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 ( nm HOFs) for in situ enzyme immobilization. Taking tetrakis(4-amidiniumphenyl) methane (TAM) and 1,3,6,8-tetrakis(p-benzoic acid) pyrene (H 4 TBAPy) as building blocks, enzymes induce the assembly of TAM and H 4 TBAPy into enzyme- nm HOF (named [email protected] ) in aqueous solution. The larger π-conjugated H 4 TBAPy building block and the electrostatic/hydrogen-bonding interactions between TAM in nm HOF and –COOH/–NH 2 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 nm HOF. Compared with [email protected] and [email protected] , [email protected] affords faster diffusion of NADH and pyruvate, thus exhibiting ultrahigh activity close to the free LDH. Meanwhile, the exoskeleton of TaTb nm HOF is capable of stabilizing enzymes through spatial confinement, rendering superior stability against external negative stimuli. The TaTb nm HOF is also used for immobilizing α-amylase and horseradish peroxidase. Our study may facilitate the development of HOFs into platform carriers for enzyme immobilization.