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N -alkyl-substituted polyacrylamides exhibit a thermal coil-to-globule transition in aqueous solution driven by an increase in hydrophobic interactions with rising temperature. With the aim of understanding the role of N -alkyl substituents in the thermal transition, this study focuses on the molecular interactions underlying the phase transition of poly( N,N -diethylacrylamide- co - N -ethylacrylamide) random copolymers. Poly( N,N -diethylacrylamide) (PDEAm), poly( N -ethylacrylamide) (PNEAm), and their random copolymers were synthesized by free radical polymerization and their chemical structure characterized spectroscopically. It was found that the values of the cloud-point temperature increased with PNEAm content, and particle aggregation processes took place, increasing the negative charge density on their surface. The cloud-point temperature of each copolymer decreased with respect to the theoretical values calculated assuming an absence of interactions. It is attributed to the formation of intra- and interchain hydrogen bonding in aqueous solutions. These interactions favor the formation of more hydrophobic macromolecular segments, thereby promoting the cooperative nature of the transition. These results definitively reveal the dominant mechanism occurring during the phase transition in the aqueous solutions of these copolymers.

Galactomannans (GM) are hemicellulosic polysaccharides composed of D-mannopyranose chains linked by β (1 → 4) glycosidic linkages with branches of D-galactopyranose linked by α (1 → 6) linkages. This polysaccharide is recognized for its hydrophilic character, as it is rich in hydroxyl groups (-OH). This chemical characteristic, combined with the absence of ionic charges, enables structural modifications such as transesterification of the fatty acid chains (FA), which provides a strategy for obtaining amphiphilic structures. The enzyme-catalyzed syntheses were carried out in DMSO with GM decanoate (GMD) and GM palmitate (GMP) at different molar ratios (0.5 and 1.0) and the resulting structures were evaluated with infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (CP/MAS 13 C NMR) and differential scanning calorimetry (DSC). The FTIR spectrum confirmed the transesterification of GM with the appearance of a C[bond, double bond]O band (1730-1750 cm -1 ). These results were confirmed by the signals observed at 177 and 30 ppm in the CP/MAS 13 C NMR spectrum, which corresponded to the C[bond, double bond]O groups of the esters and the terminal -CH 3 groups of the FA chains, respectively. Finally, DSC showed glass transition temperatures (Tg) in the range 43-51 °C, while the melting temperatures (Tm) of the GM esters (59 °C) were not affected by different degrees of esterification (DE) for GMD (0.37 and 0.71) and GMP (0.47 and 0.57)., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors. Published by Elsevier Ltd.)

This work provides the first description of the synthesis and characterization of water-soluble chitosan (Cs) derivatives based on the conjugation of both diethylaminoethyl (DEAE) and catechol groups onto the Cs backbone (Cs-DC) in order to obtain a Cs derivative with antioxidant and antimicrobial properties. The degree of substitution [DS (%)] was 35.46% for DEAE and 2.53% for catechol, determined by spectroscopy. Changes in the molecular packing due to the incorporation of both pendant groups were described by X-ray diffraction and thermogravimetric analysis. For Cs, the crystallinity index was 59.46% and the maximum decomposition rate appeared at 309.3 °C, while for Cs-DC, the values corresponded to 16.98% and 236.4 °C, respectively. The incorporation of DEAE and catechol groups also increases the solubility of the polymer at pH > 7 without harming the antimicrobial activity displayed by the unmodified polymer. The catecholic derivatives increase the radical scavenging activity in terms of the half-maximum effective concentration (EC 50 ). An EC 50 of 1.20 μg/mL was found for neat hydrocaffeic acid (HCA) solution, while for chitosan-catechol (Cs-Ca) and Cs-DC solutions, concentrations equivalent to free HCA of 0.33 and 0.41 μg/mL were required, respectively. Cell culture results show that all Cs derivatives have low cytotoxicity, and Cs-DC showed the ability to reduce the activity of reactive oxygen species by 40% at concentrations as low as 4 μg/mL. Polymeric nanoparticles of Cs derivatives with a hydrodynamic diameter ( D h ) of around 200 nm, unimodal size distributions, and a negative ζ-potential were obtained by ionotropic gelation and coated with hyaluronic acid in aqueous suspension, providing the multifunctional nanoparticles with higher stability and a narrower size distribution.

