Chitosan (CS) is an abundant and renewable polysaccharide that is reported to exhibit a great variety of beneficial properties. However, the poor solubility of chitosan in water limits its applications. In this paper, we successfully synthesized single N-quaternized (QCS) and double N-diquaternized (DQCS) chitosan derivatives, and the resulting quaternized materials were water-soluble. The degree of quaternization (DQ) of QCS and DQCS was 0.8 and 1.3, respectively. These derivatives were characterized by FTIR, ¹H NMR, ¹³C NMR, TGA, and SEM. Moreover, the antioxidant activity of the chitosan was evaluated by free radical scavenging ability (against DPPH-radical, hydroxyl-radical, and superoxide-radical) and ferric reducing power. Our results suggested that the antioxidant abilities were in the order of DQCS > QCS > CS, which was consistent with the number of quaternized groups. These data demonstrate that the number of quaternized groups of chitosan derivatives contributes to their antioxidant activity. Therefore, DQCS, with a higher number of quaternized groups and higher positive charge density, is endowed with high antioxidant activity, and can be used as a candidate material in food and pharmaceutical industries.

Hydrogels, possessing high biocompatibility and adaptability to biological tissue, show great usability in medical applications. In this research, a series of novel cross-linked chitosan quaternary ammonium salt loading with gentamicin sulfate (CTMCSG) hydrogel films with different cross-linking degrees were successfully obtained by the reaction of chitosan quaternary ammonium salt (TMCS) and epichlorohydrin. Fourier transform infrared spectroscopy (FTIR), thermal analysis, and scanning electron microscope (SEM) were used to characterize the chemical structure and surface morphology of CTMCSG hydrogel films. The physicochemical property, gentamicin sulphate release behavior, cytotoxicity, and antibacterial activity of the CTMCSG against Escherichia coli and Staphylococcus aureus were determined. Experimental results demonstrated that CTMCSG hydrogel films exhibited good water stability, thermal stability, drug release capacity, as well as antibacterial property. The inhibition zone of CTMCSG hydrogel films against Escherichia coli and Staphylococcus aureus could be up to about 30 mm. Specifically, the increases in maximum decomposition temperature, mechanical property, water content, swelling degree, and a reduction in water vapor permeability of the hydrogel films were observed as the amount of the cross-linking agent increased. The results indicated that the CTMCSG-4 hydrogel film with an interesting physicochemical property, admirable antibacterial activity, and slight cytotoxicity showed the potential value as excellent antibacterial wound dressing.

Chemical modification of chitosan is increasingly studied for its potential of providing new applications of chitosan. Here, a group of novel chitosan quaternary ammonium derivatives containing pyridine or amino-pyridine were designed and successfully synthesized through chemical modification of chitosan. Pyridine and amino-pyridine were used as functional groups to improve the antifungal activity of chitosan derivatives. The chitosan derivatives’ antioxidant activity against hydroxyl-radical and 1,1-Diphenyl-2-picrylhydrazyl (DPPH)-radical was tested in vitro. The results showed that chitosan derivatives had better water solubility and stronger antioxidant activity compared with chitosan in all assays. Especially, compounds 3C and 3E (with 3-amino pyridine and 2,3-diamino pyridine as substitute respectively) exhibited stronger hydroxyl-radical and DPPH-radical scavenging ability than other synthesized compounds. These data demonstrated that the synergistic effect of the amino group and pyridine would improve the antioxidant activity of chitosan derivatives, and the position of the amino group on pyridine could influence the antioxidant property of chitosan derivatives.

