Functionalized chitosan as a novel support for stabilizing palladium in Suzuki reactions

Catalytic system having an organotellurium ligand on graphene oxide: immobilization of Pd(0) nanoparticles and application in heterogeneous catalysis of cross-coupling reactions

First heterogeneous catalytic system, having a covalently linked hybrid bidentate organotellurium ligand [i.e., PhTe-CH2-CH2-NH2] on the surface of graphene oxide, has been synthesized with immobilized and stabilized Pd(0) nanoparticles. To the best of our knowledge, it is the first such catalytic system in which a heterogenized organotellurium ligand has been used. It has been well-characterized using different physicochemical characterization techniques viz. P-XRD, XPS, HR-TEM, EELS, FE-SEM, EDX, TGA, BET surface area analysis, FT-IR spectroscopy, and Raman spectroscopy. The Pd content of the final system has been quantified using ICP-OES. Its applications have been explored in Suzuki-Miyaura C-C cross coupling and C-O cross coupling reactions. Hot filtration experiments corroborate the heterogeneous nature of the catalysis. It is recyclable for up to five reaction cycles in Suzuki-Miyaura and C-O cross coupling with marginal loss in performance. It also catalyzes the reactions of chloroarenes such as chlorobenzene, 4-chloroaniline, 1-chloro-4-nitrobenzene, 4-chloroacetophenone, 4-chlorobenzophenone for Suzuki coupling, and 1-chloro-4-nitrobenzene, 4-chlorobenzonitrile, chlorobenzene, and 4-chlorotoluene for C-O coupling. P-XRD, FE-SEM, and EDX study reveals that the catalytic system retains its structural originality and functionality after recycling.

Chitosan-fucoidan encapsulating cinnamaldehyde composite coating films: Preparation, pH-responsive release, antibacterial activity and preservation for litchi

In this study, an edible composite film with pH-responsive release was prepared by the formation of Schiff-base imine bonds between chitosan (CS) and oxidized fucoidan (CS-FU) and encapsulating cinnamaldehyde (CA). Fourier-transform infrared, 1H nuclear magnetic resonance, X-ray photoelectron spectroscopy and gel permeation chromatography confirmed the formation of CS-FU. The result showed that, oxidation degree of FU, degrees of substitution, average molecular weight and yield of CS-FU were 25.57 %, 10.48 %, 23.3094 kDa and 45.63 ± 0.64 %, respectively. Scanning electron microscopy revealed that CA was encapsulated within the CS-FU matrix. Increasing the CA content could improve the mechanical properties and ultraviolet and visible-light resistances of the CS-FU coating films but enhance their water vapor permeabilities. The release of CA increased as the pH decreased, and the antibacterial rate at pH 5 was 2.3-fold higher than that at pH 7, indicating good pH-responsive release and antibacterial properties in mildly acidic environments. Owing to their excellent properties, the CA/CS-FU-0.1 coating films maintained the appearance and quality indices of litchis for at least eight days. Hence, multifunctional composite coating films are prospective eco-friendly and intelligently responsive controlled-release packaging materials for fruit preservation.

Intracellular infection-responsive macrophage-targeted nanoparticles for synergistic antibiotic immunotherapy of bacterial infection

Intracellular bacteria are considered to play a key role in the failure of bacterial infection therapy and increase of antibiotic resistance. Nanotechnology-based drug delivery carriers have been receiving increasing attention for improving the intracellular antibacterial activity of antibiotics, but are accompanied by disadvantages such as complex preparation procedures, lack of active targeting, and monotherapy, necessitating further design improvements. Herein, nanoparticles targeting bacteria-infected macrophages are fabricated to eliminate intracellular bacterial infections via antibiotic release and upregulation of intracellular reactive oxygen species (ROS) levels and proinflammatory responses. These nanoparticles were formed through the reaction of the amino group on selenocystamine dihydrochloride and the aldehyde group on oxidized dextran (ox-Dex), which encapsulates vancomycin (Van) through hydrophobic interactions. These nanoparticles could undergo targeted uptake by macrophages via endocytosis and respond to the bacteria-infected intracellular microenvironment (ROS and glutathione (GSH)) for controlled release of antibiotics. Furthermore, these nanoparticles could consume intracellular GSH and promote a significant increase in the level of ROS in macrophages, subsequently up-regulating the proinflammatory response to reinforce antibacterial activity. These nanoparticles can accelerate bacteria-infected wound healing. In this work, nanoparticles were fabricated for bacteria-infected macrophage-targeted and microenvironment-responsive antibiotic delivery, cellular ROS generation, and proinflammatory up-regulation activity to eliminate intracellular bacteria, which opens up a new possibility for multifunctional drug delivery against intracellular infection.

