On the interaction of flavins with phosphine-derivatives.

The interaction of flavinium salts with triphenylphosphine is described. The complexes which can be isolated in high yields in the crystalline state contain one mole triphenylphosphine per mole flavin. Triphenylphosphine is covalently bound to the N (5)-atom of the isoalloxazine ring system. Dissociation constants and rate constants have been determined spectrophotometrically. Evidence for the structure of the complex was obtained from light absorption, infrared and nuclear magnetic resonance studies. The similarities between the flavin-triphenylphosphine adduct and the earlier described flavin-sulfite adduct are described and the possible biological relevance of these complexes is discussed.