The enzymatic synthesis of lactose caprate using Candida rugosa lipase immobilized into ZIF-8 and investigation of its anticancer applications against K562 leukemia and HeLa cancer cells.

In this study, a lactose fatty acid ester was enzymatically synthesised using immobilized Candida rugosa lipase (CRL). Its anticancer property against K562 leukemia and HeLa cancer cells was carefully investigated. In the first step, a de novo strategy was applied to encapsulate CRL into a microporous zeolite imidazolate framework called ZIF-8. Various characterization techniques including powder X-ray diffraction, Fourier transform infrared spectroscopy, N2 adsorption-desorption, field-emission scanning electron microscopy and thermogravimetric analysis were used to prove the successful encapsulation of CRL molecules during the formation of ZIF-8 crystals with an enzyme loading of 98% of initial CRL. The effect of various factors such as pH and temperature, affecting the enzymatic activity and reusability of the CRL@ZIF-8 composite were assessed against the free enzyme. Additionally, enzyme catalysis parameters, such as Km and Vmax, were also assessed. The obtained biocatalyst showed excellent activity in a wide pH range of 2-9 and a temperature range of 30-60 °C. According to the experimental results, the CRL@ZIF-8 composite maintained about 63% of its initial activity after 6 cycles of use. In the next step, the synthesized catalyst was applied for the synthesis of lactose caprate via enzymatic esterification of lactose with capric acid. Further experiments were performed to obtain the cytotoxicity profile of the new derivative. The growth inhibitory effect of the produced lactose caprate on K562 leukemia and HeLa cancer cells determined by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay showed its potential anticancer effects against both cell lines (IC50, 49.6 and 57.2 µg mL-1). Our results indicate that lactose caprate might be a promising candidate for further studies on K562 leukemia and HeLa cancer cells owing to its possible therapeutic usefulness.

Carbonic Anhydrase-Embedded ZIF-8 Electrospun PVA Fibers as an Excellent Biocatalyst Candidate.

There is a growing concern that the increasing concentration of CO2 in the atmosphere contributes to a potential negative impact on global climate change. To deal with this problem, developing a set of innovative, practical technologies is essential. In the present study, maximizing the CO2 utilization and precipitation as CaCO3 was evaluated. In this manner, bovine carbonic anhydrase (BCA) was embedded into the microporous zeolite imidazolate framework, ZIF-8, via physical absorption and encapsulation. Running as crystal seeds, these nanocomposites (enzyme-embedded MOFs) were in situ grown on the cross-linked electrospun polyvinyl alcohol (CPVA). The prepared composites displayed much higher stability against denaturants, high temperatures, and acidic media than free BCA, and BCA immobilized into or on ZIF-8. During 37 days of storage period study, BCA@ZIF-8/CPVA and BCA/ZIF-8/CPVA maintained more than 99 and 75% of their initial activity, respectively. The composition of BCA@ZIF-8 and BCA/ZIF-8 with CPVA improved stability for consecutive usage in recovery reactions, recycling easiness, and greater control over the catalytic process. The amounts of calcium carbonate obtained by one mg each of fresh BCA@ZIF-8/CPVA and BCA/ZIF-8/CPVA were 55.45 and 49.15 mg, respectively. The precipitated calcium carbonate by BCA@ZIF-8/CPVA reached 64.8% of the initial run, while this amount was 43.6% for BCA/ZIF-8/CPVA after eight cycles. These results indicated that the BCA@ZIF-8/CPVA and BCA/ZIF-8/CPVA fibers could be efficiently applied to CO2 sequestration.

Preparation and characterization of nanofibrous metal-organic frameworks as efficient catalysts for the synthesis of cyclic carbonates in solvent-free conditions.

Environmental concerns, particularly global warming, represent serious threats to public health globally. Metal-organic frameworks (MOFs) are innovative materials with prominent features such as ultrahigh surface area, high porosity and tunable cavities, which make them unique materials both in adsorption of carbon dioxide and catalysis. The design of new nanocomposites by using metal-organic frameworks as building materials has received broad attention recently. Here, nanocrystals of two unique MOF structures (UiO-66 and ZIF-67) were incorporated into electrospun polyvinyl alcohol (PVA) and polystyrene (PS) fibers (noted as MOFibers) by an ex situ method, to transform non-toxic, abundant, economical and renewable CO2 gas to cyclic carbonates in a solvent-free medium. In order to improve the composites' performance, different electrospinning parameters, including applied voltage, flow rate, collection distance, PVA and PS weight fraction in solution, and MOF weight fraction relative to the polymer, were intensively investigated. The synthesized samples were characterized by multiple techniques, such as FTIR, XRD, SEM, UV-vis and TGA, as well as N2 and CO2 adsorption measurement. It was found that all of the composites show properties combining the advantages of MOFs and polymers, such as thermal, chemical, and mechanical stability, structural flexibility, lightweight, adsorption performance and catalytic properties. Additionally, all systems were environment-friendly and the PVA/MOF fibers were easily separated and recycled for consecutive cycles.

Novel bovine carbonic anhydrase encapsulated in a metal-organic framework: a new platform for biomimetic sequestration of CO2.

In this work, maximizing the utilization of CO2 and its precipitation as CaCO3 by using immobilized bovine carbonic anhydrase (BCA) was evaluated. In this way, selection of suitable carriers which have a gas adsorption function would enhance the CO2 sequestration efficiency of the carbonic anhydrase (CA). So a metal-organic framework (MOF), an excellent material for gas adsorption and enzyme immobilization was used. In this manner, BCA was encapsulated into the microporous zeolite imidazolate framework, ZIF-8, for the first time, using a bottle-around-a-ship method. Systematic characterization including powder X-ray diffraction (PXRD), UV-vis, and Fourier transform infrared (FT-IR) spectroscopies, BET, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray (EDX) confirmed that the entrapment of BCA molecules was successfully achieved during the crystal growth of ZIF-8 with an enzyme loading of ca. 100 ± 1.2 mg g-1 of BCA-ZIF-8. Optimization of the matrix for increasing the stability of the enzyme in an encapsulated form is the main aim of the present study. The de novo approach was proposed because this method provides better enzyme protection from degradation, minimizes enzyme leaching and enables multiple reuse. Then, the influence of different parameters, including pH, temperature, storage and reusability, was evaluated for enzyme@MOF composites versus free enzymes. The prepared biocatalyst exhibited outstanding activity in a wide pH and temperature range and demonstrates high storage stability up to 37 days. This efficient and simple association procedure seems well-adapted to produce an enzymatic bio-catalyst for biocatalytic hydration of CO2. The FT-IR analysis revealed that the structure of BCA was well maintained during the encapsulation process. The thermal stability and reusability of the BCA-ZIF-8 increased noticeably due to the structural rigidity and confinement of the ZIF-8 scaffolds. These two parameters are very important for practical applications.