Evaluation of photochemotherapeutic potential of a few oxo-bridged dimeric Fe(III) compounds having Salen-type ligands

Abstract

Four oxo-bridged dimeric Fe(III) complexes, viz. [(µ-O){Fe(L)}2] (1–4), where L is N,Ń-bis(naphtalidene)-ethylenediamine, (H2L1 in 1); N,Ń-bis(naphtalidene)-1,2-phenylenediamine, (H2L2 in 2); N,Ń-bis(naphtalidene)-4-nitro-1,2-phenylenediamine (H2L3 in 3) and N,Ń-bis(naphtalidene)-4-carboxyl-1,2-phenylenediamine, (H2L4 in 4) were synthesized for their potential application as photochemotherapeutic agents in low energy visible light. The solid-state structure of complex 2 was confirmed by X-ray crystallography. The complexes bind to human serum albumin (HSA) reversibly in a pH dependent manner, which could be a potential carrier of the molecules in blood plasma. They also bind to calf-thymus (ct) DNA with considerable affinity. In vitro cellular experiments show that the complexes display significant photo-enhanced cytotoxicity in human cervical cancer (HeLa) and human breast cancer (MCF-7 and MDA-MB-231) cells with low dark toxicity. ICP-MS analysis show that the complexes enter HeLa cells in a dose-dependent manner. Flow cytometric and confocal microscopic experiments demonstrate that the complexes kill cancer cells on exposure to visible light primarily via apoptosis through the generation of reactive oxygen species (ROS).