Electronic Structure Measurements of Oxidized Flavins and Flavin Complexes Using Stark-Effect Spectroscopy

Abstract

Stark-effect spectroscopy (electroabsorption) measurements were obtained for oxidized flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) in frozen glycerol/H2O glasses and N(3)-methyl-N(10)-isobutyl-7,8-dimethyl-isoalloxazine in frozen n-butanol glasses at fields of up to 5 × 105 V/cm. In all three flavins, the effect of the applied electric field on the low-energy transition (S0 → S1, 450 nm band) is significantly smaller than on the higher energy transition (S0 → S2, 370 nm band). The Stark spectra indicate that the magnitude of the permanent dipole moment in the S1 state, |μ1| is only modestly different from the S0 state, |μ0|, and that there is little change in the mean polarizability for the S0 → S1 transition. The electric field effect on the S0 → S2 transition, however, shows that the magnitude of the dipole moment of the S2 state is ∼60% larger than that of the S1 state and that the change in the mean polarizability is much larger. Concentration studies indicate that the FAD dimer o...