Enhancement of biocatalytic activity in enzymatic membrane reactors: Controlled modification with novel PAH/PDA composites as a tool to optimize reactor performance
Andrei Popkov, Magdalena Malankowska, Ziran Su, Manuel Pinelo
Abstract
This study presents a systematic design of a biocatalytic membrane reactor, where we combined physical adsorption and chemical conjugation of Alcohol Dehydrogenase (ADH) in a novel type of polyelectrolyte (PE) layer-by-layer (LbL) assembly system. The hybrid LbL structure is proposed as a strategy to simultaneously advance activity and operational stability of enzymes immobilized on a membrane surface. Using poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) sodium salt (PMAA) allowed functionalization of polysulfone (Psf) membrane for subsequent ADH immobilization with no resistance to substrate mass transfer and no decrease in water permeability (WP) (56.5 ± 8.8 Lm−2h −bar−1) compared to the pristine membrane (50.8 ± 1.7 Lm−2h−1 bar−1). Tailoring membrane surface chemistry, enzyme concentration, time, and pH during the adsorption step allowed to increase specific activity of the biocatalytic membrane from 1.13 ± 0.18 mU/cm2 for immobilization on the pristine membrane to 4.09 ± 0.53 mU/cm2 for immobilization on a PAH-modified coating. Conjugation of adsorbed ADH with PMAA layer improved reusability compared to the non-conjugated membrane (by retaining 73.4 ± 3.2% of the starting activity on the third conversion run against 58.7 ± 2.4%) and shifted pH optimum by 1 unit compared to the free ADH. The presented approach of LbL assembly synthesis provides a potential foundation for engineering of biocatalytic nanoscale reactors.