Design, synthesis and antimicrobial activity of 6-N-substituted chitosan derivatives

Preparation and bioactivities of chitosan nicotinamide derivatives and their application in the preservation of cherry tomatoes

Three pyridine-3-formyl chitosan derivatives were successfully prepared, and the preservation performance of the derivatives was examined. According to the results, the derivatives exhibited better antifungal and antioxidant properties than that of chitosan. At a supply concentration of 0.5 mg/mL, 2-ANACS could scavenge DPPH radicals at a rate of (92.82 ± 0.38)%. Additionally, all three derivatives exhibited less cytotoxicity and higher biocompatibility. In the freshness preservation studies of cherry tomatoes, the three derivatives considerably decreased the weight loss rate and postponed the drop in VC and titratable acid content. After 32 days of 2.0 g/L VPPCS treatment, the weight loss of cherry tomatoes was (4.0 ± 0.52) % among them. Still, the weight loss of cherry tomato in the chitosan treatment and blank control was (5.5 ± 1.33) % and (5.94 ± 1.02) %, respectively, which was considerably decreased by VPPCS therapy. These findings demonstrated that adding niacin improved chitosan's antifungal and antioxidant properties, extended the shelf life of cherry tomatoes, and increased the potential uses of chitosan and its derivatives in fruit preservation.

Synthesis of N, N,O and O-carboxymethyl chitosan derivatives of controllable substitution degrees and their utilization as electrospun scaffolds for bone tissue engineering

Most chitosan (CS) carboxymethylation approaches are weighed down by insufficient description protocols regarding the reaction specificity and the degree of substitution (DS). Here, we provide three carboxymethylation protocols of enhanced specificity towards the amine (N-), amine/hydroxy (N,O-) and hydroxy (O-) groups of CS. The DS for all samples was found to be ∼70 %, as confirmed by NMR analysis. To illustrate the modified materials' potential in bone tissue regeneration, each derivative was blended with poly(vinyl alcohol) to prepare scaffolds via electrospinning. Both materials and electrospun membranes were characterized in terms of their physicochemical properties by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry and water contact angle measurements. The electrospun membranes' swelling ratio, degradation, tensile strength, as well as morphology were also examined through scanning electron microscopy before and after heat treatment at 120 °C, which was used as a method of physical stabilization, leading to significantly enhanced degradation rate and mechanical strength. The three electrospun scaffold types were loaded with MC3T3-E1 pre-osteoblastic cells and their cell adhesion, viability and growth rate were assessed. Finally, osteogenic differentiation was examined by means of alkaline phosphatase activity measurement, calcium mineralization and formation of extracellular matrix markers, with all materials showing promising prospects.

Stability, challenges, and prospects of chitosan for the delivery of anticancer drugs and tissue regenerative growth factors

Chitosan, a biopolymer derived from chitin, offers significant potential for regulated anticancer drug administration and tissue regeneration growth factors, owing to its biocompatibility, low toxicity, biodegradability, and little immunogenicity. Moreover, its structure can be extensively modified, for example, to create scaffolds, hydrogels, nanoparticles, and membranes, allowing it to be engineered precisely to achieve specific outcomes However, the therapeutic utilisation of chitosan is impeded by significant challenges, such as its inadequate hemocompatibility, durability, and uniformity in commercial manufacturing. Additionally, there is insufficient research offering a thorough examination of the capabilities, limitations, and challenges related to chitosan as carriers for anticancer drugs and growth factors. This article examines the stability, challenges, and advanced application of chitosan as a drug carrier in anti-cancer therapy and growth factor delivery. The problems of unregulated chitosan degradation arising from unsuitable storage conditions are considered and potential solutions, and areas for future research, are proposed to deal with such problems. Consequently, this review is expected to be highly valuable for aspiring scientists studying chitosan-related systems for delivery of anti-cancer drugs and growth factors.

Water-Soluble Chitosan-Europium Hybrid Sensor for Singlet Oxygen Detection

The ability to effectively monitor singlet oxygen (1O2) with fluorescence probes in biological systems is severely restricted mainly by the background autofluorescence of these systems. Though the application of lanthanide complexes as 1O2 monitors successfully resolves this problem with time-gated luminescence measurements, the insolubility of these complexes in an aqueous medium heavily limits their application in biological systems. Here, we present a water-soluble 1O2 sensor based on a chitosan-europium hybrid material. A procedure for the modification of chitosan to expand its solubility to neutral and basic pH, while maintaining its free active amine groups, is described. These are then coupled covalently to a europium-based probe for the detection of 1O2. The resulting hybrid sensor is readily soluble in water across the pH scale and efficiently signals the presence of 1O2 at physiological pH, with the characteristic Eu3+ emission at 611 nm yielding up to a 15-fold increase in emission intensity and a decay time of 332 μs. Being of particular interest for time-gated measurements, this long decay time, coupled with the biocompatibility of chitosan, describes a material with potential biological applications, where 1O2 plays a vital role.

