Oxidation of hydroquinone top-benzoquinone catalyzed by Cu(II) supported on chitosan flakes

A comprehensive survey upon diverse and prolific applications of chitosan-based catalytic systems in one-pot multi-component synthesis of heterocyclic rings

Heterocyclic compounds are among the most prestigious and valuable chemical molecules with diverse and magnificent applications in various sciences. Due to the remarkable and numerous properties of the heterocyclic frameworks, the development of efficient and convenient synthetic methods for the preparation of such outstanding compounds is of great importance. Undoubtedly, catalysis has a conspicuous role in modern chemical synthesis and green chemistry. Therefore, when designing a chemical reaction, choosing and or preparing powerful and environmentally benign simple catalysts or complicated catalytic systems for an acceleration of the chemical reaction is a pivotal part of work for synthetic chemists. Chitosan, as a biocompatible and biodegradable pseudo-natural polysaccharide is one of the excellent choices for the preparation of suitable catalytic systems due to its unique properties. In this review paper, every effort has been made to cover all research articles in the field of one-pot synthesis of heterocyclic frameworks in the presence of chitosan-based catalytic systems, which were published roughly by the first quarter of 2020. It is hoped that this review paper can be a little help to synthetic scientists, methodologists, and catalyst designers, both on the laboratory and industrial scales.

Redox-Reactive Field-Effect Transistor Nanodevices for the Direct Monitoring of Small Metabolites in Biofluids toward Implantable Nanosensors Arrays

Chemically modified field-effect transistor (FET) nanodevices were shown to be a selective and extremely sensitive detection platform. In FET-based sensors, signal amplification and transduction is based on electrostatic gating of the nanometric semiconductor channel by analyte-receptor interactions, which measurably affect the transconductance of the device. However, chemically modified FETs must overcome several fundamental limitations before they can be effectively deployed as real-time sensors for bioevents occurring on their surface in complex biofluids. Here, we demonstrate the development of amperoFET devices for the real-time continuous monitoring of small molecular metabolites in biofluids. The surface of the nanowires is covalently modified with a redox reversible moiety, which is easily oxidized in the presence of H2O2. The reversible redox transformation of the surface-confined molecules is carried out by a hot electron injection mechanism, conducted simply by the modulation of the source-drain current through the nanoFET sensing device. By this approach, electrons may be injected by the nanowire element into the surface-confined redox moiety and thus maintain a whole-electrically actuated redox system in which the oxidation state is completely controlled by the current applied to the amperoFET system. The modulation of the source-drain current allows the control of the reduced versus oxidized redox moieties population on the nanowire surface, and this, in turn, is applied as the main sensing mechanism. At a given constant source-drain and gate voltage, the chemical perturbation exerted by the presence of chemical oxidants in the tested biofluid will lead to a measurable conductance change. Alteration in the concentration of the specific metabolite will chemically regulate the extent of perturbation applied to the redox system, which can be utilized for the quantification of the molecular metabolite of interest. These 'equilibrium'-type sensors are fully electrically operated and can be further used in implantable sensing applications.

Insect Cuticle-Mimetic Hydrogels with High Mechanical Properties Achieved via the Combination of Chitin Nanofiber and Gelatin

By mimicking the natural sclerotization process of insect cuticles, a novel nanofiber-reinforced gelatin hydrogel was developed with improved mechanical properties, which was further strengthened through quinone cross-linking. Because quinone cross-linking reacts between amino groups by increasing the amino group content on the chitin crystalline surface through alkali treatment, surface-deacetylated chitin nanofibers (SD-ChNFs) were prepared to facilitate the cross-linking reaction between SD-ChNF and gelatin. This technique resulted in a tough hydrogel with a dark color. In comparison to a non-cross-linked version, the quinone-cross-linked SD-ChNF/gelatin hydrogel exhibited significantly improved tensile performance. Notably, by controlling the cross-linking reaction time from 6 to 48 h, the tensile strength of the quinone-cross-linked hydrogels can be modified and can reach as high as 2.96 MPa while displaying a variable brown color. Given the eco-friendly, biocompatible, and sustainable properties of chitin and gelatin, these bioinspired hydrogels provide potential applications in the agricultural and biomedical fields.

The impact of an isoreticular expansion strategy on the performance of iodine catalysts supported in multivariate zirconium and aluminum metal–organic frameworks

A new iodine catalyst was supported in two different MOFs and the catalytic activity for the oxidation of hydroquinones and catechols was evaluated.

