Studies On Realizating Chiral Separation Of Enantiomers Of Amino Acid By Constituting Chiral Caves With Novel Surface-Molecular Imprinting Technique

In the paper, Dimethylaminoethyl methacrylate (DMAEMA) was grafted on micron-sized silica gel particles in a manner of"graft from"in a solution polymerization system by right of the mediation of the coupling agent 3-methacryloxypropyl trimethoxysilane (MPS), resulting in the grafted particles PDMAEMA/SiO₂ . The adsorption behaviours of PDMAEMA/SiO₂ towards the molecule of aspartic acid and glutamic acid were examined and the preparation of surface imprinting materials which was separately performed with L-Asp or L-Glu as template molecule. Then, both static and dynamic methods were adopted to study the recognition property for L-Asp and the separation ability towards L-Asp and D-Asp in the raceme. This research results have a significant breakthrough in the chiral separation technology of amino acid and have a very good application prospects.Micron-sized silicon particles were chemically surface-modified with coupling agent KH570, and bonding particles MPS/SiO₂ were obtained. The graft polymerization of dimethylaminoethyl methacrylate (DMAEMA) on the surfaces of particlesMPS/SiO₂ was performed in a solution polymerization system. The two kinds of particles were characterized with FTIR, TGA and SEM methods. The effects of the main factors on the graft polymerization of DMAEMA were examined. The experimental results show that in the graft polymerization process, the grafting degree of PDMAEMA can get up to 21.63g/100g by controlling the consistence of DMAEMA, the used amount of initiator, temperature and time. The suitable reaction conditions are as follows: Time=10h, T=75℃, the used amount of initiator=1.2%, Monomer concentration=6%.In this research work, the behaviours of the graft particles PDMAEMA/SiO₂ towards aspartic acid and glutamic acid were examined, the adsorption mechanism was mainly studied. The experimental results show that the tertiary amine groups has strong adsorption ability for amino acid molecule by right of the synergy of electronic interaction and hydrogen bonding interaction between the graft particles PDMAEMA/SiO₂ and amino acid molecule. Especially, PDMAEMA/SiO₂ possesses very strong adsorption ability for acidic amino acids, such as, aspartic acid and glutamic acid. the adsorption capacity can get up to 62 mg/g and 68 mg/g at 30℃temperature by their own. When the pH is less than 4.0, with the increasing pH values, absorption capacity will also rise, when the pH is greater than 4.0, as the pH increases, the adsorption capacity decreases on the contrary. Because the adsorption process is phisical adsorption, raising temperature will facilitate the adsorption process and decrease the adsorption capacity. Salinity has the shielding effec between the graft particles PDMAEMA/SiO₂ and amino acid, as salinity increased, the adsorption capacity decreased. Finally, adsorption capacity increases with the degree of the grafting degree increased.The molecule imprinting towards the grafted PDMAEMA was performed with L-Asp or L-Glu that is one enantiomer of amino acid (L-Asp or L-Glu) as template molecule and dichloroether as crosslinking agent by using the novel surface-molecular imprinting technique established by our research group, and the L-Asp or L-Glu molecule–imprinted material MIP-PDMAEMA/SiO₂ was prepared. With the other enantiomer of amino acid, D-Asp or L-Glu, as a contrast compound, both static and dynamic methods were adopted to study the recognition property for L-Asp or L-Glu and the separation ability towards amino acid in the raceme. The experiment results show that MIP-PDMAEMA/SiO₂ have obvious recognition selectivity and fine binding affinity for L-Asp or L-Glu, and the selectivity coefficient is equal to 3.24 or 3.40. Besides, MIP-PDMAEMA/SiO₂ has excellent elution property, with a diluted aqueous solution of NaOH as the eluent, the desorption ratios of L-Asp reach 99.73 % in 13 BV.