Study On Sythesis Of Amino Acids Ionic Liquids And Its Enantioseparation Of Aromatic Acid Enantiomers

::Currently, one of the major fields of interests for further and extensive studies in chemistry is the development of novel solvents with reduced toxicity, biodegradability, environmentally benign capability, and high biocompatibility. In this regard, much attention has been devoted to amino acids ionic liquids (AAILs). In this paper, several AAILs have been successfully synthesized and applied to aromatic acids separation by using high performance liquid ligand exchange chromatography. On the basis of this, AAILs coupled with Cu+/K2HPO4based aqueous two-phase system has been also constructed and applied to tryptophan enantiomers extraction and well expectation has been obtained. The contents were summarized as follows:(1) L-LeuCiNTf2and L-PheC2NTf2could be synthesized by using L-Leucine methyl ester hydrochloride, L-Phenylalanine ethyl ester hydrochloride and bistrifluoromethanesulfonimide lithium salt as raw materials. L-PheC2NTf2was confirmed to have chiral selectivities toward ofloxacin enantiomers by experiments, and then the effects of copper ion concentration, L-PheC2NTf2concentration, organic modifier ratio, pH of the mobile phase as well as temperature on efficiency of chiral separation were investigated and evaluated. Optimal separation conditions were obtained, where8mmol/L this chiral ionic liquids and4mmol/L Cu2+were dissolved in methanol/water (12:88, v/v) with pH4.8. Under the optimum conditions, well enantioseparation of ofloxacin enantiomers could be observed with the resolution of1.76. And its thermodynamical process was studied; the result revealed that the separation of ofloxacin enantiomers was an enthalpy-controlled process.(2) Four kinds of amino acids ionic liquids ([L-Pro][CF3COO],[L-Pro][NO3],[L-Pro]2[SO4] and [L-Phe][CF3COO]) were successfully synthesized and used for separation of tryptophan enantiomers. Among them,[L-Pro][CF3COO] was selected as the model ligand to optimize the separation conditions. Some factors influencing efficiency of chiral separation, such as copper ion concentration, CILs concentration, methanol ratio (methanol/H2O, v/v) and pH, were investigated. The obtained optimal separation conditions consisted of8.0mmol/L Cu(OAc)2,4.0mmol/L [L-Pro][CF3COO] and20%(v/v) methanol at pH3.6. Under the optimum conditions, acceptable enantioseparation of tryptophan enantiomers could be observed with the resolution of1.89. The results have demonstrated the good applicability of CILs with amino acids as cations for chiral separation. Furthermore, comparative study was also conducted for exploring the mechanism of the CILs as new ligand in ligand exchange chromatography.At last, the thermodynamical process was studied; the result revealed that the separation of tryptophan enantiomers was an enthalpy-controlled process.(3) Aqueous two-phase systems (ATPs) have been formed by AAILs coupled with Cu2+and K2HPO4to extract tryptophan enantiomers. Factors affecting separation efficiency were analyzed, namely, the alkyl chain length of the AAILs, the AAIL content, pH, extraction time, etc. The obtained optimal separation conditions were as follows:200μL [C4mim][L-Pro],150mg Cu(OAc)2, pH=9.0, extraction time was7min. Under the optimum conditions, acceptable separation factor of tryptophan enantiomers reached1.25, demonstrating that AAILs based metal complex aqueous two-phase system can be applied in chiral separation.