Revisiting the Determination of the Degree of Deacetylation Using Potentiometric Titration: A New Equation for Modified Chitosan.

Chitosan is a biopolymer that can be subjected to a variety of chemical modifications to generate new materials. The properties of modified chitosan are affected by its degree of deacetylation (DDA), which corresponds to the percentage of D-glucosamine monomers in its polymeric structure. Potentiometric titration is amongst the simplest, most readily available, and most cost-effective methods of determining the DDA. However, this method often suffers from a lack of precision, especially for modified chitosan resins. This is in large part because the equation used to calculate the DDA does not consider the molecular weight of the chemically modified monomeric units. In this paper, we introduce a new equation that is especially suited for modified chitosan bearing three different types of monomers. To test this equation, we prepared naphthalene-chitosan resins and subjected them to potentiometric titration. Our results show that our new equation, which is truer to the real structure of the polymeric chains, gives higher DDA values than those of the routinely used equations. These results show that the traditional equations underestimate the DDA of modified chitosan resins.

Preparation and Antioxidant Activity of New Carboxymethyl Chitosan Derivatives Bearing Quinoline Groups.

A total of 16 novel carboxymethyl chitosan derivatives bearing quinoline groups in four classes were prepared by different synthetic methods. Their chemical structures were confirmed by Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and elemental analysis. The antioxidant experiment results in vitro (including DPPH radical scavenging ability, superoxide anion radical scavenging ability, hydroxyl radical scavenging ability, and ferric reducing antioxidant power) demonstrated that adding quinoline groups to chitosan (CS) and carboxymethyl chitosan (CMCS) enhanced the radical scavenging ability of CS and CMCS. Among them, both N, O-CMCS derivatives and N-TM-O-CMCS derivatives showed DPPH radical scavenging over 70%. In addition, their scavenging of superoxide anion radicals reached more than 90% at the maximum tested concentration of 1.6 mg/mL. Moreover, the cytotoxicity assay was carried out on L929 cells by the MTT method, and the results indicated that all derivatives showed no cytotoxicity (cell viability > 75%) except O-CMCS derivative 1a, which showed low cytotoxicity at 1000 µg/mL (cell viability 50.77 ± 4.67%). In conclusion, the carboxymethyl chitosan derivatives bearing quinoline groups showed remarkable antioxidant ability and weak cytotoxicity, highlighting their potential use in food and medical applications.

Molecular modifications, biological activities, and applications of chitosan and derivatives: A recent update.

Polysaccharides arouse great interest due to their structure and unique properties, such as biocompatibility, biodegradability, and absence of toxicity. Polysaccharides from marine sources are particularly useful due to the wide variety of applications and biological activities. Chitosan, a deacetylated derivative of chitin, is an example of an interesting bioactive marine-derived polysaccharide. Moreover, a wide variety of chemical modifications and conjugation of chitosan with other bioactive molecules are responsible for improvements in physicochemical properties and biological activities, expanding the range of applications. An overview of the synthetic approaches for preparing chitosan, chitosan derivatives, and conjugates is described and discussed. A recent update of the biological activities and applications in different research fields, mainly focused on the last 5 years, is presented, highlighting current trends.

Progress in Research of Chitosan Chemical Modification Technologies and Their Applications.

Chitosan, which is derived from chitin, is the only known natural alkaline cationic polymer. Chitosan is a biological material that can significantly improve the living standard of the country. It has excellent properties such as good biodegradability, biocompatibility, and cell affinity, and has excellent biological activities such as antibacterial, antioxidant, and hemostasis. In recent years, the demand has increased significantly in many fields and has huge application potential. Due to the poor water solubility of chitosan, its wide application is limited. However, chemical modification of the chitosan matrix structure can improve its solubility and biological activity, thereby expanding its application range. The review covers the period from 1996 to 2022 and was elaborated by searching Google Scholar, PubMed, Elsevier, ACS publications, MDPI, Web of Science, Springer, and other databases. The various chemical modification methods of chitosan and its main activities and application research progress were reviewed. In general, the modification of chitosan and the application of its derivatives have had great progress, such as various reactions, optimization of conditions, new synthetic routes, and synthesis of various novel multifunctional chitosan derivatives. The chemical properties of modified chitosan are usually better than those of unmodified chitosan, so chitosan derivatives have been widely used and have more promising prospects. This paper aims to explore the latest progress in chitosan chemical modification technologies and analyze the application of chitosan and its derivatives in various fields, including pharmaceuticals and textiles, thus providing a basis for further development and utilization of chitosan.

