4-PICOLINE-2,2'-6',2''-TERPYRIDINE-PLATINUM(II) - A POTENT INTERCALATOR OF DNA

4-Picoline-2,2':6',2''-terpyridine-platinum(II) is shown in a ligation assay to unwind and so intercalate into DNA, Circular dichroism is us ed to determine an equilibrium binding constant of approximately 2 x 1 0(7) M(-1) for the most stable binding mode of 3-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 wit h a site size of about 2 base pairs. Fluorescence spectroscopy provide s further evidence for the strong equilibrium binding constant of 4-pi coline-2,2': 6',2''-terpyridine-platinum(II) in that it displaces ethi dium 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.