A Comparative Study of DNA Cleavage Ability of Copper(II)-Schiff Base-Polypyridyl Complexes

Abstract: A tridentate Schiff base ligand (saltrp/saltyr) was synthesized by coupling salicylaldehyde (sal) with amino acid - tryptophan (trp) and tyrosine (tyr). Cu(II) Complexes with salicylidene amino acid Schiff base and polypyridyl ligands i.e [Cu(II)(saltrp)(phen)] (1), [Cu(II)(saltrp)(bipy)] (2), [Cu(II)(saltyr)(phen)] (3) and [Cu(II)(saltyr)(bipy)] (4) (where phen = 1,10 phenanthroline and bipy= 2,2' bipyridine) were synthesized, characterized by various techniques and structures were proposed. Complexes display a square pyramidal geometry around Cu(II) with Schiff base coordinating through ONO donor atom and polypyridyl ligands through NN donor atoms. CT-DNA (Calf Thymus) binding studies for complexes (1-4) display an intercalative mode of binding with binding affinity of order 1>2>3>4. Since Small metal complexes that promote hydrolytic cleavage of DNA are useful in molecular biology and drug design, an attempt is made in this article to compare the DNA cleavage abilities of complexes 1-4 reported earlier and to analyze the reasoning for affinity towards DNA cleavage. The hydrolytic DNA cleavage activity of these complexes was studied by gel electrophoresis and DNA cleavage rate constant were determined. Phenanthroline complexes (1, 3) binds and cleaves DNA more effectively as compared to their corresponding bipyridine (2, 4) analogues due to the presence of extended aromatic phenyl ring which might be involved in an additional stacking interaction with DNA bases. Comparison among the amino acid systems revealed that tyrosine schiff base complexes (3, 4) show better DNA cleavage than tryptophan analogues (1, 2) and the DNA cleavage ability follow the order : 3>4>1>2.

Keywords: Amino acids, Schiff bases, Copper complexes, DNA cleavage, kinetics.