Characterization of TEMPO-oxidized chitin nanofibers with various oxidation times and its application as an enzyme immobilization support

Switchable CO2-Responsive Janus Nanoparticle for Lipase Catalysis in Pickering Emulsion

The use of convertible immobilized enzyme carriers is crucial for biphasic catalytic reactions conducted in Pickering emulsions. However, the intense mechanical forces during the conversion process lead to enzyme leakage, affecting the stability of the immobilized enzymes. In this study, a CO2-responsive switchable Janus (CrSJ) nanoparticle (NP) was developed using silica NP, with one side featuring aldehyde groups and the other side adsorbing N,N-dimethyldodecylamine. A switchable Pickering emulsion catalytic system for biphasic interface reactions was prepared by covalently immobilizing lipase onto the CrSJ NPs. The CO2-responsive nature of the CrSJ NPs allowed for rapid conversion of the Pickering emulsion, and covalent immobilization substantially reduced lipase leakage while enhancing the stability of the immobilization during the conversion process. Impressively, after repeated transformations, the Pickering emulsion still maintains its original structure. Following 10 consecutive cycles of esterification and hydrolysis reactions, the immobilized enzyme's activity remains at 77.7 and 79.5% of its initial activity, respectively. The Km of the CrSJ catalytic system showed no significant change compared to the free enzyme, while its Vmax values were 1.2 and 1.6 times that of the free enzyme in esterification and hydrolysis reactions, respectively.

Green synthesis and characterization of an orally bioactive artemisinin-zinc nanoparticle with enhanced bactericidal activity

The occurrence of multidrug-resistant bacteria necessitates the development of new antibacterial agents. This study synthesized artemisinin-zinc nanoparticles (AZ NPs) using a simple green method and investigated their physicochemical properties, antibacterial activity, and oral biological activity. A spherical shape morphology of AZ NPs was observed by scanning and transmission electron microscopy, with a particle size of 73 ± 2.604 nm. Energy dispersive spectrometry analysis showed that the AZ NPs consisted mainly of Zn, C, N, and O elements. According to differential scanning calorimeter analysis, the AZ NPs were stable up to 450 °C. Fourier-transform infrared spectroscopy revealed that artemisinin successfully bound to zinc acetate. The AZ NPs showed antibacterial activity against Salmonella and Escherichia coli, with a minimum inhibitory concentration of 0.056 mg/mL for both and minimum bactericidal concentrations of 0.21 and 0.11 mg/mL, respectively. The mechanisms by which AZ NPs mediate membrane damage were revealed by the downregulation of gene expression, and potassium ion and protein leakage. In vivo safety trials of these drugs revealed low toxicity. After AZ NPs were administered to infected mice, the intestinal bacteria decreased significantly, liver and kidney function were restored, histopathological damage to the liver and spleen were reduced, and the expression of inflammatory cytokines decreased. Therefore, AZ NPs have the potential as an oral antibacterial agent and can be used in antibiotic development and in the pharmaceutical industry.

Magnetic macroporous chitin microsphere as a support for covalent enzyme immobilization

In this study, a novel magnetic macroporous chitin microsphere (MMCM) was developed for enzyme immobilization. Chitin nanofibers were prepared and subsequently subjected to self-assembly with magnetic nanoparticles and PMMA (polymethyl methacrylate). Following this, microspheres were formed through spray drying, achieving a porous structure through etching. The MMCM serves as an effective support for immobilizing enzymes, allowing for their covalent immobilization both on the microsphere's surface and within its pores. The substantial surface area resulting from the porous structure leads to a 2.1-fold increase in enzyme loading capacity compared to non-porous microspheres. The MMCM enhances stability of the immobilized enzymes under various pH and temperature conditions. Furthermore, after 20 days of storage at 4 °C, the residual activity of the immobilized enzyme was 2.93 times that of the free enzyme. Even after being recycled 10 times, the immobilized enzyme retained 56.7 % of its initial activity. It's noteworthy that the active sites of the enzymes remained unchanged after immobilization using the MMCM, and kinetic analysis revealed that the affinity of the immobilized enzymes rivals that of the free enzymes.

Characterization and comparison of carboxymethylation and TEMPO-mediated oxidation for polysaccharides modification

In this study, carboxymethylation and TEMPO-mediated oxidation were compared for their ability to introduce carboxyl groups to polysaccharides, using cellulose and chitin as model polysaccharides. The carboxyl group contents and changes in the molecular weight of carboxymethylated and TEMPO-oxidized cellulose/chitin were measured. The results revealed that carboxymethylation achieved higher carboxyl group contents, with values of 4.99 mmol/g for cellulose and 4.46 mmol/g for chitin, whereas for TEMPO-oxidized cellulose and chitin, the values were 1.64 mmol/g and 1.12 mmol/g, respectively. As a consequence of TEMPO-mediated oxidation, polysaccharides underwent degradation, leading to a decrease in the molecular weight of 42.46 % for oxidized cellulose and 64.5 % for oxidized chitin. Additionally, the crystallinity of carboxymethylated polysaccharides decreased with an increase in the carboxyl group contents, whereas that of TEMPO-oxidized polysaccharides remained unchanged. Furthermore, TEMPO-mediated oxidation selectively oxidized C6 primary hydroxyls, while carboxylmethylation converted all the hydroxyl groups on the polysaccharides.

An efficient method for chitin production from crab shells by a natural deep eutectic solvent

Crab shells are an important feedstock for chitin production. However, their highly compact structure significantly limits their use for the production of chitin under mild conditions. Here, a green and efficient approach using a natural deep eutectic solvent (NADES) to produce chitin from crab shells was developed. Its effectiveness in isolating chitin was investigated. The results showed that most proteins and minerals were removed from crab shells and the relative crystallinity of the isolated chitin reached 76%. The quality of the obtained chitin was comparable to chitin isolated by the acid-alkali method. This is the first report on a green method for efficient chitin production from crab shells. This study is expected to open new avenues for green and efficient production of chitin from crab shells.