Towards Water Soluble Mitochondria-Targeting Theranostic Osmium(II) Triazole-Based Complexes.

Salem A E Omar,Helen E Bryant,Julia A Weinstein,Paul A Scattergood,Luke K Mckenzie,Paul I P Elliott

doi:10.3390/molecules21101382

Salem A E Omar, Helen E Bryant + Show 4 more

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https://doi.org/10.3390/molecules21101382

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Abstract

The complex [Os(btzpy)2][PF6]2 (1, btzpy = 2,6-bis(1-phenyl-1,2,3-triazol-4-yl)pyridine) has been prepared and characterised. Complex 1 exhibits phosphorescence (λem = 595 nm, τ = 937 ns, φem = 9.3% in degassed acetonitrile) in contrast to its known ruthenium(II) analogue, which is non-emissive at room temperature. The complex undergoes significant oxygen-dependent quenching of emission with a 43-fold reduction in luminescence intensity between degassed and aerated acetonitrile solutions, indicating its potential to act as a singlet oxygen sensitiser. Complex 1 underwent counterion metathesis to yield [Os(btzpy)2]Cl2 (1Cl), which shows near identical optical absorption and emission spectra to those of 1. Direct measurement of the yield of singlet oxygen sensitised by 1Cl was carried out (φ (1O2) = 57%) for air equilibrated acetonitrile solutions. On the basis of these photophysical properties, preliminary cellular uptake and luminescence microscopy imaging studies were conducted. Complex 1Cl readily entered the cancer cell lines HeLa and U2OS with mitochondrial staining seen and intense emission allowing for imaging at concentrations as low as 1 μM. Long-term toxicity results indicate low toxicity in HeLa cells with LD50 >100 μM. Osmium(II) complexes based on 1 therefore present an excellent platform for the development of novel theranostic agents for anticancer activity.

Highlights

Oligopyridyl complexes of kinetically inert d6 metals, e.g., Ru(II), Os(II), have attracted enormous interest in recent decades due to their attractive photophysical properties [1,2,3,4]
We have recently reported the synthesis and characterization of deep-red/near-IR emissive osmium(II) bitriazolyl complexes and demonstrated their use in light-emitting electrochemical cells [19]
Spectrum of 1 exhibits a characteristic singlet resonance for four equivalent triazole spectrum of 1 exhibits a characteristic singlet resonance for four equivalent triazole ring protons ring at protons at δ is9.13, whichrelative is deshielded relative to the for corresponding signal for The the free δ 9.13, which deshielded to the corresponding signal the free ligand by

Summary

Introduction

Oligopyridyl complexes of kinetically inert d6 metals, e.g., Ru(II), Os(II), have attracted enormous interest in recent decades due to their attractive photophysical properties [1,2,3,4]. These complexes typically exhibit relatively long-lived triplet metal-to-ligand charge transfer (3 MLCT) states. These states may undergo deactivation through a number of routes including phosphorescence or energy/electron transfer which enables the potential application of these complexes in light-emitting [5].

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