Lipase‐catalyzed synthesis of fatty acid sugar ester using extremely supersaturated sugar solution in ionic liquids

Abstract

The low solubility of sugars has hampered the lipase-catalyzed synthesis of fatty acid sugar esters in organic solvents and ionic liquids (ILs), because several solvents that are able to effectively dissolve sugars are detrimental to enzymes. In this work, in order to prepare a high concentration of sugars in ILs, we have developed a new procedure that entails mixing an aqueous sugar solution into ILs followed by removal of the water from the solution. The glucose concentrations in the supersaturated [Emim][TfO] and [Bmim][TfO] were 19 and 10 times higher, respectively, than the solubilities (6.1 and 4.8 g/L) of glucose in the ILs at 25 degrees C. Furthermore, the supersaturated glucose solutions in ILs were maintained over a long period of time without any significant loss of glucose. In ILs that were extremely supersaturated with glucose, lipase-catalyzed esterifications of glucose with vinyl laurate, and lauric acid were successfully carried out. The conversion increased from 8% to 96% at 1 day of reaction by using supersaturated solution in [Bmim][TfO] which had dissolved glucose concentration of 400% higher than its solubility, compared with the reaction using saturated glucose solution. By making the glucose concentration in ILs much higher than the solubility through our novel and simple method, the initial rate and conversion of the lipase-catalyzed reaction were significantly improved.

Optimization of lipase-catalyzed glucose ester synthesis in ionic liquids

“…To overcome these problems, a new procedure 'water-mediated supersaturation' was recently used to prepare highly concentrated sugars in ILs [13]. Two separate graphs in Fig.…”

“…Recently, we developed a new procedure to prepare supersaturated sugar solution in ILs through water-mediated method resulting in significantly enhanced synthetic yield and initial rate in the enzymatic transesterification of glucose with vinyl laurate [13]. Based on this method, therefore, the effect of pure ILs and their mixture, substrate ratio, water content, lipase content, and temperature on the activity and stability of lipase was studied in present work to pursue a further investigation on the optimization of reaction conditions for the lipase-catalyzed direct esterification of sugar with free fatty acid in ILs.…”

Using Ionic Liquids for the Separation of Carbohydrates

“…Similar results were reported in the literature but for different types of ILs. For example, Lee et al [18] found that the solubility of fructose in ethylmethylimidazolium tetrafluoroborate, ethylmethylimidazolium trifluorosulfonate, butylmethylimidazolium tetrafluoroborate and butylmethylimidazolium trifluorosulfonate, at 25 º C is 7.7, 32.8, 3.3, and 27 g/L, respectively, while the solubility of glucose under the same conditions was 1.1, 6.1, 0.9, and 4.8 g/L, respectively. It is clear that the effect of the anion on the extent of solubility is stronger than that of the cation.…”

Synthesis of Surfactants Using Enzymes

“…Candida antarctica lipase B was the best enzyme for synthesis of glucose esters in a two-phase system containing an ionic liquid and tert-butanol [31]. Recently, the use of supersaturated sugar solutions [32] and ultrasonic treatment [33] has been reported to make sugar ester synthesis in ionic liquids even more efficient.…”