Determination of the degree of acetylation and the distribution of acetyl groups in chitosan by HPLC analysis of nitrous acid degraded and PMP labeled products

Comparison of the Degree of Acetylation of Chitin Nanocrystals Measured by Various Analysis Methods

Chitin and its derivate chitosan have versatile properties and have been used in various applications. One key parameter determining the functionality of chitin-based materials is the degree of acetylation (DA). For DA determination, NMR and FTIR spectroscopy are often considered to be the gold standard, but these techniques may not always be available and are rather time-consuming and costly. The first derivative UV method has been suggested, although accurate measurements can be challenging for materials with high degrees of acetylation, due to hydroxymethylfurfural (HMF) formation and other side reactions occurring. In this paper, we re-evaluated the first derivate UV method for chitin and chitosan powder, chitin nanocrystals, and deacetylated chitin nanocrystals. Our results showed that the first derivative UV method is capable of measuring DA with high accuracy (>0.9), leading to values comparable to those obtained by 1H NMR, 13C NMR, and FTIR. Moreover, by-product formation could either be suppressed by selecting the proper experimental conditions, or be compensated. For chitin nanocrystals, DA calculation deviations up to 20% due to by-product formation can be avoided with the correction that we propose. We conclude that the first derivative UV method is an accessible method for DA quantification, provided that sample solubility is warranted.

Mechanical Amorphization of Chitosan with Different Molecular Weights

Mechanical amorphization of three chitosan samples with high, medium, and low molecular weight was studied. It is shown that there are no significant differences between the course of amorphization process in a planetary ball mill of chitosan with different molecular weights, and the maximum degree of amorphization was achieved in 600 s of high intensity mechanical action. Specific energy consumption was 28 kJ/g, being comparable to power consumption for amorphization of cellulose determined previously (29 kJ/g) and 5–7-fold higher than that for amorphization of starch (4–6 kJ/g). Different techniques for determining the crystallinity index (CrI) of chitosan (analysis of the X-ray diffraction (XRD) data, the peak height method, the amorphous standard method, peak deconvolution, and full-profile Rietveld analysis) were compared. The peak height method is characterized by a broader working range but provides deviated CrI values. The peak deconvolution method (with the amorphous Voigt function) makes it possible to calculate the crystallinity index of chitosan with greater accuracy, but the analysis becomes more difficult with samples subjected to mechanical processing. In order to refine the structure and calculation of CrI by the Rietveld method, an attempt to optimize the structure file by the density functional theory (DFT) method was performed. The averaged profile of amorphous chitosan approximated by an eighth-order Fourier model improved the correctness of the description of the amorphous contribution for XRD data processing. The proposed equation may be used as a universal standard model of amorphous chitosan to determine the crystallinity index both for the amorphous standard method and for peak deconvolution of XRD patterns for arbitrary chitosan samples.

Quantitative Disaccharide Profiling of Glycosaminoglycans from Two Different Preparations by PMP and Deuterated PMP Labeling

Glycosaminoglycan (GAG) fine structures from the same animal cells and tissues are controlled not only by the biosynthetic and metabolic enzymes but also by other environmental factors, such as chemicals, growth factors, nutritional factors, and isolation procedures. To facilitate direct quantitative comparison of disaccharide compositions from different GAG preparations, several stable isotope labeling strategies have been developed. In this report, 1-phenyl-3-methyl-5-pyrazolone (PMP) and deuterated d5-PMP are used for differential disaccharide labeling and profiling of chondroitin sulfate GAG by high performance liquid chromatography (HPLC) coupled with mass spectrometry (MS).

Advances in the preparation and assessment of the biological activities of chitosan oligosaccharides with different structural characteristics

Chitosan oligosaccharides (COSs) are widely used biopolymers that have been studied in relation to a variety of abnormal biological activities in the food and biomedical fields. Since different COS preparation technologies produce COS compounds with different structural characteristics, it has not yet been possible to determine whether one or more chito-oligomers are primarily responsible for the bioactivity of COSs. The inherent biocompatibility, mucosal adhesion and nontoxic nature of COSs are well documented, as is the fact that they are readily absorbed from the intestinal tract, but their structure-activity relationship requires further investigation. This review summarizes the methods used for COS preparation, and the research findings with regard to the antioxidant, anti-inflammatory, anti-obesity, bacteriostatic and antitumour activity of COSs with different structural characteristics. The correlation between the molecular structure and bioactivities of COSs is described, and new insights into their structure-activity relationship are provided.

Characterization of polysaccharides from different species of brown seaweed using saccharide mapping and chromatographic analysis

Brown seaweed polysaccharides (BSPs) are one of the primary active components from brown seaweed that has a range of pharmaceutical and biomedical applications. However, the quality control of BSPs is a challenge due to their complicated structure and macromolecule. In this study, saccharide mapping based on high-performance liquid chromatography (HPLC), multi-angle laser light scattering, viscometer, and refractive index detector (HPSEC-MALLS-Vis-RID), and Fourier transform infrared (FT-IR) were used to discriminate the polysaccharides from nine different species of brown algae (BA1-9). The results showed that BSPs were composed of β-D-glucans and β-1,3-1,4-glucan linkages. The molecular weight, radius of gyration, and intrinsic viscosity of BSPs were ranging from 1.718 × 10⁵ Da to 6.630 × 10⁵ Da, 30.2 nm to 51.5 nm, and 360.99 mL/g to 865.52 mL/g, respectively. Moreover, α values of BSPs were in the range of 0.635 to 0.971, which indicated a rigid rod chain conformation. The antioxidant activities of BSPs exhibited substantial radical scavenging activities against DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS (2, 2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid) radicals, which indicated that the use of BSPs might be a potential approach for antioxidant supplements. Thus, this study gives insights about the structure-function relationship of BSPs, which will be beneficial to improve the quality of polysaccharides derived from marine algae.

