A novel approach to chiral separation: thermo-sensitive hydrogel membranes

The application of membrane technology for separating chiral compounds is hindered due to the restricted availability of chiral recognition sites on the membrane surface. In this study, we propose a novel approach for chiral separation through a selector (bovine serum albumin, BSA) mediated thermo-sensitive membrane system. A thermo-sensitive hydrogel-coated membrane (termed PDTAN) was developed by anchoring poly(N-isopropylacrylamide) (PNIPAm) onto a polyethersulfone (PES) membrane through an adhesive and hydrophilic dopamine hydrochloride (PDA)/tannic acid (TA)/chitosan (Chi) intermediate layer. The results demonstrate outstanding chiral separation efficiency, achieving alpha L/D = 3.30 for d-phenylalanine (d-Phe) rejection at 40 degrees C on a BSA-mediated PDTAN membrane system, with significant stability and minimal fouling, surpassing previous findings. Moreover, the PDTAN membrane altered the selective properties of recognition sites in BSA, transitioning from rejecting l-Phe to rejecting d-Phe. Analysis using fourth-order derivative UV-vis, circular dichroism (CD), and in situ Fourier transform infrared spectroscopy (FTIR) techniques revealed a transition in the secondary structure of BSA from alpha-helix to beta-sheet as the temperature increased. This transition, facilitated by hydrogen bonding between BSA and PNIPAm, enabled selective recognition of d-Phe, demonstrating a distinct shift in chiral recognition properties. Importantly, with d-Phe adsorbed onto beta-sheet structures of BSA, hydrogen-bond interactions between BSA and the PDTAN membrane were significantly reduced, thereby minimizing membrane fouling and achieving the durability of membrane-based chiral separation. A novel method for chiral separation employing a thermo-sensitive hydrogel-coated membrane, facilitated by a bovine serum albumin (BSA)-mediated membrane process.