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Electron Transfer Reactions (electron + transfer_reaction)
Selected AbstractsStable ,Floating' Air Diffusion Biocathode Based on Direct Electron Transfer Reactions Between Carbon Particles and High Redox Potential LaccaseFUEL CELLS, Issue 4 2010S. Shleev Abstract We report on the assembly and characterisation of a high potential, stable, mediator-less and cofactor free biocathode based on a fungal laccase (Lc), adsorbed on highly dispersed carbonaceous materials. First, the stability and activity of Trametes hirsuta Lc immobilised on different carbon particles were studied and compared to the solubilised enzyme. Based on the experimental results and a literature analysis, the carbonaceous material BM-4 was chosen to design efficient and stable biocatalysts for the production of a ,floating' air diffusion Lc-based biocathode. Voltammetric characteristics and operational stability of the biocathode were investigated. The current density of oxygen reduction at the motionless biocathode in a quiet, air saturated citrate buffer (100,mM, pH 4.5, 23,°C) reached values as high as 0.3,mA,cm,2 already at 0.7,V versus NHE. The operational stability of the biocathode depended on the current density of the device. For example, at low current density (20,,A,cm,2), the biocathode lost only 5× of its initial power after 1 month of continuous operation. However, when the device was polarised at 150,mV it lost more than 32× of its initial power in just 10,min. We also found that co-immobilisation of Lc and peroxidase on highly dispersed carbon materials could protect the biocatalyst from rapid inactivation by hydrogen peroxide produced during electrocatalytic reactions at high-current densities. [source] The gem-Dialkyl Effect in Electron Transfer Reactions: Rapid Synthesis of Seven-Membered Rings Through an Electrochemical Annulation.CHEMINFORM, Issue 42 2005Jeffrey B. Sperry Abstract For Abstract see ChemInform Abstract in Full Text. [source] Photoinduced Electron Transfer Reactions by SmI2 in THF: Luminescence Quenching Studies and Mechanistic InvestigationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2005Edamana Prasad Dr. Abstract Photoluminescence quenching studies of SmI2 in dry THF were carried out in the presence of five different classes of compounds: ketone, alkyl chloride, nitrile, alkene and imine. The free energy change (,G,0) of the photoinduced electron transfer (PET) reactions was calculated from the redox potentials of the donor (SmI2) and acceptors. The bimolecular quenching constants (kq) derived from the Stern,Volmer experiments parallel the free energy changes of the PET processes. The observed quenching constants were compared with the theoretically derived electron transfer rate constants (ket) from Marcus theory and found to be in good agreement when a value of ,=167 kJ,mol,1 (40 kcal,mol,1) was used for the reorganization energy of the system. A careful comparison of the excited state dynamics of SmII in the solid state to the results obtained in solution (THF) provides new insight in to the excited states of SmII in THF. The activation parameters determined for the PET reactions in SmI2/1-chlorobutane system are consistent with a less ordered transition state and high degree of bond reorganization in the activated complex compared to similar ground state reactions. Irradiation studies clearly show that SmI2 acts as a better reductant in the excited state and provides an alternative pathway for rate enhancement in known and novel functional group reductions. [source] Theoretical investigation of charge transfer excitation and charge recombination in acenaphthylene,tetracyanoethylene complexINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2003Hai-Bo Yi Abstract Ab initio calculations were performed to investigate the charge separation and charge recombination processes in the photoinduced electron transfer reaction between tetracyanoethylene and acenaphthylene. The excited states of the charge-balanced electron donor,acceptor complex and the singlet state of ion pair complex were studied by employing configuration interaction singles method. The equilibrium geometry of electron donor,acceptor complex was obtained by the second-order Møller,Plesset method, with the interaction energy corrected by the counterpoise method. The theoretical study of ground state and excited states of electron donor,acceptor complex in this work reveals that the S1 and S2 states of the electron donor,acceptor complexes are excited charge transfer states, and charge transfer absorptions that corresponds to the S0 , S1 and S0 , S2 transitions arise from ,,,* excitations. The charge recombination in the ion pair complex will produce the charge-balanced ground state or excited triplet state. According to the generalized Mulliken,Hush model, the electron coupling matrix elements of the charge separation process and the charge recombination process were obtained. Based on the continuum model, charge transfer absorption and charge transfer emission in the polar solvent of 1,2-dichloroethane were investigated. