CHEMISTRY

Effects of amine ligand bulk on the rate of reaction of platinum(II) diamine complexes with guanine and methionine residues. BECCA M. DAVIS*, and KEVIN M. WILLIAMS, Department of Chemistry, Western Kentucky University, Bowling Green, KY 42101-1079.

NMR spectroscopy has been used to observe the effects of amine ligand bulk in the reaction of platinum diamine complexes with DNA and protein residues. Also studied are the effects of bulk in kinetic competition experiments. The reactions of [Pt(en)(D₂O)₂]²⁺ (en = ethylenediamine) or [Pt(Me₄en)(D₂O)₂]²⁺ (Me4en = N, N, N’, N’-tetramethylethylenediamine) with 5’GMP (guanosine 5’ monophosphate, a DNA nucleotide) and/or N-AcMet (N-acetylmethionine, an amino acid derivative) have been utilized. [Pt(en)(D₂O) ₂]²⁺, the less bulky molecule, reacted more quickly with both N-AcMet and 5’-GMP than did the bulky molecule, [Pt(Me₄en)(D₂O)]²⁺. The bulk slowed reaction of a second 5’GMP residue more than it slowed reaction with the first; reaction of a second N-AcMet does not occur. In competition studies, it was observed that [Pt(en)(D₂O)]²⁺ reacted faster with N-AcMet than with 5’-GMP, whereas [Pt(Me₄en)(D₂O)]²⁺ had a tendency to react faster with 5’-GMP than with N-AcMet. Thus, the presence of bulk may result in a greater preference for reaction with DNA compared to proteins.