A Systematic Study of the Stability of Enzyme/Zeolitic Imidazolate Framework‐8 Composites in Various Biologically Relevant Solutions

Abstract

Metal organic frameworks (MOFs) have been used to encapsulate numerous enzymes. This study has encapsulated two enzymes in zeolitic imidazolate framework-8 (ZIF-8) and examined the structural stability of the enzyme@ZIF-8 composites in solutions of various biologically relevant agents (i. e. amino acids, proteins, organic acids, organic/inorganic buffers, surfactants, polymers, carbohydrates and salts). Many of the agents were found to completely dissolve the composites or severely damage their structural integrity, causing the release of the enzymes from the composites. These agents plausibly exerted their destabilizing effects on the composites by interactions with zinc or by complexation with the enzymes in the enzyme@ZIF-8 composites. Notably, Tris and HEPES buffers were found to be supportive of the composites in the short term. The results show the need to improve the stability of the enzyme@ZIF-8 systems for certain applications and suggest triggered release of the encapsulated biomolecules from the porous matrix.

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

“…All MOFs demonstrated higher stability in sodium acetate buffer at a pH of 5 with respect to citrate buffer, as previously demonstrated using ZIF-8 . Fe-BTC and Cu-TMA released less than 1% of metal ions in acetate buffer.…”

“…23,52 All MOFs demonstrated higher stability in sodium acetate buffer at a pH of 5 with respect to citrate buffer, as previously demonstrated using ZIF-8. 29 Fe-BTC and Cu-TMA released less than 1% of metal ions in acetate buffer. This indicates that the interaction between the citrate ion and the MOFs is the determining factor, rather than the pH.…”

“…Reports have described the low hydrolytic stability ,, of MOFs, but these aspects are generally not considered in detail when examining enzyme immobilization. ,− The stability of MOFs in water is determined by the strength of the metal-linker coordination bonds and the level of saturation of metal sites, resulting in different MOFs displaying varying hydrolytic stability. Additionally, the composition of buffers commonly used in enzymatic reactions needs to be considered as the buffer can affect the MOF’s structural integrity, in particular, by disturbing the coordination bonds. ,, Breakdown of the MOF structure in buffered solutions ,, is a key challenge facing the use of MOFs for the immobilization of enzymes, as buffers are required for enzymatic activity. As an example, UiO-66 was found to rapidly degrade in both N -ethylmorpholine and phosphate buffers, while 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) was found to be the most benign buffer, and low concentrations of 2-amino-2-hydroxymethyl-propane-1,3-diol (Tris) were tolerable .…”

From Enzyme Stability to Enzymatic Bioelectrode Stabilization Processes

“…MOF can also be used to encapsulate cascade of enzymes with enhanced stability and spatial control of the proteins inside the lattices [155]. However, care should be taken with solubility of MOFs in the presence of various compounds such as amino acids, some organic acids or buffers that present high affinity for the MOF-metal, inducing leaching of the enzyme via MOF dissolution [156,157]. Covalent organic frameworks, only composed of light elements (H, C, B, N, and O) and covalent bonds, with higher stability than MOFs, can be alternatives as efficient matrices for enzymes [158].…”

Metal Organic Frameworks for Bioelectrochemical Applications

“…For example, Tris and HEPES buffers proved compatible with ZIF-8 (bio)materials [18,19] . Zn-based ZIF-8 is currently the most widely used MOF for the preparation of MOF-enzyme composites [5,18] . Zr-based carboxylate MOFs including the exemplary UiO-66 are also commonly considered for aqueous use [20] .…”