Improvement of antibacterial activity of polysaccharides via chemical modification: A review

Antibiotic residue and bacterial resistance induced by antibiotic abuse have seriously threatened food safety and human healthiness. Thus, the development and application of safe, high-efficiency, and environmentally friendly antibiotic alternatives are urgently necessary. Apart from antitumor, antivirus, anti-inflammatory, gut microbiota regulation, immunity improvement, and growth promotion activities, polysaccharides also have antibacterial activity, but such activity is relatively low, which cannot satisfy the requirements of food preservation, clinical sterilization, livestock feeding, and agricultural cultivation. Chemical modification not only provides polysaccharides with better antibacterial activity, but also promotes easy operation and large-scale production. Herein, the enhancement of the antibacterial activity of polysaccharides via acetylation, sulfation, phosphorylation, carboxymethylation, selenation, amination, acid graft, and other chemical modifications is reviewed. Meanwhile, a new trend on the application of loading chemically modified polysaccharides into nanostructures is discussed. Furthermore, possible limitations and future recommendations for the development and application of chemically modified polysaccharides with better antibacterial activity are suggested.

Evaluation of cytocompatibility and cell proliferation of electrospun chitosan/polyvinyl alcohol/montmorillonite clay scaffold with l929 cell lines in skin regeneration activity and in silico molecular docking studies

The present investigation describes the development of a novel Chitosan/Polyvinyl Alcohol/Montmorillonite Clay (CS/PVA/MMT) scaffold by adopting an electrospinning method, and their biocompatibility was evaluated in vitro with L929 fibroblast cell line to ascertain its use in wound healing applications. The fabricated scaffold was characterized using analytical techniques. FT-IR measurement exhibited the existence of relevant functional groups and XRD implies scaffolds' amorphous nature. The scaffold's morphology and pore diameter were assessed using TEM and SEM. The pore diameter of the as-prepared scaffold was approximately 125 nm. The antimicrobial assay of the scaffold was evaluated against selected pathogens which demonstrated higher antimicrobial efficacy. The scavenging activity tested using the DPPH assay showed remarkable scavenging capability. The wound healing properties were tested through the Cytotoxicity assay conducted on the L929 assay which proved the scaffold to be a suitable material for cell proliferation. Also, a Molecular docking investigation was carried out for CS/PVA/MMT ligand using human neutrophil elastase (HNE) 1H1B protein as a receptor in the CB-Dock server. Studies conducted in silico revealed strong interaction and high binding energy ratings of CS/PVA/MMT ligand with key residues of human neutrophil elastase (HNE) 1H1B proteins that help in tissue regeneration activity.

Regioselective modification at the 2,3- and 6-positions of chitosan with phenylcarbamates for chromatographic enantioseparation

Chitosan derivatives with two different phenylcarbamate pendants at the 6-position and 2,3-positions of the glucosamine unit were synthesized by triphenylmethyl as a protective group. The regioselective chitosan derivatives were prepared corresponding to coated-type chiral packed materials (CPMs), which were evaluated with thirteen chiral compounds by high-performance liquid chromatography (HPLC). The regioselective chitosan derivatives (4aⅠ/4aⅡ, 4bⅠ/4bⅡ) bearing electron-withdrawing 3,5‑chloro or 4‑chloro at the 6-position can recognize 7 or 8 of the 13 enantiomers and achieve baseline separation for enantiomers 5 and 7. They exhibited better chiral recognition abilities than the other derivatives with different substituents at the 6-position and the same 3,5-dimethylphenyl substituent at the 2,3-postion. In comparison to Chit-1 featuring a 3,5-dimethylphenyl substituent at the 2,3- and 6-positions, it was observed that the combination of both an electron-withdrawing and an electron-donating substituent of the regioselective chitosan derivatives (4aⅠ/4aⅡ, 4bⅠ/4bⅡ) showed better or similar enantioseparation abilities for racemic Compounds 7 and 6, respectively. The molecular weight-performance relationship of the regioselective chitosan derivatives was investigated in detail. It was found that with increasing molecular weight, the derivatives 4aⅡ and 4bⅡ all possessed greater enantioseparation power for 4 enantiomers, such as enantiomers 4, 7, 11, and 15, than the corresponding derivatives with low molecular weights. The molecular docking simulation results showed that excellent enantioseparation power significantly depended on the combination and interaction of multiple factors, such as steric hindrance, and polarity of the substituents on the CPMs and enantiomers.

