Combining metal-microbe and microbe-microbe dual direct electron transfer on Fe(0)-cathode of bio-electrochemical system to enhance anaerobic digestion of cellulose wastewater

Considering that cathode of microbial electrochemical system (MES) is a good electrons source for methane production via direct/indirect electron transfer to electroactive microorganisms, and that Fe(0) is also a confirmed electron donor for some electroactive microorganisms through metal-microbe direct electron transfer (DET), Fe(0)-cathode was equipped into an MES digester to enhance cathodic methane production. The results of this study indicated that the potential DET participator, Clostridium possibly obtained electrons directly from Fe(0)-cathode via metal-microbe electrons transfer, then transferred electrons directly to the definite DET participators, Methanosarcina/Methanothrix via microbe-microbe electrons transfer for CH₄ production. In addition, Methanobacterium is another specially enriched methanogen on Fe(0)-cathode, which might obtain electrons directly from Fe(0)-cathode to produce CH₄ via metal/electrode-microbe DET. The increment of conductivity of cathodic sludge in Fe(0)-cathode MES digester (R1) further confirmed the enrichment of electroactive microorganisms participating in DET process. As a consequence, a higher CH₄ production (1205–1508 mL/d) and chemical oxygen demand (COD) removal (79.0%-93.8%) were achieved in R1 compared with graphite-cathode MES digester (R2, 720–1090 mL/d and 63.6%-85.6%) and the conventional anaerobic digester (R3, 384–428 mL/d and 35.2%-41.0%). In addition, energy efficiency calculated indicated that the output energy of CH₄ production was 8.16 folds of electricity input in Fe(0)-cathode MES digester.     

Radiationless electron transfer in molten-salt systems

Theoretical concepts are applied to the effects of cations outside the coordination sphere on electron transfer between complexes in solution and in melts; the activation energy and electron-transfer matrix element are altered.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 719–723, November–December, 1990.     

Photoinduced electron transfer in photozyme systems

Photozymes are novel water-soluble polymers usually constructed by copolymerization of a mixture of water-soluble and water-insoluble comonomers, some of which contain chromophores capable of absorbing light and transmitting the excitation energy by means of the antenna effect to selected traps. The interactions between the hydrophobic and hydrophilic groups in the polymer with water cause the formation of hypercoiled pseudomicellar conformations of the polymer coil, leading to hydrophobic regions or pockets in the interior of the macromolecular coil. If the water contains hydrophobic organic molecules, they will locate preferentially in these hydrophobic polymer microdomains, and in the presence of light they can be photochemically transformed into useful products with high efficiency and selectivity. This paper reviews some recent results on photochemical reactions initiated by photoinduced electron transfer in these novel systems, and their possible commercial applications to pollution abatement, and solar production of hydrogen from water.     

Control of electron transfer in supramolecular systems

The fluorescence quantum yield of zinc porphyrin (ZnP) covalently linked to 9,10-bis(phenylethynyl)anthracene (AB) is strongly dependent upon the solvent properties. The bichromophoric system ZnP-AB exhibits 'normal' zinc porphyrin fluorescence in solvents that cannot coordinate to the central zinc atom. In contrast, if a Lewis base, such as pyridine, is added to a sufficiently polar solvent, the fluorescence is significantly quenched. Picosecond transient absorption measurements, in conjunction with fluorescence quenching and cyclic voltammetric measurements, suggest that the quenching mechanism is intramolecular electron transfer from ZnP to AB. The charge separated state. ZnP*+-AB*-, has a lifetime of not more than 220 ps before recombining. If a secondary electron acceptor, iron(III) porphyrin (FeP), is covalently connected to the AB unit, a second electron transfer from AB*- to FeP occurs and the charge separated state, ZnP*+-AB-FeP*-, has a lifetime of at least 5 ns. This demonstrates that electron transfer might be sensitively tuned (switched on) by specific solvent effects.     

Femtosecond intermolecular electron transfer in condensed systems

We have investigated the ultrafast intermolecular electron transfer (ET) from an electron-donating solvent (aniline (AN) or N, N-dimethylaniline (DMA)) to an excited dye molecule (oxazines (Nile blue and oxazine 1) or coumarins). A non-exponential time dependence was observed in AN and can be explained by solvent reorientation and nuclear motion of the reactants. However, in DMA, a single exponential process was observed for Nile blue (160 fs) and oxazine 1 (280 fs), which can be explained by assuming that the rate of ET is limited mainly by ultrafast nuclear motion. A clear substituent effect on intermolecular ET was observed for the 7-aminocoumarins. When the alkyl chain on the 7-amino group is extended and a hexagonal ring with the benzene moiety is formed, the rate of ET is reduced by three orders of magnitude. This effect can be explained by a change in the free energy difference of the reaction and by the vibrational motion of the amino group.     

