To beat competitors in the dynamic market and stay abreast with the ever changing market demands, it is imperative for banks to rethink, rework and adjust their diversification strategies appropriately in order to remain relevant in the market. A diversification strategy helps organizations to spread portfolio risks by combining a variety of investments. In fact, organizations that seeks to survive various business cycles or to stay ahead of competition look for ways to diversify and in return, grow, survive and perform well in the long term. This study sought to assess the use of diversification strategy in enhancing competitive performance at Equity Bank Kenya. The study was based on; Technology Acceptance Model, Diversification Strategy Model and the Systems Theory. To achieve the objective of the study, the researcher sought to establish how banccasurance, electronic money transfer and agency banking affects competitive performance of the bank. The researcher used a survey and a descriptive study design. The population of the study included branch managers, corporate managers and divisional managers in charge of Banccassurance, electronic money transfers and Agency banking at Equity Bank while the study sample was selected from the said population by a simple random sampling technique. Data was collected using structured questionnaires that were administered through drop and pick technique. The collected data was analyzed using SPSS version 20. A linear regression analysis was conducted to guide inferences based on diversification strategies in relation to competitive performance of Equity Bank Kenya. The results were presented using the tables appropriately. The results of the study implied that the first null hypothesis was not rejected the second null hypothesis was not rejected, the third null hypothesis was not rejected. The study findings further indicated that the competitive performance of equity bank was not significantly influenced by 0.342 bancassurance, -0.317 electronic money transfers, -0.080 agency banking. However, the study findings indicated that the diversification strategies jointly influenced the competitive performance of Equity Bank (t = -3.922; p < 0.05). It was therefore recommended that bank should innovate its bancassurance products and electronic money transfer systems, motivate employees better and use appropriate technologies that the clientele find to be useful and easy to use.

The FORCE Fitness Profile--Adding a Measure of Health-Related Fitness to the Canadian Armed Forces Operational Fitness Evaluation.

In 2013, the Canadian Armed Forces (CAF) implemented the Fitness for Operational Requirements of Canadian Armed Forces Employment (FORCE), a field expedient fitness test designed to predict the physical requirements of completing common military tasks. Given that attaining this minimal physical fitness standard may not represent a challenge to some personnel, a fitness incentive program was requested by the chain of command to recognize and reward fitness over and above the minimal standard. At the same time, it was determined that the CAF would benefit from a measure of general health-related fitness, in addition to this measure of operational fitness. The resulting incentive program structure is based on gender and 8 age categories. The results on the 4 elements of the FORCE evaluation were converted to a point scale from which normative scores were derived, where the median score corresponds to the bronze level, and silver, gold, and platinum correspond to a score which is 1, 2, and 3 SDs above this median, respectively. A suite of rewards including merit board point toward promotions and recognition on the uniform and material rewards was developed. A separate group rewards program was also tabled, to recognize achievements in fitness at the unit level. For general fitness, oxygen capacity was derived from FORCE evaluation results and combined with a measure of abdominal circumference. Fitness categories were determined based on relative risks of mortality and morbidity for each age and gender group. Pilot testing of this entire program was performed with 624 participants to assess participants' reactions to the enhanced test, and also to verify logistical aspects of the electronic data capture, calculation, and transfer system. The newly dubbed fitness profile program was subsequently approved by the senior leadership of the CAF and is scheduled to begin a phased implementation in June 2015.

Differences in mitochondrial function in homogenated samples from healthy and epileptic specific brain tissues revealed by high-resolution respirometry

Mitochondrial dysfunction and oxidative stress are strongly implicated in neurodegenerative diseases and epilepsy. Strikingly, neurodegenerative diseases show regional specificity in vulnerability and follow distinct patterns of neuronal loss. A challenge is to understand, why mitochondria fail in particular brain regions under specific pathological conditions. A potential explanation could be provided by regional or cellular specificity of mitochondrial function.We applied high-resolution respirometry to analyze the integrated Complex I- and II (CI and CII)-linked respiration, the activity of Complex IV, and the combined CI&II-linked oxidative phosphorylation (OXPHOS)- and electron-transfer system (ETS)-capacity in microsamples obtained from distinct regions of the mouse brain. We compared different approaches to assess mitochondrial density and suggest flux control ratios as a valid method to normalize respiration to mitochondrial density.This approach revealed significant differences of CI- and CII-linked OXPHOS capacity and coupling control between motor cortex, striatum, hippocampus and pons of naïve mice. CI-linked respiration was highest in motor cortex, while CII-linked respiration predominated in the striatum. To investigate if this method could also determine differences in normal and disease states within the same brain region, we compared hippocampal homogenates in a chronic epilepsy model. Three weeks after stereotaxic injection of kainate, there was a down-regulation of CI- and upregulation of CII-linked respiration in the resulting epileptic ipsilateral hippocampus compared to the contralateral one.In summary, respirometric OXPHOS analysis provides a very sensitive diagnostic approach using small amounts of distinct brain tissues. In a single assay, information is obtained on numerous OXPHOS parameters as indicators of tissue-specific mitochondrial performance.

Anilino-Substituted Multicyanobuta-1,3-diene Electron Acceptors: TICT Molecules with Accessible Conical Intersections.

