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Investigation of the enantioselectivity of different lipase enzymes during the esterification of lactic acid in ionic liquid co-solvent

Ionic liquids are composed entirely of an asymmetric cation and a weakly-coordinating anion. They are liquids at ambient or far below ambient temperature. ILs have been extensively used as a potential alternative to toxic, hazardous, flammable and highly volatile organic solvents, since they have no vapour pressure, which is a great advantage against conventional solvents. It is not negligible that the structure affects the environmentally features like biodegradability or toxicity. In our institute several experiments were carried out last years to investigate the esterification of lactic acid (2-hydroxypropionic acid). At low water content it undergoes self esterification, therefore it is essential to studying the water content during the reaction, not only for the lactic acid oligomerization but for esterification and the enzyme activity, enantioselectivity. Successful extraction of lactic acid by ionic liquids was carried out in Slovakia from fermentation mixture. As an extension of these experiments asymmetric lactic acid esterification in ionic liquids was investigated in our institute. The esterification of (D, L)-lactic acid with alcohol was carried out in a shaker incubator using Novozym 435 (Candida antarctica lipase B), Amano PS-IM and Candida rugosa enzymes. The reaction mixture contained 3, 6-7, 4-14, 5 mmol monomer lactic acid and 44 mmol ethanol, respectively, and 600 mg Cyphos 104 ionic liquid. In order to reach the higher enantiomer excess the temperature, the alcohol excess and the initial water content were modified. The above mentioned lipase enzymes showed reasonable catalytic activity, their enantioselectivity could be effectively influenced by changing the reaction parameters.

lipase; enantioselectivity; esterification; ionic liquid

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