UNDERSTANDING THE INTERACTIONS OF [PT2(POP)4]4- WITH NUCLEIC-ACIDS - PHOTOCATALYTIC HYDROGEN ABSTRACTION IN AQUEOUS-SOLUTION (POP = P2O5H2(2))

The excited state of [Pt2(pop)4]4- (pop = P2O5H24-) is an effective ag ent for the oxidation of organic substrates by hydrogen abstraction th at has also been shown to be a DNA cleavage agent. Reported here are s tudies on the photooxidation of organic substrates and model nucleotid es in aqueous solution. The complex is shown to be relatively stable i n 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 mo re stable in buffer solution and can be converted to [Pt2(pop)4]4- upo n irradiation, providing a means of generating the active complex in s itu from a stable precursor. Both complexes catalytically oxidize 1-ph enylethanol 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 sug ars and nucleotides indicate reaction by hydrogen abstraction with rat e 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.