Chitosan-Hydroxycinnamic Acids Conjugates: Emerging Biomaterials with Rising Applications in Biomedicine.

Over the past thirty years, research has shown the huge potential of chitosan in biomedical applications such as drug delivery, tissue engineering and regeneration, cancer therapy, and antimicrobial treatments, among others. One of the major advantages of this interesting polysaccharide is its modifiability, which facilitates its use in tailor-made applications. In this way, the molecular structure of chitosan has been conjugated with multiple molecules to modify its mechanical, biological, or chemical properties. Here, we review the conjugation of chitosan with some bioactive molecules: hydroxycinnamic acids (HCAs); since these derivatives have been probed to enhance some of the biological effects of chitosan and to fine-tune its characteristics for its application in the biomedical field. First, the main characteristics of chitosan and HCAs are presented; then, the currently employed conjugation strategies between chitosan and HCAs are described; and, finally, the studied biomedical applications of these derivatives are discussed to present their limitations and advantages, which could lead to proximal therapeutic uses.

Biomaterials Based on Chitosan and Its Derivatives and Their Potential in Tissue Engineering and Other Biomedical Applications-A Review.

In the times of dynamically developing regenerative medicine, more and more attention is focused on the use of natural polymers. This is due to their high biocompatibility and biodegradability without the production of toxic compounds, which means that they do not hurt humans and the natural environment. Chitosan and its derivatives are polymers made most often from the shells of crustaceans and are biodegradable and biocompatible. Some of them have antibacterial or metal-chelating properties. This review article presents the development of biomaterials based on chitosan and its derivatives used in regenerative medicine, such as a dressing or graft of soft tissues or bones. Various examples of preparations based on chitosan and its derivatives in the form of gels, films, and 3D structures and crosslinking products with another polymer are discussed herein. This article summarizes the latest advances in medicine with the use of biomaterials based on chitosan and its derivatives and provides perspectives on future research activities.

Synthesis of Hydroxypropyltrimethyl Ammonium Chitosan Derivatives Bearing Thioctate and the Potential for Antioxidant Application.

Hydroxypropyltrimethyl ammonium chloride chitosan (HACC) is one of the most important water-soluble chitosan derivatives; its derivatives have gained growing attention due to their potential biomedical applications. Here, hydroxypropyltrimethyl ammonium chitosan derivatives bearing thioctate (HACTs), with different degrees of substitution of thioctate, were prepared using HACC and α-lipoic acid as the reaction precursors, using an ion exchange method. The structural characteristics of the synthesized derivatives were confirmed by FTIR, 1H NMR, and 13C NMR spectroscopy. In addition, their antioxidant behaviors were also investigated in vitro by the assays of reducing power, and scavenging activities against hydroxyl radicals and DPPH radicals. The antioxidant assay indicated that HACTs displayed strong antioxidant activity compared with HACC, especially in terms of reducing power. Besides, the antioxidant activities of the prepared products were further enhanced with the increase in the test concentration and the degrees of substitution of thioctate. At the maximum test concentration of 1.60 mg/mL, the absorbance value at 700 nm of HACTs, under the test conditions, was 4.346 ± 0.296, while the absorbance value of HACC was 0.041 ± 0.007. The aforementioned results support the use of HACTs as antioxidant biomaterials in food and the biomedical field.

Antifungal action of chitosan in combination with fungicides in vitro and chitosan conjugate with gallic acid on tomatoes against Botrytis cinerea.

In the present work, a positive effect was obtained by using low molecular weight chitosan compounds in combination with synthetic fungicides. Antifungal activity against Botrytis cinerea, determined by the radial growth method, was more than 75%, with a 25 × 10- 10 g/L concentration of fludioxonil or difenoconazole in compounds. Metabolic activity of B. cinerea fungus was about 15% when using a chitosan compound containing fludioxonil at a concentration of 25 × 10- 7 g/L. The combined action of chitosan with difenoconazole at a fungicide concentration of 25 × 10- 4 g/L is 2-3 times more effective than the action of each component separately. Results of studies for artificially inoculated B. cinerea tomato fruit when treated with low molecular chitosan and chitosan conjugate with gallic acid reduced the frequency of rotting fruit by 50 and 83%, respectively. Chitosan-gallic acid conjugate were obtained from chitosans with Mw of 28 kDa (Ch28GA) was proved to be effective as a preventive treatment for 3 days and can potentially be used as a biofungicide against B. cinerea on tomatoes in the post-harvest period.

Comparative Evaluation of Different Chitosan Species and Derivatives as Candidate Biomaterials for Oxygen-Loaded Nanodroplet Formulations to Treat Chronic Wounds.

