Hindawi Publishing Corporation Bioinorganic Chemistry and Applications Volume 2010, Article ID 973742, 9 pages doi:10.1155/2010/973742 Research Article Synthesis, Characterization, DNA Binding, and Photocleavage Activity of Oxorhenium (V) Complexes with α-Diimine and Quinoxaline Ligands Christiana A. Mitsopoulou and Constantinos Dagas Laboratory of Inorganic Chemistry, Department of Chemistry, University of Athens, Panepistimiopolis, Zografou, Athens 157 71, Greece Correspondence should be addressed to Christiana A. Mitsopoulou, cmitsop@chem.uoa.gr Received 11 March 2010; Accepted 1 April 2010 Academic Editor: Spyros Perlepes Copyright © 2010 C. A. Mitsopoulou and C. Dagas. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The complex [ReOCl 3 pq] (1) (where pq = 2-(2 ′ pyridyl)quinoxaline) has been synthesized and fully characterized by UV-Vis, FTIR, 1 and 2D NMR, and cyclic voltammetry (CV). The DNA-binding properties of the complex 1 as well as of the compounds [ReOCl 3 bpy] (2), [ReOCl 3 phen] (3), and pq (4) were investigated by UV-spectrophotometric (melting curves), CV (cyclic voltammetry), and viscosity measurements. Experimental data suggest that complex 1 intercalates into the DNA base pairs. Upon irradiation, complex 1 was found to promote the cleavage of plasmid pBR 322 DNA from supercoiled form I to nicked form II. The mechanism of the DNA cleavage by complex 1 was also investigated. 1. Introduction For many years transition metal complexes have piqued curiosity owing to their efficient DNA binding and cleavage properties under physiological conditions [1–14]. It has been demonstrated that inorganic complexes can be used in foot- printing studies, as sequence specific DNA binding agents, as diagnostic agents in medicinal applications, and for genomic research. Among different modes of DNA cleavage, oxidative cleavage of DNA upon irradiation with visible light is of main interest due to the potential applications of such compounds in photodynamic therapy of cancer [3, 15] and references therein. On the other hand, coordination chemistry of rhenium has been extensively developed in recent years due, to a large extent, to the fact that its complexes with diimine ligands display long lifetimes and also short-lived rhenium isotopes hold promise as β-emitters in radiotherapy [14, 16, 17]. The chemistry of oxorhenium complexes arouses particular interest among these compounds not only for their implication in various reactions of industrial and biological importance, including olefin epoxidation and catalysis by cytochrome P-450 [18, 19], but also for their lipophilic character and the oxidation states of rhenium that is Re(I) to Re (VI) [17]. In this context, the design, synthesis, and reactivity of novel rhenium oxocomplexes have become the aim of several laboratories, including ours. To the best of our knowledge, studies on oxorhenium (V) complexes incorporating planar aromatic ligands that could bind to DNA have not been studied before. Nevertheless, quinoxaline (pq) has recently received considerable attention [20, 21]. The structure of the quinoxaline ligand is recognized from a great number of natural compounds such as riboflavin and molybdopterines, and can be used as antibacterial, antiviral, anticancer, antihelmintic, and insecticidal agent [22]. In addition, it adopts a planar conformation when chelates to a metal ion [20, 23, 24]. This planar appendage provides a handle for intercalative binding to DNA, positioning the complex for enhanced reactivity toward DNA. In this paper, we present the synthesis and character- ization of the oxorhenium (V) complex, [ReOCl 3 pq] (1). In order to elucidate the reactivity of this compound, we have also synthesized the complexes [ReOCl 3 bpy] (2) and [ReOCl 3 phen] (3) and studied their intercalating abilities. The ligands (2 ′ pyridyl)quinoxaline (4), 2,2 ′ bipyridine (5),