Abstract
In this work, we investigate the mode of interaction of a family of fluorescent zinc complexes with HS– and H2S. Different experiments, performed by diverse spectroscopic techniques, provide evidence that HS– binds the zinc center of all the complexes under investigation. Treatment with neutral H2S exhibits a markedly different reactivity which indicates selectivity for HS– over H2S of the systems under investigation. Striking color changes, visible to the naked eye, occur when treating the systems with HS– or by an H2S flow. Accordingly, also the fluorescence is modulated by the presence of HS–, with the possible formation of multiple adducts. The results highlight the potential of the devised systems to be implemented as HS–/H2S colorimetric and fluorescent sensors. Bioimaging experiments indicate the potential of using this class of compounds as probes for the detection of H2S in living cells.
Highlights
Over the past two decades, hydrogen sulfide (H2S) has gained increasing attention as a biological molecule which mediates important functions within the human body through its action on bioinorganic targets, joining NO and CO in the family of gasotransmitters
The biological reactivity of NO and CO has been widely clarified thanks to the numerous papers focusing on their coordination chemistry to bioinspired metal complexes.[1−4] Differently, H2S reactivity is still in a premature stage mainly owing to the fact that H2S is a weak acid, which in aqueous solution equilibrates with its anions HS− and S2− (at physiological pH (7.4), 28% of the total hydrogen sulfide exists as H2S, 72% is in the form of HS−, whereas S2− is negligible)[5] complicating the studies on H2S reactivity in biological media and the clarification of the specific chemistry associated with the specific protonation state.[6]
Some time ago, we and others focused our efforts on the study of the coordination of H2S/HS− to transition metals.[10−14] In particular, we explored both the reactivity of properly tailored molecular complexes and that of natural metalloproteins.[15−23] More recently, we focused on zinc porphyrins and on zinc tetradentate Schiffbased complexes which share many structural features targeting these systems as viable scaffolds for isolating and characterizing hydrosulfido species.[24−27] among the wide number of d10 metal complexes, zinc(II) complexes with nitrogen-containing ligands are excellent candidates for the development of luminescent materials
Summary
Over the past two decades, hydrogen sulfide (H2S) has gained increasing attention as a biological molecule which mediates important functions within the human body through its action on bioinorganic targets, joining NO and CO in the family of gasotransmitters. Stable H2S/HS− adducts of biomimetic metal complexes are still not numerous because of the propensity of metal sulfides to precipitate in addition to the redox reactivity of sulfides.[6−9] Drawing upon these considerations, some time ago, we and others focused our efforts on the study of the coordination of H2S/HS− to transition metals.[10−14] In particular, we explored both the reactivity of properly tailored molecular complexes and that of natural metalloproteins.[15−23] More recently, we focused on zinc porphyrins and on zinc tetradentate Schiffbased complexes which share many structural features (i.e., both tetradentate and planar) targeting these systems as viable scaffolds for isolating and characterizing hydrosulfido species.[24−27] among the wide number of d10 metal complexes, zinc(II) complexes with nitrogen-containing ligands are excellent candidates for the development of luminescent materials. We wanted to explore whether these different groups on the ligand structure would tune somehow the fluorescence properties of the related complexes as HS− sensors
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