Epoxy-Affixed ZIF-8/CS/Cellulase: a Sustainable Approach for Hydrolysis of Agricultural Waste to Reducing Sugars

Cellulase was effectively immobilized onto an epoxy-bound chitosan-modified zinc metal-organic framework (epoxy/ZIF-8/CS/cellulase) support, yielding a conjugation rate of 0.64 ± 0.02 mg/cm2 and retaining 80.01 ± 0.01% of its specific activity. The bare and cellulase-bound supports was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, atomic force microscopy and energy-dispersive X-ray spectroscopy. The immobilized enzyme exhibited optimal activity at pH 5.5 and a temperature of 70 ℃. The efficiency, stability and reactivity of the enzyme improved after immobilization, as evidenced by a decrease in activation energy, enthalpy and Gibbs free energy along with an increase in entropy change. The epoxy-affixed ZIF-8/CS/cellulase strip was successfully employed for rice husk hydrolysis achieving an impressive conversion efficiency of 95%. The method demonstrated a linear range from 0.1 to 0.9% (0.1 × 10-2 to 0.9 × 10-2 mg/ml) and exhibited a strong correlation (R2 = 0.998) with the widely adopted 3, 5-dinitrosalicylic acid method. The epoxy/ZIF-8/CS bound cellulase exhibited remarkable thermal stability, retaining 100% of its activity at 70 °C, in contrast to just 53% for the free enzyme and displayed a half-life of 21 days after storage at 4 °C compared to 9 days for the free enzyme. Furthermore, it retained over 95% activity after 12 h at pH levels of 4.5 and 5.5 and showcased excellent reusability, maintaining activity over 25 cycles. Overall, this method offers high conversion efficiency and selectivity under benign conditions, with no undesirable by-products, making it a cost-effective solution for the routine hydrolysis of lignocellulosic biomass feedstock.

ZIF-8 nanocarriers synthesized by co-encapsulating resveratrol and cellulase for biomedical applications

Drug conjugation with enzymes is one of the innovative antibacterial nanocarriers used as a delivery system for cancer therapy. Zeolitic imidazolate framework-8 (ZIF-8) was synthesized, dual encapsulated with cellulase (CL) enzyme, and resveratrol (Resv) drug formed ZIF-8@CL&Resv. Cellulase and resveratrol hydrophobic nature have bound them together and imparted a negative charge on the ZIF-8, resulting in the decrease of zeta potential from 22.7 mV (ZIF-8) to 3.82 mV (ZIF-8@CL&Resv). The cellulase like a scaffold regulated the pH-responsive release of resveratrol enhancing its bioavailability. Molecular docking studies provided evidence of the major interaction between the biofilm-related proteins with cellulase and resveratrol. The encapsulated cellulase showed high enzymatic activity and possibly exhibited antibacterial effects by dissolving the biofilm and exposing bacteria to resveratrol action. Resveratrol released sustainably exhibited significant antioxidant and antibacterial activity against selected bacterial species. ZIF-8@CL&Resv exhibited high biocompatibility and had a potent cytotoxic effect against triple-negative breast cancer cells MDA MB 231 with an IC50-value of 17.18 μg/mL compared to ZIF-8 control with 90.47 μg/mL. ZIF-8@CL&Resv treatment led to 61.81 % cell death, apoptosis induction, increased ROS generation, and decreased mitochondrial membrane potential. Overall, data demonstrated that ZIF-8@CL&Resv is a novel drug release system and a potential catalytic nanoparticle for antimicrobial and anticancer applications.

Cellulase immobilization on nano-chitosan/chromium metal-organic framework hybrid matrix for efficient conversion of lignocellulosic biomass to glucose

