Enzyme Immobilization on Metal Organic Frameworks: the Effect of Buffer on the Stability of the Support

Abstract

Metal organic frameworks (MOFs) have been used to encapsulate an array of enzymes in a rapid and facile manner; however, the stability of MOFs as supports for enzymes has not been examined in detail. This study examines the stability of MOFs with different compositions (Fe-BTC, Co-TMA, Ni-TMA, Cu-TMA, and ZIF-zni) in buffered solutions commonly used in enzyme immobilization and biocatalysis. Stability was assessed via quantification of the release of metals by inductively coupled plasma optical emission spectroscopy. The buffers used had varied effects on different MOF supports, with incubation of all MOFs in buffers resulting in the release of metal ions to varying extents. Fe-BTC was completely dissolved in citrate, a buffer that has a profound destabilizing effect on all MOFs analyzed, precluding its use with MOFs. MOFs were more stable in acetate, potassium phosphate, and Tris HCl buffers. The results obtained provide a guide for the selection of an appropriate buffer with a particular MOF as a support for the immobilization of an enzyme. In addition, these results identify the requirement to develop methods of improving the stability of MOFs in aqueous solutions. The use of polymer coatings was evaluated with polyacrylic acid (PAA) providing an improved level of stability. Lipase was immobilized in Fe-BTC with PAA coating, resulting in a stable biocatalyst with retention of activity in comparison to the free enzyme.

Expanding the Synthetic Toolbox: Discovery of a Robust Aldehyde Dehydrogenase for Integrated Chemocatalysis and Enzyme Catalysis

“…Besides, biocatalytic reactions were usually performed at approximately 30 °C. Therefore, the good stability at 30 °C makes the enzyme a highly attractive catalyst for the oxidation of aldehydes and the relative cascade reactions [13d,18,24] …”

Metal-Organic Frameworks: Versatile Platforms for Biomedical Innovations

“…The structure of MOFs offers novel strategies for enzyme immobilization. Shortall et al [ 45 ] investigated the stability of MOFs when used as enzyme supports. Their findings emphasized the importance of selecting the right buffer-MOF combinations and suggested that coatings, notably polyacrylic acid (PAA), further enhance stability.…”

Hollow Hierarchical Porous and Antihydrolytic Spherical Zeolitic Imidazolate Frameworks for Enzyme Encapsulation and Biocatalysis

“…Like ZIF-8, one outstanding feature is its relative good chemical and thermal stability, which is attributed to the bonding interactions between the central metal ions and nitrogen atoms in the ligands. 12 Nevertheless, it was discovered that the previously assumed robust zeolitic imidazolate framework ZIF-8 (composed of 2-MIM and zinc ions) is highly sensitive to the presence of water molecules 13 and also more prone to loss of coordination linkage at acidic pH environments 14 And some interfering anions, such as phosphate ions (PO 4 3− ) in phosphate buffer solutions, may replace 2-MIM and form noncrystalline zinc complexes. 15 The immobilized enzyme molecules may leach and be deactivated as a result of this irreversible structural breakdown.…”