Characterization of chitosan. Influence of ionic strength and degree of acetylation on chain expansion

Viability and Surface Morphology of Human Erythrocytes upon Interaction with Chitosan Derivatives

The viability and surface morphology of human erythrocytes upon interaction with oligochitosan (OCH), having a molecular weight (MW) of 6.2-15.4 kDa and a degree of acetylation (DA) of 1-2%, and interaction with N-reacetylated OCH (ROCH) with a 6.4-14.3 kDa MW and 24-30% DA were studied in isotonic saline phosphate buffer with pH 7.4. It was shown that the use of OCH caused high hemolysis and irreversible transformation of the erythrocytes. Thus, OCH having a 6.2 kDa MW and 1% DA, used at a 0.01% concentration, induced high hemolysis of erythrocytes, and their viability did not exceed the maximal value of 60%. Among the nonhemolyzed erythrocytes, about 20% reversibly transformed erythrocytes and about 20% irreversibly transformed erythrocytes were observed in comparison with the control experiments. For the first time, it was shown that ROCHs had a much lower impact on the cells. Thus, about 82% of the erythrocytes had a discoid form, while 12% and ∼6% of the cells underwent reversible and irreversible transformations, respectively, in the presence of ROCH (MW 6.4, DA 24%), used at a 0.01% concentration. It was observed that an increase in the MW and concentration of chitosan derivatives led to a decrease in the cell viability. It was supposed that the complexation of chitosan derivatives with phosphate counterions in the buffer might reduce the impact of chitosan derivatives on the viability and surface morphology of erythrocytes due to a reduction in the average zeta-potential of chitosan derivative/phosphate complexes from positive to negative values. These results supported the suggestion that reacetylation and reduction of the overall charge of chitosan molecules could improve the compatibility of chitosan derivatives with erythrocytes. This finding opens an opportunity for the construction of chitosan derivatives and their complexes that are compatible with other blood forming elements.

Physicochemical characteristics of chitosan molecules: Modeling and experiments

Chitosan, a biocompatible polysaccharide, finds a wide range of applications, inter alia as an antimicrobial agent, stabilizer of food products, cosmetics, and in the targeted delivery of drugs and stem cells. This work represents a comprehensive review of the properties of chitosan molecule and its aqueous solutions uniquely combining theoretical modeling and experimental results. The emphasis is on physicochemical aspects which were sparsely considered in previous reviews. Accordingly, in the first part, the explicit solvent molecular dynamics (MD) modeling results characterizing the conformations of chitosan molecule, the contour length, the chain diameter and the density are discussed. These MD data are used to calculate several parameters for larger chitosan molecules using a hybrid approach based on continuous hydrodynamics. The dependencies of hydrodynamic diameter, frictional ratio, radius of gyration, and intrinsic viscosity on the molar mass of molecules are presented and discussed. These theoretical predictions, comprising useful analytical solutions, are used to interpret and rationalize the extensive experimental data acquired by advanced experimental techniques. In the final part, the molecule charge, acid-base, and electrokinetic properties, comprising the electrophoretic mobility and the zeta potential, are reviewed. Future research directions are defined and discussed.

Assembling Carbon Nanotube and Graphene in Chitosan/Sodium Alginate Hydrogels for Ion Removal Applications

Hydrogels have emerged as a promising material for the removal of heavy metal ions from contaminated water owing to their high water absorption capacity and biocompatibility. Despite notable advancements in improving the adsorptive capacity of hydrogels, the demand for a more efficient structure persists. Here, we explore the ion adsorption performance of crosslinked hydrogels based on chitosan and sodium alginate with various ratios of carbon nanotubes (CNT) and graphene platelets (GNP). This study highlights the adsorption of chromium ions and the thermal stability of hydrogels for pure, single-particle, and hybrid nanocomposites. The results depict a uniform microstructure attained when CNT, GNP, or both are implemented into the hydrogel due to the strong interaction of functional moieties. The incorporation of CNT and GNP manipulates the crystalline structure of the hydrogels, lowering their crystallinity by around 28% and 13%, respectively. The synergistic effect of CNT and GNP in hybrid hydrogels raises the decomposition temperature by 16%, indicating a favorable interplay interaction between nanoparticles and polymers. Calculations of the adsorption capacity accentuate such a mutual effect between CNT and GNP in various loads of ion capture from aqueous solutions. Kinetic models fitted to the hydrogel nanocomposites reveal that the pseudo-second-order model aligns better with the experimental data in comparison to the pseudo-first-order and intraparticle diffusion models, addressing the adsorption mechanisms while capturing chromium ions.

Chitin isolation from crustaceans and mushrooms: The need for quantitative assessment

This review examines key journal articles on the isolation of chitin from mushroom biomass comparing these findings to those related to crustacean chitin. It highlights the need for standardizing chitin characterization, emphasizing that chitin comprises a family of polymers with variations in molecular weight (Mw), degree of acetylation (%DA), and acetylation patterns (PA), leading to diverse physicochemical properties and biological activities. The review positions fungi and mushrooms as emerging sources of 'vegan' chitin, being non-animal and free from allergenic proteins. Their ability to be cultivated year-round, along with rapid growth and low-cost biowaste substrates, makes them attractive alternatives to crustacean chitin. Market adoption of mushroom chitin will depend on its potential applications in high-value products. Traditionally, chitin characterization has been semi-qualitative, but there is now a growing recognition of how sample inconsistencies impact research quality. This review underscores the importance of quantitative analysis for achieving practical, repeatable, and reproducible results while addressing the challenges in characterizing fungal chitin. We argue that accurately determining the properties of fungal chitin is essential and should be a fundamental aspect of every study, as these properties significantly influence the polymer's characteristics and biological activity.

