Improved density functional description of the electrochemistry and structure-property descriptors of substituted flavins.

The energetics of electrochemical changes have been investigated for several substituted flavins with the M06-L density functional. The reduction potentials for one- and two-electron reductions of these molecules have been determined and the results are consistent with experimental findings with a mean unsigned error of only 42 mV. It is especially noteworthy that the M06-L density functional makes a significant difference in the computed free energy of the first reduction of lumiflavin, which produces a neutral semiquinone. We also investigate the effects of flavin ring substituents on the geometries, charge distributions, reduction potentials, pK(a)'s, ionization potentials, electron affinities, hardnesses, softnesses, electrophilic powers, and nucleophilicities.