Lipase-catalyzed acylation of konjac glucomannan in ionic liquids

A comparative study was made of lipase-catalyzed acylation of konjac glucomannan (KGM) with vinyl acetate as the acyl donor in five ionic liquids (ILs) and also in the presence of the organic solvent tert-butanol (t-BuOH). An obvious enhancement in enzyme activity and stability was observed using ILs as the reaction media when compared with t-BuOH. The maximum degree of substitution (DS) of the modified KGM in ILs and t-BuOH under the conditions employed is 0.71 and 0.54, respectively. The water activity (a(w)) of the reaction system affected the acylation of KGM to some extent. 1-Butyl-3-methyfimidazohum tetrafluoroborate (C4MIM.BF4) was the best IL medium for the reaction, and an a(w) of 0.75 was optimum. It was also found that the nature of both the cation and the anion of ILs had an effect on the reaction. Candida antarctica lipase B immobilized on an acrylic resin (Novozym 435) displayed no acylation activity to KGM in 1-butyl-3-methylimidazolium chloride (C(4)MIm-Cl). The optimum reaction temperature for enzymatic acylation in ILs was shown to be 45-55 degrees C. Enzymatic acylation of KGM in IL-t-BuOH co-solvent systems was also investigated. When an appropriate amount of t-BuOH was added to ILs, the DS of the modified KGM was enhanced. Additionally, the enzymatic acylation of KGM in all the media examined was shown to be regioselective, with acylation occurring predominantly at the C-6-OH. (c) 2006 Society of Chemical Industry.