Biologically active ionic chitosan Schiff base nanocomposites: Synthesis, characterization and antimicrobial activity against Helicobacter pylori

1-(2-((4-Bromophenyl)amino)-2-oxoethyl)pyridin-1-ium chloride Schiff base (CH-Py) was prepared via reacting (CH) with pyridine-3-carboxaldehyde, followed by reacting the product with N-(4-bromophenyl)-2-chloroacetamide. The structure of the resulting CH derivative was determined via1HNMR and FTIR. The CH-Py derivative was converted into nanoparticles (CH-Py-Cl NPs) using sodium tripolyphosphate (TPP). Additionally, the nanocomposites (CH-Py-Cl NPs) were prepared discretely by dispersion of 3.0 % Se and 3.0 % Fe2O3 nanoparticles into the CH-Py-Cl NPs matrix to derive the products denoted as CH-Py-Cl/Se and CH-Py-Cl/Fe, respectively aiming to develop innovative effective chitosan Schiff base nanocomposites towards H. pylori. Anti-H. pylori activity of CH-Py-Cl NPs, CH-Py-Cl/Fe, and CH-Py-Cl/Se were found to be at a minimal inhibitory concentrations MIC value of 62.5, 31.25, and 15.62 μg/mL, indicating that CH-Py-Cl/Se possessed the highest biological activity in our investigation. Finally, the CH-Py-Se-NPs nanocomposite was examined for its in vitro cytotoxicity against colon cancer cell lines (Caco-2). The results obtained indicated that the developed CH-Py-Cl/Se showed toxic effects on Caco-2 cells, with an IC50 value of 124.52 ± 1.15 μg/mL.

Green chitosan extraction from Hermetia illucens breeding waste (prepupal cases): Characterization and bioadsorption activity

Heavy metal contamination has harmful consequences for the ecosystem. They are naturally non-biodegradable, and can cause severe ecotoxicity and numerous pathologies. Several bioadsorbents have been used for metal pollution control, and chitosan is one of the biomaterials that has proven to be an efficient adsorbent. The aim of the present work is to exploit the rearing waste of Hermetia illucens (prepupal cases), commonly known as the Black Soldier Fly (BSF), to produce chitin and its derivative chitosan by microwave-assisted process, and to study the interaction of this biopolymer with zinc and cadmium. All the samples obtained were characterized by several methods, including FTIR, XRD, TGA/DSC, 1H NMR, SEM, and viscosimetric studies. The chitosan obtained has interesting physicochemical properties with an acetylation degree (DA) equal to 2.3 %, Molecular weight (Mv) equal to 155 kDa, and a crystallinity index (ICr) around 51.26 %. Chitosan was also found to have an adsorption capacity of Cd and Zn around 141.05 mg·g-1 and 45 mg·g-1 respectively by absorption atomic spectroscopy (AAS). Results confirm the effectiveness of chitosan derived from BSF, obtained through an eco-friendly method, as a sustainable and efficient bioadsorbent for addressing heavy metal contamination.

Tenebrio Molitor breeding rejects as a high source of pure chitin and chitosan: Role of the processes, influence of the life cycle stages and comparison with Hermetia illucens

This work valorizes rejects from Tenebrio Molitor TM breeding through the production of chitin and chitosan. Two processes are proposed for extracting chitin from larval exuviae and adult. The first process P1 provides chitin with high contents compared to literature data but the characterization shows the presence of impurities in the exuviae chitin responsible for the shifts in the values of the physicochemical characteristics towards those presented by γ chitin. These impurities are removed by delipidation and pure α chitin is obtained. The effective delipidation of this chitin would be linked to its fibrous surface structure. The analysis of the results of P1 led us to develop a second extraction process P2 which provides pure chitin with improved yields using delipidation followed by deproteinization. The N-deacetylation of chitin according to Kurita or Broussignac process makes possible the preparation of pure, highly deacetylated chitosan samples (2 % < DA < 12 %) with high yields and controlled molar masses (Mv). A kinetic study of molecular degradation during deacetylation is carried out. A comparison with Hermetia illucens allows to extend the use of insects as a potential source of chitin and chitosan and confirms the role of the source and the processes in the determination of their characteristics.

Synthesis of novel chitosan-Schiff bases nanoparticles for high efficiency Helicobacter pylori inhibition

Two chitosan Schiff bases were synthesized by condensation of chitosan with 2-(4-formylphenoxy)-N-phenylacetamide and N-(4-bromophenyl)-2-(4-formylphenoxy) acetamide denoted as Cs-SBA and Cs-SBBr, respectively. The molecular structures of the resulting chitosan derivatives were characterized using FTIR and 1HNMR and their thermal properties were investigated by TGA. These derivatives were treated with sodium tripolyphosphate (TPP) to produce Cs Schiff base nanoparticles. The nanoparticles physicochemical properties were determined by FTIR, XRD, TEM, and zeta potential analysis. The antimicrobial action against Helicobacter pylori (H. pylori) was evaluated and the results indicated that the anti-H. pylori activity had minimal inhibitory concentration MIC values of 15.62 ± 0.05 and 3.9 ± 0.03 μg/mL for Cs-SBA and Cs-SBBr nanoparticles (Cs-SBA NPs and Cs-SBBr NPs), respectively. The better biologically active nanoparticles, Cs-SBBr NPs, were tested for their cyclooxygenases (COX-1 and COX-2) inhibitory potential. Cs-SBBr NPs demonstrated COX enzyme inhibition activity against COX-2 (IC50 4.5 ± 0.165 μg/mL) higher than the conventional Indomethacin (IC50 0.08 ± 0.003 μg/mL), and Celecoxib (IC50 0.79 ± 0.029 μg/mL). Additionally, the cytotoxicity test of Cs-SBBr NPs showed cytotoxic effect on Vero cells (CCL-81) with IC50 = 17.95 ± 0.12 μg/mL which is regarded as a safe compound. Therefore, Cs-SBBr NPs may become an alternative to cure H. pylori and prevent gastric cancer.

Valorization of Hermetia illucens breeding rejects by chitins and chitosans production. Influence of processes and life cycle on their physicochemical characteristics

Breeding of the black soldier fly is carried out to produce proteins. It is accompanied by releases during the life cycle of this insect. This work is a study of the valorization of these rejects through the production of chitins and chitosans with controlled characteristics. An extraction process is developed with an order of treatments and reaction conditions that provide chitins with high contents. These contents increase as the stages of the life cycle progress and drop for the adult. However, the exuviae chitins present organic impurities which will be eliminated at the N-deacetylation reaction for pupe and after a purification treatment for chitosan from larval stages. All these chitins have an α structure although certain physicochemical characteristics of the larval exuviae chitins are close to those presented by γ chitin. The observed shifts are linked to the effect of impurities rather than to a difference in structure. N-deacetylation of chitins makes possible the valorization of all rejects by the production of pure chitosans with high yields which retain a porous structure for the exuviae and fibrous for the adult which allow complementary applications. These chitosans are highly to completely deacetylated and their molar masses can vary depending on the process and life stage.

