| The main structure characteristics of most lipases, as significant biocatalysts, is the α-helical structure, called “lid”, which covers the lipase catalytic center. Hence,the catalytic performance of lipase is influenced by the overturn of the “lid” direcctly.Bile salt is a kind of biosurfactants, and its rigid skeleton of sterol is both chiral and amphiphilic. Bile salt could induce the “lid” opening and activate lipase. So that, to tailor the interaction of bile salt and lipase is likely to be a promising method to improve the efficiency of the lipase-catalyzed resolution of the racemic 1-phenethanol during this interesterification. In this work, firstly, six kinds of bile salts were selected and the effect of the bile salts concentration on the catalysis of two sources of lipses(CRL from microorganism and PPL from mammalian) was studied, respectively.Secondly, six kinds of chiral selectivity support were fabricated by covalently binding the bile salts on the polyacrylonitrile for lipases immobilization, and the chiral resolutions of the immobilized lipases on these supports were analyzed, respectively.Lastly, Lithocholic acid(LCA) and Deoxycholic acid(DCA) were used as raw materials to synthesize cholic tweezers by grafting a chiral unsymmetrial urea on the two bile acids, respectively, and the catalysis of lipases mixed with these cholic tweezers were explored. The results of this research are as follows:1. The tendency of theeffect of the concentrations of the bile salts on the catalytic activity and enantioselectivity of the two lipases is samiliar: with the increase of the concentration of bile salt, the catalytic activity and E value increase firstly to reach a maximum around the CMC of each bile salt, and then decline. It indicates that the catalytic activity and E value of lipase could be enhanced simultaneously, by mixing with a certain concentration of bile salts.The degree of the effect of the concentrations of each bile salts on the catalytic activity and enantioselectivity of the two lipases is diverse: the catalytic activity of CRL is higher than that of PPL, while the E value of CRL is lower than that of PPL. It is mainly due to the difference of the structures of lipases and the sensitivity of lipases response to bile salts.2. The order of hydrophobicity of the supports modified by the bile salts is PAN-LCA>PAN-DCA>PAN-CDCA>PAN-CA>PAN-TDCA>PAN-TCA, which is determined by the hydrophobicity of bile salts. According to the characteristic of lipases which tend to adsorb on the hydrophobic surface and the bending flexibility of conjugated bile acid which might be liable to capture lipases, the order of adsorption capacity is PAN-TCA(4.40 mg/g) > PAN-TDCA(3.42 mg/g) > PAN-NH2(2.65mg/g) > PAN-LCA(2.52 mg/g) > PAN-CDCA(2.03 mg/g) > PAN-DCA(1.80mg/g) > PAN-CA(1.53 mg/g) for PPL and PAN-TCA(1.81 mg/g) > PAN-TDCA(1.54 mg/g) > PAN-NH2(1.30 mg/g) > PAN-LCA(1.05 mg/g) > PAN-CDCA(1.01 mg/g) > PAN-CA(0.92 mg/g) > PAN-DCA(0.86 mg/g) for CRL. Free lipase can aggregate and become agglomeration in organic solvent, so the catalytic activity of the immobilized lipase is more than 3-10 times than that of the free ones.As the recognition performance of bile salts on the supports, the E value of immobilized PPL is 9 times on PAN-CA and PAN-TCA, and 7.5 times on PAN-LCA,compared to that of free PPL. Similarly, the E value of immobilized CRL is 3 times on PAN-TCA and 2 times on PAN-LCA, compared to the free CRL.3. The complexation of bile acid derivative and enantiomer 1-phenethanol was analyzed by nuclear magnetic resonance spectroscopy(HNMR). As the two cholic molecule tweezers added into the transesterification reaction, the catalytic activities of the lipases inrease 5 % and 27 % for PPL with the assist of deoxycholic acid chiral asymmetrical urea molecular tweezers and lithocholic acid chiral asymmetrical urea molecular tweezers, and accordingly for CRL raising 27 % and 43 %. However, the effect of the cholic molecular tweezers on the increase of the E value of lipase is not obvious. |
PDF Full Text Request