Chitosan-based Schiff bases: Promising materials for biomedical and industrial applications

There is plenty of scope for modifying chitosan, an only polycationic natural polysaccharide, owing to its reactive functional groups, namely hydroxyl and amino groups. Although innumerable numbers of chitosan derivatives have been synthesized by modifying these groups and reported elsewhere, in this review article, an attempt has been exclusively made to demonstrate the syntheses of various chitosan-based Schiff bases (CSBs) simply by allowing the reactions of reactive amino groups of chitosan with different aldehydes/ketones of interest. Due to their very peculiar and unique characteristics, such as biodegradability, biocompatibility, metal-binding capability, etc., they are found to be very useful for diversified applications. Thus, we have also attempted to showcase their very specific biomedical fields, including tissue engineering, drug delivery, and wound healing, to name a few. In addition, we have also discussed the utilization of CSBs for industrial applications such as wastewater treatment, catalysis, corrosion inhibition, sensors, etc.

6-deoxy-6-amino chitosan: a preventative treatment in the tomato/Botrytis cinerea pathosystem

6-deoxy-6-amino chitosan (aminochitosan) is a water-soluble chitosan derivative with an additional amine group at the C-6 position. This modification has improved aqueous solubility, in vitro antifungal activity and is hypothesized to have enhanced in vivo antifungal activity compared to native chitosan. Gray mold disease in tomatoes is caused by the fungus, Botrytis cinerea, and poses a severe threat both pre- and post-harvest. To investigate the optimal concentration of aminochitosan and its lower molecular weight fractions for antifungal and priming properties in the tomato/B. cinerea pathosystem, different concentrations of aminochitosan were tested in vitro on B. cinerea growth and sporulation and in vivo as a foliar pre-treatment in tomato leaves. The leaves were monitored for photosynthetic changes using multispectral imaging and hydrogen peroxide accumulation using DAB. Despite batch-to-batch variations in aminochitosan, it displayed significantly greater inhibition of B. cinerea in vitro than native chitosan at a minimum concentration of 1 mg/mL. A concentration-dependent increase in the in vitro antifungal activities was observed for radial growth, sporulation, and germination with maximum in vitro inhibition for all the biopolymer batches and lower MW fractions at 2.5 and 5 mg/mL, respectively. However, the inhibition threshold for aminochitosan was identified as 1 mg/mL for spores germinating in vivo, compared to the 2.5 mg/mL threshold in vitro. The pre-treatment of leaves displayed efficacy in priming direct and systemic resistance to B. cinerea infection at 4, 6 and 30 days post-inoculation by maintaining elevated Fv/Fm activity and chlorophyll content due to a stronger and more rapid elicitation of the defense systems at earlier time points. Moreover, these defense systems appear to be ROS-independent at higher concentrations (1 and 2.5 mg/mL). In addition, aminochitosan accumulates in the cell membrane and therefore acts to increase the membrane permeability of cells after foliar spray. These observations corroborate the notion that aminochitosan biopolymers can exert their effects through both direct mechanisms of action and indirect immunostimulatory mechanisms. The contrast between in vitro and in vivo efficacy highlights the bimodal mechanisms of action of aminochitosan and the advantageous role of primed plant defense systems.

Antibacterial and antioxidant properties of phenolic acid grafted chitosan and its application in food preservation: A review

Chitosan is a bio-renewable natural polymeric material. The antibacterial and antioxidant activity of chitosan can be enhanced by grafting with phenolic acids to further expand its application in food. Therefore, this paper focuses on reviewing the structure, antimicrobial and antioxidant activities and their mechanisms with phenolic acid-g-CS, evaluating its cytotoxicity, and describing its application in various food preservation. In general, different reaction mechanisms of phenolic acid-g-CS synthesis lead to different product structures. Compared to chitosan, phenolic acid-g-chitosan exhibited enhanced antibacterial and antioxidant activities. The toxicity assessment showed that phenolic acid-g-CS is not cytotoxic. Moreover, phenolic acid-g-CS has been applied to a variety of food products such as fruits, vegetables and meat with good results. Overall, this review provides a certain reference for subsequent researchers to design phenolic acid-g-CS more rationally and for the subsequent development of phenolic acid-g-CS in food preservation.

