| Objective: As the smallest anion, Fluoride plays an important role in many ways. For example, lack of fluoride will result in dental care and osteoporosis, however, intake of excess fluoride may cause dental and skeletal fluorosis. Furthermore, chronic ingestion of low levels of fluoride can cause gastric and kidney disorders, urolithiasis, and death. Therefore, the detection of fluoride is of great importance. Fluorescent chemosensors for fluoride analysis not only have the high sensitivity and selectivity but also, can be used in the living system. Now, most of the reported fluorescenct chemosensors can only be used in organic system or large proportion of organic solvent to detect TBAF(tetrabutylammonium fluoride), or detect sodium fluoride in aqueous system by adding a certain part of organic solvents or surfactant, such as CTAB(cetyl trimethyl ammonium bromide) in order to improve the response rate. The objective of this research is to investigate the relationship between the response rate and sensor structure, and then find fluorescent chemosensor for fluoride that can be used in the pure water system with high response rate.Methods: 1. Design and synthesis two series of fluorescent chemosensors for fluoride. The first one is based on 6-hydroxylbenzothiazole, with TBDMS protected 6 position hydroxyl group as the fluoride detection site. 2 position connects with glucose(compound 101), methyl(compound 102), benzyl(compound 103) using amino band as linkage. The second one is based on 7-hydroxyl-4-triazolecoumarin, with TBDPS protected 7 position hydroxyl group as the fluoride detection site. Triazole group is connected with glucose(compound 201), methyl(compound 202), 4-methoxyl-benzyl(compound 203) with amido band as linkage. 2. Test the pseudo first order rate constant of each probe(10μM) under different sodium fluoride concentration(200μM, 500μM, 1000μM), then calculate the second order rate constant. 3. By comparing the second order rate constant, modify the probe. Compound 204 was obtained by adding PEG(1000 Da) to the triazole group of series 2. The second order rate constant was calculated, then the sensitivity, selectivity, cytotoxicity and cell image were tested.Result: 1. At first, 6 novel compounds were obtained and the structures were confirmed by 1H NMR, 13 C NMR and HRMS(ESI). 2. The second order rate constants were tested. The comparison results are as follows, for series 1, compound 101 > compound 102 > compound 103; for series 2, compound 201 > compound 202 > compound 203. 3. Compound 204 was obtained as a novel structure and was confirmed by 1H NMR, 13 C NMR and MS(MALDI). The second order rate constant was much higher than compound 101 and compound 201. The limit of detection is 0.34 mg L-1. Compound 204 shows a very good selectivity on fluoride against other anions. The quantum yield of compound 204 is 0.318 using coumarin 120 as standard. This probe appears no cytotoxity. After incubated with 20 μM Na F, then 10μM compound 204, MB-231 cells showed a bright fluorescence.Conclusion: At first, this paper designed and synthesized two series 6 compounds. According to the comparison of second order rate constant, the response rate of fluorescent chemosensors for fluoride are related to the hydrophily of the structures. More hydrophilic groups mean higher response rate. Based on this conclusion, compound 204 was designed and synthesized. The detection limit of compound 204 is 0.34 mg L-1, which is significantly lower than the recommended standard of fluoride in drinking water by WHO. It is a good probe with both high sensitivity and selectivity. This probe can be used in cell image without cytotoxity. |
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