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 L1–L3 and
complexes 1–6 have been thoroughly
characterized by satisfactory elemental analyses, spectral studies
(ESI-MS, IR, 1H and 13C NMR, UV–vis),
and structures of 1–3 authenticated
by X-ray single-crystal analyses. Efficient binding of 1–6 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 1–6 induce apoptosis in the order 2 > 1 > 4 > 3 > 5 > 6.
With intent to fine tune the morphological and photophysical properties, three novel AIE luminogens (BQ1-BQ3) based on quinoline-BODIPY have been synthesized. A judicious choice of substituents (-H, -CH3, -OCH3) in these systems led to nanoballs in BQ1 and BQ2, while in BQ3 it led to reticulated nanofibers with diverse photophysical behaviours.
A pyrazole-appended quinoline-based 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (L1, BODIPY) has been synthesized and used as a ligand for the preparation of iridium(III) complexes [Ir(phpy)(L1)]PF (1; phpy = 2-phenylpyridine) and [(η-CMe)Ir(L1)Cl]PF (2). The ligand L1 and complexes 1 and 2 have been meticulously characterized by elemental analyses and spectral studies (IR, electrospray ionization mass spectrometry, H andC NMR, UV/vis, fluorescence) and their structures explicitly authenticated by single-crystal X-ray analyses. UV/vis, fluorescence, and circular dichroism studies showed that complexes strongly bind with calf-thymus DNA and bovine serum albumin. Molecular docking studies clearly illustrated binding through DNA minor grooves via van der Waals forces and their electrostatic interaction and occurrence in the hydrophobic cavity of protein (subdomain IIA). Cytotoxicity, morphological changes, and apoptosis have been explored by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and Hoechst 33342 staining. IC values for complexes (1, 30 μM; 2, 50 μM) at 24 h toward the human cervical cancer cell line (HeLa) are as good as that of cisplatin (21.6 μM) under analogous conditions, and their ability to kill cancer cells lies in the order 1 > 2. Because of the inherent emissive nature of the BODIPY moiety, these are apt for intracellular visualization at low concentration and may find potential applications in cellular imaging and behave as a theranostic agent.
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