Fluorescent Probe Based On Pyrazoline For Biological Thiols

Pyrazolines are important nitrogen-containing5-membered heterocyclic compounds with a wide range of interesting properties. Furthermore, pyrazoline derivatives show stronger fluorescence, and have higher hole-transport efficiency and excellent emitting blueness property. Therefore, pyrazoline derivatives have widely been used as whitening or brightening reagents for synthetic fibers, fluorescent chemosensors for recognition of transition metal ions, hole-transport materials in the electrophotography and electroluminescence fieldsIntracellular thiols, such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), play crucial roles in maintaining biological systems. Cys deficiency is involved in many syndromes such as slow growth in children, liver damage, loss of muscle, and skin lesions. Elevated Hcy level in plasma is a risk factor for Alzheimer’s and cardiovascular diseases. As the most abundant intracellular thiol, GSH has many cellular functions. Abnormal levels of GSH can lead to cancer, aging, heart problems, and other ailments. Therefore, small-molecule probes are needed for selective and sensitive detection of thiols under physiological conditions.Disruption of copper homeostasis in cells, the deficiency or excess of copper, will cause severe dysfunction, and even result in many diseases. Mercury, as a toxic heavy metal element, will damage the human brain and nervous system, renal system, immune system, reproductive system, etc. Moreover, mercury and copper are heavy metal environmental pollutants. Therefore, the quantitative detection of metal ions, such as Cu2+and Hg2+, is of great importanceFluorescence-based detection methods have gained much attention because of their simplicity, low cost, selectivity and sensitivity. Therefore, developing pyrazoline-based fluorescent probes for discriminating thiols or metal ions, such as Cu2+and Hg2+without interference is important. The detailed work mainly contained five chapters as followed:Chapter1. Recent progress in fluorescent probe for detection of thiolsIntracellular thiols, such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), play crucial roles in maintaining biological systems. In last decade, developing small molecule probes for selective and sensitive detection of thiol under physiological conditions aroused great interest. Fluorescent and colorimetric sensors are classified into two types of reactions according to their mechanism of reaction with thiols, including the reaction mercapto with probe, the reaction mercapto and amino with probe. Therefore, in this chapter we provide a general overview of the selected recent research involving the design and application of biological thiol-selective chemosensors.Chapter2. Novel pyrazoline-based fluorescent probe for detecting glutathione and its application in cells.A novel compound,2-(1,5-diphenyl-4,5-dihydro-1H-pyrazol-3-yl)phenyl acrylate (probe4), was designed and synthesized as a highly sensitive and selective fluorescent probe for recognizing and detecting glutathione among cysteine, homocysteine and other amino acids. The structures of related compounds were characterized using IR, NMR and HRMS spectroscopy analysis. The probe is a non-fluorescent compound. On being mixed with glutathione in buffered EtOH:PBS=3:7solution at pH7.4, the probe exhibited the blue emission of the pyrazoline at474nm and a83-fold enhancement in fluorescence intensity. This probe is very sensitive and displayed a linear fluorescence off-on response to glutathione with fluorometric detection limit of8.2x10’8M. The emission of the probe is pH independent in the physiological pH range. Live-cell imaging of HeLa cells confirmed the cell permeability of the probe and its ability to selectively discriminate GSH from Cys and Hey in cells. The toxicity of the probe was low in cultured HeLa cells.Chapter3. Novel pyrazoline-based selective fluorescent probe for detecting reduced glutathione and its application in living cells and serum.A new fluorescent probe, N-(4-(1,5-diphenyl-4,5-dihydro-1H-pyrazol-3-yl)phenyl)--2,4-dinitrobenzenesulfonamide (probe10), was designed and synthesized as a highly sensitive and selective fluorescent probe for recognizing and detecting glutathione among biological thiols in aqueous media. Probe10is a nonfluorescent compound. On being mixed with biothiols under neutral aqueous conditions, the2,4-dinitrobenzenesulfoyl moiety can be cleaved off by glutathione, and the blue emission of the pyrazoline at464nm is switched on, with an fluorescence enhancement of488-fold for glutathione. Furthermore, probe10was highly selective for glutathione without interference from some biologically relevant analytes. The detection limit of glutathione was4.11×10-7M. The emission of the probe is pH independent in the physiological pH range. Moreover, the probe can be used for fluorescent imaging of cellular glutathione and can be used for detecting glutathione in calf serum.Chapter4. Novel pyrazoline-based selective fluorescent sensor for Hg2+. This chapter presents the preparation of a pyrazoline compound and the properties of its UV-vis absorption and fluorescence emission. Moreover, this compound can be used to determine Hg2+ion with selectivity and sensitivity in the EtOH:H2O=9:1(v/v) solution. This sensor forms a1:1complex with Hg2+and shows a fluorescent enhancement with good tolerance of other metal ions. This sensor is very sensitive with fluorometric detection limit of3.85x10-10M. In addition, the fluorescent probe has practical application in cells imaging.Chapter5. The optical properties of novel1,3,5-triarylpyrazoline derivatives and the fluorescent sensor for Cu2+A series of novel1,3,5-triarylpyrazoline derivatives was synthesized by the reaction of chalcone and5-aryl-2-hydrazinyl-1,3,4-thiadiazole in43.3-84.7%yields. The structures of compounds were characterized using IR,1H NMR and HRMS spectroscopy and X-ray diffraction analysis. The absorption and fluorescence characteristics of the compounds were investigated in dichloromethane, toluene, acetonitrile, N,N-dimethylformamide and tetrahydrofuran. The results showed that the absorption maxima of the compounds vary from366to370nm depending on the group bound to benzene rings. The maximum emission spectra of the compounds in dichloromethane were dependent on nature of groups in benzene ring. Furthermore, the compound16b can be used to determine Cu2+ion with high selectivity and a low detection limit in the DMF:H2O=1:1(v/v) solution.