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Biocompatible Phosphorescent Ir(III) Oxygen Sensor Functionalized with Oligo(ethylene glycol) Groups: Synthesis, Photophysics and Application in PLIM Experiments

Abstract

Phosphorescent transition metal complexes with emission in near infrared (NIR) area and appreciable quantum yield, compatible with physiological media and suitable for application as effective oxygen sensors in biological systems are still a challenge for synthetic organometallic chemistry. In addition to the sufficiently high requirements in photophysics, they also have to meet strict conditions for biocompatibility and selectivity of sensory response in a multicomponent biological medium. Building on our previous research we have synthesized three novel iridium [Ir(N^C)2(N^N)]+ complexes (N^C – metalated ligands based on benzothienyl-phenanthridine core; N^N – pyridine-triazole diimine chelate), with the periphery decorated with 1, 2 or 3 relatively small “double-tail” oligo(ethylene glycol) (OEG) {-C(O)NHCH(CH2OC2H4OC2H4OCH3)2} functions. All these complexes display desirable photophysical characteristics: excitation at the high energy limit of the “window of transparency” and NIR emission at ca. 710-720 nm, rather high quantum yield (13-15% in degassed methanol solution) and strong lifetime response onto variations in oxygen concentration. However, the study of their behavior in model biological systems (human serum albumin (HSA) and fetal bovine serum (FBS) solutions) with gel permeation chromatography and absorption/luminescent spectroscopy showed that only the complex bearing OEG functions at all three chelate ligands is compatible with the requirements of imaging experiments, i.e. is water soluble, bleaching stable, low toxic and its sensory response is insensitive to the presence of the components of biological media, temperature, and pH. Sensor properties of this molecular probe have been studied in detail and test imaging experiments in phosphorescence lifetime imaging (PLIM) mode were carried out onto cancer cell cultures. We demonstrate that the probe is accumulated in the cell cytoplasm and exhibits low cytotoxicity at the concentrations up to 125 μM (though cell’s metabolism is affected by the probe). Phosphorescence lifetime imaging microscopy (PLIM) of live mouse colorectal cancer cells (CT26) and human oral squamous carcinoma (SCC-4) stained with the probe has shown lifetimes in 1.35-2.51 μs interval with pronounced response to oxygen under hypoxic conditions thus providing the basis for qualitative detection of hypoxia and semi-quantitative oxygen concentration measurements.

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Supplementary files

Article information


Submitted
21 Mar 2020
Accepted
09 May 2020
First published
11 May 2020

New J. Chem., 2020, Accepted Manuscript
Article type
Paper

Biocompatible Phosphorescent Ir(III) Oxygen Sensor Functionalized with Oligo(ethylene glycol) Groups: Synthesis, Photophysics and Application in PLIM Experiments

I. Kritchenkov, A. Elistratova, V. Sokolov, P. S. Chelushkin, M. V. Shirmanova, M. M. Lukina, V. Dudenkova, V. I. Shcheslavskiy, S. Kalinina, K. Reess, A. Rueck and S. P. Tunik, New J. Chem., 2020, Accepted Manuscript , DOI: 10.1039/D0NJ01405B

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