Highly Selective Detection of Hypochlorous Acid by a Bis-heteroleptic Ru(II) Complex of Pyridyl-1,2,3-triazole Ligand via C(sp)-H Hydroxylation.

A Ru(II) complex () of a substituted pyridyl-1,2,3-triazole ligand () for highly selective "light-up" detection of hypochlorous acid is presented. An unusual anti-Markovnikov HOCl addition to the C═C bond of 1,2,3-triazole and a highly specific C(sp)-H hydroxylation over epoxidation made a highly selective luminescent HOCl probe. The abnormal regio- and stereoselective HOCl addition and subsequent hydroxylation mechanism in detail is supported by the combination of ESI-MS, H/C NMR spectroscopy, and H NMR titration. The hydroxylation at the C5 center in 1,2,3-triazole increases the electron density and makes a better σ-donor as well as π-donor, which in turn increases the MC-MLCT energy gap and inhibits the nonradiative decay from the excited state of and is the key reason for luminescence light-up. Most importantly, the exogenous and endogenous HOCl imaging in the living HEK293T cells is also demonstrated. The probe showed low cytotoxicity and efficiently permeated the cell membrane. The cell-imaging experiments revealed rapid staining of the extranuclear region of HEK293T cells which clearly indicates the presence of cytoplasmic HOCl. The endogenous HOCl generation and imaging, stimulated by lipopolysaccharides (LPS) and paraquat in the HEK293T cells, is also demonstrated.