Interaction of monohydrogensulfide with a family of fluorescent pyridoxal-based Zn(II) receptors

H2S and its conjugate base HS− have recently gained increasing attention for their reactivity with bioinorganic targets. However, so far, stable adducts of bioinorganic compounds with H2S/HS− are still scarce due to the propensity of sulfide to form insoluble metal sulfides. In this work, we studied the reactivity of HS− with a family of fluorescent zinc complexes via a variety of spectroscopic techniques. The complexes selected for this study feature a pyridoxal moiety with different substituent groups on the ligand framework. Interaction of the complexes under investigation with HS− results in the displacement of the coordinated ligand from the Zn center with the concomitant precipitation of ZnS in the case of complexes 1 and 3, whereas for complex 2 our data points to the coordination of HS− to the metal center likely assisted by hydrogen bonding with the OH of the pyridoxal moiety. In the presence of HS−, the fluorescence emission of complex 2 is enhanced, whereas the fluorescence emission of complexes 1 and 3 is quenched. The results highlight the potential of complex 2 to be implemented as a HS− fluorescent sensor via a coordinative-based approach.