Synthesis, characterization, and biological evaluation of new chitosan derivative bearing diphenyl pyrazole moiety

This work reports the synthesis of a new pyrazole derivative by reacting 5-amino-1,3-diphenyl pyrazole with succinic anhydride and bearing the product chemically on the chitosan chains via amide linkage to achieve a new chitosan derivative (DPPS-CH). The prepared chitosan derivative was analyzed by IR, NMR, elemental analysis, XRD, TGA-DTG, and SEM. As compared with chitosan, DPPS-CH showed an amorphous and porous structure. Coats-Redfern results showed that the thermal activation energy for the first decomposition of DPPS-CH is 43.72 KJ mol^-1 lower than that required for chitosan (88.32 KJ mol^-1), indicating the accelerating effect of DPPS on the thermal decomposition of DPPS-CH. The DPPS-CH manifested a powerful wide spectrum antimicrobial potential against pathogenic gram-positive and gram-negative bacteria and Candida albicans at minute concentrations (MIC = 50 μg mL^-1) compared to chitosan (MIC = 100 μg mL^-1). The MTT assay proved the toxic properties of DPPS-CH against a cancer cell line (MCF-7) at a minute concentration (IC50 = 15.14 μg mL^-1) while affecting normal cells (WI-38) at seven times this concentration (IC50 = 107.8 μg mL^-1). According to the current findings, the chitosan derivative developed in this work appears to be a promising material for use in biological domains.

Preparation and characterization of PVA/arginine chitosan/ZnO NPs composite films

In this study, arginineated chitosan (ACS) was used as a soft brain membrane and chelating agent to synthesize ACS-ZnO NPs, and then ACS and ACS-ZnO NPs were added to a polyvinyl alcohol (PVA) matrix as an antimicrobial agent to form films by casting. The formation and structural morphology of ACS and ACS-ZnO NPs were investigated by applying FTIR, 1H NMR, XRD, EDS, SEM, and TEM techniques, and ACS has shown better water solubility. The cytotoxicity experiments of ACS and ACS-ZnO NPs on A549 cells showed that both had good cytocompatibility. The incorporation of ACS and ACS-ZnO NPs improves the composite film's mechanical properties, water barrier, and oxygen barrier and exhibits excellent antibacterial activities against S. aureus and E. coli. More importantly, in addition to extending the shelf life of cherry tomatoes, the composite film is also biodegradable to some degree. Therefore, polyvinyl alcohol films based on ACS and ACS-ZnO NPs added as antimicrobial agents have great potential for food packaging applications.

New thiadiazole modified chitosan derivative to control the growth of human pathogenic microbes and cancer cell lines

The emergence of multidrug-resistant microbes and the propagation of cancer cells are global health issues. The unique properties of chitosan and its derivatives make it an important candidate for therapeutic applications. Herein, a new thiadiazole derivative, 4-((5-(butylthio)-1,3,4-thiadiazol-2-yl) amino)-4-oxo butanoic acid (BuTD-COOH) was synthesized and used to modify the chitosan through amide linkages, forming a new thiadiazole chitosan derivative (BuTD-CH). The formation of thiadiazole and the chitosan derivative was confirmed by FT-IR, ¹H/¹³C-NMR, GC-MS, TGA, Elemental analysis, and XPS. The BuTD-CH showed a high antimicrobial effect against human pathogens Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, and Candida albicans with low MIC values of 25-50 μg ml^-1 compared to unmodified chitosan. The in-vitro cytotoxicity of BuTD-CH was evaluated against two cancer cell lines (MCF-7 and HepG2) and one normal cell (HFB4) using the MTT method. The newly synthesized derivatives showed high efficacy against cancerous cells and targeted them at low concentrations (IC₅₀ was 178.9 ± 9.1 and 147.8 ± 10.5 μg ml^-1 for MCF-7 and HepG2, respectively) compared with normal HFB4 cells (IC₅₀ was 335.7 ± 11.4 μg ml^-1). Thus, low concentrations of newly synthesized BuTD-CH could be safely used as an antimicrobial and pharmacological agent for inhibiting the growth of human pathogenic microbes and hepatocellular and adenocarcinoma therapy.

Characterisation of products from EDC-mediated PEG substitution of chitosan allows optimisation of reaction conditions

PEGylation is a common method use to modify the physiochemical properties and increase the solubility of chitosan (CHI). Knowledge of optimal reaction conditions for PEGylation of CHI underpins its ongoing use in nanomedicine. This study synthesised methoxy polyethylene glycol grafted CHI (mPEG-CHI) using carbodiimide-mediated coupling. The effect of reagent concentrations and pH on the degree of substitution (DS) and the PEGylation yield (conversion of free PEG to conjugated PEG) was evaluated through detailed chemical characterisation. Within the parameter space investigated, optimised reaction conditions (NH₂: COOH:NHS:EDC of 3.5:1:1:10, pH = 5) resulted in a DS of 24 % and a PEGylation yield of 84 %. An EDC-derived adduct formed at pH ≥ 5.5 and a at 15-fold excess of EDC relative to COOH. The adduct was evaluated to be a guanidine derivative formed by the reaction of the amine group of CHI directly with EDC. DS ≥ 12 imparted water solubility to CHI at physiological pH and mPEG-CHI (0.2-1.0 mg/mL) was not cytotoxic against the breast cancer cell lines MCF-7 and MDA-MB-231, indicating its suitability for medical applications.