Chitosan (CS) nanosystems have potential applications for the control of microorganisms in the medical, environmental, and agrifood fields. In vivo and in vitro assays of CS nanosystems have experienced increased activity due to improved physicochemical properties, biological activity, and reactivity. Hence, it is important to determine whether their application involves toxicological risks. The aim of this study was to evaluate the mutagenic, cytotoxic, phytotoxic, and in vivo antifungal activity of chitosan-pyrrole-2-carboxylic acid nanobiocomposites (CS-PCA). The CS-PCA nanoparticles were synthesized by means of the nanoprecipitation technique with a size and ζ-potential of 502 ± 72 nm and + 54.7 ± 15.0 mV, respectively. According to the Ames test, no evidence of mutagenic activity was observed in Salmonella typhimurium strains. The cytotoxic assay showed that the incorporation of PCA into the CS matrix increased the toxic effect on ARPE-19 cells. However, fluorescence microscopy of ARPE-19 cells did not reveal morphostructural changes allusive to cell injury. CS-PCA exhibited strong phytotoxicity on lettuce seeds and the complete inhibition of seed development. The antifungal assay demonstrated that the CS-PCA delayed Aspergillus niger infection in tomato fruit until day 3; however, its use for the pre-treatment of seeds might exert adverse effects on plant development.

A wide variety of chitosan (CS) biomaterials have been loaded with different antimicrobial agents to improve the activity of CS against phytopathogenic fungi. Recently, the antimicrobial activity of 1H-pyrrole-2-carboxylic acid (PCA) has been reported as a secondary metabolite of Streptomyces griseus, which was identified as the main bioactive compound in the biological control. However, it is sensitive to light and its activity against filamentous fungi has not yet been reported. The aim of the present research work was to evaluate the biological activity of CS-PCA biocomposites for the control of Aspergillus niger. CS-PCA biocomposites were obtained through nanoprecipitation. In vitro antifungal activity was determined by viability assay, spore germination, morphometric analysis of spores and hyphae, and the analysis of cellular components by fluorescence microscopy. CS-PCA showed an average size and Z potential of 502 ± 72 nm and + 54.7 ± 15 mV, respectively. Micrographs demonstrated well-distributed biocomposites with an apparently spherical shape. A new signal at 1473 cm -1 in the FT-IR spectrum of the CS-PCA biocomposite was observed, confirming the presence of PCA in the composition of the CS-PCA nanosystem. CS-PCA biocomposites reduced the spores' viability by up to 58%. Effects on fungi morphometry, observed as an increase in the spores' average diameter, swelling, distortion, and an increase in the branching of hyphae, were observed. Fluorescence analysis showed oxidative stress and membrane and cell wall damage, mainly at early growth stages. The inhibitory effect against CS-resistant fungi, such as A. niger, opens a door for the control of CS-sensitive fungi.

The functionalization of polymeric substances is of great interest for the development of innovative materials for advanced applications. For many decades, the functionalization of chitosan has been a convenient way to improve its properties with the aim of preparing new materials with specialized characteristics. In the present review, we summarize the latest methods for the modification and derivatization of chitin and chitosan under experimental conditions, which allow a control over the macromolecular architecture. This is because an understanding of the interdependence between chemical structure and properties is an important condition for proposing innovative materials. New advances in methods and strategies of functionalization such as the click chemistry approach, grafting onto copolymerization, coupling with cyclodextrins, and reactions in ionic liquids are discussed., Competing Interests: The authors declare no conflict of interest.

