Electron exchange rate

Azo-bridged ferrocene oligomers also show a marked dependence on the redox potentials and IT-band characteristics of the solvent, as is usual for class II mixed valence complexes 21,22). As for the conjugated ferrocene dimers, 2 and 241 the effects of solvents on the electron-exchange rates were analyzed on the basis of the Marcus-Hush theory, in which the t/max of the IT band depends on (l/Dop — 1 /Ds), where Dop and Ds are the solvent s optical and static dielectric constants, respectively (155-157). However, a detailed analysis of the solvent effect on z/max of the IT band of the azo-bridged ferrocene oligomers, 252,64+, and 642+, indicates that the i/max shift is dependent not only on the parameters in the Marcus-Hush theory but also on the nature of the solvent as donor or acceptor (92). 

The physical and chemical properties of Rh(bpy)32+ generated via flash-photolytic and pulse-radiolytic methods in aqueous solutions are reported and discussed. The reduction potential -0.86 V vs SHE) and electron-exchange rate (> 109 M 1 s "1) for the Rh(bpy)33+/Rh(bpy)32+... 

Rehm-Weller method (21) for estimating the reduction potentials of excited molecules As our homologous series of reductants, we have used the RuL3 +/ RuL32+ couples (22,23), where RuL32+ is the luminescent excited state of Rul 7 The electron exchange rate constants for these couples are very large... 

Rum(bpy)33+/[RUm(bpy)2(bpy )]2+ potential, -0.81 V vs aqueous SCE in acetonitrile (25,33) is also consistent with this model. (The species [Ru (bpy)2(bpy")]2+ is Ru(bpy)3 + which has recently been assigned as a localized bound bpy radical on the basis of its resonance Raman spectrum (34).) The fact that nearly identical E /2 values are found for the reduction of Ir(bpy)3 + and Rh(bpy)3 + suggests that both involve the same reduction site — the bound bpy. (By contrast, E1/2 for metal-centered reduction of Co(bpy)3 + is 40.30 V (28).) Furthermore, as discussed above, the electron exchange rate for RhL3 +/RhL3 +, 10 s 1, being comparable to that for the... 

As has been noted (29, 31), nickel(III) poly(pyridine) complexes may be prepared. Electron-exchange rates have been determined (15) from a series of cross-reactions. The rate of the electron transfer reaction has... 

Since AF ex equals —RT ln( ex/10u M l sec. 1)> X2 can be estimated from the electron exchange rate constant kex when correction of AF ex is made for uf or when uf is small enough to be neglected. Values of AF ex have also been obtained indirectly from measurements of rate... 

The electron exchange rate k (Eq. 10.5) is a function of the transmission coefficient k (approximately 1 for reactions with substantial electronic coupling (>4 kJ), i.e., for adiabatic reactions), the effective collision frequency in solution (Z 1011 M 1 s 1 Ar2) and the free energy term AG. ... 

Application of the Marcus equation for electron transfer affords the electron exchange rate of the molybdenum radical/anion couple. The value is fcge = 3 X 10 L mol s. The high value argues that very little nuclear reorganization is needed to add an electron to the SOMO of the 17e radical. 

As large as this this value is, it corresponds to an electron exchange rate between CpMo(CO)3NCCH3+ and CpM(CO>3 of only -lO L moP s. The small value signals a large inner-shell reorganization the two sptedes differ by one coordinated molecule of solvent. 

Reactions of hydroquinone, catechol, and L-ascorbic acid with dicyanobis(l,10-phenan-thn>line)iion(III) were studied in dimethyl sulfoxide (DMSO). Application of the Marcus theory to the reactions of catechol and hydroquinone provided the electron exchange rate constant for the Fe(III/II) couple in DMSO. The self-exchange rate constant for the ascorbic acidAadical couple was estimated for the first time in DMSO. The one electron-oxidation process of L-ascorbic acid in an aprotic solvents such as DMSO may be completely different from that in aqueous solutions. 

The electron exchange rate constant of the iron(III) complex in DMSO was estimated from the cross reactions with hydroquinone and catechol, which was compared with the rate constant obtained electrochemically. The mechanism of the ascorbic acid oxidation reaction in DMSO is discussed based on the Marcus theory. 

Electrodes with large areas are advantageous, but they also tend to magnify the effects of trace impurities or other reactions on the electrode surface itself, such as adsorption of surface-active materials leading to a reduction in the electron-exchange rate or in the effective area A. 

The mediator should exhibit fast electron exchange rates with both the enzyme and the electrode to ensure that the mediator is not limited by electrode kinetics and to minimize competihon with the enzyme natural substrate, if present. 

Electron Transfer Accompanied by a Net Chemical Change 12.2.3.4.2. Cross Reactions and Electron-Exchange Rates... 

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