LAUSR

Four new platinum(II) complexes [Pt(dpen)(bpy)](ClO4)2 (1), [Pt(dpen)(phen)](ClO4)2 (2), [Pt(dpen)(dpq)](ClO4)2 (3) and [Pt(dpen)(dppz)](ClO4)2 (4) comprising of different N,N-donor ligands, viz., 2,2′-bipyridine (bpy), 1,l0-phenanthroline (phen), dipyridoquinoxaline (dpq), dipyrido-[3,2-d:2¢,3¢-f–phenazine] (dppz), and chiral ancillary ligand 1R,2R-1,2-diphenylethylenediamine (dpen) have been synthesized and characterized. The interaction of these complexes 1–4 with calf-thymus DNA (CT-DNA) has been explored using absorption, circular dichroism spectral and cyclic voltammetric studies. The absorption spectrum of complex 4 with dppz ligand exhibits a major red shift with an overall hypochromic as well as a hyperchromic effect in the presence of DNA, other complexes (1–3) show only hypochromism. From these absorption spectral studies, the intercalative ability of the complexes follows the order as, 4 > 3 > 2 > 1, which is further confirmed by CD and cyclic voltammetry measurements. CD spectral studies show that DNA becomes more A-like upon interaction with the complexes 1 & 2 but the complexes 3 & 4 bring about B-form to Z- form DNA conformational transition. The DNA cleavage study of these Pt(II) complexes 1–4 carried out by gel electrophoresis revealed that complexes 1–4 can cleave super coiled (SC) pUC18 DNA efficiently into open circular form (form II) under hydrolytic and oxidative conditions.