SYNTHESIS, CHARACTERIZATION, AND INTERACTION WITH DNA OF THE NOVEL METALLOINTERCALATOR CATIONIC COMPLEX (2,2'6',2''-TERPYRIDINE)METHYLPLATINUM(II)

A series of salts of the type [Pt(terpy)Me]X (X = Cl, NO3, PF6, ClO4, B(C6H5)(4)) containing a new organometallic complex cation of platinum (II) with 2,2':6',2 ''-terpyridine (terpy) were synthesized and charac terized by H-1, C-13, and Pt-195 NMR spectroscopy. No evidence for flu xionality of the terpyridine ligand was obtained, indicating that it i s terdentate. The fourth position in the coordination plane is occupie d by a methyl group. The resulting cation is unreactive toward substit ution and is stable in aqueous solutions under mild conditions. The pl anarity and electron delocalization of the terpy moiety lead to extens ive stacking interactions, forming dimers in dilute aqueous solution a nd larger aggregates when the concentration and/or the ionic strength increase. UV/vis and H-1 NMR spectra show characteristic dependencies on the concentration of the complex, the temperature, the solvent, and the ionic strength. Analysis of the absorption spectral data gives a value of 10 (+/-8) x 10(3) M(-1) (T = 298 K; mu = 0.101 mol L(-1)) for the dimerization equilibrium constant. Resonance light-scattering spe ctra, measured for the first time on a metal-containing noncyclic subs trate, provide evidence for the tendency of the complex to form large self-aggregates even under low ionic strength conditions. The interact ion of the cationic complex ion with calf thymus DNA was investigated by UV/vis, CD spectroscopy, resonance light-scattering, thermal denatu ration, and gel electrophoresis mobility assays. At high r(f) ratios t he complex seems to form extended aggregates on the surface of the nuc leic acid, but at lower r(f) ratios evidence was obtained for intercal ation.