A series of thermoresponsive copolymers based on chitosan-g-poly(N-vinylcaprolactam) were synthesized by amidation reaction using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride as coupling reagent. The effect of molecular architecture on the thermoresponsive properties of the graft copolymers solutions was studied by varying the chain length of the grafted poly(N-vinylcaprolactam), PVCL, (in the range from 4 to 26 kDa) and the spacing between grafted chains onto the chitosan backbone. The most interesting characteristic of these copolymers is their solubility in water at temperatures below their lower critical solution temperature (LCST). These solutions presented a LCST between 36 and 44 °C, which decreases with the spacing and length of grafted PVCL chains onto the chitosan backbone, in contrast with the limited decrease of the LCST of PVCL above a critical M¯n value around 18 kDa. This behavior offers tangible possibilities for the preparation and application of sensitive bioactive formulations and "smart" drug delivery systems., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

In this study, chitosan was chemically modified by reductive amination in a two-step process. The synthesis of N-(furfural) chitosan (FC) was confirmed by FT-IR and (1)H NMR analysis, and the degrees of substitution were estimated as 8.3 and 23.8%. The cross-linkable system of bismaleimide (BM) and FC shows that FC shared properties of furan-maleimide chemistry. This system produced non-reversible hydrogel networks by Diels-Alder cycloadditions at 85 °C. The system composed of BM and FC (23.8% substitution) generated stronger hydrogel networks than those of FC with an 8.3% degree of substitution. Moreover, the FC-BM system was able to produce hydrogel microspheres. Environmental scanning electron microscopy revealed the surface of the microspheres to be non-porous with small protuberances. In water, the microspheres swelled, increasing their volume by 30%. Finally, microspheres loaded with methylene blue were able to release the dye gradually, obeying second-order kinetics for times less than 600 min. This behavior suggests that diffusion is governed by the relaxation of polymer chains in the swelled state, thus facilitating drug release outside the microspheres., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The aim of the present study was to investigate the mechanical and thermal properties of mixed chitosan-acemannan (CS-AC) mixed gels and the antibacterial activity of dilute mixed solutions of both polysaccharides. Physical hydrogels of chitosan comprising varying amounts of non-gelling acemannan were prepared by controlled neutralization of chitosan using ammonia. As the overall acemannan concentration in the mixed hydrogel increased while fixing that of CS, the mechanical strength decreased. These results indicate that AC perturbs the formation of elastic junctions and overall connectivity as it occurs in the isolated CS network. Heterotypic associations between CS and AC leading to the formation of more compact microdomains may be at play in reducing the density of the gel network consolidated by CS, possibly due to shorter gel junctions. Micro-DSC studies at pH 12.0 seem consistent with the suggestion that molecular heterotypic associations between CS and AC may be at play in determining the overall physical properties of the mixed gel systems. In dilute solution, CS showed antimicrobial activity against Staphylococcus aureus but not against Escherichia coli; AC did not exert antimicrobial activity against any of the two bacterial species. In blended solutions of both polysaccharides, as the amount of AC increased, the antimicrobial activity of the system against S. aureus ceased. In conclusion, this study demonstrates that it is feasible to incorporate acemannan in chitosan-acemannan gels and that although the mechanical strength decreases due to the presence of AC, the gel network persists even at high amount of AC. This study anticipates that the CS-AC mixed gels may offer promise for the future development of biomaterials such as scaffolds to be used in wound therapy., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Chitosan-g-N-isopropylacrylamide (NIPAm) water-soluble copolymers were synthesized and characterized by FTIR and (1)H NMR spectroscopies combined with conductometric and potentiometric titrations. Their thermoresponsive, fully reversible, behavior in aqueous solutions was characterized by means of microcalorimetry and rheology. During heating of copolymer solutions there is a well-known endothermic effect, which coincides with a marked increase in G' and a moderate decrement in G'' due to the formation of a hydrophobic network at the expense of the net amount of sol fraction. It was also found that a straight dependence between the values of G' above the LCST and the enthalpies associated with the transition reflecting that the connectivity in the gel network is governed by the net number of formed enthalpic-hydrophobic driven-junctions. Both the LCST and the enthalpy change vary with the ionic strength of copolymer solutions, but no dependence was found with the neutralization of the polyelectrolyte chain.