Antifungal efficacy of chitosan extracted from shrimp shell on strawberry (Fragaria × ananassa) postharvest spoilage fungi

The strong demand for biological materials in the food industry places chitosan at the forefront of other biopolymers. The present study aims to evaluate the antifungal properties of chitosan extracted from shrimp shell waste (Parapenaeus longirostris) against post-harvest strawberry (Fragaria × ananassa) spoilage fungi. The physicochemical characteristics (DD, Mw, and solubility) of extracted chitosan were determined. In addition, functional characteristics were studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The antifungal effect of chitosan on mycelial growth and spore germination of Aspergillus niger, Botrytis cinerea, Fusarium oxysporum, and Rhizopus stolonifer was evaluated. Yield, degree of deacetylation, molecular weight, and solubility were 21.86%, 83.50%, 180 kDa, and 80.10%, respectively. A degree of deacetylation of 81.27% was calculated from the FTIR spectrum and a crystallinity index of 79.83% was determined from the X-ray diffraction pattern. SEM images of extracted chitosan showed a combination of fibrous and porous structure. At 3% chitosan, mycelial growth inhibition rates of A. niger, B. cinerea, F. oxysporum, and R. stolonifer ranged from 81.37% to 92.70%. At the same chitosan concentration, the percentages of spore germination inhibition of the isolated fungi ranged from 65.47% to 71.48%. The antifungal activity was highly dose-dependent. As a natural polymer, chitosan offers a convincing alternative to synthetic antimicrobials for the post-harvest preservation of strawberries. Its potential lies in its ability to inhibit the growth of spoilage fungi.

Activity of a Recombinant Chitinase of the Atta sexdens Ant on Different Forms of Chitin and Its Fungicidal Effect against Lasiodiplodia theobromae

This study evaluates the activity of a recombinant chitinase from the leaf-cutting ant Atta sexdens (AsChtII-C4B1) against colloidal and solid α- and β-chitin substrates. 1H NMR analyses of the reaction media showed the formation of N-acetylglucosamine (GlcNAc) as the hydrolysis product. Viscometry analyses revealed a reduction in the viscosity of chitin solutions, indicating that the enzyme decreases their molecular masses. Both solid state 13C NMR and XRD analyses showed minor differences in chitin crystallinity pre- and post-reaction, indicative of partial hydrolysis under the studied conditions, resulting in the formation of GlcNAc and a reduction in molecular mass. However, the enzyme was unable to completely degrade the chitin samples, as they retained most of their solid-state structure. It was also observed that the enzyme acts progressively and with a greater activity on α-chitin than on β-chitin. AsChtII-C4B1 significantly changed the hyphae of the phytopathogenic fungus Lasiodiplodia theobromae, hindering its growth in both solid and liquid media and reducing its dry biomass by approximately 61%. The results demonstrate that AsChtII-C4B1 could be applied as an agent for the bioproduction of chitin derivatives and as a potential antifungal agent.

Synthesis and biological evaluation against H. pylori of chitosan menthone Schiff base hybrid with different types of inorganic nanoparticles

The production of novel natural medicines for the treatment of Helicobacter pylori (H. pylori) has lately attracted a lot of interest. Some bacterial infections have traditionally been alleviated by terpenes. The present work intended to examine the impact of several chitosan menthone Schiff base nanocomposites on the treatment of H. pylori infection as well as on its anti-inflammatory capacity. Chitosan (Cs) was condensed with menthone with different molar ratios of Cs:menthone (1:0.5, 1:1, and 1:2) to produce chitosan Schiff bases namely; Cs-SB1, Cs-SB2, and Cs-SB3, respectively. Cs-SB3 Schiff base nanocomposites were prepared individually by adding 2%Ag, 2%Se, (1%Ag + 1%Se), and 2%Fe2O3 nanoparticles to produce compounds denoted as Cs-SB-Ag, Cs-SB-Se, Cs-SB-Ag/ Se, and Cs-SB-Fe, respectively. The anti-H. pylori activity of Cs-SB-Se was detected at a minimal inhibitory concentration MIC of 1.9 μg/mL making it the most biologically active compound in our study. Cs-SB-Se nanocomposite was tested for its cyclooxygenases (COX-1 and COX-2) inhibitory potential which demonstrated inhibitory efficacy towards COX enzymes with inhibition value against COX-1 (IC50 = 49.86 ± 1.784 μg/mL) and COX-2 (IC50 = 12.64 ± 0.463 μg/mL) which were less than the well-known Celecoxib (22.65 ± 0.081 and 0.789 ± 0.029 μg/mL) and Indomethacin (0.035 ± 0.001 and 0.08 ± 0.003 μg/mL) inhibitors. The selectivity index SI = 3.94 for tested nanocomposites indicated higher selectivity for COX-1. The cytotoxicity of the Cs-SB-Se nanocomposite was evaluated in Vero cells (CCL-81) and it showed that at a concentration of 62.5 μg/mL, cell viability was 85.43 %.

Characterisation of locust bean gum with asymmetric flow field-flow fractionation (AF4) and light scattering

We present a detailed characterisation of locust bean gum (LBG), an industrially significant galactomannan, utilising asymmetric flow field-flow fractionation (AF4) and light scattering. Molecular weight and size determination of galactomannans is complicated by their tendency to aggregate, even in dilute solutions; AF4 allows us to confirm the presence of aggregates, separate these from well-dispersed polymer, and characterise both fractions. For the dispersed polymer, we find Mw=9.2×105 g mol-1 and Rg,z=82.1 nm; the distribution follows Flory scaling (Rg∼Mν) with ν∼ 0.63, indicating good solvent conditions. The aggregate fraction exhibited radii of up to 1000 nm and masses of up to 3×1010 g mol-1. Furthermore, we demonstrate how both fractions are influenced by changes to filtration procedure and solvent conditions. Notably, a 200 nm nylon membrane effectively removes the aggregated fraction; we present a concentration-dependent investigation of solutions following this protocol, using static and dynamic light scattering, which reveals additional weak aggregation in these unfractionated samples. Overall, we demonstrate that AF4 is highly suited to LBG characterisation, providing structural information for both well-dispersed and aggregated fractions, and expect the methods employed to apply similarly to other galactomannans and associating polymer systems.

