Novel hybrid materials on the basis of nanostructured tin dioxide and a lipase from Rhizopus delemar with improved enantioselectivity

We obtained novel hybrid materials on the basis of covalently bounded to amino-grafted tin dioxide lipase from Rhizopus delemar (NH2-nano-SnO2-RhD). Under the optimal condition, the protein loading yielded of 14.7 mg/g NH2-nano-SnO2, while the adsorption capacity of the unmodified nano-SnO2 for the same enzyme was 38.5 mg/g. At the same time, NH2-nano-SnO2-RhD exhibited specific hydrolytic activity of 77.6 U/mg prot. which is 2.5-fold higher in comparison to that of the physically adsorbed on nano-SnO2 lipase (nano-SnO2-RhD). In ten reaction cycles of tributyrin hydrolysis, up to 70% of the activity of NH2-nano-SnO2-RhD was preserved. Upon immobilization the enantioselectivity of the lipase for the reaction of acylation of (±)-menthol was improved. For the two biocatalysts, the highest yield of (−)-menthyl acetate (more than 35%) was obtained when glyceryl triacetate was used as acylating reagent, however, the enantiomeric excess was only 89.5% for the covalently bonded lipase and 85.0% for the physically adsorbed one. Higher enantiomeric excess was obtained when vinyl acetate was used as an acylating reagent; however, the conversion in that case did not exceed 20%. The addition of small amounts of pyrrolidinium-based ionic liquids, 1-methyl-1-octyl-pyrrolidinium bis(trifluoromethyl)sulfonyl imide [MOPyrro][NTf2], 1-methyl-1-octyl-pyrrolidinium hexafluorophosphate [MOPyrro][PF6], and 1-methyl-1-octyl-pyrrolidinium tetrafluoroborate [MOPyrro][BF4], to the reaction mixture resulted in decrease of (±) menthol conversion rate. All tested ionic liquids enhanced the enantioselectivity of nano-SnO2-RhD, and the best result was obtained in presence of [MOPyrro][PF6] (enantiomeric ratio >140).