Development Of Near-infrared Fluorescent Probes For Biothiols And Thiophenols And Their Application In Environmental Analysis

At present,some pollutants in the environment,such as thiol-containing compounds,have gradually attracted people's attention.Thiol-containing compounds include thiols and thiophenols,which have different roles in environmental and biological systems and industrial production.Biothiols include hydrogen sulfide?H₂S?,cysteine?Cys?,homocysteine?Hcy?and glutathione?GSH?.The industrial production of H₂S-containing sewage flowing into environment will cause unimaginable pollution of the surrounding air,water and soil,ultimately affecting the health of the surrounding residents.Cysteine,homocysteine,and glutathione play important roles in human physiology.Thiophenols play an important role in organic synthesis and are widely used in the preparation of agrochemicals and pharmaceuticals.In recent years,the detection of thiols and thiophenols in biological and environmental samples has caused great interest among the majority of scholars.Near-infrared?NIR?fluorescent probes have minimal light damage to the sample,can penetrate deep into the tissue,and reduce interference from the autofluorescence of the sample itself,so they have become the preferred choice for biological and environmental monitoring.In this paper,hemicyanine dyes were selected as a platform to develop two NIR probes for the detection of thiols and thiophenol.?1?The hemi-cyanine dye was modified to synthesize two NIR fluorescent probes NIR-NBD and ArSH-probe,respectively.Their structures were identified by mass spectrometry,NMR,and others.?2?NIR-NBD was successfully employed for simultaneously detection and differentiation cysteine?cys?/homocysteine?Hcy?,glutathione?GSH?and hydrogen sulfide?H₂S?in aqueous solutions.The fluorescent probe used NIR-OH as the fluorophore and NBD ether as the reaction site.The probe achieved dual excitation and emission fluorescent response to Cys/Hcy through nucleophilic substitution and intramolecular re-arrangement,but only single emission response to GSH and H₂S,while other interfering substances did not cause significant changes in the spectrum.In addition,the probe had a unique absorption at 550 nm induced by H₂S.Moreover the probe reacted with Cys faster than Hcy.Thus,the probe was capable of the detection and differentation of these four thiols.Spectroscopic results showed that the fluorescent intensity of the probe molecules was proportional to Cys at 0-1?M,Hcy at 0-10?M,GSH at 0-10?M,and H₂S at 0-100?M,and thus could be used for quantitative detection of these four substances.The probe can be also used to detect H₂S in the actual water sample,and the recovery rate is as high as 98%or more.Moreover,the probe can usually detect Cys,GSH and H₂S in living cells with the help of fluorescence microscopy technique.?3?ArSH-probe was utilized to monitor thiophenols in aqueous solutions and living cells.The probe used ArSH-OH as a fluorophore,2,4-dinitrofluorobenzene as a reaction site and quencher group,both of them were linked via an ether group.Upon the addition of thiophenol,the probe solution released strong fluorescence at 741nm due to the cleavage of the ether bond.When the concentration of thiophenol in the solution was 0-10?M,there was a good linear relationship between the fluorescence intensity of the probe molecule and the thiophenol concentration.After adding40-equiv thiophenol,the reaction was complete,with about 91-fold enhancement in fluorescence intensity,and the detection limit was 0.54?M.The experimental results showed that the probe molecule can be successfully used to locate mitochondria and quantitatively detect thiophenol in actual water samples and living cells.