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 23,35, 2003 [source] Onium Salts of Amino Acids as Co-Initiators in Photoinduced Free-Radical PolymerizationMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2006Franciszek, cigalski Abstract Summary: The onium salts of selected aliphatic and aromatic amino acids were investigated as electron donors in photoinduced free radical polymerization, in conjunction with either DIBF or BP as sensitizer. The laser flash photolysis experiments unmistakably documented that the free radical formation occurs via an electron transfer reaction from the amino acid salt to the chromophore triplet state. The kinetic studies clearly showed that either the DIBF or BP onium salts of selected aliphatic and aromatic sulfur-containing amino acids exhibit a significant increase in the efficiency of free-radical polymerization of TMPTA as compared to non-sulfur-containing co-initiators and that the efficiency of all tested electron donors is only slightly dependent on the cation type coupled with co-initiators tested. Possible mechanism for the free radical photoinitiated polymerization. [source] Effect of a nonhost-selective toxin from Alternaria alternata on chloroplast-electron transfer activity in Eupatorium adenophorumPLANT PATHOLOGY, Issue 5 2005S. Chen AAC-toxin, a putative nonhost-selective phytotoxin, was obtained from Alternaria alternata causing a brown leaf spot disease of Crofton weed (Eupatorium adenophorum). The effect of AAC-toxin on the electron transfer reaction of chloroplasts showed that the activity of photosystem II, but not photosystem I, was completely inhibited by the toxin. AAC-toxin affected the following chlorophyll fluorescence parameters: coefficient of photochemical quenching (qP), the half-time value of fluorescence rise, and the O,J,I,P fluorescence induction kinetics curve, but not the ratio values of Fv/Fm (the quantum yield of photosystem II) and the half-time value of fluorescence quenching. It was concluded that the toxin inhibited electron transfer from QA to QB (primary and secondary quinine acceptors of photosystem II) in photosystem II by competing with QB for the binding site in D1 protein on the thylakoid membrane. [source] Redox Activity and Structural Transition of Heptyl Viologen Adlayers on Cu(100),CHEMPHYSCHEM, Issue 7 2010Min Jiang Dr. Abstract The redox behaviour and potential-dependent adsorption structure of heptyl viologen (1,1,-diheptyl-4,4,-bipyridinium dichloride, DHV2+) on a Cu(100) electrode was investigated in a chloride-containing electrolyte solution by cyclic voltammetry (CV) and in situ electrochemical scanning tunneling microscopy (EC,STM). The dicationic DHV molecules generate a few pairs of current waves in CV measurements which are ascribed to two typical one-electron transfer steps. STM images obtained in a KCl-containing electrolyte solution disclose a well-ordered c(2×2) chloride adlayer on a Cu(100) electrode surface. After injecting DHV2+ molecules into the KCl electrolyte solution, a highly ordered 2D "dot-array" structure in STM images emerges on the c(2×2)-Cl modified Cu(100) electrode surface. DHV2+ molecules spontaneously arrange themselves with their molecular planes facing the electrode surface and their long molecular axis parallel to the step edge. Such adsorption structure can be described by mirror domains and rotational domains which stably exist between 200 mV and ,100 mV. One-electron reduction of the dications DHV2+ around ,150 mV causes a phase transition from a ,dot-array' assembly to a stripe pattern formed by DHV.+ radical monocations in STM images which has a bilayer structure. With a further decrease of the applied electrode potential, the structure of the DHV.+ adlayer undergoes a change from a loose stripe phase to a more compact stripe phase, a subsequent decay of the compact structure, and finally the formation of a new dimer phase. A further electron transfer reaction at ,400 mV causes the formation of an amorphous phase on the chloride free electrode surface. In a reverse anodic sweep, the reproduction of the ordered DHV.+ stacking phase occurs again on top of the chloride lattice. [source] Electrochemistry of Mitochondria: A New Way to Understand Their Structure and FunctionELECTROANALYSIS, Issue 14 2008Jing Zhao Abstract In this article, electrochemistry of mitochondria is achieved. Cyclic voltammograms of freshly prepared mitochondria were obtained by immobilizing mitochondria together with glutaraldehyde and bovine serum albumin on the surface of a pyrolytic graphite electrode. Two pairs of redox peaks could be observed which were ascribed to the electron transfer reactions of cytochrome c and FAD/FADH2. Study of submitochondrial particles was also conducted, which could confirm the results of the study of the entire mitochondria. The redox wave of NADH could be obtained due to the destruction of the membrane of mitochondria. We have also checked the function of succinate in mitochondria by employing the electrochemical method. This work is not only the first to be able to obtain the direct electrochemistry of mitochondria, but is also beneficial to the further understanding of the structure and function of mitochondria in vitro. [source] Insights into the design of a hybrid system between Anabaena ferredoxin-NADP+ reductase and bovine adrenodoxinFEBS JOURNAL, Issue 4 2003Merche Faro The opportunity to design enzymatic systems is becoming more feasible due to detailed knowledge of the structure of many proteins. As a first step, investigations have aimed to redesign already existing systems, so that they can perform a function different from the one for which they were synthesized. We have investigated the interaction of electron transfer proteins from different systems