Regular articleA one-pot method for lipase-catalyzed synthesis of chitosan palmitate in mixed lonic liquids and its characterization

•A new enzymatic method was developed for synthesis of chitosan ester in mixed ILs.•Selective acylation at 6-OH of chitosan was achieved without any protection steps.•Long-chain chitosan esters were synthesized under mild and green conditions.•Under optimized reaction conditions, the maximal DS value of 0.214 was reached.

Long-chain fatty acid chitosan esters are important chitosan products with attractive application prospects in biological and biomedical applications. A new enzymatic method for synthesis of chitosan esters via transesterification with methyl palmitate has been developed. A reaction system containing a hydrophilic ionic liquid (IL) 1-ethyl-3-methyl imidazoliumacetate and a hydrophobic IL 1-Butyl-3-methylimidazolium tetrafluoroborate enables the transesterification of chitosan with high DS and selectivity in a homogeneous phase. FT-IR and NMR analysis confirmed that the chitosan ester was formed and the lipase selectively catalyzed the acylation of the 6-OH groups of chitosan without protection of its −NH2 groups. The effects of several key reaction factors were investigated and the maximal degree of substitution (DS) value of 0.214 was obtained under the optimum conditions. The X-ray diffraction analysis showed that morphological and crystallographic properties of native chitosan were largely destroyed after modification. Thermogravimetric analysis showed that the thermal stability of chitosan palmitate was reduced. This is the first time that long-chain chitosan esters was biocatalytically synthesized in ILs and the biocatalytic method presented here showed potential application for chitosan modification processes of industrial interest.