Voltametric Sensor Based on Magnetic Chitosan Acetylindole-Based Nanocomposite for the Determination of Sulfamethazine

Sulfamethazine (SMZ), a persistent antibiotic, is frequently detected in drinking water and milk. For this reason, our research aimed to develop a novel electrochemical sensor based on a magnetic nanocomposite supported on chitosan modified by 3-acetylindole through the formation of chitosan acetylindole Schiff base (Chs-Aci). The objective was to detect extremely low concentrations of SMZ in milk. The synthesized nanocomposites were characterized by various techniques, including FT-IR, XRD, EDX, SEM, and TEM. To enhance the electrocatalytic efficiency for sensitive SMZ detection in food samples, a magnetic chitosan acetylindole nanocomposite (M-Chs-Aci) was employed as a modifier for a carbon paste electrode (CPE). The electrochemical measurements revealed that the M-Chs-Aci/CPE exhibits good electrocatalytic performance compared to a bare CPE. Moreover, low detection limit, repeatability, and stability were achieved at 0.021 μM, 3.83%, and 94.87%, respectively. Finally, the proposed M-Chs-Aci/CPE proved to be highly effective in detecting SMZ in milk samples. The obtained findings paved the way for the effective usability of M-Chs-Aci/CPE as a sensor for detecting SMZ in real samples, with acceptable recoveries of 95%-98.87%.

Preparation and properties of polyvinyl alcohol/chitosan-based hydrogel with dual pH/NH3 sensor for naked-eye monitoring of seafood freshness

To address the issue of food spoilage causing health and economic loss, we developed a pH/NH3 dual sensitive hydrogel based on polyvinyl alcohol/chitosan (PVA/CS) containing chitosan-phenol red (CP). The CP was synthesized via Mannich reaction and immobilized it in PVA/CS hydrogel through freezing/thawing method to prepare the final PVA/CS/CP hydrogel. The synthesis of CP was confirmed by 1H NMR, FT-IR, XRD, UV-vis, and XPS. The characteristics of hydrogel were evaluated by FT-IR, XRD, SEM, mechanical properties, thermal stability, leaching, and color stability tests. The PVA/CS/CP hydrogel showed distinctly different color at various pH and NH3 vapor levels (yellow to purple). The hydrogel exhibited obvious color changes (ΔE = 46.95) in response to shrimp spoilage, stored at 4 °C. It showed positive and strong correlation between the ΔE values of the indicator hydrogel and total volatile basic nitrogen (TVB-N) as (R2 = 0.9573) and with pH as (R2 = 0.8686), respectively. These results clearly show that the PVA/CS/CP hydrogel could be applied for naked-eye real-time monitoring of seafood freshness in intelligent packaging.

Pd nanoparticles embedded in nanolignin (Pd@LNP) as a water dispersible catalytic nanoreactor for Cr(VI), 4-nitrophenol reduction and CC coupling reactions

The use of water-dispersible and sustainable Pd nanocatalysts to reduce toxic heavy metal ions and catalyze important organic reactions has profound significance for the environmental remediation and the catalytic industry. In this work, a novel water-dispersible and recyclable Pd@LNPs nanoreactor composed of Pd nanoparticle cluster core and LNPs shell was developed in microwave reactor in aqueous solution. It turned out that Pd nanoparticles grew uniformly and stably inside LNPs nanosphere due to the coordinated binding and interaction between Pd and the functional groups in LNPs, which was significantly different from surface loading. The green and biodegradable LNPs nanospheres are not only used as reducing agents for Pd (II) and nanocarriers, but also act as individual nanocontainers to provide favorable sites for reactions and effectively control the entry and release of reactants and products. Furthermore, the excellent and efficient catalytic properties of Pd@LNPs were exhibited by CC coupling reactions and the reduction of Cr(VI) and 4-nitrophenol. The Pd@LNPs prepared in this study have the advantages of excellent dispersion, great recyclability, high turnover frequency and better green sustainability metrics. It will have a great significance for the development of the potential high-value of lignin and the progress in the field of bio-nanocatalysts.

