In depth interaction studies between calf thymus
deoxyribonucleic acid (CT-
DNA) and a series of four structurally relative
palladium(II) complexes [Pd(en)(HB)](NO3)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 (Cc50) values much lower than
cisplatin.