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 analysedby various physicochemical methods. Surprisingly, these metal complexes produce different interactionpatterns with DNA in spite of their profound structural similarity. Indeed, important modifications aredetected in the characteristic UV-Vis bands of [PtCl(Terpy)]Cl upon addition of ct-DNA, while the spectrumof [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 thepHV14 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 highconcentration, and increase its Tm value. Remarkably, the analysed metal-complex/DNA interaction patternsdepend 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 firstinteracts electrostatically with the DNA surface, with subsequent slow formation of some coordinative bonds.