Issue 26, 2019

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

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

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
21 fev 2019
Accepted
26 mar 2019
First published
27 mar 2019

Dalton Trans., 2019,48, 9692-9702

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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