Solid-state mechanochemical synthesis of chitosan from mud crab (Scylla serrata) chitin

This study presents a method for solvent-free mechanochemical synthesis of chitosan from chitin, sourced from the shells of mud crabs (Scylla serrata). The procedure involves a sequence of demineralization and deproteinization to extract chitin from the crab shells, followed by mechanochemical deacetylation. The chitin was deacetylated by grinding it as a solid blend with sodium hydroxide (NaOH) using a stainless steel mortar and pestle. After grinding, chitosan is isolated from the blend by repetitive washing and centrifugation. The chitosan product is then characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction analysis. These characterization techniques confirm the successful deacetylation of chitin to form chitosan. A high degree of deacetylation (DD) is achieved when the weight ratio of NaOH to chitin is 1:1 or higher, implying that the DD value can be enhanced by increasing this weight ratio. The mechanochemical reaction mechanism involves the hydroxyl groups on the NaOH particles reacting with the acetamide groups of the chitin strands, yielding solid chitosan and sodium acetate. This mechanochemical deacetylation approach is more practical than the conventional heterogeneous deacetylation in strong basic solutions, since it could suppress depolymerization of the resulting chitosan and requires significantly less base. This makes it a promising method for large-scale industrial applications.

Chitosan Polysaccharides from a Polarizable Multiscale Approach

We report simulations of chitosan polysaccharides in the aqueous phase, at infinite dilute conditions and zero ionic strength. Those simulations are performed by means of a polarizable multiscale modeling scheme that relies on a polarizable all atom force field to model solutes and on a polarizable solvent coarse grained approach. Force field parameters are assigned only from quantum chemistry ab initio data. We simulate chitosan monomer units, dimers and 50-long chains. Regarding the 50-long chains we simulate three sets of ten randomly built chain replica at three different pH conditions (corresponding to different chain protonation states, the chain degree of deacetylation is 85%). Our simulations show the persistence length of 50-long chitosan chains at strong acidic conditions (pH <5) to be 24 ± 2 nm (at weak/negligible ionic strength conditions), and to be 1 order of magnitude shorter at usual pH conditions. Our simulation data support the most recent simulation and experimental studies devoted to chitosan polysaccharides in the aqueous phase.

Polysaccharide/Carbon Quantum Dots Composite Film on Model Colloidal Particles-An Electro-Optical Study

Negatively charged carbon dots (Cdots) were successfully impregnated into chitosan/alginate film formed on model colloidal particles as a result of the attractive interactions with the chitosan molecules. The electrical properties of the produced films were studied by electrokinetic spectroscopy. In this study, the electric light scattering method was applied for first the time for the investigation of suspensions of carbon-based structures. The electro-optical behavior for the suspension of polymer-coated particles showed that the electric polarizability of the particle-covered layer from alginate was significantly higher compared to that of the layer from chitosan due to the higher charge density of alginate. The presence of a low concentration of Cdots in the film results in partial charge screening. It was confirmed that the polarizability of counterions with lower mobility along the adsorbed polyion chains was responsible for the registered electro-optical effect from the suspension of polymer-coated particles and that the participation of diffuse H+ counterions of Cdots in the creation of the electro-optical effect was negligible. The observed oscillation behavior in the evolution of the film thickness was interpreted through the participation of compensatory effects due to the additional adsorption/desorption of polyelectrolyte complexes from the film surface. The concentration of Cdots in the film was determined, and the loaded amount was ca. 6.6 µg/mL per layer.

Chitosan (CS)/Hydroxyapatite (HA)/Tricalcium Phosphate (β-TCP)-Based Composites as a Potential Material for Pulp Tissue Regeneration

This research focused on developing new materials for endodontic treatments to restore tissues affected by infectious or inflammatory processes. Three materials were studied, namely tricalcium phosphate β-hydroxyapatite (β-TCP), commercial and natural hydroxyapatite (HA), and chitosan (CS), in different proportions. The chemical characterization using infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis confirmed the composition of the composite. Scanning electron microscopy (SEM) demonstrated that the design and origin of the HA, whether natural or commercial, did not affect the morphology of the composites. In vitro studies using Artemia salina (A. salina) indicated that all three experimental materials were biocompatible after 24 h, with no significant differences in mortality rate observed among the groups. The subdermal implantation of the materials in block form exhibited biocompatibility and biodegradability after 30 and 60 days, with the larger particles undergoing fragmentation and connective tissue formation consisting of collagen type III fibers, blood vessels, and inflammatory cells. The implanted material continued to undergo resorption during this process. The results obtained in this research contribute to developing endodontic technologies for tissue recovery and regeneration.

Synthesis and characterization of poly(3-hydroxybutyrate)/chitosan-graft poly (acrylic acid) conjugate hyaluronate for targeted delivery of methotrexate drug to colon cancer cells

Anti-cancer medications that are delivered specifically to the tumor site possess greater efficacy with less negative effects on the body. So, the current research relies on a novel method for intercalating the anticancer medication methotrexate in poly(3-hydroxybutyrate)/chitosan-graft poly (acrylic acid) conjugated with sodium hyaluronate. The graft copolymers were synthesized through persulfate-initiated grafting of acrylic acid onto a binary mixture of various amounts of chitosan and poly(3-hydroxybutyrate) (2/1, 1/1 and 1/2, w/w) using microwave irradiation. The graft copolymer was conjugated with sodium hyaluronate for targeted delivery of methotrexate drug specifically to colon cancer cell lines (Caco-2). The graft copolymers were characterized by many physical techniques. The maximum drug loading efficiency was observed in case of the graft copolymer/hyaluronate rich in chitosan content 69.7 ± 2.7 % (4.65 mg/g) with a sustained release about 98.6 ± 1.12 %, at pH 7.4. The findings of severe cytotoxicity having a value of the IC₅₀ of 11.7 μg/ml, a substantial proportion of apoptotic cells (67.88 %), and an elevated level of DNA breakage inside the treated Caco-2 cells verified the effective release of methotrexate from the loaded copolymer matrix. Besides, the high stability and biological activity of the released drug was exhibited through occurrence of greater increment of reactive oxygen species and effect on the extent of expression of genes connected to apoptosis and anti-oxidant enzymes within the treated cells. Ultimately, this system can be recommended as potent carrier for methotrexate administration to targeted cancerous cells in the colon.

Evaluation of chitosan salt properties in the production of AgNPs materials with antibacterial activity

In this study, water-soluble chitosan salts (chitosan amine sulfopropyl salts) were prepared from chitosan samples with different molecular weights and deacetylation degrees. These soluble-in-water polymer salts allowed us to produce, in an eco-friendly and facile method, silver nanoparticles (AgNPs) with better control on size and polydispersity, even at large silver concentrations than their corresponding chitosan sample. Chitosan salt-based materials (films and scaffolds) were analyzed in terms of antibacterial properties against Staphylococcus aureus ATCC23915 or Pseudomonas aeruginosa ATCC 27853. 3D scaffolds enhanced the effect of the chitosan-AgNPs combination compared to the equivalent films.

