Further Computational Studies on the Conformation of 1,5-Dihydrolumiflavin

Abstract

The optimized geometry of 1,5-dihydrolumiflavin has been calculated using density functional theory (DFT). Reduced lumiflavin was found to be bent along the N5-N10 axis, 25° from planarity, which is nearly the same as previously reported restricted Hartree-Fock (RHF) calculations, which predict a bending angle of 27°. The major difference in the DFT calculation is that the N10 methyl group adopts a more pseudoequatorial disposition and is only bent 13° above the plane of the isoalloxazine ring system as opposed to 59° in the RHF calculations. These computational results are compared with x-ray crystal structures of flavin models and flavoproteins. DFT calculation of 1,5-dihydroisoalloxazine resulted in a more modestly bent geometry of 17°. This indicates that both electronic and steric interactions of the N10 methyl group of reduced lumiflavin contribute to the bent geometry.