Osmium(ii) polypyridyl polyarginine conjugate as a probe for live cell imaging; a comparison of uptake, localization and cytotoxicity with its ruthenium(ii) analogue

Abstract

A first investigation into the application of a luminescent osmium(ii) bipyridine complex to live cell imaging is presented. Osmium(ii) (bis-2,2-bipyridyl)-2(4-carboxylphenyl) imidazo[4,5f][1,10]phenanthroline was prepared and conjugated to octaarginine, a cell penetrating peptide. The photophysics, cell uptake and cytotoxicity of this osmium complex conjugate were performed and compared with its ruthenium analogue. Cell uptake and distribution of both ruthenium and osmium conjugates were very similar with rapid transmembrane transport of the osmium probe (complete within approx. 20 min) and dispersion throughout the cytoplasm and organelles. The near-infrared (NIR) emission of the osmium complex (λmax 726 nm) coincides well with the biological optical window and this facilitated luminescent and luminescence lifetime imaging of the cell which was well resolved from cell autofluorescence. The large Stokes shift of the emission also permitted resonance Raman mapping of the dye within CHO cells. Rather surprisingly, the osmium conjugate exhibited very low cytotoxicity when incubated both in the dark and under visible irradiation. This was attributed to the remarkable stability of this complex which was reflected by the complete absence of photo-bleaching of the complex even under extended continuous irradiation. In addition, when compared to its ruthenium analogue its luminescence was short-lived in water therefore rendering it insensitive to O2.

Heterobimetallic Complexes for Theranostic Applications

“…Ruthenium complexes have been long time studied as DNA light‐switch intercalators, oxygen sensors, and lately as cell imaging probes . However, Os II –polypyridyl complexes have been only considered to bear biological applications very recently as a potential cell imaging agent by Keyes and co‐workers . In the case of cyclometallated Ir III complexes, their emission process is mainly due to a 3 MLCT process, althought intraligand ( 3 IL), ligand‐to‐ligand ( 3 LLCT) and σ‐bond‐to‐ligand charge transfer (SBLCT) could also influence the luminescence.…”

“…The wide use of Ir III as cell imaging agent would be an excellent starting point to outline a prototype and reach an optimized Ir III ‐based heterobimetallic teranostic agent. In the case of Os II species, a good strategy would be to relay in the photophysical similarities with that of Ru II species, as only one example has been described dealing with Os II derivatives as cell imaging agents …”

“…[21] However,O s II -polypyridyl complexes have been only considered to bear biological applicationsv ery recently as a potentialc ell imaging agent by Keyes and co-workers. [22] In the case of cyclometallated Ir III complexes, their emission process is mainly due to a 3 MLCT process, althought intraligand( 3 IL), ligand-to-ligand ( 3 LLCT) and s-bond-to-ligand charge transfer (SBLCT)c ould also influence the luminescence. Their HOMOs, largely localized on the metal and metallated aryl units and their LUMOs on the pyridyl units, allow their energy levels to be tune independently and thus, af acile color tuning is achieved.…”

Electrochemiluminescent Array to Detect Oxidative Damage in ds-DNA Using [Os(bpy)2(phen-benz-COOH)]2+/Nafion/Graphene Films

“…Pyrolytic graphite (PG, 2.5 × 2.5 × 0.3 cm 3 ) wafers were from GraphiteStore.com (http://www.graphitestore.com), and basal plane PG was from Advanced Ceramics. [Os(bpy) 2 (phen-benz-COOH)] 2+ was synthesized by refluxing Os(bpy) 2 Cl 2 with 4-(1,10-phenanthrolin-6-yl) benzoic acid in ethanol/ water (1:1) for 16 h (Scheme S1, Supporting Information (SI)), 35 and characterized by 1 H NMR, HPLC, and spectroscopy (Figures S1 and S2 of the SI). …”

One Scaffold, Many Possibilities – Copper(I)‐Catalyzed Azide–Alkyne Cycloadditions, Strain‐Promoted Azide–Alkyne Cycloadditions, and Maleimide–Thiol Coupling of Ruthenium(II) Polypyridyl Complexes

“…Biological applications are particularly limited by the choice of linkage given that bioorthogonal conditions have to be applied. Click chemistry approaches such as the copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC), strain‐promoted azide–alkyne cycloaddition (SPAAC), and maleimide–thiol coupling represent advantageous strategies to link sensitive (bio)molecules with functional units, for example, photosensitizers or other imaging agents, and the control of the coupling is dependent on the corresponding functionalities. For photodynamic therapy (PDT), one feasible approach is to couple selectivity‐mediating biomolecules to photosensitizers such as Ru II polypyridyl complexes .…”