23Na NMR study of the interaction between DNA and the platinum (II) compounds:: Cis-DDP, trans-DDP and TDP

The interaction of calf thymus DNA with cis-DDP, trans-DDP and TDP was studied by Na-23 NMR in aqueous solutions at pH = 7.0, with Pt(II) compounds/DNA(P) (P=Phosphate) molar ratios r increasing from 0 till to 1P. Na-23 NMR results are interpreted on one hand, with the help of a "two states model" with R-F and R-B relaxation rates, and, on the other hand, using the "entropy of fluctuations." concept developed by Lenk. We have established that, for the studied platinum compounds, the preference to interact with DNA phosphate sites -interpreted as a perturbation of the counterions environment- is in a decreasing order: TDP >> cis-DDP > trans-DDP. These results are discussed with regard to the interaction of DNA with the hard bication Mg++ and the soft bication Cu++.