Persistent hypoxia is a main clinical feature of chronic wounds. Intriguingly, oxygen-loaded nanodroplets (OLNDs), filled with oxygen-solving 2H,3H-decafluoropentane and shelled with polysaccharides, have been proposed as a promising tool to counteract hypoxia by releasing a clinically relevant oxygen amount in a time-sustained manner. Here, four different types of chitosan (low or medium weight (LW or MW), glycol-(G-), and methylglycol-(MG-) chitosan) were compared as candidate biopolymers for shell manufacturing. The aim of the work was to design OLND formulations with optimized physico-chemical characteristics, efficacy in oxygen release, and biocompatibility. All OLND formulations displayed spherical morphology, cationic surfaces, ≤500 nm diameters (with LW chitosan-shelled OLNDs being the smallest), high stability, good oxygen encapsulation efficiency, and prolonged oxygen release kinetics. Upon cellular internalization, LW, MW, and G-chitosan-shelled nanodroplets did not significantly affect the viability, health, or metabolic activity of human keratinocytes (HaCaT cell line). On the contrary, MG-chitosan-shelled nanodroplets showed very poor biocompatibility. Combining the physico-chemical and the biological results obtained, LW chitosan emerges as the best candidate biopolymer for future OLND application as a skin device to treat chronic wounds.

Grafting of 18ß-Glycyrrhetinic Acid and Sialic Acid onto Chitosan to Produce a New Amphipathic Chitosan Derivative: Synthesis, Characterization, and Cytotoxicity.

Chitosan is the only cationic polysaccharide found in nature. It has broad application prospects in biomaterials, but its application is limited due to its poor solubility in water. A novel chitosan derivative was synthesized by amidation of chitosan with 18ß-glycyrrhetinic acid and sialic acid. The chitosan derivatives were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and measurement of the zeta potential. We also investigated the solubility, cytotoxicity, and blood compatibility of chitosan derivatives. 18ß-glycyrrhetinic acid and sialic acid could be grafted onto chitosan molecular chains. The thermal stability of the synthesized chitosan derivatives was decreased and the surface was positively charged in water and phosphate-buffered saline. After chitosan had been modified by 18 ß-glycyrrhetinic acid and sialic acid, the solubility of chitosan was improved greatly in water and phosphate-buffered saline, and percent hemolysis was <5%. Novel amphiphilic chitosan derivatives could be suitable polymers for biomedical purposes.

Chitin/chitosan derivatives and their interactions with microorganisms: a comprehensive review and future perspectives.

Chitosan, obtained as a result of the deacetylation of chitin, one of the most important naturally occurring polymers, has antimicrobial properties against fungi, and bacteria. It is also useful in other fields, including: food, biomedicine, biotechnology, agriculture, and the pharmaceutical industries. A literature survey shows that its antimicrobial activity depends upon several factors such as: the pH, temperature, molecular weight, ability to chelate metals, degree of deacetylation, source of chitosan, and the type of microorganism involved. This review will focus on the in vitro and in vivo antimicrobial properties of chitosan and its derivatives, along with a discussion on its mechanism of action during the treatment of infectious animal diseases, as well as its importance in food safety. We conclude with a summary of the challenges associated with the uses of chitosan and its derivatives.

Synthesis and Characterization of N,N,N-trimethyl-O-(ureidopyridinium)acetyl Chitosan Derivatives with Antioxidant and Antifungal Activities.

Chitosan is an active biopolymer, and the combination of it with other active groups can be a valuable method to improve the potential application of the resultant derivatives in food, cosmetics, packaging materials, and other industries. In this paper, a series of N,N,N-trimethyl-O-(ureidopyridinium)acetyl chitosan derivatives were synthesized. The combination of chitosan with ureidopyridinium group and quaternary ammonium group made it achieve developed water solubility and biological properties. The structures of chitosan and chitosan derivatives were confirmed by FTIR, 1H NMR spectra, and elemental analysis. The prepared chitosan derivatives were evaluated for antioxidant property by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging ability, hydroxyl radical scavenging ability, and superoxide radical scavenging ability. The results revealed that the synthesized chitosan derivatives exhibited improved antioxidant activity compared with chitosan. The chitosan derivatives were also investigated for antifungal activity against Phomopsis asparagus as well as Botrytis cinerea, and they showed a significant inhibitory effect on the selected phytopathogen. Meanwhile, CCK-8 assay was used to test the cytotoxicity of chitosan derivatives, and the results showed that most derivatives had low toxicity. These data suggested to develop analogs of chitosan derivatives containing ureidopyridinium group and quaternary ammonium group, which will provide a new kind of promising biomaterials having decreased cytotoxicity as well as excellent antioxidant and antimicrobial activity.