A molecularly imprinted material was developed from hydrogels of chitosan (CS) cross-linked with genipin (GNP) using o-xylene as the template molecule. Gelling time, mechanical, and diffusion properties of CS-GNP hydrogels were initially investigated to establish optimal conditions to prepare molecularly imprinted hydrogels (MIHs). The elastic modulus was found to be directly proportional to the degree of cross-linking (R = moles of genipin/moles of glucosamine) while the diffusion of water, as monitored by magnetic resonance imaging, decreased with R. CS-GNP hydrogels of varying R were imprinted with o-xylene (MIH(o-xylene)). The adsorption capacity of o-xylene by MIH(o-xylene) was greater than the corresponding control hydrogels, particularly at R = 0.25. Freundlich isotherms yielded a better fitness than Langmuir ones and afforded n and Q(max)values of 2.55 and 103.3 mg/g, respectively. The imprinted hydrogel showed the highest adsorption capacity for o-xylene; however, the material was not highly selective as it also exhibited the capacity to adsorb m- and p-xylene isomers. In turn, the MIH(o-xylene) showed a low adsorption when 2-fluorotoluene was used in rebinding experiments, suggesting that molecular recognition by the binding sites is influenced by the electronic and steric properties of the analyte molecule, thus effectively confirming the imprinting effect within the MIH(o-xylene) network. This work opens the possibility to future development of materials with the capacity to adsorb o-xylene analogue molecules such as contaminants bearing chlorinated aromatic structures.

Accurate determination of chitin and protein contents in crustacean biomass and the intermediate products during the industrial isolation of chitin cannot be made directly from the total nitrogen content, unless the appropriate corrections are applied. This method, however, is affected by the presence of other nitrogen-containing chemical species that are formed endogenously or by the action of microorganisms during the handling of the sample. Therefore, an alternative rapid method to estimate the contents of these components can be very useful both in research and in various fields of application. An original method has been developed to address this problem. The method consists of the development of a set of equations based on the stoichiometric contents of nitrogen of chitin and protein whereby the amounts of each component can be estimated from the value of the total nitrogen content, provided the rest of the proximate composition of the sample is accurately known. In order to validate the procedure, a set of model mixtures of pure chitin and protein concentrate in the solid state, both extracted from shrimp head waste, are used. Excellent agreement between the predicted and real values of chitin and protein are obtained (R2=0.98, slope=0.90). When the proposed method is tested in the analysis of real samples obtained from five different processing protocols of pretreatment of raw shrimp head, it is found that in general the values of protein and chitin contents throughout the various stages of the process vary as expected. [GRAPH: SEE TEXT] Variation of the measured total nitrogen versus calculated stoichiometric total nitrogen of the chitin-protein mixtures.

N-Acylation of chitosan with carboxylic anhydrides in dilute acetic acid/methanol has been a well documented strategy to selectively modify chitosan. Although this reaction is known to lead to irreversible gel formation, the kinetics and mechanism of this process have not so far been addressed. To this purpose, gel formation during the N-isobutyrylation of chitosan was investigated as a function of the reaction stoichiometry (R), chitosan concentration, and temperature by small deformation oscillatory rheology. Gel formation follows closely the chemical reaction and it proceeds predominantly under second-order kinetics as established from the dependence of critical gel time, t(gel), on R and concentration. The activation energy value derived from t(gel) vs 1/T data (E(a) = 68.29 +/- 1.80 kJ/mol) was almost identical to values reported for the chitosan N-acetylation reaction in previous studies. An excess isobutyric anhydride is suggested to be necessary for nucleation and hydrophobic association. The potential application of N-isobutyrylchitosan (NIBC) hydrogels in the design of thermally sensitive materials is also demonstrated.