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Alkyl chain modified cyclometalated iridium complexes as tunable anticancer and imaging agent


Five mononuclear cyclometalated iridium complexes [1](PF6)-[5](PF6) are prepared using imidazole based ligands of varying alkyl chain length. The complexes are characterised by various analytical techniques. The single crystal X-ray structures of [2](PF6), [3](PF6) and [4](PF6) reveal their expected distorted Oh structures around the metal centre; however, the chain length is found to play a crucial role in deciding the overall geometry. Theoretical investigation demonstrates that the HOMOs are mainly contributed by iridium and cyclometalated ligands, whereas LUMOs are constituted by bpy/phen unit. The complexes are found to be luminescent with moderate emission quantum yield and lifetime in CH3CN. The in vitro growth inhibition assay of the complexes with shorter alkyl chain ([4]+ and [5]+) displays higher anticancer activity (IC50 < 0.5 µM) as compared to the complexes of longer alkyl chain ([1]+ - [3]+) (IC50 < 30 µM) against human breast cancer (MCF-7) cells. The complexes [4]+ and [5]+ also display moderate cancer cell selectivity (~ 3 times) over normal breast (MCF-10) cells. The flow cytometry assay and fluorescence microscopy analysis suggest that cellular accumulation is primarily responsible for the variation of anticancer activity. Interestingly, without possessing any anticancer activity or toxicity ((IC50 > 50 µM), the complex [1]+ mainly accumulates near the cell membrane outside the cell and displays clear image of the cell membrane. The light microscopy images and western blot analysis reveal that complex [4]+ induces combined apoptosis and paraptosis. Thus, tuning of anticancer activity and cellular imaging property mediated by alkyl chain would be of great importance and be useful in anticancer research.

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Publication details

The article was received on 15 Jun 2018, accepted on 11 Oct 2018 and first published on 12 Oct 2018

Article type: Paper
DOI: 10.1039/C8DT02461H
Citation: Dalton Trans., 2018, Accepted Manuscript
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    Alkyl chain modified cyclometalated iridium complexes as tunable anticancer and imaging agent

    S. Patra, P. Laha, U. De, N. Dehury, F. Chandra, H. S. Kim and S. Khullar, Dalton Trans., 2018, Accepted Manuscript , DOI: 10.1039/C8DT02461H

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