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

•Amino-grafted and non-functionalized nanosized tin dioxide was synthesized.•Lipase from Rhizopus delemar was stabilized via immobilization on the two carriers.•The covalently bonded lipase was more active than the physically adsorbed one.•The covalently bonded lipase was active in 10 consequtive cycles.•Pyrrolidinium-based ionic liquids improved enantioselectivity of the biocatalysts.

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).

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