Bridge-dependent electron transfer in porphyrin-based donor-bridge-acceptor systems.

Photoinduced electron transfer in donor-bridge-acceptor systems with zinc porphyrin (or its pyridine complex) as the donor and gold(III) porphyrin as the acceptor has been studied. The porphyrin moieties were covalently linked with geometrically similar bridging chromophores which vary only in electronic structure. Three of the bridges are fully conjugated pi-systems and in a fourth, the conjugation is broken. For systems with this bridge, the quenching rate of the singlet excited state of the donor was independent of solvent and corresponded to the rate of singlet energy transfer expected for a F?rster mechanism. In contrast, systems with a pi-conjugated bridging chromophore show a solvent-dependent quenching rate that suggests electron transfer in the Marcus normal region. This is supported by picosecond transient absorption measurements, which showed formation of the zinc porphyrin radical cation only in systems with pi-conjugated bridging chromophores. On the basis of the Marcus and Rehm-Weller equations, an electronic coupling of 5-20 cm(-)(1) between the donor and acceptor is estimated for these systems. The largest coupling is found for the systems with the smallest energy gap between the donor and bridge singlet excited states. This is in good agreement with the coupling calculated with quantum mechanical methods, as is the prediction of an almost zero coupling in the systems with a nonconjugated bridging chromophore.     

Tunnelling electron transfer from bulk electron centers of magnesium oxide to adsorbed molecules of nitrous oxide

Tunneling electron transfer from bulk F⁺-centers of MgO to molecules of N₂O adsorbed on MgO surface has been detected and studied.

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F⁺- N₂O, .

     

Quantum chemical approach to electron transfer in molecular systems

A theoretical treatment of electron transfer in and between molecules is presented. The nuclei are assumed to move classically. A time-dependent electron probability density is calculated using general equations given by Nikitin. Variational methods of different kinds may be employed in these equations. In the present paper some examples are studied at the extended Hückel level for the systems H₂-H ₂ ⁺ , H₂-O^2–-H ₂ ⁺ , H₂-S^2–-H ₂ ⁺ and H₂-H₂-H ₂ ⁺ .     

Theory of electron transfer in systems with intermediate link

A theory is proposed for electron transfer through an intermediate link, the theory being based on solution of the time-dependent wave equation of the system with the exact Hamiltonian by assigning a wave function in form of a linear combination of wave functions of the initial state (electron on the donor), intermediate state (electron on the intermediate link), and final state (electron on the acceptor). The squares of the moduli of the time-dependent coefficients in these wave functions represent the probabilities of finding electrons in the indicated states. The coefficients have been determined by means of Laplace transforms, and an expression has been obtained for the rate of electron transfer through the intermediate link.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 3, pp. 288–293, May–June, 1985.     

Bioenergetics and extracellular electron transfer in microbial fuel cells and microbial corrosion

Bioenergetics can be used to analyze the theoretical voltage output of a microbial fuel cell (MFC) and the thermodynamic driving force in microbiologically influenced corrosion (MIC). MFCs involve both inward and outward extracellular electron transfer (EET), whereas only inward EET is behind EET–MIC caused by an electroactive biofilm's harvest of energy from a metal. EET is often rate-limiting, and it is an important process in microbial energy metabolism. EET is critical to the understanding of MFCs and EET–MIC bioelectrochemical processes. Many advances have been made in the past decade on EET by MFC and MIC researchers. Gene manipulations have been used to improve EET in MFCs, leading to enhanced energy output. They have also been used to elucidate the EET processes for better understanding of EET–MIC, which aids in MIC analysis and decision-making of biocide treatment and its efficacy assessment. Researchers are starting to integrate EET knowledge from both fields.     

TTF-porphyrin dyads as novel photoinduced electron transfer systems

A TTF-linked porphyrin dyad and its zinc complex have been synthesized as novel photosystems with a redox-active pendant. The two chromophores of these dyads are not interactive in the absorption spectra, but the fluorescence of the porphyrin chromophore is dramatically quenched by intramolecular electron transfer from the TTF pendant.     

