Biological and catalytic evaluation of Ru(II)-p-cymene complexes of Schiff base ligands: Impact of ligand appended moiety on photo-induced DNA and protein cleavage, cytotoxicity and C-H activation

Two organometallic Ru(II)-p-cymene complexes of the type [Ru(eta(6)-p-cymene)(L)Cl]PF6 1 and 2, where L is N,N-bis(4-isopropylbenzylidene)ethane-1,2-diamine (bien, L1) or N,N-bis (pyren-2-ylmethylene)ethane-1,2-diamine (bpen, L2) have been prepared and characterized well. Because of appended pyrenyl groups in coordinated bpen ligand, the complex 2 exhibits higher DNA and protein binding than complex 1 in which isopropylbenzyl groups are incorporated. Interestingly, the luminescent characteristic complex 2 is unique in displaying DNA cleavage after light activation by UVA light at 365 nm through oxygen dependent mechanism. AFM analysis attests the photo-induced DNA fragmentation ability of complex 2. Also, the complex 2 cleaves the protein after light exposure in a non-specific manner suggesting that it can act as a protein photo cleaving agent. In contrast to the trend of DNA and protein interaction of complexes, the complex 1 exhibits cytotoxic activity against human breast carcinoma (MCF-7) and liver carcinoma (HepG2) with potency higher than that of complex 2 due to enhanced hydrophobicity of isopropyl groups present in p-cymene and bien ligands. Indeed, complex 2 is inactive against MCF-7 and HepG2 cancer cell lines even up to 200 mu M concentration. The AO/EB staining assay reveals that the complex 1 is able to induce late apoptotic mode of cell death in breast cancer cells, which is further confirmed by inter-nucleosomal DNA cleavage. Furthermore, the complexes 1 and 2 are evaluated for their catalytic activities and found to be working well for the beta-carboline directed C-H arylation to afford the desired products in good yield (40-47%).