Resolução de álcoois alílicos catalisada por diferentes lipases imobilizadas em nanotubos de carbono de paredes múltiplas

Abstract

The aim of this work was to evaluate the catalytic efficiency of lipases, free and immobilized in multi walled carbon nanotubes (MWCNTs), for the enzymatic kinetic resolution of allylic alcohols with vinyl acetate. Firstly, three commercial lipases were screened such as porcine pancreas (PPL), Candida rugosa AY "Amano" 30 (AY30) and Burkholderia cepacia "Amano" (PS) in the resolution of (RS) -1- octen-3-ol. The enzyme that presented the highest performance was PS. Therefore, PS was selected to continue the immobilization studies in MWCNTS, as well as to evaluate the different reaction conditions in the resolution of allylic alcohols. The immobilization yields obtained for lipase PS in MWCNTs without functionalization (MWCNTs-SF) were more than 91% in 24 h. The best enzyme:support ratio in (RS)-1-octen-3-ol resolution was 5: 1 (w/w), forming the corresponding ester (S)-1-octen-3-yl acetate in conversion of 22%, eep of 51%, thus resulting in E value of 4. Moreover, a 2.5-fold increase in the conversion was observed when the immobilized lipase was used. The studies related to pH effects on PS immobilization applied in the resolution of (RS)-1-hexen-3-ol, (RS)- 1-octen-3-ol and (RS)-(E)-4-phenyl-3-buten-2-ol with vinyl acetate presented better results in acid or neutral pH values (5.0 – 7.0). When the pH was basic (8.0), the catalytic efficiency declined for all substrates. Furthermore, the substituent groups attached to the asymmetric carbon were found to have significantly influenced on the values of enantiomeric ratio (E), being approximately 25 higher for the aromatic [(RS)- (E)-4-phenyl-3-buten-2-ol] substrate than the aliphatics [(RS)-1-hexen-3-ol and (RS)- 1-octen-3-ol]. When (RS)-1-hexen-3-ol and (RS)-(E)-4-phenyl-3-buten-2-ol were used, the conversions to the respective product were of 52 and 51%, respectively, in 6 h of reaction. Using (RS)-1-octen-3-ol, the degree of conversion was 35% in 24 h of reaction. The best catalytic efficiency obtained for the resolution of the three substrates was using PS immobilized in MWCNTs-SF and MWCNTs-N (treated with APTES). Increasing the amount of immobilized enzyme, from 5 to 15 mg, the conversion degrees increased about 1.8 and 1.4 times for the aliphatic and aromatic alcohols, respectively. In the study of the reaction temperature effect, the best results for resolution the 3 substrates were obtained at 55 ° C. The organic solvent influenced the selectivity of the enzyme, and it was observed that the solvent-free system presented higher potential for the studied reactions. The results showed that the commercial PS lipase immobilized in MWCNTS had catalytic potential for the application in the kinetic resolution of secondary allylic alcohols, being the values of conversion, eep and E higher than those obtained using the free form.