Water-soluble amino functionalized chitosan: Preparation, characterization, antioxidant and antibacterial activities

Amino functionalized chitosan has attracted much attention because of the fascinated bioactivities. In our study, a novel water-soluble amino functionalized chitosan bearing free amino group at C-2 and quaternary ammonium moiety contained free amino group at C-6 (5c) was prepared by a four-step method. The structural characterization was identified by FTIR and ¹H NMR spectroscopy. The water-solubility and antioxidant activities against hydroxyl, DPPH radicals and reducing power were estimated. The results displayed that amino functionalized chitosan 5c exhibited improved water-solubility and antioxidant ability, especially its DPPH scavenging rate reached about 90 % at the minimum test concentration of 0.10 mg/mL. Besides, antibacterial tests showed that amino functional chitosan 5c had best antibacterial activities, which indicated that amino group made main contribution to the enhanced bioactivities. In short, the novel chitosan 5c possessed enhanced water-solubility and excellent antioxidant and antibacterial activities, which could provide novel strategy for the development of antioxidant and antibacterial agents in biomedicine and food fields.

Novel Chitosan Derivatives and Their Multifaceted Biological Applications

Chitosan is a rather attractive material, especially because of its bio-origins as well as generation from exoskeletal waste. As the mantle has been effectively transferred from chitin to chitosan, so has it been extrapolated to in-house synthesized novel chitosan derivatives. This review comprehensively lists the available novel chitosan derivatives (ChDs) and summarizes their biological applications. The fact that chitosan derivatives do comprise multifaceted biological applications is attested by the voluminous reports on their varied contributions. However, this review points out to the fact that there has been selective focus on bio functions such as antifungal, antioxidant, antibacterial, whereas other biomedical applications and antiviral applications remain relatively less explored. With their current functionality record, there is definitely no doubt that the plethora of synthesized ChDs will have a profound impact on the unexplored biological aspects. This review points out this lacuna as room for future exploration.

General Characteristics, Biomedical and Dental Application, and Usage of Chitosan in the Treatment of Temporomandibular Joint Disorders: A Narrative Review

The aim of this narrative review was to present research investigating chitosan, including its general characteristics, properties, and medical and dental applications, and finally to present the current state of knowledge regarding the efficacy of chitosan in the treatment of temporomandibular disorders (TMDs) based on the literature. The PICO approach was used for the literature search strategy. The PubMed database was analyzed with the following keywords: (“chitosan”[MeSH Terms] OR “chitosan”[All Fields] OR “chitosans”[All Fields] OR “chitosan s”[All Fields] OR “chitosane”[All Fields]) AND (“temporomandibular joint”[MeSH Terms] OR (“tem-poromandibular”[All Fields] AND “joint”[All Fields]) OR “temporomandibular joint”[All Fields] OR (“temporomandibular”[All Fields] AND “joints”[All Fields]) OR “temporo-mandibular joints”[All Fields]). After screening 8 results, 5 studies were included in this review. Chitosan presents many biological properties and therefore it can be widely used in several branches of medicine and dentistry. Chitosan promotes wound healing, helps to control bleeding, and is used in wound dressings, such as sutures and artificial skin. Apart from its antibacterial property, chitosan has many other properties, such as antifungal, mucoadhesive, anti-inflammatory, analgesic, antioxidant, antihyperglycemic, and antitumoral properties. Further clinical studies assessing the efficacy of chitosan in the treatment of TMD are required. According to only one clinical study, chitosan was effective in the treatment of TMD; however, better clinical results were obtained with platelet-rich plasma.

