Assessment of Enzyme Functionality at Metal–Organic Framework Interfaces Developed through Molecular Simulations

The catalytic efficiency and unrivaled selectivity with which enzymes convert substrates to products have been tapped for widespread chemical transformations within biomedical technology, biofuel production, gas sensing, and the upgrading of commodity chemicals, just to name a few. However, the feasibility of enzymes implementation is challenged by the lack of reusability and loss of native catalytic activity due to the irreversible biocatalyst denaturation at high temperatures and in the presence of industrial solvents. Enzyme immobilization, a prerequisite for enzyme reusability, offers controllable strategies for increased functional viability of the biocatalyst in a synthetic environment. Herein we used molecular dynamics (MD) simulations and probed the noncovalent interactions between model enzymes of technological interest, i.e., carbonic anhydrase (CA) and myeloperoxidase (MPO), with selected metal–organic frameworks (MOFs; MIL-160 and ZIF-8) of proven industrial implementation. We found that the CA and MPO can bind to MIL-160 at optimal binding energies of 201 and 501 kJ mol–1, respectively, that are strongly influenced by the increased incidence of hydrogen bonding between enzymes and the frameworks. The free energy of binding of enzymes to ZIF-8, on the other hand, was found to be less strongly influenced by hydrogen bonding networks relative to the occurrence of hydrophobic–hydrophobic interactions that yielded 106 kJ mol–1 for CA and 201 kJ mol–1 for MPO

Elucidation of Structure–Function Relationships of Hyaluronic Acid-Based Polymers via Combinatorial Approaches

Hydrogels have been identified as biomaterials of significant interest owing to their unique propertieshydrophilic structures, high degree of structural flexibility, low toxicity, biocompatibilitythat qualify them as ideal candidates in a wide range of biomedical and pharmaceutical applications from wound dressing surface coatings, to drug delivery composites, and tissue scaffolds. However, such desired properties of hydrogels simultaneously endow these materials with inherent shortcomings that have hindered their prolific implementation in even more industrial applications; specifically, hydrogels suffer from low mechanical stability and loss of native function upon exposure to industrial solvents. One proposed technique to overcome these challenges and thus functionalize hydrogels to increased their wider range of industrial applications is their chemical modification to elicit controllable changes in their structure and function to thus fulfill the user-defined end goal. The chemical modification strategy further drives the need for an in-depth understanding of the physical and chemical phenomena that control the assembly of modified biopolymers and thus determine their functionality. We hypothesize that a combinatorial approach employing both molecular dynamics (MD) simulations and analytical techniques could be used to probe the self-assembly of alkyl chain-modified hyaluronic acid (HYA)model biopolymer chosen for its hydrophilicity, relative abundance, biocompatibility, and periodic carboxylate reactive groupand thus will allow us to control the assembly dynamics and its end structure properties when alkyl-chain-modified HYA networks are to be constructed, especially porosity, average pore aperture size, and accessible surface area. For this purpose, modified HYA chains were synthesized via (1)-ethyl-3-(3-dimethylaminopropyl) carbodiimide chloride (EDC)-mediated amine group attachment of dodecylamine to the periodic carboxylate group onto the HYA backbone. Material characterization including Fourier transform infrared spectroscopy, nuclear magnetic resonance, and thermogravimetric analysis was conducted to confirm the expected EDC reaction chemistry and further assess the water uptake capacity of the resulting modified hydrogels. MD simulations of both unmodified HYA and modified HYA chainswith varied lengths of attached alkyl groups as well as varied degrees of alkyl group substitution on the HYA backbonewere carried out to analyze the self-assembly dynamics of such chains and thus determine how differences in chemical modification eventuate the critical differences in the end structure properties of the resulting networks. Our findings demonstrate that targeted, atomic-level investigation and corroborated analytical analyses of the assembly of chemically modified hydrogels are necessary to develop the next generation of fully optimized biomaterials that have extended applicability in industrial settings

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

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

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

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