THE INTERACTION OF RHODIUM(III) WITH DNA BY CIRCULAR-DICHROISM STUDIES - COMPARATIVE BEHAVIOR OF DIMETHYLTIN(IV) AND THALLIUM(I)

The effect of RhCl3 on DNA helix conformation was studied by circular dichroism spectroscopy and compared to the behaviour of Me2SnCl2 and T INO3; the latter metal-DNA systems have been further studied by ultrav iolet and thermal denaturation techniques. Both rhodium(III) and tin(I V) react with the bases of DNA and induce appreciable alterations of t he double-helical conformation. Rhodium(III) at low binding ratio caus es a stabilization of the DNA B conformation, while at higher structur al changes are interpreted in terms of a B to C transition. Tin(IV) pr oduces a psi form geometry; only at high binding ratios does interacti on with the phosphate groups seem to occur. The data for thallium(I) a re interpreted in terms of a preferential interaction with the phospha te groups of the DNA chain, causing a stabilization of the double-heli cal structure of DNA.