Jingquan Yan

3,6-O-[N-(2-Aminoethyl)-acetamide-yl]-chitosan exerts antibacterial activity by a membrane damage mechanism

A novel chitosan derivative, 3,6-O-[N-(2-aminoethyl)-acetamide-yl]-chitosan (AACS), was successfully prepared to improve water solubility and antibacterial activity of chitosan. AACS had good antibacterial activity, with minimum inhibitory concentrations of 0.25mg/mL, against Escherichia coli and Staphylococcus aureus. Cell membrane integrity, electric conductivity and NPN uptake tests showed that AACS caused quickly increasing the release of intracellular nucleic acids, the uptake of NPN, and the electric conductivity by damaging membrane integrity. On the other hand, hydrophobicity, cell viability and SDS-PAGE experiments indicated that AACS was able to reduce the surface hydrophobicity, the cell viability and the intracellular proteins through increasing membrane permeability. SEM observation further confirmed that AACS could kill bacteria via disrupting their membranes. All results above verified that AACS mainly exerted antibacterial activity by a membrane damage mechanism, and it was expected to be a new food preservative.

Characterization and biocompatibility of injectable microspheres-loaded hydrogel for methotrexate delivery

Injectable thermosensitive hydrogels have widely been studied as drug delivery systems for their minimally invasive administration and localized drug release. However, burst drug release limits clinical applications of such hydrogels. A double-component injectable formulation (microspheres-loaded hydrogel, CMs-CS-HG) was thus fabricated to eliminate the limitation. Gelation temperature, gelation time, complex viscosity and syringeability tests for CMs-CS-HG demonstrated excellent injectability. After injection, the drug-loaded chitosan-based microspheres (CMs) were localized within the hydrogel, leading to localized drug release. Moreover, CMs-CS-HG had good hemocompatibility and histocompatibility, and had non-genotoxicity and non-cytotoxicity to Kunming mice. In addition, both in vitro and in vivo methotrexate (MTX) releasing efficiencies were evaluated, demonstrating long-term sustained MTX release from MTX-loaded CMs-CS-HG. These results showed the double-component CMs-CS-HG not only maintained good injectability and biocompatibility but also prolonged drug-releasing time in comparison with the single-component CS-HG or CMs, suggesting that CMs-CS-HG may be a promising drug delivery system.

Preparation, characterization and antibacterial activity of O-acetyl-chitosan-N-2-hydroxypropyl trimethyl ammonium chloride

Chitosan-N-2-hydroxypropyl trimethyl ammonium chloride (QTS) was prepared by reaction of chitosan (CS) and glycidyl trimethylammonium chloride. Later, O-acetyl-chitosan-N-2-hydroxypropyl trimethyl ammonium chloride (AQTS) was synthesized by reaction of QTS with acetic acid in the presence of SOCl2. Both derivatives were characterized by FTIR, (1)H NMR, TGA, and XRD techniques. The degree of quaternization of QTS was 85.5%, and the degree of acetyl (DA) of AQTS was from 1.63 to 2.31. Compared with CS, the solubility of QTS and AQTS was improved at different levels, especially AQTS, it could be dissolved in many organic solvents, water, and aqueous solution. Notably, the solubility of AQTS in organic solvents increased as DA increased, while the solubility in water was reversed. The results of CS, QTS, and AQTS against Escherichia coli and Staphylococcus aureus showed that QTS and AQTS exhibited higher antibacterial activity than CS, and the antibacterial activity of AQTS decreased with increased DA. Moreover, the inhibition effect was AQTS1 (DA 1.63)>AQTS2 (DA 2.02)>QTS>AQTS3 (DA 2.31). On the basis of the results of the present study, it could be emphasized that hydrophobicity and positive charge density might strongly affect the antibacterial activity of quaternary ammonium chitosan derivatives.

Preparation and characterization of N-benzoyl-O-acetyl-chitosan

A novel amphipathic chitosan derivative, N-benzoyl-O-acetyl-chitosan (BACS), was prepared by using the selective partial acylation of chitosan (CS), benzoyl chloride, and acetic acid under high-intensity ultrasound. The chemical structure and physical properties of BACS were characterized by FTIR, (1)H NMR, TGA, and XRD techniques. The degrees of substitution of benzoyl and acetyl for the chitosan derivatives were 0.26 and 1.15, respectively, which were calculated from the peak areas in NMR spectra by using the combined integral methods. The foaming properties of CS and BACS were determined and the results suggested BACS had better foam capacity and stability than those of chitosan. In addition, the antimicrobial activities of CS and BACS were also investigated against two species of bacteria (Escherichia coli and Staphylococcus aureus) and a fungus (Aspergillus niger), the results indicated that the antibacterial and antifungal activities of BACS were much stronger than those of the parent chitosan. These findings suggested that BACS was preferable for use as a food additive with a dual role of both foaming agent and food preservative.

