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Synthesis, Structure, DNA/Protein Binding, and Anticancer Activity of Some Half-Sandwich Cyclometalated Rh(III) and Ir(III) Complexes

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posted on 28.09.2015, 00:00 by Sujay Mukhopadhyay, Rakesh Kumar Gupta, Rajendra Prasad Paitandi, Nishant Kumar Rana, Gunjan Sharma, Biplob Koch, Love Karan Rana, Maninder Singh Hundal, Daya Shankar Pandey
The Schiff base ligands benzylidene­(4-tert-butylphenyl)­amine 4-methyl ester (L1), (4-nitrobenzylidene)­(4-tert-butylphenyl)­amine (L2), and (4-cyanobenzylidene)­(4-tert-butylphenyl)­amine (L3) and the new series of cyclometalated mononuclear piano-stool complexes [(η5-C5Me5)­RhCl­(L1)] (1), [(η5-C5Me5)­RhCl­(L2)] (2), [(η5-C5Me5)­RhCl­(L3)] (3), [(η5-C5Me5)­IrCl­(L1)] (4), [(η5-C5Me5)­IrCl­(L2)] (5), and [(η5-C5Me5)­IrCl­(L3)] (6) have been synthesized. The ligands L1L3 and complexes 16 have been thoroughly characterized by satisfactory elemental analyses, spectral studies (ESI-MS, IR, 1H and 13C NMR, UV–vis), and structures of 13 authenticated by X-ray single-crystal analyses. Efficient binding of 16 with calf thymus DNA (CT DNA) have been established by UV–vis and emission spectroscopic studies. Protein binding (bovine serum albumin, BSA) has been investigated by UV–vis, fluorescence, synchronous, and 3D fluorescence spectroscopy. Binding of the complexes with DNA through minor groove and hydrophobic interaction with proteins via sub domain IIA cavity has been substantiated by molecular docking studies. The complexes exhibited significant cytotoxicity against the human lung cancer cell line (A549), and 1 and 2 showed better activity than cisplatin. The cytotoxicity, morphological changes, and apoptosis have been assessed by MTT assay, Hoechst 33342/PI staining, cell cycle analysis by fluorescence-activated cell sorting (FACS), and reactive oxygen species (ROS) generation by DCFH-DA dye. The complexes 16 induce apoptosis in the order 2 > 1 > 4 > 3 > 5 > 6.