Molecular Recognition of Metal Complexes by DNA: A Comparative Study of the Interactions of the Parent Complexes [PtCl(TERPY)]Cl and [AuCl(TERPY)]Cl ₂ with Double Stranded DNA

Abstract

The interactions of the parent complexes [AuCl(Terpy)]Cl₂ and [PtCl(Terpy)]Cl with DNA were analysed by various physicochemical methods. Surprisingly, these metal complexes produce different interaction patterns with DNA in spite of their profound structural similarity. Indeed, important modifications are detected in the characteristic UV-Vis bands of [PtCl(Terpy)]Cl upon addition of ct-DNA, while the spectrum of [AuCl(Terpy)]Cl₂ is almost unaffected. Gel electrophoresis studies confirm these findings: [PtCl(Terpy)]Cl — but not [AuCl(Terpy)]Cl₂ — retards significantly the mobility of the supercoiled form of the pHV14 plasmid after a short incubation time. Ultrafiltration studies indicate that the affinity of [PtCl(Terpy)]Cl for ct-DNA is significantly greater than that of [AuCl(Terpy)]Cl₂. On the other hand, both [AuCl(Terpy)]Cl₂ and [PtCl(Terpy)]Cl induce important changes in the CD spectrum of ct-DNA, at high concentration, and increase its T_m value. Remarkably, the analysed metal-complex/DNA interaction patterns depend critically on the incubation times. We propose that [PtCl(Terpy)]Cl quickly intercalates DNA; then, formation of coordinative bonds progressively takes place with time. At variance, [AuCl(Terpy)]Cl₂ first interacts electrostatically with the DNA surface, with subsequent slow formation of some coordinative bonds.