Synthesis, characterization, and evaluation of poly(aminoethyl) modified chitosan and its hydrogel used as antibacterial wound dressing

This study aims to develop new antibacterial hydrogel wound dressings composed of poly(aminoethyl) modified chitosan (PAEMCS). FTIR, 1H NMR, and elemental analysis demonstrated that PAEMCS was successfully synthesized via grafting poly(aminoethyl) groups onto hydroxyl groups on chitin first, and removing acetyl groups from the grafted polymer afterward. XRD and TGA implied its well-defined crystallinity and thermostability. Furthermore, a series of hydrogels were fabricated under the participation of dipotassium hydrogen phosphate (DHP). The gelation tests suggested that the higher concentration of PAEMCS or DHP was beneficial to the formation of hydrogels. The pH values of hydrogels at 37°C were all in the range of 7.12-7.50. The rheological tests indicated that PAEMCS-based hydrogels were of lower DHP addition and higher elasticity than CS-based hydrogels to achieve the same gelation temperature under the same polymers concentration. Additionally, the swelling, anti-bacteria, and cytotoxicity experiments showed that PAEMCS-based hydrogels possessed excellent hygroscopicity, high antibacterial activity against E. coli, S. aureus, or S. epidermidis, and good cytocompatibility toward L929 cells or HUVECs, respectively. All the results implied that PAEMCS-based hydrogels not only maintained inherent multiple properties of chitosan but also possessed excellent antibacterial activity, and might be promising antibacterial hydrogel dressings used in wound therapy.

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.

Heterotrophic nitrogen removal by a newly-isolated alkalitolerant microorganism, Serratia marcescens W5

A new microbe, Serratia marcescens W5 was successfully isolated. Its feasibility in purification of excessively nitrogen-containing wastewater was evaluated using inorganic nitrogen media. Single factor tests showed that W5 exhibited high ammonium removal rates (above 80%) under different culture conditions (pH 7-10, C/N ratios of 6-20, 15-35°C, 0-2.5% of salinity, respectively). Besides various organic carbon sources, W5 was able to utilize calcium carbonate with 28.05% of ammonium removed. Further experiments indicated that W5 was capable of resisting high-strength ammonium (1200mg/L) with the maximum removal rate of 514.13mgL(-1)d(-1). The nitrogen removal pathway of W5 was also tested, showing that both nitrite and nitrate were efficiently removed only in the presence of ammonium, with hydroxylamine as intermediate, which was different from the conventional nitrogen removal pathway. All the results verified that W5 was a good candidate for the purification of excessively nitrogenous wastewater.

Itaconic acid grafted carboxymethyl chitosan and its nanoparticles: Preparation, characterization and evaluation

This work aims to synthesize a novel itaconic acid (IA) grafted carboxymethyl chitosan (PICMCS), and further fabricate its nanoparticles for potential biomedical applications. First, PICMCS was prepared via free-radical polymerization of IA monomer, in the presence of ammonium persulfate as an initiator and nitrogen as a protector. Its chemical structure was confirmed by FTIR and 1H NMR. The IA substitution degree calculated by elemental analysis data was 1.85, implying that IA was successfully grafted to carboxymethyl chitosan (CMCS). XRD and TGA patterns illustrated its well-defined crystallinity and thermostability. Second, PICMCS nanoparticles were fabricated by electrostatic attraction between carboxyl and amino groups in the absence of any additional agent, which were of obvious core-shell structures with an average particle size of 144nm and a polydispersity index of 0.11. PICMCS nanoparticles exhibited excellent physical stability after storage at 25°C for 30days, without any aggregation. PICMCS nanoparticles with high negative surface charge also indicated the good stability, especially in neutral or alkaline media. Additionally, the cytotoxicity experiments showed that either PICMCS or its nanoparticles had better cytocompatibility toward L929 cells than CMCS. These findings above suggested that PICMCS was a kind of promising material for preparing nanoparticles used in biomedical field.