Chitosan Natural Polymer Material for Improving Antibacterial Properties of Textiles

In recent years, the textile industry has been seeking to develop innovative products. It is a good choice to organically combine materials with superior functional characteristics and commercial textiles to form products with excellent performance. In particular, textiles made of biological functional materials are often beneficial to human health, which is an interesting research direction. As a biopolymer material, chitosan has the advantages of strong availability, low cost, excellent safety, outstanding performance, etc., particularly the antibacterial property, and has broad application prospects in the textile field. This review provides an overview of the latest literature and summarizes recent innovations and state-of-the-art technologies that can add value to textiles. To this end, preparation of chitosan fiber, synthesis of chitosan nanofiber, antibacterial activity of chitosan fiber, antibacterial activity of chitosan nanofiber, etc., will be discussed. Furthermore, the challenges and prospects of chitosan-based materials used in textiles are evaluated. Importantly, this review can not only help researchers understand the development status of antibacterial textiles, but also help researchers discover and solve problems in this field through comparative reading.

Phenolic-containing chitosan quaternary ammonium derivatives and their significantly enhanced antioxidant and antitumor properties

A class of phenolic-chitosan quaternary ammonium derivatives have been designed and synthesized. Three chitosan derivatives possess effective structure of hydroxycinnamic acid have been obtained through chemical modification to get chitosan derivatives owning high antioxidant activity and antitumor activity. In this study, the scavenging ability of DPPH, hydroxyl (•OH), and superoxide (O²•-) free radical and reducing power have been tested to evaluate the antioxidant activity of the synthesized chitosan derivatives. Base on the value of IC₅₀, the chitosan derivatives have the best inhibitory property of 0.019 mg/mL (DPPH), 0.016 mg/mL (•OH), and 0.008 (O²•-), respectively; and the chitosan derivatives with conjugate structure of ferulic acid and sinapic acid (4b and 4c) show promising antitumor activity toward A549 cells with the IC₅₀ of 0.046 and 0.052 mg/mL. These data indicate that the chitosan derivatives with phenolic group give much stronger antioxidant activity and antitumor activity. On the other hand, the synthesized chitosan derivatives show no cytotoxicity for L929 cells at the testing concentrations. These results demonstrate that the introduction of phenol group improves the antioxidant activity of chitosan obviously, and the antioxidant or free radical scavenger based on nature polymers and phenol shows potentials application.

Chitosan: A Natural Biopolymer with a Wide and Varied Range of Applications

Although chitin is of the most available biopolymers on Earth its uses and applications are limited due to its low solubility. The deacetylation of chitin leads to chitosan. This biopolymer, composed of randomly distributed β-(1-4)-linked D-units, has better physicochemical properties due to the facts that it is possible to dissolve this biopolymer under acidic conditions, it can adopt several conformations or structures and it can be functionalized with a wide range of functional groups to modulate its superficial composition to a specific application. Chitosan is considered a highly biocompatible biopolymer due to its biodegradability, bioadhesivity and bioactivity in such a way this biopolymer displays a wide range of applications. Thus, chitosan is a promising biopolymer for numerous applications in the biomedical field (skin, bone, tissue engineering, artificial kidneys, nerves, livers, wound healing). This biopolymer is also employed to trap both organic compounds and dyes or for the selective separation of binary mixtures. In addition, chitosan can also be used as catalyst or can be used as starting molecule to obtain high added value products. Considering these premises, this review is focused on the structure and modification of chitosan as well as its uses and applications.

Cationic chitosan derivatives as potential antifungals: A review of structural optimization and applications

The increasing resistance of pathogen fungi poses a global public concern. There are several limitations in current antifungals, including few available fungicides, severe toxicity of some fungicides, and drug resistance. Therefore, there is an urgent need to develop new antifungals with novel targets. Chitosan has been recognized as a potential antifungal substance due to its good biocompatibility, biodegradability, non-toxicity, and availability in abundance, but its applications are hampered by the low charge density results in low solubility at physiological pH. It is believed that enhancing the positive charge density of chitosan may be the most effective approach to improve both its solubility and antifungal activity. Hence, this review mainly focuses on the structural optimization strategy of cationic chitosan and the potential antifungal applications. This review also assesses and comments on the challenges, shortcomings, and prospect of cationic chitosan derivatives as antifungal therapy.

Antimicrobial Chitosan Conjugates: Current Synthetic Strategies and Potential Applications

As a natural polysaccharide, chitosan possesses good biocompatibility, biodegradability and biosafety. Its hydroxyl and amino groups make it an ideal carrier material in the construction of polymer-drug conjugates. In recent years, various synthetic strategies have been used to couple chitosan with active substances to obtain conjugates with diverse structures and unique functions. In particular, chitosan conjugates with antimicrobial activity have shown great application prospects in the fields of medicine, food, and agriculture in recent years. Hence, we will place substantial emphasis on the synthetic approaches for preparing chitosan conjugates and their antimicrobial applications, which are not well summarized. Meanwhile, the challenges, limitations, and prospects of antimicrobial chitosan conjugates are described and discussed.

