Azide and sulfonylazide functionalized fluorophores for the selective and sensitive detection of hydrogen sulfide

Abstract

Three fluorescent probes (1–3) for the selective and sensitive detection of hydrogen sulfide have been synthesized and characterized. Probe 1 is a coumarin derivative functionalized with an azide moiety whereas 2 contain the azide reactive group into a naphthalene fluorophore backbone. Probe 3 is composed also by a naphthalene fluorophore but, in this case, functionalized with a sulfonylazide reactive moiety. Probes 1 and 3 are non-fluorescent whereas 2 is weakly emissive in HEPES (10mM, pH 7.4)–DMSO 99:1 (v/v). The emission behavior of the three probes was tested against selected anions, bio-thiols and oxidant molecules. Of all the chemical species tested, only HS− is able to induce an enhancement in the emission intensity (50, 11 and 20-fold for 1, 2 and 3, respectively). The observed emission in the presence of hydrogen sulfide is ascribed, in the case of probes 1 and 2, to an azide–amine reduction induced by HS− anion, whereas for probe 3 the sensing mechanism is related with a sulfonylazide–sulfonamide conversion. The three probes are very sensitive to HS− anion with limits of detection of 0.17, 0.20 and 0.40mM for 1, 2 and 3 respectively. Cell viability studies demonstrated that 1–3 probes are essentially non-toxic at concentrations 10–50μM and are well suited for in vivo studies. Finally, probe 1 was used for the detection on intracellular HS− anion in HeLa cells by means of confocal microscopy.