Novel Molecular Fluorescent Probes For Hydrogen Sulfide: Molecular Design, Synthesis And Properties

Hydrogen sulfide (H2S) is the third endogenously produced gaseous signalingmolecule following the two well-known gaseotransmitters: nitric oxide (NO) andcarbon monoxide (CO). In order to understand its important physiological andpathological role, it’s crucial to trace and determine H2S distributing in biologicalsystems. Traditional methods such as methylene-blue-based spectrophotometry,nanotube-based electrochemical detection and so on could get a sensitivedetermination for H2S, but most of them couldn’t achieve on-line analysis or real-timemonitoring, furthermore, maybe destroy biological sample. In contrast, fluorescencespectroscopy is provided with sample operation, great temporal and spatial resolution,high sensitivity as well as real-time imaging, and especially realizes non-destructivedetection of target biomolecules in live cells or tissues. Based on a variety of designstrategies, such as good reducing property, strong nucleophilicity and so on, numerousmolecular fluorescent probes have been developed till now. Some of them can detectH2S in vitro, and some of them can detect H2S in vivo, and even some of them canrealize the detection of trace amounts of H2S in subcellular organelles. However, up tonow, molecular fluorescent probes targeted to subcellular organelles are still limited,and the general design strategy is like this: introduce lysosome-targetable group intousual probe, and then lysosome-targetable group guides probe into the specialsubcellular organelle to detect target molecule. In this design, imperfect target andnonspecific distribution of target molecule make the detection procedure inevitablyexist background fluorescence from cytoplasm and other subcellular organelles. On theother hand, the complexity of biological systems makes a lot of molecular probesprohibitive. In contrast, ratiometric probes employing the ratio of the emissionintensity at two different wavelengths can effectively solve this problem. Although afew ratiometric fluorescent probes for H2S have been reported, most of them stilldisplay a relatively long response time. Therefore, it is still very important to developexcellent probes with faster response time, more obvious phenomenon and higherpracticability. For questions existing in H2S detection in subcellular organelles andresearch status of H2S molecular probes in complex biological system, this papercarried out the following works:(1) Based on that the spirolactam of rhodamine derivatives can be activated under acidic conditions and H2S can reduce-N3into-NH2, a simultaneous H2S andproton-activatable lysosome-targetable fluorescent probe Lyso-Rh-H2S has beendeveloped. In this design, spirolactam is introduced as a recognition group for H+, and-N3is introduced as a recognition group for H2S, and morpholine is introduced as alysosomal localization group. Neither H+nor H2S alone can activate the fluorescenceof probe unless both of them are presented together. Under acidic environment oflysosomes, the spirolactam of rhodamine derivatives can be activated, so the probe canachieve specific detection and fluorescence imaging of H2S in lysosomes.(2) Based on internal charge transfer (ICT), a ratiometric probe has beendeveloped for H2S detection in complex biological systems. A new fluorophoreconnecting coumarin and merocyanine through an ethylene group was got. Because ofinternal charge transfer (ICT), the new fluorophore displayed near-infraredfluorescence emission. Under the presence of H2S, nucleophilic addition reactionbetween H2S and the probe happens, which causes the destruction of molecular planarstructure, blocking the ICT process. Therefore, the fluorescence of the longwavelength decreases, and the fluorescence of coumarin enhances, so realizing a fastcolorimetric and ratiometric fuorescence response to H2S.