Preparation And Antibacterial Properties Research Of Amphiphilic Quaternary Ammonium Salt Of Chitosan Oligosaccharide

Compared with antimicrobial organic molecules, antimicrobial peptides posse many advantages, such as broad spectrum, drug resistance, biocompatibility and biodegradable. In this thesis, Chitosan has been modified to prepare a series of amphiphilic antibacterial materials. Those amphiphilic molecules were designed from the structure of natural antibacterial peptide which antibacterial properties have been studied in detail. The thesis was divided into three parts:The first part is about the preparation the quaternary ammonium salt of amphiphilic chitosan oligosaccharideThe basic model of the antimicrobial peptides consists of a hydrophilic group and a hydrophobic group with a good antibacterial property. Therefore, it can be synthesized as a template to get the aqueous antimicrobial material. Chitosan oligosaccharide as a low molecular skeleton to introduce glycidyl trimethyl ammonium chloride under the amino group, and then to introduce alkyl chain group which is hydrophobic side. This study showed that the substitution degree of hydrophobic side chain will improve when adding the ratio of aldehyde is higher. The quaternary chitosan oligosaccharide is easy to hydrolyze in a low pH and is benefit to prevent hydrolysis in a neutral solution. It was found that quaternary ammonium salts was hydrolyzed but grafting the hydrophobic substitution of side chain increased under weakly acidic conditions. Finally, the structure of the chitosan derivatives were confirmed with FT-IR and NMR, and the degree of substitution of side chain can be calculated.The antibacterial properties of the N-alkyl chitosan oligosaccharide derivatives with quaternary ammonium salt were assayed by the flat colony counting method and the turbidimetric method. The result showed that chitosan oligosaccharide derivatives with quaternary ammonium salt performance anti-Staphylococcus aureus better than antiEscherichia coli. The antibacterial effect of N-chitosan oligosaccharide quaternary ammonium stronger when the alkane chain length increases, but chitosan oligosaccharide quaternary ammonium performed strongest in anti- Staphylococcus aureus. Compare to different alkanes, the relationship between hydrophobic chain length and its antibacterial properties was no obvious, the solubility of amphiphilic materials with the longer hydrophobic side chain was not ideal, hence antibacterial performance measurement under neutral condition has the certain restrictions. Those chitosan oligosaccharide derivative have 99% inhibitory effect on Staphylococcus aureus with its concentrations of 400 ppm while have antibacterial effect on Escherichia coli above 1800 ppm.According to the antibacterial experiment, amphiphilic quaternary ammonium salt of chitosan oligosaccharide has obvious antibacterial effect, which was closely related with the number of hydrophobic side chain. Those results were in accordance with our original intention of material design.The second part is about the synthesis of N-alkyl chitosan derivatives with quaternary ammonium salt.This section of synthetic design is introduced based on the same amino group-NH2,which can form ammonium salt and graft hydrophobic group. Firstly, the amino methylation on the chitosan oligosaccharide's free amino group has been performed by Weller Clark methylation reaction. Then, the methylated product was introduced bromo-hydrocarbon to form quaternary ammonium salt cationic charge with good water solubility, for product. Finally those productions were characterized by Fourier transform infrared spectroscopy(FT-IR), nuclear magnetic resonance(NMR) and element analysis to understand its structure and determine the substitution degree. The experimental results showed that the basic feasible solution, to the preparation of hydrophilic and hydrophobic groups in a side chain quaternary ammonium salt derivatives. Unfortunately, one paper with very similar idea has been published in the Biomacromolecular, which is an international journal. This article showed that chitosan quaternary ammonium salt has excellent antibacterial properties. Therefore we had to stop the research of this subject.The third part is for the chemical degradation of chitosan.As chitosan is easy to form hydrogen bonds itself and the applications of chitosan are limited by its poor solubility. Therefore, the degradation of chitosan by hydrogen peroxide was used, which is a non-polluting, efficient and economical to get low molecular weight chitosan. We investigated the mechanism of the degradation of hydrogen peroxide. The results showed that the degradation of chitosan by hydrogen peroxide was consistent with the non-specific rule and the rate of degradation chitosan was fast before 3 h, while the time of degradation was very slow and the yield of degradation decreases after 7 h.