| Zinc ion, the important transition-metal ion in the human body, plays crucial role in many important biological processes in acting as the structural and catalytic cofactors, neural signal transmitters or modulators, and regulators of gene expression, and apoptosis. The disorder of zinc metabolism is closely associated with many severe neurological diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Guam ALS-Parkinsonism dementia Parkinson's disease, hypoxiaischemia and epilepsy. Moreover, it also plays farreaching role in the environment systems. It would reduce the soil microbial activity leading to the phytotoxicity effect and existed in the agricultural and food product in pollution style. Therefore, controlling detection of Zn2+ is becoming essentially important both in the environment and biological systems. The fluorescence chemosensors have many advantages, such as the high selectivity, good sensitivity, easy use, inexpensive. Moreover, they are noninvasive detection that has no negative effect on sample and could be rapid, real time, in situ detection and quantitative analysis for sample. Therefore, the fluorescence chemosensors become increasingly popular and get people's attention. Amino acids are widely used as binding group in the chemosensors because they have many binding sites as carboxyl and amino, good water solubility, wide variety of source and low price. Moreover, amino acids play crucial role in the biological systems such as the component of proteins. Therefore, we design and synthesize several fluorescence chemosensors based on Schiff Base using amino acids as the binding group. In the aqueous solution (Tris-HCl buffer solution), we measure the probes'identification property through fluorescence ion titration experiments, and we thoroughly study the signal mechanisms using several experimental ways. The mainly studies are as followings: 1. We designed and synthesized the fluorescence chemosensor based on Schiff Base, 2-((2-hydroxynaphthalen-1-yl) methyleneamino)-3-(1H-indol-3-yl) propanoic acid (1). This senor could be easily synthesized through one step reaction between 2-hydroxy-1-naphthaldehyde and tryptophan, and the productivity is 40%. In the aqueous solution, 1 had high selectivity and sensitivity for zinc ion and the detection limit approached 1μM. This probe could avoid the Cd2+ interference when detected zinc ion as they existed together. The study on the Zn2+-sensing behaviors of 1 in cells was carried out by fluorescence microscopy demonstrated the possibility that this probe could be used in the biological systems. We studied the signal mechanism and the configuration of 1 and Zn2+ detailed by the organic combination of the theoretical and experiment data. In the theoretical section, we used the H-B Equation and the Job's Plot to prove that the binding ratio of 1 and Zn2+ is 1 to 1, the geological configuration of the complex 1/Zn2+ was optimized by Density Functional Theory in B3LYP/6-31G level using Gaussian 03. In the experimental section, FT-IR and 1H NMR experiments were conducted regarding 1 and the complex of 1/Zn2+ and the results were consistent with the theoretical calculation, showing that the proposed configuration of the complex was rational and the prevention of C=N isomerization resulted in the fluorescence change of probe 1 upon the addition of Zn2+. The full study on the signal mechanism facilitated in the design and optimization of zinc ion probes in the future.2. Based on the study of 1, we changed the tryptophan of 1 into other small-sized amino acids and hoped the change could slightly rearrange the probe's configuration, then resulting in the better sensitivity of probe to zinc ion and the occurrence of intermolecular charge transfer and C=N isomerization mechanism at the same time. In this charter, therefore, we used histidine and serine instead of tryptophan to synthesized probe 2, 2-((2-hydroxynaphthalen-1-yl) methyleneamino)-3-(1H- imidazol-5-yl)propanoic acid, and probe 3, 2-hydroxy-2- ((2-hydroxynaphthalen-1 -yl)methyleneamino)acetic acid. These two new probes have the similar property. In the buffer solution, they could selectively detected zinc ion in higher sensitively than that of 1. In addition, they could avoid the interference from Cd2+ when they detected zinc ion in the aqueous solution. Consider the fact that Na+, K+, Ca2+,Mg2+ are abundant in water and biological systems, their interference experiments ware also carried out and the results showed that the two new probes had little influence from them detecting zinc ion. Based on the H-B Equation, we got that 2 and 3 combined Zn2+ in 1:1 form and their geological configurations were optimized by Density Functional Theory in B3LYP/6-31G level using Gaussian 03. Although the complexes of 2/Zn2+ and 3/Zn2+ have same geological configurations with that of 1/Zn2+, they have different signal mechanisms compared with 1/Zn2+'s. The probe 1 only relied on the C=N isomerization mechanism, and the two new ones also included Intermolecular Charge Transfer (ICT), which made the bigger blue shift of the UV - visible absorption spectroscopy when 2 and 3 reacted with Zn2+ than that of 1 and Zn2+. Through the compare the results among 1, 2 and 3 reacted with zinc ions, we concluded that the amino acid size of space had big impact on the signal mechanisms in the chemosensors. This found is helpful for our design and optimization of other metal ions fluorescence probes in the future.In summary, we have successfully designed a series of high water solubility, high efficient zinc ion chemosensors with the amino acid as the main binding sites. In addition, we used the Fluorescence Spectroscopy, UV-visible Absorption Spectroscopy, Nuclear Magnetic Resonance Spectroscopy, Infrared Spectroscopy and Gaussian 03 to study the recognition model and the signal mechanism, which provided the base for the further design and optimization of zinc ion or other metal ion fluorescence probes.
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