in order to check the possibility of heterologous reconstitution among members of different chains. Here, it is shown that ferredoxin-NADP+ reductase from Anabaena and adrenodoxin from bovine adrenal glands are able to form optimal complexes for thermodynamically favoured electron transfer reactions. Thus, electron transfer from ferredoxin-NADP+ reductase to adrenodoxin seems to proceed through the formation of at least two different complexes, whereas electron transfer from adrenodoxin to ferredoxin-NADP+ reductase does not take place due because it is a thermodynamically nonfavoured process. Moreover, by using a truncated adrenodoxin form (with decreased reduction potential as compared with the wild-type) ferredoxin-NADP+ reductase is reduced. Finally, these reactions have also been studied using several ferredoxin-NADP+ reductase mutants at positions crucial for interaction with its physiological partner, ferredoxin. The effects observed in their reactions with adrenodoxin do not correlate with those reported for their reactions with ferredoxin. In summary, our data indicate that although electron transfer can be achieved in this hybrid system, the electron transfer processes observed are much slower than within the physiological partners, pointing to a low specificity in the interaction surfaces of the proteins in the hybrid complexes. [source] Kinetics and mechanism of oxidation of 2-mercaptosuccinic acid by bis(,-oxo)- manganese(III,IV)-cyclam complex in aqueous medium: Influence of externally added copper(II)INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2004Nizamuddin Shaikh Kinetic studies on the oxidation of 2-mercaptosuccinic acid by dinuclear [Mn2III/IV(,-O)2(cyclam)2](ClO4)3] (1) (abbreviated as MnIII,MnIV) (cyclam = 1,4,8,11-tetraaza-cyclotetradecane) have been carried out in aqueous medium in the pH range of 4.0,6.0, in the presence of acetate buffer at 30°C by UV,vis spectrophotometry. In the pH region, two species of complex 1 (MnIII,MnIV and MnIII,MnIVH, the later being ,-O protonated form) were found to be kinetically significant. The first-order dependence of the rate of the reactions on [Thiol] both in presence and absence of externally added copper(II) ions, first-order dependence on [Cu2+] and a decrease of rate of the reactions with increase in pH have been rationalized by suitable sequence of reactions. Protonation of ,-O bridge of 1 is evidenced by the perchloric acid catalyzed decomposition of 1 to mononuclear Mn(III) and Mn(IV) complex observed by UV,vis and EPR spectroscopy. The kinetic features have been rationalized considering Cu(RSH) as the reactive intermediate. EPR spectroscopy lends support for this. The formation of a hydrogen bonded outer-sphere adduct between the reductant and the complex in the lower pH range prior to electron transfer reactions is most likely to occur. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 170,177 2004 [source] Hydrolysis of aliphatic naphthalene diimides: effect of charge placement in the side chainsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2008Michelle B. Kim Abstract Water-soluble naphthalene diimides (NDIs) have found uses in a wide variety of applications including as electron acceptors in electron transfer reactions and as molecules that undergo spontaneous organization in aqueous solution. Many studies have looked at their interaction with nucleic acids including work with DNA duplexes, triplexes, quadruplexes, hairpins, and DNA,RNA heteroduplexes. In many of these interactions the NDIs serve as threading intercalators. Herein we describe the reversible hydroxide-catalyzed hydrolysis of NDIs bearing aliphatic side chains, with ring opening first to the monoimide and then to the diamide. Examples with N -methylpyrrolidinium groups placed two (1) and three (5) atoms from the central core were studied. The Ka values for the first and second hydrolyses for 1 were 2.5,±,0.2,×,105 and 2.0,±,0.1,×,102,M,1, respectively; for 5 they were 1.4,±,0.1,×,105 and 44,±,2,M,1, respectively. NDI 1 hydrolyzed 6.8 times faster than 5. The rates for the first and second ring opening of 1 in 100,mM hydroxide measured by stopped-flow were 17.0,±,0.2 and 0.53,±,0.01,s,1, respectively. Capillary electrophoresis in borate buffer showed separation of the diimide and monoimide with the former eluting first. Nuclear magnetic resonance (NMR) showed both the syn and anti isomers of the diamide species. Overall, the rate of hydrolysis of the NDI is increased when the cationic charge is moved closer to the NDI core. Copyright © 2008 John Wiley & Sons, Ltd. [source] Catalysis in electron transfer reactions: facts and mechanistic insights,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2002Shunichi Fukuzumi Abstract Catalysis in electron transfer reactions between electron donors and acceptors is described and the important mechanistic insight is provided by showing a number of examples of both thermal and photochemical reactions that involve metal ion-catalyzed electron transfer processes as the rate-determining steps. The quantitative measure of Lewis acidity of metal ions was obtained from the gzz values of ESR spectra of superoxide,metal ion complexes which vary significantly depending on the type of metal ions. Copyright © 2002 John Wiley & Sons, Ltd. [source] Looking for a contribution of the non-equilibrium solvent polarization to the activation barrier of the SN2 reactionJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 