Effect of CHAPS on the selective synthesis of (S)-n-octyl ibuprofen ester in AOT reverse micelle catalyzed by lipase

Abstract

CHAPS (3-[(3-cholamidopropyl) dimethylammonio]-1-propane sulfonate), a biocompatible zwitterionic surfactant derived from bile salt, has attracted great attention due to its distinct molecular structure and aggregation behavior. Addition of a low level of CHAPS to AOT (sodium bis(2-ethylhexyl) sulfosuccinate) reverse micelles has been found to be able to enhance the catalytic activity of the solubilized lipase. In this study, the effect of CHAPS on the lipase-catalyzed selective synthesis of (S)-n-octyl ibuprofen ester was investigated in AOT reverse micelles at 37 °C. The results demonstrate that the presence of CHAPS in AOT reverse micelle enhances both the yield and the enantiomeric excess (ee) value of (S)-n-octyl ibuprofen ester, especially at low water content. With 8 mM CHAPS in AOT reverse micelle ([AOT] = 100 mM, [H2O]/[AOT] = 12, pH = 7.0), a 48-hour yield of 34.2 % could be obtained, which is approximately twice that without CHAPS. In addition, the ee value of the product is increased from 89.1 % to 98.2 %. To understand the mechanism of the CHAPS effect, dynamic light scattering, fluorescence emission spectroscopy and Fourier transform infrared spectroscopy techniques were used to characterize the size of the reverse micelle, the conformation of the solubilized lipase and the activity of the bulk water in the reverse micelle. It reveals that at low water content, the addition of CHAPS enlarges the size of AOT reverse micelle, stabilizes the lipase conformation and reduces the nucleophilicity of bulk water in AOT reverse micelle. The synergistic effect of the aforementioned factors results in the improvement of the enzymatic synthesis of the ester. The above research provides scientific support for the lipase-based preparation of chiral acids/alcohols in the reverse micellar system.