Fabrication and characterization of dihydromyricetin-loaded microcapsules stabilized by glyceryl monostearate and whey protein-xanthan gum

Dihydromyricetin (DMY) is a lipophilic nutrient with various potential health benefits; however, its poor storage stability and low solubility and bioavailability limit its applications. This study aims to encapsulate DMY in microcapsules by membrane emulsification and freeze-drying methods to overcome these issues. Glyceryl monostearate (GMS, solid lipid) and octyl and decyl glycerate (ODO, liquid lipid) were applied as the inner cores. Whey protein and xanthan gum (XG) were used as wall materials. The prepared microcapsules had an irregular blocky aggregated structure with rough surfaces. All the microcapsules had a DMY loading of 0.85 %-1.1 % and encapsulation efficiency (EE) >85 %. GMS and XG increased the DMY loading and EE. The addition of GMS and an increased XG concentration led to a decrease in the rehydration rate. The in vitro release and digestion studies revealed that GMS and XG controlled the release and digestion of DMY. The chemical stability results indicated that GMS and XG protected DMY against oxidation. An antioxidant capacity study showed that GMS and XG helped DMY in the microcapsules exert antioxidant effects. This research study provides a platform for designing microcapsules with good stability and high bioavailability to deliver lipophilic bioactive compounds.

Highly dispersed palladium nano-catalyst anchored on N-doped nanoporous carbon microspheres derived from chitosan for efficient and stable hydrogenation of quinoline

Under the background of green chemistry, the synthesis of N-heterocycles using efficient, stable and long-life catalysts has still faced great challenges. Herein, we used biomass resource chitosan to fabricate a nanoporous chitosan carbon microsphere (CCM), and successfully designed a stable and efficient Pd nano-catalyst (CCM/Pd). Various physicochemical characterizations provided convincible evidences that the palladium nanoparticles (NPs) were tightly and evenly dispersed on the CCM with a mean diameter of 2.28 nm based on the nanoporous structure and abundant functional N/O groups in CCM. Importantly, the graphitized constructure, the formed defects and larger surface area in CCM were able to promote the immobilization of Pd NPs and the electron transfer between Pd and CCM, thereby significantly improving the catalytic activity. The CCM/Pd catalyst was applied for hydrogenation of quinoline compounds, which showed excellent catalytic activity and durability, as well as good substrate applicability. The application of renewable biomass-based catalysts contributes to the progression of a green/sustainable society.

Fabrication of Gelatin-Derived Gel Electrolyte Using Deep Eutectic Solvents through In Situ Derivatization and Crosslinking Strategy for Supercapacitors and Flexible Sensors

The facile fabrication of gel polymer electrolytes is crucial to the development of flexible electronics, and the use of natural polymers as sources has obtained great attention due to their abundant, low-cost, biodegradable, easy modification, and biocompatible features. In this article, a facile fabrication protocol to engineer gelatin into gel electrolytes was developed by taking the advantages of both deep eutectic solvent (DES) (including its good solubility to gelatin and satisfactory electrochemical properties) and rich active functional groups of gelatin, through in situ derivatization and crosslinking strategy. A double-crosslinked DES gel electrolyte was prepared with the dissolution of gelatin in choline chloride and alcohol-based DES and a further crosslinking with Fe3+ ions. The obtained DES gel presented outstanding mechanical properties, excellent ionic conductivity (up to 101-102 mS/cm), a wide operating temperature range (-40 to 80 °C), satisfactory self-healing property, and good degradability. Moreover, the obtained DES gel electrolyte was successfully applied to supercapacitors and flexible sensors, showing excellent electrochemical performance and strain-response properties. In a word, our study provides a facile protocol to engineer gelatin into gel electrolytes by using deep eutectic solvent, showing significant insights into the design and preparation of sustainable gel polymer electrolytes and having great application potential in next-generation high-performance flexible electronics.

