The excited state of [Pt2(pop)4]4- (pop = P2O5H24-) is an effective agent for the oxidation of organic substrates by hydrogen abstraction that has also been shown to be a DNA cleavage agent. Reported here are studies on the photooxidation of organic substrates and model nucleotides in aqueous solution. The complex is shown to be relatively stable in buffer solution, although there is a buffer-catalyzed decomposition that can deplete the concentration of [Pt2(pop)4]4- in 5 mM phosphate buffer by 10% in 1 h. The oxidized complex [Pt2(pop)4Cl2]4- is much more stable in buffer solution and can be converted to [Pt2(pop)4]4- upon irradiation, providing a means of generating the active complex in situ from a stable precursor. Both complexes catalytically oxidize 1-phenylethanol to acetophenone with a maximum of 10(2) turnovers. The pH dependence of the turnover number suggests that ligand hydrolysis and reaction of a dihydride intermediate with water contribute to catalyst deactivation. The kinetics of the reaction of [Pt2(pop)4]4-* with sugars and nucleotides indicate reaction by hydrogen abstraction with rate constants in the range 10(5)-10(6) M-1 s-1. The rate constants for a wide range of model substrates are presented, and the implications of these data on the DNA photochemistry are discussed.