Intermolecular electron transfer reactions

A simple reaction of the former molecule with H2 would reduce its two clusters again. The final level of reduction of the Ee-S clusters would then only depend on the effective redox potential in the system. Under 1 per cent H2 at pH 6, where the redox potential is about —295 mV, part of the Fe-S clusters are oxidized. At this pH they only reduce under f 00 per cent H2. At pH 8 or higher, however, the redox potential of both fOO per cent H2 and 1 per cent H2 is low enough to keep all clusters fully reduced. So via intermolecular, one-electron transfer reactions the Fe-S clusters can presumably follow the current potential imposed upon the system by H2 even in the absence of redox mediators. Of course, the presence of such mediators facilitates electron (re)distribution. 

Organic photochemical synthesis has developed to an important and pervasive field within current organic chemistry. In photochemical reactions and photobiological reactions, electron transfer, transfer of excited energy, and photoinduced intramolecular and intermolecular isomerizations are important and fundamental. Photolysis, photosynthesis, photopolymerization, and photochemical isomerization arise by excited atoms and molecules under irradiation by light. These reactions are different from reactions carried out thermally, under pressure, or by catalysis. 

Wang 0, Akhremitchev B and Walker G 0 1997 Femtosecond infrared and visible spectroscopy of photoinduced intermolecular electron transfer dynamics and solvent-solute reaction geometries Coumarin 337 in dimethylaniline J. Rhys. Chem. A 101 2735-8... 

The next important phenomena that the result of supramolecular effect are the concentration and proximity effects concerning the components of analytical reaction, even through they are considerably different in hydrophobicity, charge of the species, complexing or collisional type of interaction. The concentration and proximity effects determine the equilibrium of analytical reaction, the efficiencies of intramolecular or intermolecular electronic energy or electron transfer and as a result the sensitivity of analytical reactions. 

Figure15.9 (a) Reaction scheme of photoinduced intermolecular electron-transfer in C oN cluster- MePH system, (b) MFEs on A = Abs(BT)/Abs(0T) in CeoN -MePH inTHF-HjO (2 1) mixed solvent.

The second group of intermolecular reactions (2) includes [1, 2, 9, 10, 13, 14] electron transfer, exciplex and excimer formations, and proton transfer processes (Table 1). Photoinduced electron transfer (PET) is often responsible for fluorescence quenching. PET is involved in many photochemical reactions and plays... 

One striking prediction of the energy gap law and eq. 11 and 14 is that in the inverted region, the electron transfer rate constant (kjjj. = ket) should decrease as the reaction becomes more favorable (lnknr -AE). Some evidence has been obtained for a fall-off in rate constants with increasing -AE (or -AG) for intermolecular reactions (21). Perhaps most notable is the pulse radiolysis data of Beitz and Miller (22). Nonetheless, the applicability of the energy gap law to intermolecular electron transfer in a detailed way has yet to be proven. 

The aim in solution studies on metalloprotein is to be able to say more about intermolecular electron transfer processes, first of all by studying outer-sphere reactions with simple inorganic complexes as redox partners. With the information (and experience) gained it is then possible to turn to protein-protein reactions, where each reactant has its own complexities... 

The systems that we investigated in collaboration with others involved intermolecular and intramolecular electron-transfer reactions between ruthenium complexes and cytochrome c. We also studied a series of intermolecular reactions between chelated cobalt complexes and cytochrome c. A variety of high-pressure experimental techniques, including stopped-flow, flash-photolysis, pulse-radiolysis, and voltammetry, were employed in these investigations. As the following presentation shows, a remarkably good agreement was found between the volume data obtained with the aid of these different techniques, which clearly demonstrates the complementarity of these methods for the study of electron-transfer processes. 

Application of pulse-radiolysis techniques revealed that the following intramolecular and intermolecular electron-transfer reactions all exhibit a significant acceleration with increasing pressure. The reported volumes of activation are -17.7 0.9, 18.3 0.7, and... 

In order to obtain further information on the magnitude of the overall reaction volume and the location of the transition state along the reaction coordinate, a series of intermolecular electron-transfer reactions of cytochrome c with pentaammineruthenium complexes were studied, where the sixth ligand on the ruthenium complex was selected in such a way that the overall driving force was low enough so that the reaction kinetics could be studied in both directions (153, 154). The selected substituents were isonicotinamide (isn), 4-ethylpyr-idine (etpy), pyridine (py), and 3,5-lutidine (lut). The overall reaction can be formulated as... 

Recent investigations on a series of intramolecular electron transfer reactions, closely related to the series of intermolecular reactions described above, revealed nonsymmetrical volume profiles (159). Reactions of the type... 

For the intermolecular interactions between IV-methylphthalimide and alkenes, two reactions paths are possible183. The first is the regio- and stereocontrolled (2n+2a) cycloaddition of the alkene to the C—N bond to generate dihydrobenzazepinedione (equation 126), while the second is the electron transfer initiated addition(equation 127). 

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