| A series of fluorescent and colorimetric chemosensors were designed and synthesized for selective detection of the environmentally and biologically significant species, such as Cu2+, Zn2+, cysteine, glutathione, as well as enzymes and proteins. In addition, it was found that these optical chemosensors could be used for intracellular imaging to monitor the level of those important species; the results are summarized as follows:1. A coumarin azine derivative (SR01) was synthesized and characterized. It was used as a colorimetric chemosensor for Hg2+. The absorption maximum of SR01 shows a large red shift from 490 nm to 565 nm (Δ=75 nm) in the presence of Hg2+. The change in color is very easily observed by naked eyes, while other metal cations, Fe2+, Co2+, Ni2+, Zn2+, Cd2+, Cu2+, Fe3+, Ag+, Pb2+, alkali metal and alkaline earth metal cations do not induce such a change.2. A coumarin Schiff-base derivative (WSCU) was synthesized and used as a colorimetric chemosensor for Cu2+ recognition in aqueous solution. The absorption maximum of the chemosensor shows a large red-shift (Δ=70 nm) in the presence of Cu2+. The change in color (from orange to red) is very easily observed by naked eyes, while other metal cations, Ag+,Fe3+,Fe2+, Co2+, Ni2+, Zn2+, Cd2+, Hg2+, Pb2+, alkali metal and alkaline earth metal cations do not induce such a change. To investigate the practical application of WSCU, a test kit was prepared for the fast detection of Cu2+ in aqueous solution.3. A novel coumarin derivative (WSZN) was designed and synthesized as a fluorescent chemosensor for Zn2+ detection in aqueous solution, the solution of the WSZN has weak fluorescence emission, and the fluorescence is greatly enhanced (10 times) upon addition of Zn2+, while other metal cations, Fe2+, Co2+, Ni2+, Zn2+, Cd2+, Hg2+, Pb2+, alkali metal and alkaline earth metal cations do not induce such a change. Furthermore, recognition model was demonstrated by X-ray analysis, and the novel chemosensor was successfully employed for Zn2+ imaging in HepG2 cells4. A coumarin thiozolidine derivative (ligand 1) was designed and synthesized, which can take a spontaneous and quantitative oxidation reaction to yield a strong fluorescence emission compound laser dye coumarin-6. Such an anomalous oxidation reaction was inhibited upon mercury ligation to form a non-fluorescence emissive unusual complex HgL as a novel chemosensor. X-ray analysis shows that HgL has strong Hg-S and weak Hg-N bonds packed in a unidirectional fashion through bridging Hg-S (3.112 ?). The chemosensor demonstrated a high selectivity in the recognition of thiol containing chemical species such as cysteine (Cys) and glutathione (GSH). Based on the differential responses of HgL to GSH and GSSG, the fluorescent and visualization assay of glutathione reductase (GR) using HgL was demonstrated by comparison to a series of proteins/enzymes.5. A novel coumarin thiosemicarbazide derivative (ligand 2) shows a strong fluorescence emission in aqueous solution. It was ligated with mercury to construct a novel regenerative chemosensor Hg2L2, which is non-emissive in aqueous solution. Both molecular structures of ligand 2 and Hg2L2 were characterized by X-ray analysis. Thiol (-SH) compounds react with Hg2L2 to release strong fluorescent species Ligand 2, and Hg2L2 can be regenerated upon addition of HgCl2. The fluorescence can be repeatedly quenched and recovered for more than 10 times upon alternate addition of HgCl2 and cysteine. Hg2L2 shows good selectivity to the reduced form of glutathione (GSH) than the oxidized form of glutathione (GSSG) in aqueous solution. Based on this result, a convenient method of detection for Glutathione reductase (GR) was established, and the interaction process could be easily observed by naked eyes or fluorescence spectrum. Furthermore, the novel chemosensor Hg2L2 was empolyed successfully in intracellular thiol (-SH) imaging.
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