Effects of Chitosan Molecular Weight and Degree of Deacetylation on Chitosan-Cellulose Nanocrystal Complexes and Their Formation

This study was conducted to determine the effects of chitosan molecular weight and degree of deacetylation (DD) on chitosan-cellulose nanocrystal (CNC) polyelectrolyte-macroion complexes (PMCs) and their formation. Chitosan samples with three different molecular weights (81, 3 · 10³, 6 · 10³ kDa) and four different DDs (77, 80, 85, 89%) were used. The effects on PMC formation were determined by turbidimetric titration. An effect of the molecular weight of chitosan was not observed in turbidimetric titrations. Turbidity levels were higher for CNCs with lower sulfate group density and larger hydrodynamic diameter than for CNCs with higher sulfate group density and smaller hydrodynamic diameter. Conversely, turbidity levels were higher for chitosans with higher DD (higher charge density) than for chitosans with lower DD (lower charge density). PMC particles from chitosans with different molecular weights were characterized by scanning electron microscopy, laser Doppler electrophoresis, and dynamic light scattering. PMCs from high-molecular-weight chitosan were more spherical and those from medium-molecular-weight chitosan had a slightly larger hydrodynamic diameter than PMCs from the respective other two chitosans. The molecular weight of the chitosan was concluded to have no effect on the formation of chitosan-CNC PMC particles and only a minor effect on the shape and size of the particles. The higher turbidity levels for CNCs with lower sulfate group density and larger hydrodynamic diameter and for chitosans with higher DD were attributed to a larger number of CNCs being required for charge compensation.

A polysaccharide/chitin hydrogel wound dressing from a Periplanattica americana residue: coagulation, antioxidant activity, and wound healing properties

Pharmaceuticals derived from the raw materials of Periplanattica americana have been applied for wound healing, liver disease treatment, and antitumor therapy. However, the resulting residues of P. americana have not been well exploited. We found that P. americana residues comprised high amounts of chitin (PC) and polysaccharides (PAP) exhibit good biological activity. Compared to shrimp-derived chitin, PC has a smaller molecular weight (Mv), lower crystallinity, and looser molecular structure, demonstrating stronger antioxidant activity and degradability. After adding the PAP, the PC solution rapidly lost fluidity and formed a hydrogel (P/PCGEL) that had antioxidation, biodegradability, and injectability properties and exhibited rapid coagulation, good water absorption and retention, and a low hemolysis rate (HR). In vivo studies reported that the P/PCGEL reduced edema during burns, accelerated collagen synthesis and deposition, reduced reactive oxygen species (ROS) levels, and increased superoxide dismutase (SOD) levels, thereby reducing the inflammatory response, avoiding oxidative stress, and effectively promoting wound healing. Furthermore, the P/PCGEL demonstrated good biocompatibility, rapid biodegradation, and injectability, thereby reducing the risk of trauma and infection engendered by repeated wound opening and dressing changes. These properties also demonstrated the potential application for this hydrogel in preparing injectable hydrogel excipients. Hence, this study provided a hydrogel-formed wound dressing comprising pure natural ingredients and offering convenient administration, economic availability, and strong tissue repair ability.

Exploring Saduria entomon (Crustacea Isopoda) as a New Source for Chitin and Chitosan Isolation

Chitin and chitosan demand is growing very fast due to interest from industries such as pharmaceutical, cosmetic, agricultural and others. New sources for chitin and chitosan isolation are being extensively searched to fulfil this demand. In this paper, Saduria entomon a Baltic benthic crustacean, is evaluated as a source for chitin and chitosan isolation. Chitin and chitosan yield from S. entomon were 14.8 and 8.2%, respectively, in a similar range to other sources. Samples were characterized in terms of physicochemical properties (acetylation degree, molecular weight, thermal stability, and crystallinity) and two biological properties, antimicrobial activity and antioxidant activity were evaluated. Chitosan S. entomon exhibited antimicrobial activity against S. aureus but not against E. coli. An antioxidant activity of 20.98 TROLOX µmol equivalent/g polymer was detected for the chitosan sample. These properties are very promising for the use of this organism as a source for chitin and chitosan isolation in the biomedical field.

Physicochemical Properties and Functional Characteristics of Ecologically Extracted Shrimp Chitosans with Different Organic Acids during Demineralization Step

The current study aims to develop eco-friendly and economical chitosans with a wide range of applications using organic acids for shrimp shells demineralization. Chitosan samples were extracted from shrimp (Parapenaeus longirostris) shells and the demineralization step was performed with three organic acids (citric, acetic, and lactic) and two mineral acids (hydrochloric and sulfuric). The chitosans were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The chitosans’ physicochemical properties were also determined. The characteristic bands and functional groups of the chitosans were identified by FTIR spectra. The chitosans’ crystallinity order was as follows: ChHCl > ChCitric > ChH2SO4 > ChLactic > ChAcetic. The chitosans’ morphological characteristics revealed a smooth surface and fibrous structures with pores. Chitosans extracted by organic acids showed the highest extraction yields. ChHCl and ChCitric had higher degrees of deacetylation values; 83.67% and 81.47%, respectively. The solubility was proportional to the degree of deacetylation. Furthermore, ChH2SO4 and ChCitric had lower molecular weight values; 149 kDa and 183 kDa, respectively. Organic acids are as effective as mineral acids for shrimp shells demineralization. The developed process opens up possibilities to produce chitin and chitosan in a more eco-friendly way and at a lower cost in many industrial sectors.

Chitosan characteristics in electrolyte solutions: Combined molecular dynamics modeling and slender body hydrodynamics

Molecular dynamics modeling was applied to predict chitosan molecule conformations, the contour length, the gyration radius, the effective cross-section and the density in electrolyte solutions. Using various experimental techniques the diffusion coefficient, the hydrodynamic diameter and the electrophoretic mobility of molecules were determined. This allowed to calculate the zeta potential, the electrokinetic charge and the effective ionization degree of the chitosan molecule as a function of pH and the temperature. The chitosan solution density and zero shear dynamic viscosity were also measured, which enabled to determine the intrinsic viscosity increment. The experimental results were quantitatively interpreted in terms of the slender body hydrodynamics exploiting molecule characteristics derived from the modeling. It is also confirmed that this approach can be successfully used for a proper interpretation of previous literature data obtained under various physicochemical conditions.