Versatile Triphenylphosphine-Containing Polymeric Catalysts and Elucidation of Structure-Function Relationships

Synthetic polymers are a modular solution to bridging the two most common classes of catalysts: proteins and small molecules. Polymers offer the synthetic versatility of small-molecule catalysts while simultaneously having the ability to construct microenvironments mimicking those of natural proteins. We synthesized a panel of polymeric catalysts containing a novel triphenylphosphine acrylamide monomer and investigated how their properties impact the rate of a model Suzuki-Miyaura cross-coupling reaction. Systematic variation of polymer properties, such as the molecular weight, functional density, and comonomer identity, led to tunable reaction rates and solvent compatibility, including full conversion in an aqueous medium. Studies with bulkier substrates revealed connections between polymer parameters and reaction conditions that were further elucidated with a regression analysis. Some connections were substrate-specific, highlighting the value of the rapidly tunable polymer catalyst. Collectively, these results aid in building structure-function relationships to guide the development of polymer catalysts with tunable substrates and environmental compatibility.

Magnetic ethylene-based periodic mesoporous organosilica supported palladium: An efficient and recoverable nanocatalyst for Suzuki reaction

In the present study, a novel magnetic ethylene-based periodic mesoporous organosilica supported Pd-Schiff base complex (Fe₃O₄@PMO/SB-Pd) was prepared, characterized and applied as a recoverable nanocatalyst for green synthesis of Suzuki products. Chemical composition, magnetic and thermal behavior, morphology and particle size of Fe₃O₄@PMO/SB-Pd were investigated by using FT-IR, TGA, EDX, VSM, PXRD, TEM and Scanning electron microscopy (SEM) analyses. The Fe₃O₄@PMO/SB-Pd nanocomposite was applied as an efficient nanocatalyst in the Suzuki reaction under ultrasonic conditions giving corresponding products in high yield. Some advantages of this study are simple purification of products, the use of water solvent, easy catalyst separation, short reaction time and high catalyst efficiency and recoverability.

Palladium Supported on Bioinspired Materials as Catalysts for C–C Coupling Reactions

In recent years, the immobilization of palladium nanoparticles on solid supports to prepare active and stable catalytic systems has been deeply investigated. Compared to inorganic materials, naturally occurring organic solids are inexpensive, available and abundant. Moreover, the surface of these solids is fully covered by chelating groups which can stabilize the metal nanoparticles. In the present review, we have focused our attention on natural biomaterials-supported metal catalysts applied to the formation of C–C bonds by Mizoroki–Heck, Suzuki–Miyaura and Sonogashira reactions. A systematic approach based on the nature of the organic matrix will be followed: (i) metal catalysts supported on cellulose; (ii) metal catalysts supported on starch; (iii) metal catalysts supported on pectin; (iv) metal catalysts supported on agarose; (v) metal catalysts supported on chitosan; (vi) metal catalysts supported on proteins and enzymes. We will emphasize the effective heterogeneity and recyclability of each catalyst, specifying which studies were carried out to evaluate these aspects.

Efficient and Eco-Friendly Perspectives for C-H Arylation of Benzothiazole Utilizing Pd Nanoparticle-Decorated Chitosan

In this contribution, an eco-friendly, sustainable, and efficient palladium nanoparticle-decorated chitosan (Pd@Chitosan) catalyst was synthesized by a simple impregnation method. The synthesized material was utilized as a heterogeneous catalyst for the C-H arylation of benzothiazole under ultrasonic irradiation. The Pd@Chitosan catalyst efficiently catalyzed the conversion of aryl iodides and bromides to 1-(4-(benzothiazol-2-yl)phenyl)ethan-1-one selectively. A single product of 83–93% yield was obtained in N,N-dimethylformamide solvent at 80 °C for 2.5h. This study reveals that Pd@Chitosan is an efficient catalyst, which catalyzes the C-H arylation with good reaction yields. The activity of the Pd@Chitosan is due to the presence of highly dispersed Pd(0) nanoparticles on the surface of the chitosan and Pd2+; a tentative mechanism was proposed based on the XPS results of the fresh catalyst and spent catalyst.