In the current work, cellulase from Aspergillus niger was successfully immobilized on a novel epoxy-affixed chromium metal-organic framework/chitosan (Cr@-MIL-101/CS) support via covalent method using glutaraldehyde as a crosslinker. The bare and cellulase-bound support was characterized by using various microscopic and spectroscopic techniques. Immobilized cellulase exhibited a high immobilization yield of 0.7 ± 0.01 mg/cm2, retaining 87.5 ± 0.04% of its specific activity and displaying enhanced catalytic performance. The immobilized enzyme was maximally active at pH 5.0, temperature 65 °C and 0.9 × 10-2 mg/ml saturating substrate concentration and the half-lives of free and immobilized cellulases were approximately 9 and 19 days, respectively. The decrease in activation energy, enthalpy change, and Gibbs free energy change, coupled with an increase in entropy change upon immobilization, indicated that the enzyme's efficiency, stability, and spontaneity in catalyzing the reaction were enhanced by immobilization. Additionally, the immobilized cellulase efficiently converted rice husk cellulose to glucose, with a quantification limit of 0.05%, linear measurement ranging from 0.1 to 0.9%, and 8.5% conversion efficiency. The present method exhibited a strong correlation (R2 = 0.998) with the DNS method, validating its reliability. Notably, the epoxy/Cr@-MIL-101/CS-bound cellulase demonstrated impressive thermal and pH stabilities, retaining 50% of its activity at 75 °C and over 96% at pH levels of 4.5 and 5.0 after 12 h. Furthermore, it showed excellent reusability, preserving 80% of its activity after 15 cycles and maintaining 50% of its activity even after 20 days of storage. These results suggest that epoxy/Cr@-MIL-101/CS/cellulase composites could be very effective for large-scale cellulose hydrolysis applications.

Cellulase immobilization to enhance enzymatic hydrolysis of lignocellulosic biomass: An all-inclusive review

Cellulase-mediated lignocellulosic biorefinery plays a crucial role in the production of high-value biofuels and chemicals, with enzymatic hydrolysis being an essential component. The advent of cellulase immobilization has revolutionized this process, significantly enhancing the efficiency, stability, and reusability of cellulase enzymes. This review offers a thorough analysis of the fundamental principles underlying immobilization, encompassing various immobilization approaches such as physical adsorption, covalent binding, entrapment, and cross-linking. Furthermore, it explores a diverse range of carrier materials, including inorganic, organic, and hybrid/composite materials. The review also focuses on emerging approaches like multi-enzyme co-immobilization, oriented immobilization, immobilized enzyme microreactors, and enzyme engineering for immobilization. Additionally, it delves into novel carrier technologies like 3D printing carriers, stimuli-responsive carriers, artificial cellulosomes, and biomimetic carriers. Moreover, the review addresses recent obstacles in cellulase immobilization, including molecular-level immobilization mechanism, diffusion limitations, loss of cellulase activity, cellulase leaching, and considerations of cost-effectiveness and scalability. The knowledge derived from this review is anticipated to catalyze the evolution of more efficient and sustainable biocatalytic systems for lignocellulosic biomass conversion, representing the current state-of-the-art in cellulase immobilization techniques.

A review on pectinase properties, application in juice clarification, and membranes as immobilization support

Pectic substances cause haziness and high viscosity of fruit juices. Pectinase enzymes are biological compounds that degrade pectic compounds. Nontoxicity and ecofriendly nature make pectinases excellent biocatalysts for juice clarification. However, the poor stability and nonreusability of pectinases trim down the effectiveness of the operation. The immobilization techniques have gained the attention of researchers as it augments the properties of the enzymes. Literature has reported the stability improvement of enzymes like lipase, laccase, hydrogen peroxidase, and cellulase upon immobilization on the membrane. However, only a few research articles divulge pectinase immobilization using a membrane. The catalysis-separation synergy of membrane-reactor has put indelible imprints in industrial applications. Immobilization of pectinase on the membrane can enhance its performance in juice processing. This review delineates the importance of physicochemical and kinematic properties of pectinases relating to the juice processing parameters. It also includes the influence of metal-ion cofactors on enzymes' activity. Considering the support and catalytic-separation facets of the membrane, the prediction of the membrane as support for pectinase immobilization has also been carried out.

Cellulose-deconstruction potential of nano-biocatalytic systems: A strategic drive from designing to sustainable applications of immobilized cellulases

Nanostructured materials along with an added value of polymers-based support carriers have gained high interest and considered ideal for enzyme immobilization. The recently emerged nanoscience interface in the form of nanostructured materials combined with immobilized-enzyme-based bio-catalysis has now become research and development frontiers in advance and applied bio-catalysis engineering. With the involvement of nanoscience, various polymers have been thoroughly developed and exploited to nanostructured engineer constructs as ideal support carriers/matrices. Such nanotechnologically engineered support carriers/matrix possesses unique structural, physicochemical, and functional attributes which equilibrate principal factors and strengthen the biocatalysts efficacy for multipurpose applications. In addition, nano-supported catalysts are potential alternatives that can outstrip several limitations of conventional biocatalysts, such as reduced catalytic efficacy and turnover, low mass transfer efficiency, instability during the reaction, and most importantly, partial, or complete inhibition/deactivation. In this context, engineering robust and highly efficient biocatalysts is an industrially relevant prerequisite. This review comprehensively covered various biopolymers and nanostructured materials, including silica, hybrid nanoflower, nanotubes or nanofibers, nanomembranes, graphene oxide nanoparticles, metal-oxide frameworks, and magnetic nanoparticles as robust matrices for cellulase immobilization. The work is further enriched by spotlighting applied and industrially relevant considerations of nano-immobilized cellulases. For instance, owing to the cellulose-deconstruction features of nano-immobilized cellulases, the applications like lignocellulosic biomass conversion into industrially useful products or biofuels, improved paper sheet density and pulp beat in paper and pulp industry, fruit juice clarification in food industry are evident examples of cellulases, thereof are discussed in this work.