Quaternary Ammonium Chitosans: The Importance of the Positive Fixed Charge of the Drug Delivery Systems.

As a natural polysaccharide, chitosan has good biocompatibility, biodegradability and biosecurity. The hydroxyl and amino groups present in its structure make it an extremely versatile and chemically modifiable material. In recent years, various synthetic strategies have been used to modify chitosan, mainly to solve the problem of its insolubility in neutral physiological fluids. Thus, derivatives with negative or positive fixed charge were synthesized and used to prepare innovative drug delivery systems. Positively charged conjugates showed improved properties compared to unmodified chitosan. In this review the main quaternary ammonium derivatives of chitosan will be considered, their preparation and their applications will be described to evaluate the impact of the positive fixed charge on the improvement of the properties of the drug delivery systems based on these polymers. Furthermore, the performances of the proposed systems resulting from in vitro and ex vivo experiments will be taken into consideration, with particular attention to cytotoxicity of systems, and their ability to promote drug absorption.

Glycosylated-Chitosan Derivatives: A Systematic Review.

Chitosan derivatives, and more specifically, glycosylated derivatives, are nowadays attracting much attention within the scientific community due to the fact that this set of engineered polysaccharides finds application in different sectors, spanning from food to the biomedical field. Overcoming chitosan (physical) limitations or grafting biological relevant molecules, to mention a few, represent two cardinal strategies to modify parent biopolymer; thereby, synthetizing high added value polysaccharides. The present review is focused on the introduction of oligosaccharide side chains on the backbone of chitosan. The synthetic aspects and the effect on physical-chemical properties of such modifications are discussed. Finally, examples of potential applications in biomaterials design and drug delivery of these novel modified chitosans are disclosed.

Synthesis, characterization and anticoagulant activity of chitosan derivatives.

Chitosan derivatives are reported as anticoagulants in the literature. This work was undertaken to develop novel chitosan derivatives as anticoagulants. The sulfonated derivatives of chitosan were formed by the reaction of chitosan derivatives with chlorosulfonic acid in N,N-dimethylformamide. The structures of these derivatives were established by FTIR and 1H NMR spectra. The prepared derivatives were evaluated for their in vivo anticoagulant effects by the tail bleeding method in Wistar rats utilizing nicoumalone as a standard drug. The results revealed that the sulfonation of the chitosan increases its anticoagulant activity. The developed compounds exhibited faster onset of action and potency than nicoumalone after one hour of the drug administration. The sulphated N-alkyl derivatives of chitosan were more potent anticoagulants than sulfated quaternary derivatives/sulfated chitosan. It is also suggested to develop analogs of Ethyl chitosan sulfate (4b) and Benzyl chitosan sulfate (4c), which may provide some more fruitful anticoagulants having faster onset of action as well as longer duration of action and possessing a balanced hydrophilic/lipophilic character.

Crosslinkable-Chitosan-Enabled Moisture-Resistant Multilayer Gas Barrier Thin Film.

Chitosan-based films exhibit good oxygen barrier that degrades when exposed to high humidity. In an effort to overcome this drawback, a multilayer nanocoating consisting of crosslinkable chitosan (CHQ) and poly(acrylic acid) [PAA] is deposited on polyethylene terephthalate (PET) using layer-by-layer assembly. Chitosan is functionalized with glycidyl methacrylate to introduce acrylic functionalities within the film. The deposited films are crosslinked using a free radical initiator and this crosslinking is confirmed by FTIR and reduced film thickness. A 10-bilayer (BL) crosslinked CHQ/PAA film, which is only 165 nm thick, results in a 36× reduction of the oxygen transmission rate of PET at 90% relative humidity. To achieve these same results without crosslinking, a 15-BL unmodified chitosan (CH)/PAA film, which is almost 5× thicker, must be deposited on PET. This environmentally friendly, transparent nanocoating is promising for food packaging or protection of flexible electronics, especially in high-humidity environments.

Antibacterial, Antibiofilm, and Antiadhesive Properties of Different Quaternized Chitosan Derivatives.