Chitosan: A Sustainable Material for Multifarious Applications

Due to the versatility of its features and capabilities, chitosan generated from marine crustacean waste is gaining importance and appeal in a wide variety of applications. It was initially used in pharmaceutical and medical applications due to its antibacterial, biocompatible, and biodegradable properties. However, as the demand for innovative materials with environmentally benign properties has increased, the application range of chitosan has expanded, and it is now used in a variety of everyday applications. The most exciting aspect of the chitosan is its bactericidal properties against pathogens, which are prevalent in contaminated water and cause a variety of human ailments. Apart from antimicrobial and water filtration applications, chitosan is used in dentistry, in water filtration membranes to remove metal ions and some heavy metals from industrial effluents, in microbial fuel cell membranes, and in agriculture to maintain moisture in fruits and leaves. It is also used in skin care products and cosmetics as a moisturizer, in conjunction with fertilizer to boost plant immunity, and as a bi-adhesive for bonding woods and metals. As it has the capacity to increase the life span of food items and raw meat, it is an unavoidable component in food packing and preservation. The numerous applications of chitosan are reviewed in this brief study, as well as the approaches used to incorporate chitosan alongside traditional materials and its effect on the outputs.

Antibacterial porous sponge fabricated with capric acid-grafted chitosan and oxidized dextran as a novel hemostatic dressing

This work aims to fabricate multifunctional hemostatic sponges (C-ODs). Porous C-ODs were first constructed by using capric acid-modified chitosan (CSCA) and oxidized dextrans (ODs) with different oxidation degrees. Batches of experiments showed that (i) CSCA (33.39% of grafting degree), ODs, and C-ODs (100-200 μm in pore size) were synthesized, evidenced by FT-IR, ¹H NMR, elemental analysis, hydroxylamine hydrochloride titration, and SEM results; (ii) among C-ODs, C-OD₂ had appropriate porosity (85.0%), swelling (20 times its dry weight), absorption, water retention, water vapor transmission, and mechanical properties; (iii) C-OD₂ possessed low toxicity (relative cell viability > 86%), low hemolysis rate (0.65%), suitable tissue adhesion (4.74 kPa), and strong antibacterial efficacy (five strains); and (iv) C-OD₂'s dynamic blood clotting was within 30 s. In three animal injury models, C-OD₂'s hemostasis time and blood loss were fairly lower than commercial gelatin sponge. Totally, C-OD₂ might serve as an ideal hemostatic dressing.

Progresses in chitin, chitosan, starch, cellulose, pectin, alginate, gelatin and gum based (nano)catalysts for the Heck coupling reactions: A review

Heck cross-coupling reaction (HCR) is one of the few transition metal catalyzed CC bond-forming reactions, which has been considered as the most effective, direct, and atom economical synthetic method using various catalytic systems. Heck reaction is widely employed in numerous syntheses including preparation of pharmaceutical and biologically active compounds, agrochemicals, natural products, fine chemicals, etc. Commonly, Pd-based catalysts have been used in HCR. In recent decades, the application of biopolymers as natural and effective supports has received attention due to their being cost effective, abundance, and non-toxicity. In fact, recent studies demonstrated that biopolymer-based catalysts had high sorption capacities, chelating activities, versatility, and stability, which make them potentially applicable as green materials (supports) in HCR. These catalytic systems present high stability and recyclability after several cycles of reaction. This review aims at providing an overview of the current progresses made towards the application of various polysaccharide and gelatin-supported metal catalysts in HCR in recent years. Natural polymers such as starch, gum, pectin, chitin, chitosan, cellulose, alginate and gelatin have been used as natural supports for metal-based catalysts in HCR. Diverse aspects of the reactions, different methods of preparation and application of polysaccharide and gelatin-based catalysts and their reusability have been reviewed.

Chitosan immobilization and Fe3O4 functionalization of olive pomace: An eco-friendly and recyclable Pb2+ biosorbent

An effective and sustainable biosorbent (MagOPIC) was prepared from chitosan and olive pomace by the combined action of immobilization and magnetic modification to remediate Pb²⁺-contaminated waters. Pb²⁺ sorption yield at the end of the equilibrium (45 min) period was estimated to be 98.56 ± 0.28% at pH 5.5. Agitation speed, ionic strength, and temperature did not significantly affect the Pb²⁺ biosorption. Biosorption kinetics are successfully fitted by the pseudo-second-order equation while the equilibrium biosorption data are properly modeled using the Freundlich and D-R isotherms. MagOPIC has also exhibited a high biosorption yield in the column tests (≥99%) and showed remarkable stability up to twenty consecutive regeneration cycles. Furthermore, it was successfully used for the treatment of Pb²⁺ containing real wastewater. The findings of this work highlighted the potential use of MagOPIC as a novel, cost-effective and eco-friendly biosorbent for the Pb²⁺ removal from the contaminated aquatic phase.