Preparation, Characterization and Study of the Dissociation of Naproxen from Its Chitosan Salt

Salts of naproxen (NAP) with chitosan (CTS) and reticulated chitosan (CEP) were prepared under optimized conditions to maximize the yield of reaction. The objective was to evaluate the dissociation in water, which can guide studies of release of the drug from biopolymeric salts in pharmaceutical applications. Higher salification was found after 24 h of reaction at 60 °C in a molar ratio 1:1.05 (CTS:NAP, mol/mol), resulting in a degree of substitution (DS) of 17% according to ¹³C NMR, after neutralization of the –NH₂ group of the biopolymer by the carboxylic group of the drug. The presence of NAP salt is evidenced by FTIR bands related to the –NH₃⁺ group at 856 cm⁻¹, a decrease in crystallinity index in XRD diffractograms as well as changes in mass loss ratios (TG/DTG/DTA) and increased thermal stability of the salt regarding CTS itself. The CEPN crosslinked salt presented a DS = 3.6%, probably due to the shielding of the –NH₂ groups. Dissociation studies revealed that at pH 2.00, dissociation occurred faster when compared to at pH 7.00 in the non-reticulated salt, while the opposite was observed for the reticulated one.

Mucoadhesive, Antibacterial, and Reductive Nanogels as a Mucolytic Agent for Efficient Nebulized Therapy to Combat Allergic Asthma

Asthma is an intractable disease involving the infiltration of inflammatory cells and mucus plugging. Despite small molecular mucolytics having the ability to break the disulfide bonds of mucins, offering a potential way to overcome the airflow obstruction and airway infection, these mucolytics have limited therapeutic effects in vivo. Therefore, in this work, arginine-grafted chitosan (CS-Arg) is ionically cross-linked with tris(2-carboxyethyl)phosphine (TCEP) to obtain nanogels as a mucolytic agent. The positively charged nanogels effectively inhibit the formation of large aggregates of mucin in vitro, probably thanks to the formation of an ionic interaction between CS-Arg and mucin, as well as the breakage of disulfide bonds in mucin by the reductive TCEP. Moreover, the nanogels show good cytocompatibility at concentrations up to 5 mg mL^-1, exhibiting effective inhibitory effects against the proliferation of both Staphylococcus aureus and Escherichia coli at 5 mg mL^-1. After the administration of the nanogels by nebulization into a Balb/c mouse model with allergic asthma, they can efficiently reduce the mucus obstruction in bronchioles and alveoli and relieve airway inflammation. Therefore, these CS-Arg/TCEP nanogels potentially represent a promising mucolytic agent for the efficient treatment of allergic asthma and other muco-obstructive diseases.

Chitosan Schiff bases-based polyelectrolyte complexes with graphene quantum dots and their prospective biomedical applications

Chitosan (Cs) bis-aldehyde Schiff base derivatives were synthesized by condensation of Cs with three bis-aldehydes namely; butane-1,4-diyl bis(4-formylbenzoate), N,N'-(butane-1,4-diyl)bis(2-(4-formylphenoxy)acetamide) and 4,4'-(butane-1,4-diylbis(oxy))dibenzaldehyde. The prepared Cs derivatives were blended with carboxymethyl chitosan(CMC) and graphene quantum dots (GQDs) to produce semi-IPNs polyelectrolyte complexes (PECs). and characterized with respect to their molecular structure and physio-chemical properties. The antibacterial activity against H. pylori (and in vitro Inosine 5'-monophosphate dehydrogenase IMPDH inhibitory assay) was evaluated. Additionally, a preliminary in vitro assessment for wound healing was performed against PECs in which wound closure percentages, and rates were investigated indicating an accelerated wound healing compared with untreated cells. The PEC based on Schiff base PEC containing amide linkage showed the highest wound healing ability. A minimal inhibitory concentration (MIC) was obtained for the PEC sample containing Cs Schiff base derived from 4,4'-(butane-1, 4-diylbis(oxy))dibenzaldehyde at a dose of 0.98 μg/ml inhibiting H. pylori growth by 100%. Additionally, the selected above-mentioned compound was selected to test its inhibitory activity against the HpIMPDH enzyme in addition to its selectivity towards the hIMPDH2 enzyme and was found to have promising activity against the HpIMPDH enzyme with IC₅₀ value of 0.65 μM, and to be safer and less active against the hIMPDH2 enzyme with IC₅₀ > 10 μM, reflecting its selectivity.

Evaluating Non-Conventional Chitosan Sources for Controlled Release of Risperidone

In this work, two chitosan samples from cuttlebone and squid pen are produced and characterized. We studied the formation of thermoresponsive hydrogels with β-glycerol phosphate and found proper formulations that form the hydrogels at 37 °C. Gel formation depended on the chitosan source being possible to produce the thermoresponsive hydrogels at chitosan concentration of 1% with cuttlebone chitosan but 1.5% was needed for squid pen. For the first time, these non-commercial chitosan sources have been used in combination with β-glycerol phosphate to prepare risperidone formulations for controlled drug delivery. Three types of formulations for risperidone-controlled release have been developed, in-situ gelling formulations, hydrogels and xerogels. The release profiles show that in-situ gelling formulations and particularly hydrogels allow an extended control release of risperidone while xerogels are not appropriate formulations for this end since risperidone was completely released in 48 h.

Conformation and persistence length of chitosan in aqueous solutions of different ionic strengths via asymmetric flow field-flow fractionation

Conformation of chitosan in acidic aqueous solutions is strongly influenced by ionic strength, but the conventional employed size exclusion chromatography is limited to high ionic strength. Here we show that conformation of chitosan in acetate buffer down to millimolar ionic strength can be studied via asymmetric flow field-flow fractionation (AF4), where the separation is governed by the diffusion properties of the chitosan molecules and assisted by the electrostatic repulsion of the polyelectrolyte from the channel membrane. The size of chitosan decreases with ionic strength due to increasing screening of the polyelectrolyte effect. The persistence length of chitosan in the solutions, obtained by fitting the conformation plot by the wormlike chain model, decreases linearly with the Debye screening length from 44.5 nm at a salt concentration of 1.25 mM dominated by the electrostatic contribution to 8.6 nm in 800 mM acetate buffer close to its intrinsic persistence length of 7.7 nm.

Microstructure and Mechanical Strength Properties of Chitosan Sponges Obtained from Polymer Solutions in Carbonic Acid

Abstract

Polymer sponges based on chitosan are first obtained from chitosan solutions in carbonic acid and gels based on these solutions crosslinked by a noncytotoxic agent of natural origin, genipin. A comparative analysis of the structure and mechanical strength properties of sponges prepared from chitosan solutions in carbonic and acetic acids is carried out. It is shown that the addition of genipin in an amount of ~2 wt % to a chitosan solution in carbonic acid leads to a decrease in the average pore size by ~2.5 times and a significant increase in the strength characteristics of the material in comparison with the sponge prepared without genipin.