In the era of antimicrobial resistance, the identification of new antimicrobials is a research priority at the global level. In this regard, the attention towards functional antimicrobial polymers, with biomedical/pharmaceutical grade, and exerting anti-infective properties has recently grown. The aim of this study was to evaluate the antibacterial, antibiofilm, and antiadhesive properties of a number of quaternized chitosan derivatives that have displayed significant muco-adhesive properties and wound healing promotion features in previous studies. Low (QAL) and high (QAH) molecular weight quaternized chitosan derivatives were synthetized and further modified with thiol moieties or pendant cyclodextrin, and their antibacterial activity evaluated as minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations (MBC). The ability of the derivatives to prevent biofilm formation was assessed by crystal violet staining. Both QAL and QAH derivatives exerted a bactericidal and/or inhibitory activity on the growth of P. aeruginosa and S. epidermidis. The same compounds also showed marked dose-dependent anti-biofilm activity. Furthermore, the high molecular weight derivative (QAH) was used to functionalize titanium plates. The successful functionalization, demonstrated by electron microscopy, was able to partially inhibit the adhesion of S. epidermidis at 6 h of incubation. The shown ability of the chitosan derivatives tested to both inhibit bacterial growth and/or biofilm formation of clinically relevant bacterial species reveals their potential as multifunctional molecules against bacterial infections.

The Importance of Reaction Conditions on the Chemical Structure of N,O-Acylated Chitosan Derivatives.

The structure of acylated chitosan derivatives strongly determines the properties of obtained products, influencing their hydrodynamic properties and thereby their solubility or self-assembly susceptibility. In the present work, the significance of slight changes in acylation conditions on the structure and properties of the products is discussed. A series of chitosan-acylated derivatives was synthesized by varying reaction conditions in a two-step process. As reaction media, two diluted acid solutions-i.e., acetic acid and hydrochloric acid)-and two coupling systems-i.e., 1-ethyl-3-(3-dimethyl-aminopropyl)-1-carbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (EDC/NHS)-were used. The chemical structure of the derivatives was studied in detail by means of two spectroscopic methods, namely infrared and nuclear magnetic resonance spectroscopy, in order to analyze the preference of the systems towards N- or O-acylation reactions, depending on the synthesis conditions used. The results obtained from advanced 1H-13C HMQC spectra emphasized the challenge of achieving a selective acylation reaction path. Additionally, the study of the molecular weight and solution behavior of the derivatives revealed that even slight changes in their chemical structure have an important influence on their final properties. Therefore, an exact knowledge of the obtained structure of derivatives is essential to achieve reaction reproducibility and to target the application.

Antimicrobial Activity of Amino-Derivatized Cationic Polysaccharides.

To improve the antimicrobial property of chitosan, water-soluble chitosan modified in their quaternary ammonium groups were synthesized. The antimicrobial properties were evaluated against Escherichia coli, Bacillus subtilis, Saccharomyces cerevisiae and Candida tropicalis. The activities increased with increasing cationic charges and the length of the alkyl chain as follows amino-chitosan, dimethylaminoethyl-chitosan, dimethylpropyl amino-chitosan, dimethylamino-1-propyl-chitosan, diethylaminoethyl (DEAE)-chitosan, and quaternized DEAE-chitosan. The modified cationic chitosans showed high antimicrobial property against B. subtilis-Gram-positive bacteria, but were less active towards yeast (C. tropicalis and S. cerevisiae) and E. coli-Gram-negative bacteria. The simple structure of the Gram-positive bacteria may explain why the cationic chitosan derivatives are more active towards B. subtilis than yeast and E. coli. The target sites of the chitosan derivatives are assumed to be the cytoplasmic membranes of microorganisms. The antimicrobial activities were strongly dependent on the cationic charge and the molecular weight. It can be suggested that these cationic chitosan derivatives have potential as antimicrobial agents.

Novel Water Soluble Chitosan Derivatives with 1,2,3-Triazolium and Their Free Radical-Scavenging Activity.

Chitosan is an abundant and renewable polysaccharide, which exhibits attractive bioactivities and natural properties. Improvement such as chemical modification of chitosan is often performed for its potential of providing high bioactivity and good water solubility. A new class of chitosan derivatives possessing 1,2,3-triazolium charged units by associating "click reaction" with efficient 1,2,3-triazole quaternization were designed and synthesized. Their free radical-scavenging activity against three free radicals was tested. The inhibitory property and water solubility of the synthesized chitosan derivatives exhibited a remarkable improvement over chitosan. It is hypothesized that triazole or triazolium groups enable the synthesized chitosan to possess obviously better radical-scavenging activity. Moreover, the scavenging activity against superoxide radical of chitosan derivatives with triazolium (IC50 < 0.01 mg mL-1) was more efficient than that of derivatives with triazole and Vitamin C. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radical-scavenging assay, the same pattern were observed, which should be related to the triazolium grafted at the periphery of molecular chains.