Entering the spotlight: Chitosan oligosaccharides as novel activators of CaCCs/TMEM16A

Calcium-activated chloride channels (CaCCs)/TMEM16A control diverse fundamental physiological functions, and abnormal function of TMEM16A will lead to various diseases including asthma, hypertension, gastrointestinal hypomotility and cancers. Therefore, TMEM16A as drug targets for related diseases has been increasingly concerned by researchers. In this work, COS were reported as novel natural activators of TMEM16A. It was demonstrated that COS can activate TMEM16A in a concentration dependent manner, with an EC₅₀ of 74.5 μg/mL. Then, fluorescence experiments and inside-out patch clamp experiments were combined to confirm that COS can directly activate TMEM16A. Further, we compared the activation effects of COS monomers DP2 to DP6, with DP3 the best activator. Molecular simulation was performed to find that the binding sites between DP3 and TMEM16A are E143 and E146 in TMEM16A, and it was speculated that COS and TMEM16A may be combined by electrostatic interaction. Finally, we verified that guinea pig ileum contraction was promoted by COS and the monomers through activating TMEM16A. Collectively, COS are novel efficient natural activators of TMEM16A, with potential to be developed to treatment diseases caused by down-regulation of TMEM16A including gastrointestinal hypomotility.

d-Glucosamine production from chitosan hydrolyzation over a glucose-derived solid acid catalyst

A glucose-based solid acid catalyst (GSA) was synthesized by hydrothermal carbonization and its physicochemical properties were explored by various characterization techniques including IR, TG and SEM. In addition, its catalytic performance towards d-glucosamine formation from the hydrolysis of chitosan was extensively investigated to determine the effects of reaction parameters, such as reaction temperature, time and mass ratio of catalyst and reactants. The experimental results revealed that the yield of targeted product d-glucosamine could reach as high as 98.1% under optimal conditions (temperature: 110 °C; time: 6 h). After six catalytic cycles, no evident deactivation was observed, suggesting the satisfactory stability of the investigated solid acid catalyst. This might provide insight on the development of suitable catalyst systems for d-glucosamine formation to replace homogeneous catalysts.

A method for preparing d-glucosamine in aqueous phase by chitosan degradation by a solid acid, which resulted in high yields.

Determination of the Deacetylation Degree of Chitooligosaccharides

The methods for determination of chitosan content recommended in the Chinese Pharmacopoeia and the European Pharmacopoeia are not applicable for evaluation of the extent of deacetylation (deacetylation degree, DD) in chitooligosaccharides (COS). This study explores two different methods for assessment of DD in COS having relatively high and low molecular weights: an acid-base titration with bromocresol green indicator and a first order derivative UV spectrophotometric method for assessment of DD in COS. The accuracy of both methods as a function of molecular weight was also investigated and compared to results obtained using ¹H NMR spectroscopy. Our study demonstrates two simple, fast, widely adaptable, highly precise, accurate, and inexpensive methods for the effective determination of DD in COS, which have the potential for widespread commercial applications in developing country.

An Overview of the Protective Effects of Chitosan and Acetylated Chitosan Oligosaccharides against Neuronal Disorders

Chitin is the second most abundant biopolymer on Earth and is mainly comprised of a marine invertebrate, consisting of repeating β-1,4 linked N-acetylated glucosamine units, whereas its N-deacetylated product, chitosan, has broad medical applications. Interestingly, chitosan oligosaccharides have therapeutic effects on different types of neuronal disorders, including, but not limited to, Alzheimer’s disease, Parkinson’s disease, and nerve crush injury. A common link among neuronal disorders is observed at a sub-cellular level, such as atypical protein assemblies and induced neuronal death. Chronic activation of innate immune responses that lead to neuronal injury is also common in these diseases. Thus, the common mechanisms of neuronal disorders might explain the general therapeutic effects of chitosan oligosaccharides and their derivatives in these diseases. This review provides an update on the pathogenesis and therapy for neuronal disorders and will be mainly focused on the recent progress made towards the neuroprotective properties of chitosan and acetylated chitosan oligosaccharides. Their structural features and the underlying molecular mechanisms will also be discussed.

All Biomass and UV Protective Composite Composed of Compatibilized Lignin and Poly (Lactic-acid)

Utilization of carbon-neutral biomass became increasingly important due to a desperate need for carbon reduction in the issue of global warming in light of replacing petroleum-based materials. We used lignin, which was an abundant, low cost, and non-food based biomass, for the development of all biomass-based films and composites through reactive compatibilization with poly (lactic-acid) (PLA). Using a facile and practical route, the hydrophilic hydroxyl groups of lignin were acetylated to impose the compatibility with PLA. The solubility parameter of the pristine lignin at 26.3 (J/cm³)^0.5 was altered to 20.9 (J/cm³)^0.5 by acetylation allowing the good compatibility with PLA at 20.2 (J/cm³)^0.5. The improved compatibility of lignin and PLA provided substantially decreased lignin domain size in composites (12.7 μm), which subsequently gave transparent and UV-protection films (visual transmittance at 76% and UV protection factor over 40). The tensile strength and elongation of the developed composite films were increased by 22% and 76%, respectively, and the biobased carbon content was confirmed as 96 ± 3%. The developed PLA/lignin composites provided 100% all-biomass contents and balanced optical and mechanical properties that could broaden its eco-friendly applications in various industries.

Evaluation of the degree of chitosan deacetylation via induced-electrical properties

The properties and functionalities of chitosan are closely related to its degree of deacetylation (DD).