Chitosan is an abundant and renewable polysaccharide, its derivatives exhibit attractive bioactivities and the wide applications in various biomedical fields. In this paper, two novel cationic chitosan derivatives modified with quaternary phosphonium salts were successfully synthesized via trimethylation, chloride acetylation, and quaternization with tricyclohexylphosphine and triphenylphosphine. The structures and properties of synthesized products in the reactions were characterized by FTIR spectroscopy, ¹H-NMR, ³¹P-NMR, elemental and thermogravimetric analysis. The antifungal activities of chitosan derivatives against four kinds of phytopathogens, including Phomopsis asparagi, Watermelon fusarium, Colletotrichum lagenarium, and Fusarium oxysporum were tested using the radial growth assay in vitro. The results revealed that the synthesized cationic chitosan derivatives showed significantly improved antifungal efficiency compared to chitosan. It was reasonably suggested that quaternary phosphonium groups enabled the obviously stronger antifungal activity of the synthesized chitosans. Especially, the triphenylphosphonium-functionalized chitosan derivative inhibited the growth of Phomopsis asparagi most effectively, with inhibitory indices of about 80% at 0.5 mg/mL. Moreover, the data demonstrated that the substituted groups with stronger electron-withdrawing ability relatively possessed greater antifungal activity. The results suggest the possibility that cationic chitosan derivatives bearing quaternary phosphonium salts could be effectively employed as novel antifungal biomaterials for application in the field of agriculture.

In this paper, quaternary ammonium salts of chitosan bearing halogenated acetate, including N,N,N-trimethyl chitosan chloroacetate (TMCSC), N,N,N-trimethyl chitosan dichloroacetate (TMCSDC), N,N,N-trimethyl chitosan trichloroacetate (TMCSTC), and N,N,N-trimethyl chitosan trifluoroacetate (TMCSTF), were prepared via N,N,N-trimethyl chitosan iodide (TMCSI). The obtained chitosan derivatives were characterized by FT-IR, ¹H NMR spectra, ¹³C NMR spectra, and elemental analysis. Their antifungal property against Fusarium oxysporum f. sp. cucumebrium Owen (F. oxysporum f. sp. cucumebrium Owen), Botrytis cinerea (B. cinerea), and Phomopsis asparagi (P. asparagi) were evaluated by hyphal measurement method at concentrations ranging from 0.08 mg/mL to 0.8 mg/mL. Meanwhile, two common bacteria, Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), were selected as the model Gram-negative and Gram-positive bacteria to evaluate the antibacterial property of the chitosan derivatives by agar well diffusion method. The results showed that TMCSC, TMCSDC, TMCSTC, and TMCSTF had better antifungal and antibacterial activities than chitosan and TMCSI. In particular, a rule showed that the inhibitory activity decreased in the order: TMCSTF > TMCSTC > TMCSDC > TMCSC > TMCSI > chitosan, which was consistent with the electron-withdrawing property of different halogenated acetate. Apparently, the quaternary ammonium salts of chitosan with stronger electron withdrawing ability possessed relatively greater antifungal and antibacterial activities. This experiment provides a potentially feasible method for the further utilization of chitosan in fields of antifungal and antibacterial biomaterials.

With the specialty of improving the water solubility of chitosan, quaternary ammonium salts have broadened the application of this polysaccharide in food, medicine and pesticides. To identify the effect of quaternary ammonium salts’ quantity, single quaternized chitosan N-phenmethyl-N,N-dimethyl chitosan (PDCS), double quaternized chitosan N-(1-pyridylmethyl-2-ylmethyl)-N,N-dimethyl chitosan (MP2MDCS), N-(1-pyridylmethyl-3-ylmethyl)-N,N-dimethyl chitosan (MP3MDCS), and N-(1-pyridylmethyl-4-ylmethyl)-N,N-dimethyl chitosan (MP4MDCS) were designed and synthesized successfully through chemical modification of chitosan. Besides, three kinds of antioxidant activities, including hydroxyl radicals, superoxide radicals, and 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radicals were tested in vitro. As shown in this paper, the scavenging ability was ranking in order of MP3MDC > MP4MDCS > MP2MDCS > PDCS > chitosan at 1.6 mg/mL in all assays. All double quaternary ammonium salts were better than chitosan or the single quaternary ammonium salt. In addition, MP3MDCS could scavenge hydroxyl radicals totally at 1.6 mg/mL. MP2MDCS and MP4MDCS with more than 90% scavenging indices both had great scavenging ability on hydroxyl radicals or DPPH radicals. Furthermore, these data demonstrated that the increasing number of the positive charge would improve the antioxidant property of chitosan derivatives, and the N-pyridinium position would influence the scavenging radical ability.