effects of extending of co-planarity in a series of structurally relative polypyridyl palladium[II] complexes on DNA-binding and cytotoxicity properties

ABSTRACT

In depth interaction studies between calf thymus deoxyribonucleic acid [CT-DNA] and a series of four structurally relative palladium[II] complexes [Pd[en][HB]][NO[3]][2] [a-d], where en is ethylenediamine and heterocyclic base [HB] is 2, 2›-bipyridine [bpy, a]; 1, 10-phenanthroline [phen, b]; dipyridoquinoxaline [dpq, c] and dipyridophenazine [dppz, d] [Figure 1], were performed. These studies have been investigated by utilizing the electronic absorption spectroscopy, fluorescence spectra and ethidium bromide [EBr] displacement and gel filtration techniques. a-d complexes cooperatively bind and denature the DNA at low concentrations. Their concentration at midpoint of transition, L1/2, follows the order a >> b > c > d. Also the g, the number of binding sites per 1000 nucleotides, follows the order a >> b c > d. EBr and Scatchard experiments for a-d complexes suggest efficient intercalative binding affinity to CT-DNA giving the order d > c > b > a. Several binding and thermodynamic parameters are also described. The biological activity of these cationic and water soluble palladium complexes were tested against chronic myelogenous leukemia cell line, K562. b, c and d complexes show cytotoxic concentration [Cc[50]] values much lower than cisplatin