Adjustable bidirectional extracellular electron transfer between Comamonas testosteroni biofilms and electrode via distinct electron mediators

Bidirectional extracellular electron transfer of strain Comamonas testosteroni I2 was for the first time investigated with electrochemical active biofilms developed under different conditions. The electrochemical active biofilm developed under microbial fuel cell conditions was capable of anodic electron transfer via attached redox species with standard potential of 0.04 V (vs. SCE). Meanwhile the above redox species lost its catalytic capability when the biofilm was developed under a constant potential (− 0.4 V vs. SCE). Instead, the microbe adjusted its electron transfer strategy to a soluble shuttle (standard potential − 0.20 V vs. SCE) and enabled a cathodic current. Air exposure experiment verified that the soluble shuttle at negative potential had a positive response to the oxygen; meanwhile the anodic electron transfer via the attached species was rarely influenced.     

Spectroscopic detection of excited-state electron transfer in porphyrin viologen systems

Pulsed laser excitation (354.7 nm, 10 ns pulse) of a pyridyltritolylporphyrin chromophore covalently linked to a dibenzylviologen, Bz₂V²⁺, electron acceptor (porphyrin—viologen, PV²⁺) in CH₃CN leads to intramolecular electron transfer quenching of the porphyrin singlet excited state within the laser pulsewidth to reduce the linked Bz₂V²⁺ to Bz₂V^+·. Transient Bz₂V^+· can be detected directly by resonance Raman spectroscopy. The same transient features are obtained from pulsed laser excitation of a mixture of porphyrin (P) and dibenzylviologen in CH₃CN where Bz₂V²⁺ quenches the porphyrin fluorescence, establishing bimolecular excited state electron transfer quenching to yield Bz₂V^+·. Confirmation of our assignment of the transient Bz₂V^+· comes from comparison of the spectra with the resonance Raman spectrum of an authentic sample of Bz₂V^+·, and of electrochemically reduced PV²⁺ which has been spectroscopically confirmed to form PV^+·. Fluorescence lifetime determinations for PV²⁺ and P yield a rate constant for intramolecular electron transfer, k_et = 8 × 10⁷ s⁻¹, consistent with the ability to observe electron transfer within the laser pulsewidth     

Modulate photoinduced electron transfer efficiency of bipolar dendritic systems

Covalent linkage of dendritic carbazole-based donors and 1,3,4-oxdiazole-based acceptors renders novel bipolar dendrimers that can efficiently facilitate the photoinduced electron transfer (PET) process. Photodynamic studies indicated that the PET rate of bipolar dendrimers DA1 and DA2 can be modulated by the number of acceptors presented in the molecule.     

微孔分子筛主-客体复合体系及其电子转移过程

沸石分子筛是一类带有规则微孔结构的硅铝酸盐晶体,因其骨架具有独特的电子给受能力而备受关注．由此,许多以微孔分子筛为主体的电子转移体系被构建并深入研究．与溶液相中自由基的快速衰减不同,产生于微孔分子筛内部的自由基受其纳米孔道的限制,具有有限的迁移率和较长的寿命,有助于人们利用传统光谱技术确定反应机理．本文主要对当前微孔分子筛主-客体复合体系中的电子转移过程和机制的研究现状加以论述．     

Graphene oxide dispersions in organic solvents

The dispersion behavior of graphene oxide in different organic solvents has been investigated. As-prepared graphite oxide could be dispersed in N, N-dimethylformamide, N-methyl-2-pyrrolidone, tetrahydrofuran, and ethylene glycol. In all of these solvents, full exfoliation of the graphite oxide material into individual, single-layer graphene oxide sheets was achieved by sonication. The graphene oxide dispersions exhibited long-term stability and were made of sheets between a few hundred nanometers and a few micrometers large, similar to the case of graphene oxide dispersions in water. These results should facilitate the manipulation and processing of graphene-based materials for different applications.     

Quinone-modified polymers as electron transfer relay systems in amperometric glucose sensors

A polysiloxane and an acrylonitrile–ethylene copolymer with covalently attached p-hydroquinone/benzoquinone moieties were prepared and tested as electron transfer relay systems in amperometric glucose biosensors. Using experiments involving cyclic voltammetry and stationary potential measurements, it was shown that the polysiloxane relay system can efficiently mediate electron transfer from reduced glucose oxidase to a conventional carbon-paste electrode. Sensors containing this polymeric relay system and glucose oxidase respond rapidly to low (<0.1 mm) glucose concentrations, with steady state current responses achieved in less than 1 min. The acrylonitrile–ethylene copolymer was found to be less efficient than the polysiloxane system at mediating the electron transfer from reduced glucose oxidase to the electrode. The dependence of the sensor response on the nature of the polymer backbone is discussed.