Chitosan/Polyvinyl Alcohol/Tea Tree Essential Oil Composite Films for Biomedical Applications

Tissue engineering is crucial, since its early adoption focused on designing biocompatible materials that stimulate cell adhesion and proliferation. In this sense, scaffolds made of biocompatible and resistant materials became the researchers’ focus on biomedical applications. Humans have used essential oils for a long time to take advantage of their antifungal, insecticide, antibacterial, and antioxidant properties. However, the literature demonstrating the use of essential oils for stimulating biocompatibility in new scaffold designs is scarce. For that reason, this work describes the synthesis of four different film composites of chitosan/polyvinyl alcohol/tea tree (Melaleuca alternifolia), essential oil (CS/PVA/TTEO), and the subdermal implantations after 90 days in Wistar rats. According to the Young modulus, DSC, TGA, mechanical studies, and thermal studies, there was a reinforcement effect with the addition of TTEO. Morphology and energy-dispersive (EDX) analysis after the immersion in simulated body fluid (SBF) exhibited a light layer of calcium chloride and sodium chloride generated on the material’s surface, which is generally related to a bioactive material. Finally, the biocompatibility of the films was comparable with porcine collagen, showing better signs of resorption as the amount of TTEO was increased. These results indicate the potential application of the films in long-term biomedical needs.

Biocompatibility Study of Electrospun Nanocomposite Membranes Based on Chitosan/Polyvinyl Alcohol/Oxidized Carbon Nano-Onions

In recent decades, the number of patients requiring biocompatible and resistant implants that differ from conventional alternatives dramatically increased. Among the most promising are the nanocomposites of biopolymers and nanomaterials, which pretend to combine the biocompatibility of biopolymers with the resistance of nanomaterials. However, few studies have focused on the in vivo study of the biocompatibility of these materials. The electrospinning process is a technique that produces continuous fibers through the action of an electric field imposed on a polymer solution. However, to date, there are no reports of chitosan (CS) and polyvinyl alcohol (PVA) electrospinning with carbon nano-onions (CNO) for in vivo implantations, which could generate a resistant and biocompatible material. In this work, we describe the synthesis by the electrospinning method of four different nanofibrous membranes of chitosan (CS)/(PVA)/oxidized carbon nano-onions (ox-CNO) and the subdermal implantations after 90 days in Wistar rats. The results of the morphology studies demonstrated that the electrospun nanofibers were continuous with narrow diameters (between 102.1 nm ± 12.9 nm and 147.8 nm ± 29.4 nm). The CS amount added was critical for the diameters used and the successful electrospinning procedure, while the ox-CNO amount did not affect the process. The crystallinity index was increased with the ox-CNO introduction (from 0.85% to 12.5%), demonstrating the reinforcing effect of the nanomaterial. Thermal degradation analysis also exhibited reinforcement effects according to the DSC and TGA analysis, with the higher ox-CNO content. The biocompatibility of the nanofibers was comparable with the porcine collagen, as evidenced by the subdermal implantations in biological models. In summary, all the nanofibers were reabsorbed without a severe immune response, indicating the usefulness of the electrospun nanocomposites in biomedical applications.

Determination of indicators allowing to evaluating the hemostatic activity of chitosan without a biological experiment

The biopolymer chitosan is widely used for the development of local hemostatic agents. However, the physicochemical parameters of chitosan that determine its hemostatic properties have not yet been determined. Standard quality control of chitosan-containing raw materials and medical products on its basis do not allow us to make a conclusion about the effectiveness of their use for stopping bleeding. The most reliable method for assessing hemostatic activity remains in vivo experiment on large animals. The aim of this study was to determine additional physicochemical parameters of chitosan, which would make it possible to predict its hemostatic activity without conducting a biological experiment. In this work, using the methods of nuclear magnetic resonance spectroscopy, spectrophotometry and viscometry, it has been shown that the ability to initiate hemostasis is depending of the molecular weight and degree of deacetylation of chitosan, but not enough linearly. The hemostatic properties in vitro increases in a series of samples with a relatively constant molecular weight with an increase in the degree of deacetylation. As well as in a series with the same degree of deacetylation with an increase in molecular weight. However, at molecular weight values more than 300 kDa, the viscosity of the polymer causes the opposite effect: with an increase in the degree of deacetylation, the hemostatic activity decreases. The best ability to initiate hemostasis have chitosan samples with a degree of deacetylation of 90.0%–97.4% and molecular weight 145.7–284.7 kDa, in which at pH of solution close to physiological, a significant part of the molecules transitioned from conformation state rigid rod to state globule. It was accompanied by an abrupt change in light transmission of the solution. It was concluded, that it is possible to study conformational states by spectrophotometry to assess the hemostatic activity of chitosan samples without performing biological experiment.

Characterization of Chitosan Extracted from Fish Scales of the Colombian Endemic Species Prochilodus magdalenae as a Novel Source for Antibacterial Starch-Based Films

Scales of Prochilodus magdalenae, a Colombian endemic fish species, were used to obtain chitosan for application as an antibacterial agent integrated into starch-based films. Analysis of its composition during the demineralization and deproteinization process indicated that minerals and protein were both removed successfully. At this point, mild conditions for the deacetylation process were employed, namely, 2, 4, and 6 wt.% NaOH at room temperature for 16 h. Chitosan processed under 2 wt.% NaOH had low molecular weight, with the lowest value of 107.18 ± 24.99 kDa, which was closely related to its antibacterial activity. Finally, this chitosan was integrated into a banana starch-based film, and its antibacterial activity was assayed in Escherichia coli and Staphylococcus aureus cultures, with positive results in the former culture, especially due to the low-molecular-weight characteristic of chitosan.