Preparation, characterization and antibacterial properties of 6-deoxy-6-arginine modified chitosan

In this study, 6-deoxy-6-arginine modified chitosan (DAC), was synthesized and characterized by Fourier Transform Infrared Spectroscopy (FTIR), ¹H and ¹³C nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and elemental analysis. The arginine was grafted onto C6 groups of chitosan. Antibacterial activity of DAC against gram-negative bacteria Escherichia coli (E. coli) and gram-positive bacteria Staphylococcus aureus (S. aureus) were investigated at concentration between 0.02 mg/mL and 10 mg/mL. Cell viability assessment was estimated in vitro with Caco-2 and L929 cells. Water solubility of DAC at different pH was also evaluated. The results showed that the minimum inhibitory concentration (MICs) of DAC against S. aureus and E. coli were 0.078 mg/mL and 0.312 mg/mL, respectively. The minimum bactericidal concentration (MBC) against S. aureus and E. coli was 0.625 mg/mL. The cytotoxicity of chitosan and DAC was not significantly different. It demonstrated that DAC might be a potential safe antibacterial agent.

Radical Scavenging Activities of Novel Cationic Inulin Derivatives

Many saccharides are attractive targets for biomaterial applications, due to their abundance, biocompatibility, and biodegradability. In this article, a synthesis process of 6-N-substituted cationic inulin derivatives, including 6-pyridyl-6-deoxyinulin bromide (PIL), 6-(2-amino-pyridyl)-6-deoxyinulin bromide (2APIL), 6-(3-amino-pyridyl)-6-deoxyinulin bromide (3APIL), 6-(4-amino-pyridyl)-6-deoxyinulin bromide (4APIL), 6-(2,3-diamino-pyridyl)-6-deoxyinulin bromide (2,3DAPIL), 6-(3,4-diamino-pyridyl)-6-deoxyinulin bromide (3,4DAPIL), and 6-(2,6-diamino-pyridyl)-6-deoxyinulin bromide (2,6DAPIL) was described. The C₆-OH of inulin was first activated by PPh₃/N-bromosuccinimide (NBS) bromination. Then, pyridine and different kinds of amino-pyridine groups (different position and different numbers of amino) were grafted onto inulin, respectively, via nucleophilic substitution. Then, we confirmed their structure by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. After this, their radical scavenging activities against hydroxyl radical and diphenylpicryl phenylhydrazine (DPPH) radical were tested in vitro. Each derivative showed a distinct improvement in radical scavenging activity when compared to inulin. The hydroxyl-radical scavenging effect decreased in the following order: 3APIL > PIL > 3,4DAPIL > 4APIL > 2,3DAPIL > 2,6DAPIL > 2APIL. Amongst them, 3APIL revealed the most powerful scavenging effect on hydroxyl radicals, as well as DPPH radicals. At 1.6 mg/mL, it could completely eliminate hydroxyl radicals and could clear 65% of DPPH radicals. The results also showed that the steric hindrance effect and the substitute position of the amino group had an effect on the radical scavenging activity. Moreover, the application prospects of inulin derivatives as natural antioxidant biomaterials are scientifically proven in this paper.

Synthesis of Novel Chitin Derivatives Bearing Amino Groups and Evaluation of Their Antifungal Activity

Chemical modification is one of the most effective methods to improve the biological activity of chitin. In the current study, we modified C3-OH and C6-OH of chitin (CT) and successfully synthesized 6-amino-chitin (NCT) and 3,6-diamino-chitin (DNCT) through a series of chemical reactions. The structure of NCT and DNCT were characterized by elemental analyses, FT-IR, 13C NMR, XRD, and SEM. The inhibitory effects of CT, NCT, and DNCT against six kinds of phytopathogen (F. oxysporum f. sp. cucumerium, B. cinerea, C. lagenarium, P. asparagi, F. oxysporum f. niveum, and G. zeae) were evaluated using disk diffusion method in vitro. Meanwhile, carbendazim and amphotericin B were used as positive controls. Results revealed that 6-amino-chitin (NCT) and 3,6-diamino-chitin (DNCT) showed improved antifungal properties compared with pristine chitin. Moreover, DNCT exhibited the better antifungal property than NCT. Especially, while the inhibition zone diameters of NCT are ranged from 11.2 to 16.3 mm, DNCT are about 11.4⁻20.4 mm. These data demonstrated that the introduction of amino group into chitin derivatives could be key to increasing the antifungal activity of such compounds, and the greater the number of amino groups in the chitin derivatives, the better their antifungal activity was.