6 2002Jan S. Jaworski Abstract The solvent effect on the activation free energy of the Finkelstein reaction between methyl iodide and Cl, ions was analysed in terms of the recent Marcus theory unifying the SN2 and the electron transfer reactions. The homolytic bond dissociation energy and the related resonance energy of interaction of the states seem to be almost solvent independent. The sum of the work term wr and the solvent reorganization energy ,0/4 depends strongly on the solvent acidity parameter, e.g. ETN, describing the solvation/desolvation of anions. However, after removing the contribution of the specific solvation the linear increase of the remaining part of ,0/4 with the Pekar factor, describing the non-equilibrium solvent polarization, was observed for six aprotic solvents. Copyright © 2002 John Wiley & Sons, Ltd. [source] Ultraviolet Resonance Raman Microprobe Spectroscopy of Photosystem IIPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2008Jun Chen Photosystem II (PSII) carries out photosynthetic oxygen production and is responsible for the maintenance of aerobic, heterotrophic life. In PSII, protein amino acid residues play an important role in the light-driven electron transfer reactions. Here, we describe an approach to enhancing vibrational signals from PSII proteins through ultraviolet resonance Raman (UVRR) and a microprobe jet flow technique. Our work shows that pump-probe UVRR can be used to monitor intermediates during photosynthetic oxygen evolution. [source] Molecular dissection of photosystem I in higher plants: topology, structure and functionPHYSIOLOGIA PLANTARUM, Issue 3 2003Poul Erik Jensen Photosystem I catalyses the light driven electron transfer from plastocyanin/cytochrome c6 on the lumenal side of the thylakoid membrane to ferredoxin/flavodoxin at the stromal side. Photosystem I of higher plants consists of 18 different protein subunits. Fourteen of these make up the chlorophyll a -containing core, which also contains the cofactors involved in the electron transfer reactions, and four make up the peripheral chlorophyll a/b -containing antenna. Arabidopsis plants devoid of the nuclear-encoded photosystem I subunits have been obtained either by different suppression techniques or by insertional knock-out of the genes. This has allowed a detailed analysis of the role and function of the individual subunits. This review is focused on recent developments in the role of the individual subunit in the structure and function of photosystem I of higher plants. [source] Redox-dependent structural changes in archaeal and bacterial Rieske-type [2Fe-2S] clustersPROTEIN SCIENCE, Issue 12 2002Nathaniel J. Cosper Abstract Proteins containing Rieske-type [2Fe-2S] clusters play important roles in many biological electron transfer reactions. Typically, [2Fe-2S] clusters are not directly involved in the catalytic transformation of substrate, but rather supply electrons to the active site. We report herein X-ray absorption spectroscopic (XAS) data that directly demonstrate an average increase in the iron,histidine bond length of at least 0.1 Å upon reduction of two distantly related Rieske-type clusters in archaeal Rieske ferredoxin from Sulfolobus solfataricus strain P-1 and bacterial anthranilate dioxygenases from Acinetobacter sp. strain ADP1. This localized redox-dependent structural change may fine tune the protein,protein interaction (in the case of ARF) or the interdomain interaction (in AntDO) to facilitate rapid electron transfer between a lower potential Rieske-type cluster and its redox partners, thereby regulating overall oxygenase reactions in the cells. [source] Review: Studies of ferric heme proteins with highly anisotropic/highly axial low spin (S = 1/2) electron paramagnetic resonance signals with bis-Histidine and histidine-methionine axial iron coordination,BIOPOLYMERS, Issue 12 2009Giorgio Zoppellaro Abstract Six-coordinated heme groups are involved in a large variety of electron transfer reactions because of their ability to exist in both the ferrous (Fe2+) and ferric (Fe3+) state without any large differences in structure. Our studies on hemes coordinated by two histidines (bis-His) and hemes coordinated by histidine and methionine (His-Met) will be reviewed. In both of these coordination environments, the heme core can exhibit ferric low spin (electron paramagnetic resonance EPR) signals with large gmax values (also called Type I, highly anisotropic low spin, or highly axial low spin, HALS species) as well as rhombic EPR (Type II) signals. In bis-His coordinated hemes rhombic and HALS envelopes are related to the orientation of the His groups with respect to each other such that (i) parallel His planes results in a rhombic signal and (ii) perpendicular His planes results in a HALS signal. Correlation between the structure of the heme and its ligands for heme with His-Met axial ligation and ligand-field parameters, as derived from a large series of cytochrome c variants, show, however, that for such a combination of axial ligands there is no clear-cut difference between the large gmax and the "small g -anisotropy" cases as a result of the relative Met-His arrangements. Nonetheless, a new linear correlation links the average shift ,,, of the heme methyl groups with the gmax values. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 1064,1082, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | |||||||||||||