DNA Binding and Anti-Cancer Activity of Redox-Active Heteroleptic Piano-Stool Ru(II), Rh(III), and Ir(III) Complexes Containing 4‑(2-Methoxypyridyl)phenyldipyrromethene

The synthesis of four novel heteroleptic dipyrrinato complexes [(η6-arene)­RuCl­(2-pcdpm)] (η6-arene = C6H6, 1; C10H14, 2) and [(η5-C5Me5)­MCl­(2-pcdpm)] (M = Rh, 3; Ir, 4) containing a new chelating ligand 4-(2-methoxypyridyl)-phenyldipyrromethene (2-pcdpm) have been described. The complexes 1–4 have been fully characterized by various physicochemical techniques, namely, elemental analyses, spectral (ESI-MS, IR, 1H, 13C NMR, UV/vis) and electrochemical studies (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)). Structures of 3 and 4 have been determined crystallographically. In vitro antiproliferative and cytotoxic activity of these complexes has been evaluated by trypan blue exclusion assay, cell morphology, apoptosis, acridine orange/ethidium bromide (AO/EtBr) fluorescence staining, and DNA fragmentation assay in Dalton lymphoma (DL) cell lines. Interaction of 1–4 with calf thymus DNA (CT DNA) has also been supported by absorption titration and electrochemical studies. Our results suggest that in vitro antitumor activity of 1–4 lies in the order 2 > 1 > 4 > 3.