User-Tailored Metal–Organic Frameworks as Supports for Carbonic Anhydrase

Abstract

Carbonic anhydrase (CA) was previously proposed as a green alternative for biomineralization of carbon dioxide (CO2). However, enzyme’s fragile nature when in synthetic environment significantly limits such industrial application. Herein, we hypothesized that CA immobilization onto flexible and hydrated “bridges” that ensure proton-transfer at their interfaces leads to improved activity and kinetic behavior and potentially increases enzyme’s feasibility for industrial implementation. Our hypothesis was formulated considering that water plays a key role in the CO2 hydration process and acts as both the reactant as well as the rate-limiting step of the CO2 capture and transformation process. To demonstrate our hypothesis, two types of user-synthesized organic metallic frameworks [metal–organic frameworks (MOFs), one hydrophilic and one hydrophobic] were considered as model supports and their surface characteristics (i.e., charge, shape, curvature, size, etc.) and influence on the immobilized enzyme’s behavior were evaluated. Morphology, crystallinity and particle size, and surface area of the model supports were determined by scanning electron microscopy, dynamic light scattering, and nitrogen adsorption/desorption measurements, respectively. Enzyme activity, kinetics, and stability at the supports interfaces were determined using spectroscopical analyses. Analysis showed that enzyme functionality is dependent on the support used in the immobilization process, with the enzyme immobilized onto the hydrophilic support retaining 72% activity of the free CA, when compared with that immobilized onto the hydrophobic one that only retained about 28% activity. Both CA–MOF conjugates showed good storage stability relative to the free enzyme in solution, with CA immobilized at the hydrophilic support also revealing increased thermal stability and retention of almost all original enzyme activity even after heating treatment at 70 °C. In contrast, free CA lost almost half of its original activity when subject to the same conditions. This present work suggests that MOFs tunable hydration conditions allow high enzyme activity and stability retention. Such results are expected to impact CO2 storage and transformation strategies based on CA and potentially increase user-integration of enzyme-based green technologies in mitigating global warming.

Thin Films of Metal-Organic Framework Interfaces Obtained by Laser Evaporation

“…ZIF-8 was also chosen because previous preparation of thin films from this framework was shown to pose significant difficulties since the bulk material is usually made as brittle crystals or insoluble powders that are not amenable to common surface-processing techniques [ 38 , 39 ]. Above applications are also supported by known N 2 adsorption data, which showed that ZIF-8′s Brunauer–Emmett–Teller surface area was 1070.7 m 2 /g, while its Langmuir surface area was 1315.6 m 2 /g [ 40 ], both in the range of other supporting reports [ 41 ].…”

Fast Immobilization of Human Carbonic Anhydrase II on Ni-Based Metal-Organic Framework Nanorods with High Catalytic Performance

“…However, the poor stability and reusability of carbonic anhydrase limits its application in practice [6,8]. Enzyme immobilization on solid supports has been developed to overcome these shortcomings [9][10][11][12][13]. Previous immobilization studies mainly focused on commercial carbonic anhydrase on a wide range of solid supports such as: polyurethane foam [14], SBA-15 [15], mesoporous silica [16], MIL-160 [9] and ZIF-8 [17].…”

“…Enzyme immobilization on solid supports has been developed to overcome these shortcomings [9][10][11][12][13]. Previous immobilization studies mainly focused on commercial carbonic anhydrase on a wide range of solid supports such as: polyurethane foam [14], SBA-15 [15], mesoporous silica [16], MIL-160 [9] and ZIF-8 [17]. However, high cost and protracted immobilization processes greatly limit the application of immobilized CA [4,10,12].…”

<p>Toxicity screening of two prevalent metal organic frameworks for therapeutic use in human lung epithelial cells</p>

“…Considering that such single-point assays also suffer from interference from reagents normally used in classical cellular approaches that could potentially influence MOF-induced toxicity assessment,25 we proposed to screen for cellular behavior upon exposure to MOFs of prevalent use by using only cell-based bio-sensorial approaches. To demonstrate the validity and applicability of the proposed approaches, we used MIL-160, a microporous hydrophilic aluminum-based MOF10,26 with a five-membered ring and an oxygen heteroatom,10 and ZIF-8, a hydrophobic framework of zeolitic imidazolate 10,27. Human bronchial epithelial (BEAS-2B) cells were employed as a pertinent model for toxicity assessment 28.…”

“…Human bronchial epithelial (BEAS-2B) cells were employed as a pertinent model for toxicity assessment 28. MOF selection was based on their demonstrated wide integration for gas storage applications,29 enzyme-based green technologies10 and drug delivery systems,30,31 while cell selection was based on demonstrated intrinsic sensitivity of such systems to convert biological activity into electrical measurements to be recorded in real time with an electric cell impedance sensing platform (ECIS) 25. By simply relying on the natural sensitivity of cells, our analysis demonstrates high-throughput, rapid and accurate screening and differentiation of toxicity based on MOFs physicochemical properties, as well as the capability for extension and large-scale screening of other MOF materials.…”