DNA Interaction Studies of a Cobalt(II) Mixed-Ligand Complex Containing Two Intercalating Ligands: 4,7-Dimethyl-1, 10-Phenanthroline and Dipyrido[3,2-a:-c]phenazine

A new cobalt(II) complex [Co(dppz)2(4,7-dmp)]2+ (4,7-dmp = 4,7-dimethyl-1,10-phenanthrolline) and dppz = dipyrido[3,2-a:2′-3′-c]phenazine has been synthesized and characterized by elemental analysis (CHN), FT-IR, and UV-visible (UV-Vis) spectroscopic techniques. The DNA-binding property of the complex has been investigated employing absorption spectroscopy, fluorescence spectroscopy, circular dichroism, and viscosity measurements. The experimental results show that the complex can bind to DNA in an intercalation mode. In comparison with previous study, the DNA-binding affinity of [Co(dppz)2(4,7-dmp)]2+ ( ？M？1) is smaller than that of complex [Co(dppz)2(2,9-dmp)]2+ ( ？M？1). 1. Introduction Cobalt was accepted as an essential metal element widely distributed in the biological systems such as cells and body, and thus the interaction of DNA with cobalt complex has attracted much attention [1]. The biological role of cobalt is mainly focused on its presence in the active center of vitamin B12, which regulates indirectly the synthesis of DNA. Additionally, cobalt is involved in the coenzyme of vitamin B12 used as a supplement of the vitamin [2], and at least eight cobalt-dependent proteins have been reported [3]. Since the first reported studies into the biological activity of cobalt complexes [4], diverse structurally characterized cobalt complexes showing antitumor antiproliferative [5, 6], antimicrobial [7, 8], antifungal [9, 10], antiviral [11, 12], and antioxidant [13] activities have been reported. Deoxyribonucleic acid (DNA) plays a significant role in the life process because it carries the inheritance information and leads the biological synthesis of proteins and enzymes through the replication and transcription of genetic information in living cells. DNA is especially a good target for metal complexes as it gives a wide variety of potential metal binding sites [14–16]. For example, the rich DNA electron bases and phosphate groups are suitable for direct covalent coordination at the metal centre. There are noncovalent binding behaviors such as hydrogen bonding and electrostatic binding in the grooved regions of the DNA, along with the intercalation of planar aromatic ligands in the stacked base pairs [17–23]. The interaction of DNA with transition metal complexes has gotten intensive attention in the last few years in order to develop new novel nonradioactive probes of DNA structure [24, 25], new therapeutic agents that cleave DNA [26–28] and DNA-mediated electron transfer reactions [29]. Recently, binding of metal complexes with 1,10-phenanthroline