The synthesis of sulfonated polyethersulfone (SPES) and the preparation of its membranes as matrix in the immobilization of Candida antarctica lipase B (Cal-B)

Abstract

The immobilization of lipases is often used in biotechnology to improve the performance, reusability, and stability of the enzyme. Candida antarctica lipase B (Cal-B) has been used as a catalyst in trans-esterification reaction. To improve the utilization of Cal-B, therefore the immobilization of Cal-B onto a polymer matrix became crucial. In this study, polyethersulfone (PES) and sulfonated polyethersulfone (SPES) membranes were used as matrices of Cal-B immobilization. SPES was previously synthesized by modifying PES using chlorosulfonic acid (ClSO3H) to improve the immobilization of Cal-B. SPES-PSf (polysulfone) blended membranes were also successfully prepared by blending SPES, PSf, and PEG in N-methylpyrrolidone (NMP) as the solvent using phase-inversion method. The attenuated total reflectance (ATR)–FTIR spectrum showed characteristic peaks of the immobilized Cal-B on the matrix at peak 3184.03 cm−1 (–N–H bonds) and 1683.49 cm−1 (–CH deformation bonds). The Raman spectroscopy of the PES-based membranes before and after sulfonation reaction showed the deviations from the symmetrical structure of PES, with specific Raman shifts at 784.11 cm−1, 1150.95 cm−1, and 1588.9 cm−1. Cal-B was successfully immobilized and loaded onto SPES membrane. By Lowry assay, it was detected that 140.3 μg/cm2 enzyme was successfully loaded into the 17.3 cm2 of membrane. The value was one and a half times higher than PES (91.0 μg/cm2 in 17.3 cm2). However, the hydrolytic activity of Cal-B immobilized onto SPES membrane (17.0 p-NP/min/cm2) was five times lower than Cal-B immobilized onto PES membrane (80.4 p-NP/min/cm2).