An electron paramagnetic resonance study of flavin anion radicals

Abstract

The electron paramagnetic resonance spectra of lumiflavin (LF), Flavin mononucleotide (FMN), and riboflavin (RF) anion radicals in alkaline aqueous solutions of sucrose, dextrose hydrate, and glycerol have been recorded. Rotational correlation times of the radicals have been established through computer simulations of the experimental spectra. It is found that Flavin radicals undergo strongly anisotropic motions in solution. Analysis of the dependences of the rotational correlation time and the residual linewidths of the flavin spectra indicate that all three flavins form molecular aggregates with the solutes in order of increasing strength: glycerol < sucrose < dextrose. The nature of the flaving solute interaction is dependent upon the solute rather than the Flavin. The electron paramagnetic resonance spectra of 8-hydroxyriboflavin, 8-formylriboflacin, and 8-carboxyroboflavin anion radical are presented. It is proposed that the observed linewidth effects are due to a mechanism such as exchange narrowing.