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 23Na 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. 23Na 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++.