Spectrophotometric investigation of products formed following the initial one-electron electrochemical reduction of nicotinamide adenine dinucleotide (NAD+)

On electrolysis of NAD⁺ in aqueous solution at a potential corresponding to the initial one-electron reduction of NAD⁺ to a free radical, a greenish-yellow color appears which fades when electrolysis is complete. Literature ultraviolet absorption data for the resulting dimer show considerable variation. When the electrolysis is conducted in darkness, the colored product has ?₃₄₀ of approx. 5700 M^?1 · cm^?1 and ?₂₅₉ of approx. 31000 M^?1 · cm^?1. On ultraviolet and visible illumination, the color disappears, the 340-nm peak decreases and the 259-nm peak increases. On only visible illumination, the color disappears, both peaks increases, the dimer's polarographic oxidation wave decreases and the wave due to 1-substituted nicotinamide reduction increases. The data suggest that the dimer decomposes to NAD⁺ and 1,4-NADH.