Dansyl-appended CuII-complex-based nitroxyl (HNO) sensing with living cell imaging application and DFT studies

Abstract

We introduce herein, a novel copper complex-based fluorescent probe [Cu^II(DQ₄₆₈)Cl]⁺ that exhibits a significant fluorescence turn-on response towards nitroxyl (HNO) with high selectivity over other biological reactive oxygen, nitrogen and sulfur species, including nitric oxide (NO). A smart strategy, involving HNO-induced reduction of paramagnetic [Cu^II(DQ₄₆₈)Cl]⁺ to diamagnetic [Cu^I(DQ₄₆₈)]⁺ with concomitant fluorescence enhancement via a PET mechanism is focused here. This reduction-based strategy was also supported by X-band EPR response and mass spectroscopy. The metal free probe (DQ₄₆₈) showed high affinity towards Cu²⁺ to form [Cu^II(DQ₄₆₈)Cl]⁺ with a 0.091 μM detection limit, which subsequently enabled the detection of HNO in an organo-aqueous medium at biological pH (7.4) in the green wavelength region (λ_em = 543 nm) with a LOD of 0.41 μM. The ground-state geometries of DQ₄₆₈, [Cu^II(DQ₄₆₈)Cl]⁺ and [Cu^I(DQ₄₆₈)]⁺ were optimized by DFT calculations, which revealed that the central metal ion in [Cu^II(DQ₄₆₈)Cl]⁺ is in a distorted tetrahedral geometry with the C1 point group. Additionally, the negligible cytotoxicity and good biocompatibility make the developed probe useful for the in vitro detection of HNO.