| Coumarin is an outstanding candidate fluorophore in designing fluorescent probe molecules, having high fluorescence quantum yield, large stokes shift, adjustable photophysical and photochemical properties and good light stability, etc. Small molecular thiols such as cysteine(Cys), homocysteine(Hcy) and glutathione(GSH) involves vital cell processes, including redox balance and cell growth. Mercury is widely distributed in nature with very small amount. Environment inorganic mercury becomes organic mercury then is absorbed by the organism and will cause some harm to human health through the food chain. Thus, detection of thiols and mercury ions greatly increased protection of human health. So in this paper, coumarin was chosen to prepare fluorescent probes for sensing thiols and mercury ions.This paper summarizes the research progress and mechanisms of fluorescent probes, and further information on the progress of coumarin fluorescent probes for mercury ion and thiol fluorescent probes and their synthesis.We designed and synthesized different coumarins with ABCDE five series. 7-Hydroxy-4-methyl-chromen-2-one, 3-acetyl-7-hydroxy-chromen-2-one and 3-hydroxy-benzo [c]chromen-6-one were the mother compounds of coumarin fluorescent probe. In A-series, thiocarbonyl group was the mercury ion recognition group, a thiol acid lipid derivatives was recognition group; in B-series, hydrazides was identification of mercury ions coumarin group, a thiol acid lipid derivatives was recognition group; because the mercury ions can react with double and triple bonds, thiols can react with aldehyde group and conjugated olefins, based on this principle, C-series, D-series and E-series were designed and synthesized. Synthetic conditions were explored to find the optimum reaction conditions. The chemical structures of the synthesized compounds were characterized by IR, 1H NMR, 13 C NMR and MS spectra.Two typical fluorescent probe molecules A2 and E1 were selected for sensing Hg(II) ions and cysteine through ultraviolet-visible absorption spectra and fluorescence emission spectra measurements. Detection of mercury ions and thiol molecules on its sensitivity, response time, as well as detecting mechanism probe pH tolerance were studied. Test results show that the fluorescence intensity of probe A2(20 μM) reaches maximum in the excitation wavelength of 320 nm when the proportion of acetonitrile and water in the solution is 8:2. The biggest fluorescence emission wavelength is 451 nm. And the intensity of fluorescence emission wavelength increases 2 times with Hg2+(0.6 equiv.). In the excitation wavelength of 445 nm, the fluorescence intensity of probe A2(20 μM) increases 4.5 times with cysteine(Cys) and 14 times with thiophenol. Otherwise the response time to thiophenol is very short, just 1 minute. Probe A2 can be highly sensitived to thiophenol. The fluorescence intensity of probe A2 enhances 16 times with thiophenol(0.125 equiv.). Only Cys can significantly enhances the intensity of probe A2 in the comparative test of histidine(His), glycine(Gly), phenylalanine(Phe), valine(Val), asparagine(Asn) and glutamate(Glu). The fluorescence intensity of probe E1(20 μM) reaches maximum in the excitation wavelength of 272 nm when the proportion of EtOH and water in the solution is 1:9, and probe pH tolerance is 4 to 11. The strongest fluorescence intensity peak of probe E1 shifts obviously from 458 nm to 400 nm upon addition of Hg2+(0.6 equiv.). In contrast, other ions such as Ca2+, Cu2+, Zn2+, Ce3+, Co2+, Sr2+, Mn2+, Bi3+, Ni2+, Mg2+, Na+ and Li+ did not cause the shift of the peak. Cys can reduce the fluorescence intensity of probe E1 to 0.07 times in the excitation wavelength of 375 nm. Meanwhile, thiophenol can reduce to 0.01 times in the excitation wavelength of 233 nm. Furthermore, probe E1 is highly sensitive to Cys and its fluorescence intensity reduces to 0.5 times upon addition of Cys(0.6 equiv.). |
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