Long-range Electron Transfer in Cobalt-labeled Cytochrome C


Book Description

In order to investigate the relationship between intramolecular electron transfer kinetics and redox site separation distance, a semisynthetic two-site donor/acceptor system, in which the distance between redox sites was fixed and known, was prepared. The approach taken involved attachment of the macrocyclic cage complex (Co(diAMsar)) $sp{3+}$ to various sites on the surface of horse heart cytochrome c. In this way, a second redox site, in addition to the heme, was introduced. Labelling of the protein at several surface sites, allowed several donor/acceptor distances to be evaluated within the same protein system. The attachment procedure utilized the water-soluble carbodiimide, 1-ethyl-3-(3-(dimethylamino)propyl) carbodiimide (EDC), to promote the condensation of carboxylates provided by the protein with pendant amine groups furnished by the cobalt complex, resulting in a stable amide-bond linkage. Purification of the reaction products allowed isolation of seven different singly modified derivatives. Tryptic peptide mapping experiments, coupled with the results of amino acid analysis, peptide sequencing, and FAB-MS (MS/MS), established the unique modification site in each of these cobalt-labeled proteins. The long-lived excited state of Ru(bpy)$sb3sp{2+}$ was used as both a powerful photooxidant and photoreductant in flash photolysis experiments designed to measure the intramolecular electron transfer rate constants (k$sb{rm et}$) from Co(II) $to$ Fe(III) in the thermodynamically unstable mixed-valence state. Although the results of molecular modelling studies established that derivatives spanned a range of heme edge-to-cobalt distances of 10 to 20 A, each displayed similar values for k$sb{rm et}$ (1-3 s$sp{-1}$). Possible explanations for this apparent lack of a distance dependence are discussed. The modified protein derivatives were also covalently attached to the surface of an edgeplane pyrolytic graphite electrode in an effort to electrochemically measure k$sb{rm et}$ using a second independent technique. Although this approach was unsuccessful in yielding a rate constant, due to the presence of large background currents, the procedure did allow for the development of a novel directional attachment procedure. Through proper control of such variables as reaction pH, or electrode potential, the protein was able to be attached in specific molecular orientations with respect to the electrode surface.




Electron Transfer in Chemistry and Biology


Book Description

Electron Transfer in Chemistry and Biology An Introduction to the Theory Alexander M. Kuznetsov Russian Academy of Sciences, Moscow, Russia Jens Ulstrup Technical University of Denmark, Lyngby, Denmark Electron transfer is perhaps the single most important physical event in chemical, electrochemical, photochemical, biochemical, and biophysical processes. The focus and ubiquity of electron transfer is intriguing and exciting but a coherent and comprehensive approach to this topic is at the same time a challenge. Electron Transfer in Chemistry and Biology provides a thorough and didactic approach to the theoretical basis of electron transfer phenomena. Not only does it offer a full introduction to this area and a discussion of its historical development, it also gives detailed explanations of difficult issues, for example, long-range electron transfers, stochastic and dynamic processes, and biological features. A wide variety of readers will find this volume of great interest, ranging from final year undergraduate students, postgraduate students and university lecturers, to research staff in numerous fields including medical companies, electronics industry, catalysis research and development, chemical industry and some hospitals.




Electron Transfer


Book Description

an integrated approach to electron transfer phenomena This two-part stand-alone volume in the prestigious Advances in Chemical Physics series provides the most comprehensive overview of electron transfer science today. It draws on cutting-edge research from diverse areas of chemistry, physics, and biology-covering the most recent developments in the field, and pointing to important future trends. This initial volume includes: * A historical perspective spanning five decades * A review of concepts, problems, and ideas in current research * Electron transfer in isolated molecules and in clusters * General theory, including useful algorithms * Spectra and electron transfer kinetics in bridged compounds The second volume covers solvent control, ultrafast electron transfer and coherence effects, molecular electronics, electron transfer and chemistry, and biomolecules. Electron transfer science has seen tremendous progress in recent years. Technological innovations, most notably the advent of femtosecond lasers, now permit the real-time investigation of intramolecular and intermolecular electron transfer processes on a time scale of nuclear motion. New scientific information abounds, illuminating the processes of energy acquisition, storage, and disposal in large molecules, clusters, condensed phase, and biophysical systems. Electron Transfer: From Isolated Molecules to Biomolecules is the first book devoted to the exciting work being done in nonradiative electron transfer dynamics today. This two-part edited volume emphasizes the interdisciplinary nature of the field, bringing together the contributions of pioneers in chemistry, physics, and biology. Both theoretical and experimental topics are featured. The authors describe modern approaches to the exploration of different systems, including supersonic beam techniques, femtosecond laser spectroscopy, chemical syntheses, and methods in genetic and chemical engineering. They examine applications in such areas as supersonic jets, solvents, electrodes, semi- conductors, respiratory and enzymatic protein systems, photosynthesis, and more. They also relate electron transfer and radiationless transitions theory to pertinent physical phenomena, and provide a conceptual framework for the different processes. Complete with over two hundred illustrations, Part One reviews developments in the field since its inception fifty years ago, and discusses electron transfer phenomena in both isolated molecules and in clusters. It outlines the general theory, exploring areas of the control of kinetics, structure-function relationships, fluctuations, coherence, and coupling to solvents with complex spectral density in different types of electron transfer processes. Timely, comprehensive, and authoritative, Electron Transfer: From Isolated Molecules to Biomolecules is an essential resource for physical chemists, molecular physicists, and researchers working in nonradiative dynamics today.