Characterization and antibacterial mechanism of poly(aminoethyl) modified chitin synthesized via a facile one-step pathway

This work aims to synthesize poly(aminoethyl) modified chitin (PAEMC) and ascertain its antibacterial activity and mechanism. FTIR and ¹H NMR results proved aminoethyl moieties were grafted to C6OH and C3OH on chitin backbone in the form of polymerization. XRD and TG/DTG analyses manifested its well-defined crystallinity and thermostability. PAEMC, with average molecular weight (MW) of 851.0 kDa, degree of deacetylation (DD) of 27.95%, and degree of substitution (DS) of 1.77, had good solubility in aqueous solutions over the pH range of 3-12, and also possessed high antimicrobial activity against Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Bacillus proteus, and Klebsiella pneumoniae, commonly causing chronic wound infections. Nucleic acid release, protein leakage, increased inner membrane permeability, and decreased cell surface hydrophobicity implied bacterial cytomembranes were substantially compromised in the presence of PAEMC. Microscopically, PAEMC visually perturbed bacteria, illustrating deformed and even collapsed morphologies. Overall, PAEMC possessed good solubility, effectively destroyed bacteria via a membrane damage mechanism, and might serve as an antibacterial agent for treatments of chronic wound infections.

Synthesis, characterization, and antifungal evaluation of diethoxyphosphoryl polyaminoethyl chitosan derivatives

Botrytis cinerea, Phytophthora capsici Leonian, and Fusarium solani are important plant pathogenic fungi which can cause great crop losses worldwide, but their control methods are limited. It is necessary to develop efficient and green fungicides from abundant marine resources. Chitosan is a non-toxic, biodegradable, biocompatible marine polysaccharide which has prospective applications in agriculture. In this paper, to increase the antifungal activity of chitosan for application, novel water-soluble functional chitosan derivatives were synthesized by grafting polyaminoethyl and diethoxyphosphoryl groups in accordance with a strategy of improving protonation potential. The derivatives were characterized by FTIR, NMR, XRD, SEM, Gaussian 09 and elemental analysis. The antifungal activities against the three fungi and the cytotoxicity were estimated in vitro. The results showed that the derivatives had better antifungal activities and water solubility than chitosan, and had good biocompatibility. They confirmed that these chitosan derivatives can be developed as antifungal agents for plant protection purposes.

Microwave Assisted Preparation of Antimicrobial Chitosan with Guanidine Oligomers and Its Application in Hygiene Paper Products

Guanidinylated chitosan (GCS) was prepared by grafting guanidine oligomers onto chitosan under microwave irradiation. The structure of GCS characterized by FT-IR and ¹H NMR verified the covalent bonding between the guanidine oligomers and chitosan; the effects of molar ratio, reaction temperature, and time were investigated and the degree of substitution of GCS reached a maximum of 25.5% under optimized conditions in this work. The resulting GCS showed significantly enhanced antimicrobial activities. The results obtained from the dynamic UV absorption of Escherichia coli (E. coli) and atomic force microscopy (AFM) revealed that the deactivation of E. coli by GCS was due to the destructing of the cell membrane and the prompt release of cytoplasm from the bacterial cells. The adsorption of GCS onto cellulose fibers and the antimicrobial efficiency of the hygiene papers with GCS were also investigated. Microwave irradiation as a green assisted method was applied to promote this reaction. This facile approach allowed chitosan to be guanidinylated without tedious preparation procedures and thus broadened its application as a biocompatible antimicrobial agent.

Preparation, characterization, and evaluation of 3,6-O-N-acetylethylenediamine modified chitosan as potential antimicrobial wound dressing material

This work aims to prepare 3,6-O-N-acetylethylenediamine modified chitosan (AEDMCS) and evaluate its potential use as an antimicrobial wound dressing material. UV, FTIR, and ¹H NMR results demonstrated N-acetylethylenediamine groups were successfully grafted to C3OH and C6OH on polysaccharide skeletons. TGA, XRD, and solubility tests indicated that as compared with chitosan, AEDMCS had diminished thermostability, decreased crystallinity, and greatly improved solubility. AEDMCS, with degrees of deacetylation and substitution being respectively 90.3% and 0.72, exhibited higher antibacterial activity than chitosan against six bacteria generally causing wound infections. Meanwhile, AEDMCS had permissible hemolysis and cytotoxicity and low BSA adsorption even at a AEDMCS concentration of 25mg/mL. Acute toxicity tests showed AEDMCS was nontoxic. Moreover, the wound healing property was preliminarily evaluated, illustrating that AEDMCS enhanced wound healing rates as expected and had no significant differences as compared with chitosan. These results suggested AEDMCS might be a potential material used as antibacterial wound dressings.