Preparation of C-6 Substituted Chitin Derivatives under Homogeneous Conditions

Structure and properties of sulfopropyl chitins prepared in NaOH/urea aqueous solutions

A series of sulfopropyl chitins (SCs) with the degree of substitution (DS) ranging from 0.11 to 0.40 and high degree of acetylation (DA ≥ 0.82) were homogeneously synthesized by reacting chitin with sodium 3-chloro-2-hydroxypropanesulfonate (SCHPS) in NaOH/urea aqueous solutions under mild conditions. The structure and properties of SCs were characterized with 1H NMR, CP/MAS 13C NMR, FT-IR, XPS, XRD, elemental analysis, GPC, AFM, ζ-potential and rheological measurements. The mild reaction conditions resulted in less N-deacetylation and uniform structures with substitution occurring predominantly at the hydroxyl groups at C6 of the chitin backbone. The DS value for SC soluble in dilute alkali solution is as low as 0.16. SC exhibited good solubility in distilled water when its DS value reached 0.28. Water-soluble SCs self-assembled in water into micelles by the attractive hydrophobic and hydrogen-bonding interactions between polymer chains. The water-insoluble SC-2 with lower DS could thermally form smart hydrogels at body temperature (37 °C) in physiological condition. Moreover, the SCs exhibited good biocompatibility, making them suitable for biomedical applications.

Choline chloride-zinc chloride deep eutectic solvent mediated preparation of partial O-acetylation of chitin nanocrystal in one step reaction

An efficient and one step production of acetylated and esterified chitin nanocrystals (CNCs) was successfully achieved using choline chloride-zinc chloride deep-eutectic solvent (ChCl-ZnCl₂ DES). In this method, ChCl-ZnCl₂ DES with a mole ratio of 1:2, was used for the esterification and O-acetylation of chitin at 90 °C for 3 h and 6 h. This strategy consisted in using ChCl-ZnCl₂ DES as a green and non-volatile solvent for chitin under heterogeneous condition that, upon addition of acetic anhydride or acetic acid, simultaneous acetylation or esterification and hydrolysis occurred. The DES act as an efficient catalysis of the functional reaction. The acetylation and hydrolysis proceeded efficiently and the yield of partial acetylated CNCs was ca. 61.6% with DS (degree of substitution) of 0.23 under the optimized conditions. Acetic acid was used to substituted acid anhydride to produce CNCs. The yield of acetic acid induced CNCs was ca. 62.0% with higher DS of 0.34. A thorough investigation of the physicochemical characteristics changes of chitin pointed out that the main skeletal structure of obtained CNCs was intact. The thermal stability of CNCs decreased after treated by ChCl/ZnCl₂. In addition, thermal stability of CNCs functionalized with acetic acid is lower than the ones functionalized with acetic anhydride. DES showed low expenditure and toxicity. This approach provides a novel method for production of functional chitin nanocrystals.

Galactosylated chitosan triptolide nanoparticles for overcoming hepatocellular carcinoma: Enhanced therapeutic efficacy, low toxicity, and validated network regulatory mechanisms

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths worldwide. Current therapies present significant limitations. Triptolide (TP) is highly effective against multiple cancers including HCC. However, high toxicity, low water solubility, and unknown therapeutic targets limit its clinical application. Herein, we designed galactosylated-chitosan-TP-nanoparticles (GC-TP-NPs) with high drug loading capacities for targeted delivery to HCC. In addition to a sustained release pattern, an efficient asialoglycoprotein receptor mediated cellular uptake in vitro, and high liver tumor accumulation in vivo, GC-TP-NPs showed lower systemic and male reproductive toxicities than free TP. Importantly, GC-TP-NPs retained the anti-cancer activities of the free TP, exerting the same pro-apoptotic and anti-proliferative effects on HCC cells in vitro, and displayed higher efficacies in reducing tumor sizes in vivo. Further investigation revealed that GC-TP-NPs induced cancer cell apoptosis via blocking TNF/NF-κB/BCL2 signaling. Collectively, GC-TP-NP represents a promising candidate in halting liver cancer progression while minimizing systemic toxicity.

