Photoelectron-transfer reactions of flavin analogues with tetra-alkyltin compounds

The fluorescence of flavin analogues (3-methyl-10-phenylisoalloxazine and 3-methyl-10-phenyl-5-deazaisoalloxazines) in the absence and presence of Mg²⁺ ion in acetonitrile was quenched by the electron-transfer reactions with tetra-alkyltin compounds. The quenching rate constants as well as the rate constants for electron-transfer reactions of the tetra-alkyltin compounds with iron(III) complexes [Fe(N-N)₃]³⁺ (N-N = 2,2′-bipyridine and various substituted 1,10-phenanthrolines) agree with those calculated by using the Marcus theory for outer-sphere electron-transfer reactions over a wide spread of values of the Gibbs energy change from the highly exothermic to the endothermic region. The intrinsic barrier λ for the electron-transfer reactions of tetra-alkyltin compounds is found to be significantly large, i.e., λ = 170 kJ mol^-1 compared with those of organic compounds (typically, λ = 40 kJ mol^-1). A flavin analogue (3-methyl-10-phenylisoalloxazine) catalyses the photo-oxidation of tetra-alkyltin compounds by oxygen in the presence of Mg²⁺ ion in acetonitrile, which proceeds via the photoelectron-transfer from tetra-alkyltin compounds to the excited state of the flavin.