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Issue 26, 2019
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Iridium(iii) polypyridine complexes with a disulfide linker as biological sensors and cytotoxic agents

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Abstract

The synthesis, characterization, and photophysical properties of two novel cyclometalated iridium(III) PEG complexes with a disulfide linkage [Ir(N^C)2(bpy-SS-PEG)](PF6) (bpy-SS-PEG = 4-(N-(2-((N-(2-(ω-methoxypoly(1-oxapropyl))ethyl)amino)cabonylethoxy)dithiolethoxy)carbonylamino)methyl-4′-methyl-2,2′-bipyridine; HN^C = methyl 2-phenyl-4-quinolinecarboxylate (pqe) (1a), 2-phenylquinoline (pq) (2a)), their PEG-free counterparts [Ir(N^C)2(bpy-SS-py)](PF6) (HN^C = pqe (1b), pq (2b)), their disulfide-free counterparts [Ir(N^C)2(bpy-CONH-PEG)](PF6) (bpy-CONH-PEG = 4-N-(2-(ω-methoxypoly-(1-oxapropyl))ethyl)aminocarbonyl)-4′-methyl-2,2′-bipyridine; (HN^C = pqe (1c), pq (2c)), and a bimetallic iridium(III)–rhenium(I) complex [Ir(pqe)2(bpy-SS-py)Re(Me4-phen)(CO)3](PF6)(CF3SO3) (Me4-phen = 3,4,7,8-tetramethyl-1,10-phenathroline) (3) are reported. Upon irradiation, the complexes displayed intense green to red emission under ambient conditions. Complex 3 containing two communicating luminophores exhibited large spectral overlap and was found to have a theoretical FRET efficiency of 0.79. In the presence of GSH, the bimetallic disulfide-containing complex 3 would be cleaved which was followed by a 8-fold increase in emission intensity of the rhenium(I) moiety. The reaction was found to be specific toward Cys, GSH, and H2S compared to other biothiols. Cell-based assays on complex 1a demonstrated that the addition of GSH to induce cleavage of the disulfide linkage would provide a more cytotoxic agent due to the release of the appended PEG pendant. Cellular localization studies by laser-scanning confocal microscopy in live HeLa cells indicated that complexes 1a–c exhibited punctate staining in the mitochondria.

Graphical abstract: Iridium(iii) polypyridine complexes with a disulfide linker as biological sensors and cytotoxic agents

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Submitted
21 Feb 2019
Accepted
26 Mar 2019
First published
27 Mar 2019

Dalton Trans., 2019,48, 9692-9702
Article type
Paper

Iridium(III) polypyridine complexes with a disulfide linker as biological sensors and cytotoxic agents

S. P. Li, J. Shum and K. K. Lo, Dalton Trans., 2019, 48, 9692
DOI: 10.1039/C9DT00793H

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