Chiral Potentiometric Sensors Based On Chiral Salen Metal Complexes And The Synthesis And Test Of Crosslinked Polyaniline With Enhanced Conductivity

a-Mandelic acid, as a chiral molecule, been widely used in asymmetric synthesis. Those drugs which made by D/L-MA has better effection on patients than the racemation of MA, expecially in its lower side effect, so it is necessary to develop a fast, sensitive, high selective and cheap method for determination D/L-MA in complex sample matrices. As is known, chiral metallosalen complexes have been developed as highly enantioselective bionic catalysts, as excellent ionophores have been successfully employed for the potentiometric analysis using liquid membrane electrodes towards anion or metal ion, due to the following features:ease of ligand preparation, high complexation ability of the ligand with a wide variety of metal ions, and their structural diversity. Herein, we use chiral Salen Mn(Ⅲ), Co(Ⅱ) complex as a novel chiral electrochemical selector for enantiomeric recognition of MA, the sensor performance (selectivity, detection limit ect.) and response mechanism were investigated. In addition, the crosslinked conductive polyaniline had been designed and synthesized, their srtucture and conductivity also been tested, we try to use the enhanced conductive polymer as conductor materials in sensors in order to improve the perfomance. The main contents are as following:1. Based on chiral Salen Mn(Ⅲ) complex as neutral ionophore for L-mandelic acid sensorThe chiral Salen Mn(Ⅲ)(Cl) complex, (R,R)-N,N’-Bis(3,5-di-tert-butyl-salicylidene)-1,2-cyclohexanediaminatomanganese(Ⅲ) chloride was prepared and used as an excellent ionophore in fabrication of an enantioselective, potentiometric membrane sensor for the determination of L-mandelic acid (L-MA).The influence of membrane composition and pH on the response properties of the electrodes were investigated. In the pH range of 7.0-10.2, the best enantioselectivityhave been obtained by Salen Mn(III) based electrode, with the composition of 31.6 wt.% PVC,64.6 wt.% plasticizer and 3.81 wt.% ionophore, and o-nitrophenyl octly ether(o-NPOE) as plasticizer. Optimized sensor has a linear dynamic range of 1.0×10-5to 1.1×10-1 mol/L, with a Nernstian slope of-58.1±0.5 mV/decade, and detection limit 7.2×10-6 mol/L. The enantioselectivity coefficients (log KL/MA,D-MApot) of the sensors for the counterisomers were about -4.02. It can be used for at least one month without considerable divergence in potentials. The mechanism of chiral molecular recognition between the Salen Mn(Ⅲ) and L-MA, leading to potentiometric signal generation, is discussed using HF method in HF/STO-3G theoretical levelof quantum chemistry.2. Enantioselective ITO glass electrode modified with chiral Salen Co(Ⅱ) complexIn our experiments, an enantioselective potentiometric sensor was constructed based on chiral Salen Co(Ⅱ) complex immobilizing on an indium tin oxide (ITO) electrode modified. (3-aminopropyl) triethoxysilane (APTES) was modifidied on the surface of ITO electrode by self-assembled monolayer, which connected APTES with chiral Salen Co(Ⅱ) by coordination bond for the selective response D-MA sensor. The effects of soaking concentration, reaction time and the pH of solution on the enantioselective potential response of the modified ITO electrode were examined. The results indicate that the proposed sensor displayed with of an excellent Nernstian slope of-58.6±0.6 mV/decade toward D-MA in a linear range of 1×10-5-1×10-2 mol/L. Their enantioselectivity coefficient for the counter isomer (L-MA) was -2.71 by using mixing solution methode, indicating that the sensor possesses excellent chiral discrimination ability with quick response time and relatively stable. Besides, the mechanism and behavior of chiral recognition is discussed using HF method in HF/STO-3G theoretical level of quantum chemistry, which surpported our experimental result.3. The synthesis and characterization of crosslinked electrial conductive polyanilineThe new crosslinked conductive polyaniline was prepared by solution polymerization with aniline,p-phenylenediamine and triphenylamine (TPA), H2SO4 as dopant, ammonium peroxydisulfate (APS) as oxidant. Various synthesis conditions had been discussed including monomer concentration, the kinds of acid, ratio of oxidants to aniline and cross-linker influence on the conductivity and structure of polyaniline, in order to obtain the enhanced electrical conductive polyaniline. The four-point method has been used for the determination of conductivity of polymers. The crosslinked PANI displayed a conductivity increase of up to 25% compared with the linear one. The FT-IR, UV-vis spectrometer, XPS, TGA, DSC were used to investigate the characteristic and their structure of the copolymer.