Structural Assessment and Catalytic Oxidation Activity of Hydrophobized Whey Proteins

Chemical modification of whey proteins allows manipulation of their characteristics, such as surface charge and hydrophobicity. Herein, we report the influence of hydrophobization accomplished by a preacetylation stage and a subsequent combined acetylation-heating process on some characteristics of whey proteins. Hydrophobization extensively (≥90%) acetylated the available free amino groups of whey proteins. The produced protein particles were nanoscaled (75 nm) and had a significantly low isoelectric point (3.70). Hydrophobization increased the β-sheet content of whey proteins and significantly decreased the solvent exposure of tyrosine residues. It also conferred a less compact tertiary structure to the proteins and decreased the extent of disulfide-bond formation by heating. The mobility of α-lactalbumin in nonreducing electrophoresis gel increased as a consequence of hydrophobization. Then, the ability of whey proteins to catalyze hydroquinone autoxidation was examined, and it was found that the activity decreased as a result of hydrophobization. The catalytic activity of the proteins was associated with the free-amino-group content, which determined the extent of cation-π attractive interactions; ζ-potential, which determined the extent of anion-π repulsive interactions; and π-stacking between hydrophobic residues and the electron cloud of the quinone ring.

Make room for iodine: systematic pore tuning of multivariate metal–organic frameworks for the catalytic oxidation of hydroquinones using hypervalent iodine

A multivariate approach has been to to establish the right balance between iodine loading and pore size for catalytic oxidative dearomatizations in MIL-53 (Al) and UiO-66 (Zr) MOFs.

The enhancement of the hydrolysis of bamboo biomass in ionic liquid with chitosan-based solid acid catalysts immobilized with metal ions

Three kinds of sulfonated cross-linked chitosan (SCCR) immobilized with metal ions of Cu(2+), Fe(3+) and Zn(2+) individually were synthesized and firstly used as solid acid catalysts in the hydrolysis of bamboo biomass. FTIR spectra showed that metal ions had been introduced into SCCR and the N-metal ions coordinate bound was formed. The particle sizes of these catalysts were about 500-1000μm with a pore size of 50-160μm. All of the three kinds of catalysts performed well for bamboo hydrolysis with 1-butyl-3-methyl-imidazolium chloride used as solvent. The most effective one was sulfonated cross-linked chitosan immobilized with Fe(3+) (Fe(3+)-SCCR). TRS yields were up to 73.42% for hydrolysis of bamboo powder in [C4mim]Cl with Fe(3+)-SCCR at 120°C and 20RPM after 24h. These novel chitosan-based metal ions immobilized solid acid catalysts with ionic liquids as the solvent might be promising to facilitate cost-efficient conversion of biomass into biofuels and bioproducts.

Thermal gelation of chitosan in an aqueous alkali-urea solution

Chitosan can readily dissolve in a precooled aqueous alkali-urea solution, a solvent that has previously been developed to dissolve cellulose. Upon heating, the resulting solutions quickly become a gel. The thermal gelling of the chitosan solutions was studied by rheology. Initially, a temperature ramp test was used to determine the gelation temperatures (Tgel). It was found that Tgel does not significantly change with chitosan concentration. The in situ formed gels liquefy on cooling, but the liquefication temperature (Tliq) is considerably lower than Tgel, indicating a large hysteresis in the cooling process. In addition, Tliq decreases with increasing polymer concentration. The kinetics of thermal gelation was then studied by isothermal curing. The solution gels were cured not only at temperatures above the Tgel, which was determined in the temperature ramp test, but also at temperatures far below the Tgel, provided that the solution is cured at the temperature for a long enough time. The solutions become gel faster when cured at higher temperatures. When cured at the same temperature, higher concentration solutions become gel faster. The apparent activation energy for the thermal gelation of the chitosan solutions was determined to be ∼200 kJ mol(-1). Physical gels of pure chitosan were obtained by repeated soaking the in situ formed gels in water. Preliminary test shows that new gels are highly biocompatible.

Degradation of trichloroethylene by Fe(II) chelated with cross-linked chitosan in a modified Fenton reaction

Degradation of trichloroethylene (TCE) by a modified Fenton reaction was investigated in aqueous solution. Fenton reaction can be significantly enhanced in the presence of Fe(II) chelated by cross-linked chitosan (CS) with glutaraldehyde (GLA) at neutral pH. A remarkable oxidative degradation of TCE (1.838 h(-1)) was observed in the modified Fenton system with Fe(II)-CS/GLA (10 mM and 2 g L(-1), respectively) and H(2)O(2) (318 mM), while no significant degradation (0.005 h(-1)) was observed in the classic Fenton reaction system with Fe(II) (10 mM) and H(2)O(2) (318 mM) at pH 7 in 5 h. The kinetic rate constants for the degradation of TCE in the modified Fenton system was dependent on the initial suspension pH, Fe(II) loading, CS/GLA dosage, and concentration of H(2)O(2). We observed the formation of surface Fe(II)-CS/GLA complex using microscopic analyses and identified Fe oxidation (Fe(II) to Fe(III)) coupled with H(2)O(2) reduction on the Fe(II)-CS/GLA surfaces during the modified Fenton reaction.