DNA and RNA noncovalent interaction of Platinum(II) polypyridine complexes

A comparative investigation of the noncovalent interaction of the platinum(II) polypyridine complexes [Pt(dipy)(nRPY)2](2+) and [Pt(4,4'-Me2dipy)(2-RPY)2](2+) (dipy = 2,2'-dipyridine; Me = CH3; n = 2-4; R = H or CH3) with doublehelical DNA (calf thymus) and RNA [poly(A)-poly(U)] has been conducted. With the exception of [Pt(dipy)(2-Mepy)(2)](2+), all of the complexes interact strongly, by intercalation, with both nucleic acids giving rise to large changes in the electronic spectra and induced circular dichroism signals; in addition, viscosity experiments on rodlike DNA and RNA show that both biopolymers elongate upon interaction with the complexes. The binding constant values, K-B, determined at 25 degrees C, indicate that, at 0.101 M ionic strength, the affinity for poly(A)-poly(U) is strongly dependent on the complexes nature, while for DNA it is leveled off. [Pt(dipy)(2-MePY)(2)](2+) binds to DNA but does not interact appreciably with poly(A)-poly(U).