1-乙基-3-甲基咪唑L-乳酸盐作为手性配体用于氨基酸的手性拆分

基于手性配体交换机理,研究了以手性离子液体1-乙基-3-甲基咪唑L-乳酸盐([EMIM][L-Lac])为手性配体拆分色氨酸对映体(Trys)、苯丙氨酸对映体(Phes)和酪氨酸对映体(Tyrs)的方法。实验考察了背景电解质和中心离子种类、手性配体与中心离子的浓度及比例、运行缓冲液pH等因素对Trys、Phes和Tyrs手性拆分的影响。研究发现,当运行缓冲液为40.0 mmol/L [EMIM][L-Lac]、20.0 mmol/L氯化铜(pH 4.5)时,3对对映体均能得到良好的手性拆分。为了验证[EMIM][L-Lac]的良好性能,实验进一步将L-乳酸(L-Lac)作为手性配体用于Trys的手性拆分。对比实验发现,单独使用L-乳酸,DL-Try只能得到部分拆分,加入离子液体1-乙基-3-甲基咪唑醋酸盐(EMIM-Ace)后,DL-Try分离情况得到了很大改善,但出峰时间延长至30 min以上。而使用[EMIM][L-Lac]时,Trys的出峰时间均在15 min以内。实验最后还对手性拆分机理做了进一步讨论。实验结果表明:在EMIM-Ace辅助L-Lac体系中,EMIM-Ace仅被用于抑制电渗流,并未参与手性配体交换反应;而在[EMIM][L-Lac]体系中,参与手性配体交换反应的主要是未解离的[EMIM][L-Lac],而不是解离后的L-乳酸根离子形成的L-乳酸。

Application of 1-ethyl-3-methyl imidazole L-lactate as the chiral ligand for the enantioseparation of amino acids

Enantioseparation of tryptophan enantiomers (Trys), tyrosine enantiomers (Tyrs) and phenylamine enantiomers (Phes) by chiral ligand exchange capillary electrophoresis (CLE-CE) using 1-ethyl-3-methyl imidazole L-lactate ([EMIM][L-Lac]) as the chiral ligand was studied. The effects of background electrolytes and central ions, the molar ratio and concentration of the chiral ligand and central ion, running buffer solution pH on the enantioseparation of Trys, Phes and Tyrs were investigated. Good enantioseparation of three pairs of enantiomers were obtained with 40.0 mmol/L [EMIM][L-Lac] and 20.0 mmol/L cupric chloride (pH 4.5). To validate the good behavior of [EMIM][L-Lac], L-lactate (L-Lac) was further used as the chiral ligand for the enantioseparation of Trys. The contrast experiment showed that Trys could only be partially enantioseparated by L-Lac. Moreover, the enantioseparation was improved by adding 1-ethyl-3-methyl imidazole acetate (EMIM-Ace) which markedly prolonged the migration time of Trys to more than 30 min. In contrast, the migration time of Trys was obtained in 15 min by [EMIM][L-Lac]. Finally, the enantioseparation mechanism was further discussed. The experimental results showed that in the EMIM-Ace assisting L-Lac system, EMIM-Ace was only used to suppress the electroosmotic flow and was not involved in the chiral ligand exchange reaction, while in the [EMIM][L-Lac] system, the chiral ligand taking part in the reaction was mainly unionized [EMIM][L-Lac] rather than L-Lac formed by ionized L-Lac ions.