Nano-sized mesoporous hydrogen-bonded organic frameworks for in situ enzyme immobilization

Hydrogen-bonded organic frameworks (HOFs) are promising carriers for enzyme immobilization. HOFs suitable for enzyme reactions containing nicotinamide cofactors and/or larger molecule substrates are to be explored. Herein, we report the first example of nano-sized mesoporous HOFs (nmHOFs) for in situ enzyme immobilization. Taking tetrakis(4-amidiniumphenyl) methane (TAM) and 1,3,6,8-tetrakis(p-benzoic acid) pyrene (H4TBAPy) as building blocks, enzymes induce the assembly of TAM and H4TBAPy into enzyme-nmHOF (named enzyme@TaTb) in aqueous solution. The larger π-conjugated H4TBAPy building block and the electrostatic/hydrogen-bonding interactions between TAM in nmHOF and –COOH/–NH2 residues in enzymes trigger the formation of TaTb with pore aperture of 2.4 nm and particle size from 19.9 ± 6.4 to 56.4 ± 20.1 nm. As a demonstration, lactate dehydrogenase (LDH) that can convert pyruvate into lactate in the presence of NADH is immobilized in TaTb nmHOF. Compared with LDH@ZIF-8 and LDH@Bio-HOF-1, LDH@TaTb affords faster diffusion of NADH and pyruvate, thus exhibiting ultrahigh activity close to the free LDH. Meanwhile, the exoskeleton of TaTb nmHOF is capable of stabilizing enzymes through spatial confinement, rendering superior stability against external negative stimuli. The TaTb nmHOF is also used for immobilizing α-amylase and horseradish peroxidase. Our study may facilitate the development of HOFs into platform carriers for enzyme immobilization.