Amino Functionality Enables Aqueous Synthesis of Carboxylic Acid-Based MOFs at Room Temperature by Biomimetic Crystallisation

Enzyme immobilisation within Metal-Organic Frameworks (MOFs) is a promising solution to avoid denaturation and thereby utilise the desirable properties of enzymes outside of their native environments. The biomimetic mineralization strategy employs biomacromolecules as nucleation agents to promote the crystallisation of MOFs in water at room temperature, thus overcoming pore size limitations presented by traditional post-assembly encapsulation. Most biomimetic crystallisation studies reported to date have employed zeolitic imidazole frameworks (ZIFs). Herein, we expand the library of MOFs suitable for biomimetic mineralisation to include zinc(II) MOFs incorporating functionalised terephthalic acid linkers, and study the catalytic performance of the enzyme@MOFs. Amine functionalisation of terephthalic acids is shown to accelerate the formation of crystalline MOFs enabling new enzyme@MOFs to be synthesised. The structure and morphology of the enzyme@MOFs were characterised by PXRD, FTIR and SEM-EDX and the catalytic potential was evaluated. Increasing the linker length whilst retaining the amino moiety,
gave rise to a family of linkers, however, MOFs generated with the 2, 2’-amino terephthalic acid linker displayed the best catalytic performance. Our data also illustrates that the pH of the reaction mixture affects the crystal structure of the MOF and this structural transformation impacts the catalytic performance of the enzyme@MOF.