Interfacially crystallized Enzyme@MOFs biocatalytic membranes for highly efficient synthesis of D-amino acids via continuously recirculating stereoinversion

D-Amino acids (D-AAs) constitute essential building blocks found in many pharmaceuticals and fine chemicals. We herein presented the coating of polyvinylidene fluoride (PVDF) hollow fiber membrane with L-amino acid oxidase (LAAO) embedded zeolitic imidazolate framework-8 (ZIF-8) layer by a single-step interfacial biomineralization strategy for efficient synthesis of D-AAs. The ZIF-8 skeleton and PVDF membrane structure not only guaranteed free enzyme activity and stability, but also reinforced the applicability of this bioreactor for continuous enzymatic reactions. By placing the prepared biocatalytic membrane in the constructed circulation device, only the L-AAs can be specifically oxidized. The D-AAs are accumulated and synthesized after multiple rounds of continuously recirculating stereoinversion. Impressively, using tryptophan (Trp) as the model molecule, the thus-designed bioreactor exhibited an excellent conversion rate (92.10%) and ee% (99.41%) of D-Trp with a shorter time under constant flow conditions. This study provides an unprecedented protocol for highly efficient synthesis of D-AAs, and immensely advances the promising application field of membrane bioreactors.