α-glucosidase immobilization on magnetic core-shell metal-organic frameworks for inhibitor screening from traditional Chinese medicines

In this work, a simple and rapid screening strategy was developed combining capillary electrophoresis analysis with enzymatic assay based on immobilized α-glucosidase. For α-glucosidase immobilization, magnetic core-shell metal-organic frameworks composite (Fe₃O₄@CS@ZIF-8) was fabricated by a step-by-step assembly method, and α-glucosidase was in situ encapsulated in crystal lattice of ZIF-8. The composite was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and vibrating sample magnetometer. After immobilization, α-glucosidase exhibited enhanced tolerance to temperature and pH, and its reusability was greatly improved with 74 % of initial enzyme activity after being recycled 10 times. The Michaelis-Menten constant of immobilized enzyme was calculated to be 0.47 mM and its inhibition constant and IC₅₀ for acarbose were 0.57 μM and 0.18 μM, respectively. The immobilized enzyme was subsequently applied to inhibitor screening from 14 TCMs, and Rhei Radix et Rhizoma was screened out. Among the commercially available 10 components presented in Rhei Radix et Rhizoma, gallic acid, (+)-catechin and epicatechin exhibited the strongest inhibitory effect on α-glucosidase. Their binding sites and modes with α-glucosidase were simulated via molecular docking to further verify the inhibition screening assay results. The positive results indicated that the Fe₃O₄@CS@ZIF-8-based screening strategy may provide a new avenue for discovering enzyme inhibitors from TCMs.

Preparation of Chitosan/Magnetic Porous Biochar as Support for Cellulase Immobilization by Using Glutaraldehyde

In this work, porous biochar was obtained from sugarcane bagasse by alkali activation and pyrolysis and then magnetized with γ-Fe₂O₃ by calcination. After functionalization with chitosan and activation with glutaraldehyde, the as-prepared chitosan/magnetic porous biochar served as a support to immobilize cellulase by covalent bonds. The immobilization amount of cellulase was 80.5 mg cellulase/g support at pH 5 and 25 °C for 12 h of immobilization. To determine the enzymatic properties, 1% carboxymethyl cellulose sodium (CMC) (dissolved in 0.1 M buffer) was considered as a substrate for hydrolysis at different pH values (3–7) and temperatures (30–70 °C) for 30 min. The results showed that the optimum pH and temperature of the free and immobilized cellulase did not change, which were pH 4 and 60 °C, respectively. The immobilized cellulase had a relatively high activity recovery of 73.0%. However, it also exhibited a higher Michaelis–Menten constant (K_m) value and a slower maximum reaction velocity (V_max) value compared to the free enzyme. In the reusability assay, the immobilized cellulase showed initial glucose productivity of 330.9 mg glucose/g CMC and remained at 86.0% after 10 uses. In conclusion, the chitosan/magnetic porous biochar has great potential applications as a support for enzyme immobilization.

Lipase immobilization on UiO-66/poly(vinylidene fluoride) hybrid membranes and active catalysis in the vegetable oil hydrolysis

This is the first report in which UiO-66/PVDF hybrid membranes with high immobilization efficiency for lipase were constructed.

A facile synthesis of a ZIF-derived ZnS/ZnIn2S4 heterojunction and enhanced photocatalytic hydrogen evolution

A novel heterostructure of ZIF-derived ZnS/ZnIn₂S₄ is formed by nano-ZnS uniformly dispersed in ZnIn₂S₄ flower, which displays enhanced photocatalytic reactions.

Thermostable enzyme-immobilized magnetic responsive Ni-based metal–organic framework nanorods as recyclable biocatalysts for efficient biosynthesis of S-adenosylmethionine

A novel magnetic responsive Ni-based metal–organic framework material was developed to efficiently separate and immobilize thermal enzymes with high catalytic performance.