PtL3 X-ray absorption studies of Pt model compounds and [(NH3)2Pt(OH)2Pt(NH3)2]2+ bound to DNA

The Pt L3 X-ray absorption spectra of a series of Pt compounds have been recorded and their extended fine structure (EXAFS) analysed to investigate the sensitivity of EXAFS to non-first-shell PtPt distances. The Pt L3 EXAFS spectra of complexes formed between [(NH3)2Pt(OH)2Pt(NH3)2]2+ and calf thymus DNA were also recorded. PtPt vectors could not be detected in these spectra. When combined with the model compound studies, this result rules out Pt dimer structures for the PtDNA complex which involve rigidly bridged, adjacent Pt atoms. Such structures, based on dimeric bonding of a hydroxo dimer intermediate to DNA, have been proposed as models for cisplatin antitumor activity. These types of models now seem unlikely.