[Study of the interaction of a DNA molecule with coordination compounds of divalent platinum. I. Effect of cis-diaminodichloroplatinum on molecular parameters of DNA in solution].

DNA interaction with cis-diaminodichloroplatinum (cis-DDP in solutions of different ionic strength was studied by flow birefringence, viscometry, circular dichroism. Though cis-DDP is not an electrolyte, electrostatic interactions are important for binding of cis-DDP with DNA probably for transporting cis-DDP to a macromolecule. The charges aqua-complex is formed by cis-DDP. The complexation being dependent on the platinum/DNA ratio in solution. Along with the increase of platinum concentration, it forms first the complexes with phosphate groups, then with bases without destruction of the DNA secondary structure. The next type of complex formation is accompanied by the local destruction of the hydrogen bonds and stacking interactions. And when the Pt/DNA ratio grows high enough, DNA is denatured. It is suggested that the stability of the complex is provided by nitrogen groups of the bases incorporated in the platinum first coordination sphere. The phosphate DNA groups play the role of counterions in the external coordination sphere.