Design And Synthesis Of Novel Small Molecule Fluorescent Probes And Their Application In Biological Imaging Of Sulfur-containing Compounds

Sulfur-containing small molecule compounds include biological thiols（cysteine,homocysteine,glutathione）,sulfur dioxide,thiophenol,etc.They play an important role in biological systems,industrial and agricultural production.Biological thiols are involved in physiological and pathological processes such as redox homeostasis and intracellular signal transduction in biological systems.Sulfur dioxide is one of the main components of air pollutants.Its derivative SO₃^2-/HSO₃^-has the effects of anti-oxidation,inhibiting bacterial growth,and preventing enzymatic browning,so it is often used as an antioxidant and preservative in pharmaceutical products and food.Thiophenol is an organic sulfur compound widely used in the pharmaceutical industry and agricultural production.When thiophenol enters the organism,it will cause a series of adverse reactions,and it is also a serious environmental pollutant.Fluorescent probe detection methods have the advantages of non-destructive,real-time,low detection limit,high sensitivity,etc.Therefore,the use of organic small molecule fluorescent probes to specifically detect these sulfur-containing compounds is one of the hotspots in the field of medical research in recent years.In this subject,quinoline and carbazole were used as molecular frameworks,and five types of fluorescent probes were synthesized by modifying their structures.After systematic screening and verification,probe QN-DNP,QN-Cys,and CA-SO₂ have good performance and can achieve selective detection of thiophenol,cysteine and sulfur dioxide derivatives.The specific research content are listed as follows:1.In the first part,a novel fluorophore QN-OH based on the quinoline-xanthene structure was developed,which contains a modifiable hydroxyl structure.2,4-Dinitrophenyl was introduced as the recognition group,and a fluorescent probe QN-DNP for specific detection of thiophenol was synthesized.Thiophenol can undergo an aromatic nucleophilic substitution reaction with the 2,4-dinitrophenyl on the probe structure,thereby releasing the QN-OH fluorophore and generating a near-infrared fluorescence signal.The probe has high selectivity and sensitivity for the detection of thiophenol,with a detection limit as low as 78 n M,and can specifically detect thiophenol in a wide p H range.The probe QN-DNP has good biocompatibility and low cytotoxicity,and has large Stokes shift（105nm）and near-infrared fluorescence（λem=685 nm）emission properties,which can be used for detection and imaging of thiophenol in cells and zebrafishs.2.In the second part,the quinoline-xanthene fluorophore QN-OH was further modified,and an acrylate group was inserted into the hydroxyl position as the recognition site of Cysteine（Cys）,the near-infrared fluorescent probe QN-Cys for cystine was designed and synthesized.The acrylate part of probe structure undergoes Michael addition reaction and intramolecular cyclization with the sulfhydryl group in the Cys structure,releasing QN-OH fluorophores,and Homocysteine（Hcy）and Glutathione（GSH）with similar structures is difficult to quickly react with the probe to release the fluorophore due to the limitation of the cyclization reaction rate and steric hindrance,therefore the probe has high specificity and sensitivity for the detection of Cysteine.The probe QN-Cys has good biocompatibility,low cytotoxicity and large Stokes shift（105 nm）,and can be used for the detection and imaging of endogenous and exogenous cysteine in cells and zebrafishs.3.In the third part,a rigid conjugated structure of carbazole was used as the backbone structure,which was conjugated with benzothiazole to design and synthesize fluorescent probe CA-SO₂ that can specifically detect sulfur dioxide derivatives.The probe showed a strong fluorescent signal at 589 nm.The nucleophilic addition reaction of HSO₃^-and the conjugated double bond resulted in the destruction of the conjugated structure,and the fluorescent signal was significantly weakened.The probe CA-SO₂ has a very fast response（less than 2 min）,and the addition of HSO₃^-can change the color of the probe solution from orange to colorless,enabling the naked eye to observe the probe’s response to HSO₃^-.The probe also has a large Stokes shift（129 nm）,good biocompatibility and low cytotoxicity,and can be used for sensitive detection and imaging of sulfur dioxide in cells and zebrafishs.