Electron transfer biological, mechanism

Moser, C.C., Dutton, P.L. Biological electron transfer measurement, mechanism, engineering requirements. In Quantum mechanical simulation methods for studying biological systems, D. Bicout and M. Field, eds. Springer, Berlin (1996) 201-214. 

Fluorescence imaging is the most powerful technique currently available for continuous observation of the dynamic intracellular processes of living cells. Fluorescein is widely employed as the core of various fluorescence probes used in imaging important biological effectors. Despite the extensive use of fluorescein derivatives and the importance of the applications, the mechanism that controls the quantum yield of fluorescence has not been fully established. I report herein photoinduced electron transfer (PeT) mechanism that can control the fluorescence quantum yields of fluorescein and boron dipyrromethene (BODIPY) derivatives. 

In conclusion therefore it is felt that electrochemistry does offer a valuable technique to study the electron-transfer reactions of biologically-impor-tant molecules. The mechanisms and products observed electrochemically do appear to be similar in many instances to those of the biological reactions. In cases where the biological products or mechanisms are not known electrochemical studies should prove useful in suggesting potential reaction routes and products. 

SCHEME 1 Schematic illustration of the biological process of 02 dismutation into 02 and H202 catalyzed by Cu, Zn-SOD via a cyclic oxidation-reduction electron transfer mechanism. (Reprinted from [98], with permission from Elsevier.)... 

The rate constant of electron transfer (ks) and anodic and cathodic electron transfer coefficients (aa and ac) of the SODs at various pH values were estimated with Laviron s equation and summarized in Table 6.5. Interestingly, the fastest electron transfer of the SODs was essentially achieved in a neutral solution, probably in agreement with the biological conditions for the inherent catalytic mechanisms of the SODs for 02" dismutation, although the electrode processes of the SODs follow a different mechanism. 

Nowadays, studies of direct electrochemistry of redox proteins at the electrodesolution interface have held more and more scientists interest. Those studies are a convenient and informative means for understanding the kinetics and thermodynamics of biological redox processes. And they may provide a model for the study of the mechanism of electron transfer between enzymes in biological systems, and establish a foundation for fabricating new kinds of biosensors or enzymatic bioreactors. 

A very brief introduction to the important topic of bioinorganic electron transfer mechanisms has been included in Section 1.8 (Electron Transfer) of Chapter 1. Discussions of Marcus theory for protein-protein electron transfer and electron or nuclear tunneling are included in the texts mentioned in Chapter 1 (references 3-7). A definitive explanation of the underlying theory is found in the article entitled Electron-Transfer in Chemistry and Biology, written by R. A. Marcus and N. Sutin and published in Biochem. Biophys. Acta, 1985, 811, 265-322. 

The several theoretical and/or simulation methods developed for modelling the solvation phenomena can be applied to the treatment of solvent effects on chemical reactivity. A variety of systems - ranging from small molecules to very large ones, such as biomolecules [236-238], biological membranes [239] and polymers [240] -and problems - mechanism of organic reactions [25, 79, 223, 241-247], chemical reactions in supercritical fluids [216, 248-250], ultrafast spectroscopy [251-255], electrochemical processes [256, 257], proton transfer [74, 75, 231], electron transfer [76, 77, 104, 258-261], charge transfer reactions and complexes [262-264], molecular and ionic spectra and excited states [24, 265-268], solvent-induced polarizability [221, 269], reaction dynamics [28, 78, 270-276], isomerization [110, 277-279], tautomeric equilibrium [280-282], conformational changes [283], dissociation reactions [199, 200, 227], stability [284] - have been treated by these techniques. Some of these... 

Spin trapping is an often-used technique in the study of possible radical production in biological systems (for reviews see Kalyanaraman, 1982 Mason, 1984 Mottley and Mason, 1989), particularly by the detection and monitoring of spin adducts of the hydroxyl and hydroperoxyl ( OOH) radicals in view of their relation to possible damage mechanisms. This is a large area of research which it is not possible to cover in a limited review, and the treatment will therefore be restricted to a discussion of the electron transfer properties of biochemical systems (for a review on the application of the Marcus theory to reactions between xenobiotics and redox proteins, see Eberson, 1985) and... 

The amide functionality plays an important role in the physical and chemical properties of proteins and peptides, especially in their ability to be involved in the photoinduced electron transfer process. Polyamides and proteins are known to take part in the biological electron transport mechanism for oxidation-reduction and photosynthesis processes. Therefore studies of the photochemistry of proteins or peptides are very important. Irradiation (at 254 nm) of the simplest dipeptide, glycylglycine, in aqueous solution affords carbon dioxide, ammonia and acetamide in relatively high yields and quantum yield (0.44)202 (equation 147). The reaction mechanism is thought to involve an electron transfer process. The isolation of intermediates such as IV-hydroxymethylacetamide and 7V-glycylglycyl-methyl acetamide confirmed the electron-transfer initiated free radical processes203 (equation 148). 

Part A. Quantum-Mechanical Theory of Diffusion Independent Electron Transfer in Biological Systems by Ephraim Buhks (University of Delaware)... 

Electrochemistry is essentially based on the relationships between chemical changes and flows of electrons (i.e. the passage of electricity). In this connection it is well known that electron transfer processes play an essential role in many physical, chemical and biological mechanisms and a number of such examples will be illustrated in the text. Perhaps in no other field of chemical reactivity has one looked for and found so many relationships between theory and experimental measurements. 

In recent years, electrochemical charge transfer processes have received considerable theoretical attention at the quantum mechanical level. These quantal treatments are pivotal in understanding underlying processes of technological importance, such as electrode kinetics, electrocatalysis, corrosion, energy transduction, solar energy conversion, and electron transfer in biological systems. 

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