Customized hierarchical porous metal organic frameworks engenders stable enzymatic nanoreactors

Abstract

Compartmentalization is largely found in living organisms to control physical interactions between enzymes and their substrates, which enhances reaction kinetics and channels the production of the needed metabolic intermediates. Enzyme-catalyzed reactions occur in a molecularly crowded environment such as on a tight surface or confined receptor pocket. Taking inspiration from nature, researchers have developed a plethora of enzymes encapsulating vehicles including liposomes, polymeric capsules, protein cages, porous solids, DNA nanocontainers and coordination cages. Carefully pre-designed precursors and extensive synthetic protocols are however almost always required to prepare a well-defined molecular host. Metal Organic frameworks (MOFs) have recently proved to be excellent candidates for various high-end applications. Enzyme encapsulation has been successfully established with water-stable coordination frameworks such as NU-1000, Tb-TATB, PCN and ZIF families that overcome the microporous regime restriction. MIL101 encompasses a huge surface area and pore size of 3.5-3.4 nm. These dimensions worked perfectly for encapsulation and delivery of small drug molecules but are unpractical for large proteins entrapment.Engineering hierarchical micro/ meso pores has been established via selective etching of MOFs. However, since MOF crystals are generally homogenous, designing them with different composition or stability is critical for selective etching. In this work, a facile method to prepare big-pore (BP) MIL 101 by template free etching is presented. BP-MIL 101 could effectively immobilize Catalase, which is a relatively large protein (6 x 10 nm) that breaks down hydrogen peroxide. To the best of our knowledge, no reports on encapsulating large proteins (10 nm) by diffusion through customized big pore frameworks have been reported thus far.