[en] Nonadiabatic electron transfer has been studied in glycerol in which the solvent relaxation time (tau/sub L/ is varied (by temperature) from 10^-8 to 10^-1 s. A strong dependence of rate on tau is observed with kappa approx. (tau/sub L/)^-06. A qualitative rationale suggests that the actual dependence for a nonadiabatic process can range from (tau/sub L/ )⁰ to (tau/sub L/)^-1 depending on whether the electronic coupling strength or solvent polarization determines the frequency factor for reaction. Such intermediate cases may be significant in a variety of condensed-phase electron-transfer processes

[en] Kinetic isotope effects have been measured for redox reactions of the iron hydrates (from the title) with a series of M/sup III/ (bipyridinium)₃ oxidants. M = iron III,, ruthenium III, chromium III. The rate ratios k(¹⁶OH₂)/k(¹⁸OH₂) have been predicted in the literature. Deuterium isotope effect measurements are complicated by the difference of the aqueous iron²⁺/³⁺[Fe(aq)²⁺/³⁺] reduction potential in water and heavy water (D₂O): E⁰/sub Fe³⁺/H₂O/ - E⁰/sub Fe³⁺/D₂O/ = -0.040 V. After correcting the observed rates for the change in reaction driving force, an isotope effect of 1.3 is estimated for the cross reactions involving Fe(aq)²⁺/³⁺ (at ΔE = O). This value is larger than predicted and 20% greater than that observed in the ¹⁶OH₂ vs ¹⁸OH₂ experiments, possibly reflecting a contribution of frozen O-H modes in the reaction coordinate. 4 figures, 2 tables

[en] Rapid mixing of ferrocytochrome c peroxidase [cyt c peroxidase(II)] and ferricytochrome c [cyt c(III)] results in the reduction of cyt c(III) by cyt c peroxidase(II). In 10 mM phosphate, pH 7.0, the rate of decay of cyt c peroxidase(II) and the rate of accumulation of cyt c(II) give equal first-order rate constants. Equivalent results are obtained by pulse radiolysis using isopropanol radical as the reducing agent. This rate is independent of the initial cyt c(III):cyt c peroxidase(II) ratios. These results are consistent with unimolecular electron transfer occurring within a cyt c(III)-cyt c peroxidase(II) complex. When cyt c is replaced by porphyrin cyt c (iron-free cyt c), a complex still forms with cyt c peroxidase. On radiolysis intracomplex electron transfer occurs from the porphyrin cyt c anion radical to cyt c peroxidase(III). This large rate increase suggest that the barrier for intracomplex electron transfer is large. Finally, the authors have briefly investigated how the cyt c peroxidase(II) → cyt c(III) rate depends on the primary structure of cyt c(III). They find the reactivity order to be as follows: yeast > horse > tuna

[en] This paper reports on work addressing unusual luminescence properties in semiconductors. The idea that coupling an electron transfer mechanism with a random distribution of trap sites is applicable to electron transfer reactions in systems as far afield as protein-protein couples is examined