Photocatalytic reduction of nicotinamide coenzymes in the presence of titanium dioxide: The influence of aliphatic aminoacids

Illumination of a TiO2 dispersion in a weakly alkaline solutions of nicotinamide coenzymes (NMN+, NAD(+), NADP(+)) leads in the presence of aminoacids (glycine, lysine, serine and aspargine as well as EDTA and DTT) to one-electron reduction of the coenzymes. The formation of the respective dimers observed in the initial stage of illumination at 365 nm was confirmed by polarographic, spectrophotometric and enzymatic analysis. The relative efficiency of photoreduction strongly depends on the nature of the electron donor. Effects of pH and coenzyme concentration on the efficiency of photoconversion process were investigated. Prolonged irradiation leads to tetrahydroderivatives and/or hydration products of the respective dimers. (C) 1997 Elsevier Science S.A.