A chemical preparation of pure reduced viologens for use as biomolecular reducing reagents.

A chemical method is reported for conveniently preparing a variety of pure, reduced low-potential viologens for use as biomolecular reductants. The free radical, semiquinone viologen form is prepared anaerobically in aqueous solution by coproportionation of the dihydroviologen with the fully oxidized viologen according to the following reaction, using methyl viologen (MV) as an example: MV + MVH2 = 2 MV.. By varying the substituents on the viologen nitrogen atoms, a series of viologens of varying charge and reduction potential is easily obtained. Applications involving the reduction of various metalloproteins are presented.