Preparation of chitosan from waste shrimp shells fermented with Paenibacillus jamilae BAT1

In this study, chitin extraction from shrimp shell powder (SSP) using locally isolated Paenibacillus jamilae BAT1 (GenBank: MN176658), the preparation of chitosan from the extracted chitin, and the characterization and biological activity (antimicrobial and antioxidant) of the prepared chitosan (PC) were investigated. It was determined that P. jamilae BAT1 did not have chitinase activity but showed high protease activity and protein removal potential. Optimum pH, shell concentration and incubation time for deproteinization were determined as 7.0, 60 g/L and 4 days, respectively. Addition of KH₂PO₄ or MgSO₄ did not affect chitin extraction and deproteinization yield. The maximum yields of deproteinization, demineralization and chitin extraction yields were 87.67, 41.95 and 24.5%, respectively. The viscosity-average molecular weight of PC was determined as 1.41 × 10⁵ g/mol. The deacetylation degree of PC (86%) was found to be higher that of commercial chitosan (CC) (78%). DPPH scavenging activity of PC (IC₅₀ 0.59 mg/mL) was higher than that of CC (IC₅₀ 3.72 mg/mL). PC was found to have higher antimicrobial activity against the bacteria E. coli and S. aureus and the yeast C. albicans when compared to CC. This is the first study on the use of the bacterium P. jamilae in biological chitin extraction.

Combined Analytical Approaches to Standardize and Characterize Biomaterials Formulations: Application to Chitosan-Gelatin Cross-Linked Hydrogels

A protocol based on the combination of different analytical methodologies is proposed to standardize the experimental conditions for reproducible formulations of hybrid hydrogels. The final hybrid material, based on the combination of gelatin and chitosan functionalized with methylfuran and cross-linked with 4-arm-PEG-maleimide, is able to mimic role, dynamism, and structural complexity of the extracellular matrix. Physical-chemical properties of starting polymers and finals constructs were characterized exploiting the combination of HP-SEC-TDA, UV, FT-IR, NMR, and TGA.

The Kinetics of Chitosan Degradation in Organic Acid Solutions

This paper presents a comparative study on chitosan degradation in organic acid solutions according to their different dissociation characteristics. More precisely, the aim of the study was to determine the kinetics of the degradation process depending on the different acid dissociation constants (pKa values). The scientists involved in chitosan to date have focused mainly on acetic acid solutions. Solutions of lactic, acetic, malic, and formic acids in concentrations of 3% wt. were used in this research. The progress of degradation was determined based on the intrinsic viscosity measurement, GPC/SEC chromatographic analysis, and their correlation. Changes in the viscosity parameters were performed at a temperature of 20 °C ± 1 °C and a timeframe of up to 168 h (7 days). The chemical structure and DDA of the initial chitosan were analyzed using 1H-NMR spectroscopy analysis. The results of this study can be considered of high importance for the purpose of electrospinning, production of micro- and nano-capsules for drug delivery, and other types of processing. Understanding the influence of the dissociation constant of the solvent on the kinetics of chitosan degradation will allow the selection of an appropriate medium, ensuring an effective and stable spinning process, in which the occurrence of polymer degradation is unfavorable.

Electrosteric stabilization of oil/water emulsions by adsorption of chitosan oligosaccharides-An electrokinetic study

The present study was focused on investigation of electrokinetic behaviour of lecithin-stabilized oil/water emulsions in the presence of chitosan oligosaccharides (COS). The oligosaccharides give unique opportunity for precisely characterization of the properties of chitosan as a function of the degree of acetylation (DA) and degree of polymerization (DP) of the polymer. For the study were chosen well characterized ultra pure COS molecules with completely acetylated monomers and mixture of COS molecules with acetylated and deacetylated monomers. The obtained results confirmed experimentally for the first time, the suggestion for the predominant contribution of hydrophobic (at high DA) and electrostatic (at low DA) interactions between chitosan monomers and the lecithin-covered droplet surface.

Monitoring the infection process of Rhizopus stolonifer on strawberry fruit during storage using films based on chitosan/polyvinyl alcohol/polyvinylpyrrolidone and plant extracts

Different formulations based on nanoparticles of chitosan-plant extracts were evaluated to detect the infection process from the earliest stage of the fungus Rhizopus stolonifer on strawberry fruit during storage. Chitosan/polyvinyl alcohol (Ch/PVA) and chitosan/polyvinylpyrrolidone (Ch/PVP) films enriched with nanoparticles (NPs) of chitosan blended with plant extracts were prepared. They were placed inside a plastic package containing inoculated fruits and stored at 25 °C for 72 h. The thickness values of the films were in the range of 0.10 to 0.25 mm. All samples showed a maximum absorbance peak of about 300-320 nm; however, the Ch/PVP films enriched with NPs of chitosan and 10% of radish extract had an evident decrease in the optical absorbance as the fungal infection progressed. Additionally, as observed by scanning electron microscopy, the cross-section and surface morphology of films were not modified during storage, and the growth of R. stolonifer was evident after 48 h. Therefore, the Ch/PVP films enriched with chitosan NPs blended with 10% radish extract could be a reliable indicator of this fungus's growth.

Chitosan-based smart hybrid materials: a physico-chemical perspective

Chitosan is one of the most studied cationic polysaccharides. Due to its unique characteristics of being water soluble, biocompatible, biodegradable, and non-toxic, this macromolecule is highly attractive for a broad range of applications. In addition, its complex behavior and the number of ways it interacts with different components in a system result in an astonishing variety of chitosan-based materials. Herein, we present recent advances in the field of chitosan-based materials from a physico-chemical perspective, with focus on aqueous mixtures with oppositely charged colloids, chitosan-based thin films, and nanocomposite systems. In this review, we focus our attention on the physico-chemical properties of chitosan-based materials, including solubility, mechanical resistance, barrier properties, and thermal behaviour, and provide a link to the chemical peculiarities of chitosan, such as its intrinsic low solubility, high rigidity, large charge separation, and strong tendency to form intra- and inter-molecular hydrogen bonds.

Fast-forward approach of time-domain NMR relaxometry for solid-state chemistry of chitosan

Chitosans with different average degrees of acetylation and weight molecular weight were analyzed by time-domain NMR relaxometry using the recently proposed pulse sequence named Rhim and Kessemeier - Radiofrequency Optimized Solid-Echo (RK-ROSE) to acquire ¹H NMR signal of solid-state materials. The NMR signal decay was composed of faster (tenths of μs) and longer components, where the mobile-part fraction exhibited an effective relaxation transverse time assigned to methyl hydrogens from N-acetyl-d-glucosamine (GlcNAc) units. The higher intrinsic mobility of methyl groups was confirmed via DIPSHIFT experiments by probing the ¹H-¹³C dipolar interaction. RK-ROSE data were modeled by using Partial Least Square (PLS) multivariate regression, which showed a high coefficient of determination (R² > 0.93) between RK-ROSE signal profile and average degrees of acetylation and crystallinity index, thus indicating that time-domain NMR consists in a promising tool for structural and morphological characterization of chitosan.