4-Picoline-2,2':6',2"-terpyridine-platinum(II) - a potent intercalator of DNA.

4-Picoloine-2,2':6',2"-terpyridine-platinum(II) is shown in a ligation assay to unwind and so intercalate into DNA. Circular dichroism is used to determine an equilibrium binding constant of approximately 2 x 10(7) M(-1) for the most stable binding mode of 4-picoline-2,2':6',2"-terpyridine-platinum(II) to poly[d(A-T)2] with a site size of about 4 base pairs, and about 1 x 10(6) M(-1) for a second binding mode with a site size of about 2 base pairs. Fluorescence spectroscopy provides further evidence for the strong equilibrium binding constant of 4-picoline-2,2':6',2"-terpyridine-platinum(II) in that it displaces ethidium bromide bound to DNA. The double positive charge on 4-picoline-2,2':6',2"-terpyridine-platinum(II), together with the intercalative binding mode is probably responsible for the large binding constant.