The derivatization and antitumor mechanisms of polysaccharides

At present, the polysaccharide antitumor research is focused on how to further improve the antitumor activity of polysaccharides. The structural modification of polysaccharides can enhance their antitumor activity to a certain extent. The antitumor mechanisms of polysaccharide derivatives mainly contain the inducing apoptosis of tumor cells, effecting on the cycle of tumor cells, enhancing the antioxidant activity of organism, activating the body's immune response and inhibiting the tumor angiogenesis. Herein, the common methods of polysaccharide modification, such as sulfation, carboxymethylation, phosphorylation and acetylation, were summarized. At the same time, the effects of chemical modification of polysaccharides on their antitumor mechanisms and activity were analyzed and discussed.

A Biodegradable Polycationic Paint that Kills Bacteria in Vitro and in Vivo

Bacterial colonization and subsequent formation of biofilms onto surfaces of medical devices and implants is a major source of nosocomial infections. Most antibacterial coatings to combat infections are either metal-based or nondegradable-polymer-based and hence limited by their nondegradability and unpredictable toxicity. Moreover, to combat infections effectively, the coatings are required to display simultaneous antibacterial and antibiofilm activity. Herein we report biocompatible and biodegradable coatings based on organo-soluble quaternary chitin polymers which were immobilized noncovalently onto surfaces as bactericidal paint. The polycationic paint was found to be active against both drug-sensitive and -resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium (VRE), and β-lactam-resistant Klebsiella pneumoniae. The cationic polymers were shown to interact with the negatively charged bacterial cell membrane and disrupt the membrane integrity, thereby causing leakage of intracellular constituents and cell death upon contact. Importantly, surfaces coated with the polymers inhibited formation of biofilms against both Gram-positive S. aureus and Gram-negative E. coli, two of the most clinically important bacteria that form biofilms. Surfaces coated with the polymers displayed negligible toxicity against human erythrocytes and embryo kidney cells. Notably, the polymers were shown to be susceptible toward lysozyme. Furthermore, subcutaneous implantation of polymer discs in rats led to 15-20% degradation in 4 weeks thereby displaying their biodegradability. In a murine model of subcutaneous infection, polymer-coated medical-grade catheter reduced MRSA burden by 3.7 log compared to that of noncoated catheter. Furthermore, no biofilm development was observed on the coated catheters under in vivo conditions. The polycationic materials thus developed herein represent a novel class of safe and effective coating agents for the prevention of device-associated infections.

Preparation and characterization of chitin benzoic acid esters

Chitin benzoic acid esters were prepared using a phosphoryl mixed anhydride method. The products were characterized by 1H-NMR and FT-IR spectroscopy. FT-IR analysis revealed that the degree of O-acyl substitution of the products was in a range of 1.17-1.83. Morphological surface changes in the parent molecule due to the introduction of benzoic acid moieties were observed by scanning electron microscopy. The surface of the products was porous, in contrast to the sheet-shape of the parent molecules. The solubility of the products, which improved with increased degree of acid substitution, was tested in various organic solvents.

Application of spectroscopic methods for structural analysis of chitin and chitosan

Chitin, the second most important natural polymer in the world, and its N-deacetylated derivative chitosan, have been identified as versatile biopolymers for a broad range of applications in medicine, agriculture and the food industry. Two of the main reasons for this are firstly the unique chemical, physicochemical and biological properties of chitin and chitosan, and secondly the unlimited supply of raw materials for their production. These polymers exhibit widely differing physicochemical properties depending on the chitin source and the conditions of chitosan production. The presence of reactive functional groups as well as the polysaccharide nature of these biopolymers enables them to undergo diverse chemical modifications. A complete chemical and physicochemical characterization of chitin, chitosan and their derivatives is not possible without using spectroscopic techniques. This review focuses on the application of spectroscopic methods for the structural analysis of these compounds.

Chitin and chitosan: functional biopolymers from marine crustaceans

Chitin and chitosan, typical marine polysaccharides as well as abundant biomass resources, are attracting a great deal of attention because of their distinctive biological and physicochemical characteristics. To fully explore the high potential of these specialty biopolymers, basic and application researches are being made extensively. This review deals with the fundamental aspects of chitin and chitosan such as the preparation of chitin and chitosan, crystallography, extent of N-acetylation, and some properties. Recent progress of their chemistry is then discussed, focusing on elemental modification reactions including acylation, alkylation, Schiff base formation and reductive alkylation, carboxyalkylation, phthaloylation, silylation, tosylation, quaternary salt formation, and sulfation and thiolation.