Ionic chitosan Schiff bases supported Pd(II) and Ru(II) complexes; production, characterization, and catalytic performance in Suzuki cross-coupling reactions

Taking the advantage of multifunctional characteristics of chitosan (CS), we have developed new scaffolds (imidazolium-vanillyl-chitosan Schiff bases (IVCSSBs)) for supporting Pd(II) and Ru(II) ions in catalyzing Suzuki coupling reactions. The structures of new materials were described based on their elemental, spectral, thermal, and microscopic analysis. The strong interactions between the binding sites of IVCSSB ligand (OH, H-C=N, and OCH₃ groups) and Pd(II) ions resulted in the formation of an excellent heterogeneous catalyst (Pd(II)IVCSSB1) with amazing catalytic activity (up to 99%) and highly stable in the reaction medium. The reusability experiments for Pd(II)IVCSSB₁ revealed that there is no appreciable decrease in its catalytic activity even after five consecutive operation runs. Furthermore, this heterogeneous catalyst showed an excellent selectivity toward the cross-coupling reaction where no homo-coupling byproducts were observed in the ¹H NMR spectra of the obtained products. Consequently, the present ionic catalytic system may open a new window for a novel generation of ionic bio-based catalysts for organic transformations.

Magnetic chitosan stabilized palladium nanostructures: Potential catalysts for aqueous Suzuki coupling reactions

This work describes the preparation of palladium-based catalyst supported on magnetic chitosan (Pd@IO-Chitosan) for Suzuki Miyaura C-C coupling reaction. The Pd@IO-Chitosan catalyst was characterized using different spectroscopic and microscopic techniques such as Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), vibrating sample magnetometer (VSM), X-ray powder diffraction (XRD), X-ray Absorption Near Edge Structure (XANES) Spectroscopy and X-ray photoelectron spectroscopy (XPS). Pd@IO-Chitosan was further analysed by thermogravimetric analysis (TGA) in order to determine its thermal behavior. The catalyst comprised Pd, PdO species stabilised by chitosan that facilitated Suzuki coupling reactions. Palladium loading as low as 0.0055 mol% was found to be effective for aqueous Suzuki cross-couplings with excellent yields of over 99%. The catalyst could be recycled and reused at least 12 times with no significant decrease in its catalytic activity.

Design of nanostructured palladium catalyst supported by chitosan/Co3O4 microspheres and investigation of its catalytic behavior against synthesis of benzonitriles

Designing of eco-friendly, low cost, and thermally stable stabilizing/supporting agents are always desired for production of catalyst systems which provide good catalytic performance in organic reactions. In this study, a novel, green, and efficient stabilizer containing chitosan/Co₃O₄ microspheres (CS/Co₃O₄) was developed. Palladium nanoparticles (Pd NPs) were then successfully immobilized on CS/Co₃O₄ as a heterogeneous nanocatalyst (Pd NPs/CS/Co₃O₄). Characterization of the designed materials were performed by FT-IR, TEM, FE-SEM, XRD, and EDS and it was determined that Pd NPs formed as approximately 20 nm. Catalytic behavior of Pd NPs/CS/Co₃O₄ was investigated in the production of different substituted benzonitriles via aryl halide cyanation. Catalytic studies indicate that electron-rich or poor aromatic halides were smoothly cyanated with good reaction yields by Pd NPs/CS/Co₃O₄ nanocatalyst by using K₄[Fe(CN)₆] as the cyanating agent. Moreover, it was found that Pd NPs/CS/Co₃O₄ nanocatalyst provided not only good reaction yields and but also good recovery/reusability for six times in the aryl halide cyanations. This paper displays that Pd NPs/CS/Co₃O₄ nanocatalyst has a great catalytic and recycling potential for aryl halide cyanations.