A theoretical investigation based on DFT, TD-DFT, and CASSCF/CASPT2 methods has been carried out to elucidate the photophysics of two anilino-substituted pentacyano- and tetracyanobuta-1,3-dienes (PCBD and TCBD, respectively). These molecules exhibit exceptional electron-accepting properties, but their effective use in multicomponent systems for photoinduced electron transfer is limited because they undergo ultrafast (∼1 ps) radiationless deactivation. We show that the lowest-energy excited states of these molecules have a twisted intramolecular charge-transfer character and deactivate to the ground state through energetically accessible conical intersections (CIs). The topology of the lowest-energy CI, analyzed with a linear interpolation of the two branching-space vectors (g and h), indicates it is a sloped CI, ultimately responsible for the ultrafast deactivation of this class of compounds.

Adipose tissue mitochondrial respiration and lipolysis before and after a weight loss by diet and RYGB

To study adipose tissue mitochondrial respiration and lipolysis following a massive weight loss. High resolution respirometry of adipose tissue biopsies and tracer determined whole body lipolysis. Sixteen obese patients with type 2 diabetes (T2DM) and 27 without (OB) were studied following a massive weight loss by diet and Roux-en-Y gastric bypass (RYGB). The mitochondrial respiratory rates were similar in OB and T2DM, and the mass-specific oxygen flux increased significantly 4 and 18 months post-surgery (P < 0.05). With normalization to mitochondrial content, no differences in oxidative capacity after RYGB were seen. The ratio between the oxidative phosphorylation system capacity (P) and the capacity of the electron transfer system (E) increased 18 months after RYGB in both groups (P < 0.05). Lipolysis per fat mass was similar in the two groups and was increased (P < 0.05) and lipid oxidation during hyperinsulinemia decreased 4 months post-surgery. In T2DM, visceral fat mass was always higher relative to the body fat mass (%) compared to OB. Adipose tissue mitochondrial respiratory capacity increases with RYGB. Adipocytes adapt to massive weight loss by increasing the phosphorylation system ratio (P/E), suggesting an increased ability to oxidize substrates after RYGB. Lipolysis increases in the short term post-surgery, and insulin sensitivity for suppression of lipolysis increases with RYGB.

Dissipaton Equation of Motion with Controlled Truncation

This work aims at a priori accuracy controlled truncation to the dissipaton equation of motion formalism for non-perturbative quantum dissipative dynamics. A new truncation scheme is proposed by adopting the Markovian and high-temperature approximation similar to the Caldeira-Leggett master equation made at the termination level. An accuracy criterion to determine the truncation level is put forward via a Markovianicity analysis. Performances of both the new truncation scheme and the control criterion are illustrated via dynamics simulation of electron transfer systems.

Isobutanol production from an engineered Shewanella oneidensis MR-1.

Shewanella oneidensis MR-1 is one of the most well-known metal-reducing bacteria and it has been extensively studied for microbial fuel cell and bioremediation aspects. In this study, we have examined S. oneidensis MR-1 as an isobutanol-producing host by assessing three key factors such as isobutanol synthetic genes, carbon sources, and electron supply systems. Heterologous Ehrlich pathway genes, kivD encoding ketoisovalerate decarboxylase and adh encoding alcohol dehydrogenase, were constructed in S. oneidensis MR-1. Among the composition of carbon sources examined, 2% of N-acetylglucosamine, 1.5% of pyruvate and 2% of lactate were found to be the most optimal nutrients and resulted in 10.3 mg/L of isobutanol production with 48 h of microaerobic incubation. Finally, the effects of metal ions (electron acceptor) and direct electron transfer systems on isobutanol production were investigated, and Fe(2+) ions increased the isobutanol production up to 35%. Interestingly, deletion of mtrA and mtrB, genes responsible for membrane transport systems, did not have significant impact on isobutanol production. Finally, we applied engineered S. oneidensis to a bioelectrical reactor system to investigate the effect of a direct electron supply system on isobutanol production, and it resulted in an increased growth and isobutanol production (up to 19.3 mg/L). This report showed the feasibility of S. oneidensis MR-1 as a genetic host to produce valuable biochemicals and combine an electron-supplying system with biotechnological applications.

Electron transfer pathways in mixed-valence paracyclophane-bridged bis-triarylamine radical cations.

A series of paracyclophane (PC) bridged mixed-valence (MV) bis-triarylamine radical cations with different ([2.2], [3.3], [4.4]) linkers, with and without additional ethynyl spacers, have been studied by quantum-chemical calculations (BLYP35-D3/TZVP/COSMO) of ground-state structures, thermal electron-transfer barriers, hyperfine couplings, and lowest-lying excited states. Such PC-bridged MV systems are important intra-molecular model systems for inter-molecular electron transfer (ET) via π-stacked aromatics, since they allow enforcement of a more or less well-defined geometrical arrangement. Closely comparable ET barriers and electronic couplings for all [2.2] and [3.3] bridges are found for these class-II MV systems, irrespective of the use of pseudo-para and pseudo-meta connections. While the latter observation contradicts notions of quantum interference for off-resonant conduction through molecular wires, it agrees with the less intricate nodal structures of the highest occupied molecular orbitals. The ET in such MV systems may be more closely connected with hole conduction in the resonant regime. Computations on model cations, in which the [2.2] linkers have been truncated, confirm predominant through-space π-π electronic coupling. Systems with [4.4] PC bridges exhibit far more structural flexibility and concomitantly weaker electronic interactions between the redox centers.