Preparations Of Two Nanopartical Systems And Researches On Their Antibacterial Activities

Two chitosan derivatives—oleoyl-quaternized chitosan(QCS) and oleic acid grafted chitosan oligosaccharide(OA-OCS) are synthesized. Their structures are characterized by FTIR. And the self-assembled behavior of the copolymers in water solution is investigated. Two nanoparticle systems are prepared and the characteristics are evaluated. Gram-negative Escherichia coli and gram-positive Staphylococcus aureus are chosen as models to estimate the antibacterial activities of the nanoparticle samples.Chitosan(Mw=52kDa, DD=87.45%) is degraded with HCl first. And QCS copolymers with different degrees of amino substitution (DS) are synthesized. The successful modification is confirmed by the results of FTIR. QCS exhibite good solubility in aqueous solutions. The solubility of QCS has no change as the increase of pH value. QCS nanoparticles are obtained by using an emulsification method and the self-assembling properties are analyzed by using the fluorescence probe test. With the increasing of DS, the critical aggregation concentration (CAC) of QCS nanoparticles decrease and the CAC determined for QCS copolymers with different DS are 0.0616mg/ml, 0.0436mg/ml and 0.0323mg/ml respectively. The formation of QCS nanoparticles are characterized by transmission electron microscopy (TEM) and dynamic laser light scattering. The particle size decreases as DS increased and the mean diameters of QCS nanoparticles with different DS are 303nm, 264nm and 205nm, respectively. The TEM observation demonstrate the spherical shape of self-aggregates with a integrated form.We get the molecular weight of chitosan oligosaccharide(OCS, 3.7 kDa) by Acetyl-acetone method. The oleic acid is gratfed to a portion of the aminoes of CSO by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) mediated reaction. Various QCS copolymers with different DS are prepared by changing the free mole ratios of oleic acid to OCS and the DS is determined by a titration method. The structure of OA-OCS copolymers is identified by FTIR. The amphiphilic copolymers is found to be form micelles spontaneously by self-assembled in aqueous solution. The self-assembled OA-OCS nanoparticles solution is obtained by sonication. By a fluorometry in the presence of pyrene as a fluorescent probe, the CAC is measured. The CAC determined for OA-OCS copolymers with DS 6.0%,11.1% and 21.3% are 0.056mg/ml, 0.038mg/ml and 0.028mg/ml respectively. The properties of OA-OCS nanoparticles are analyzed using the TEM and dynamic laser light scattering. The nanoparticles are spherical shape, and at 1mg/ml of copolymer concentration, the particle size of micelles is less than 100 nm of number average hydrodynamic diameter.The antibacterial activities of nanoparticles against E.coli and S.aureus are measured. The nanoparticles show inhibitory effect against E.coli and S.aureus. Because of the quaternized, the antibacterial activities of QCS nanoparticles are higher than OA-OCS nanoparticles. The minimum inhibitory concentrations (MIC) of QCS and OA-OCS nanoparticle samples are 62.5 mg/l and 250 mg/l against S. aureus respectively, and the MIC of the samples are 31.25 mg/l and 125 mg/l against E.coli respectively. The antibacterial activities increase as the concentration of nanoparticle samples increased. No marked difference is found among different DS of nanoparticle samples tested in relation to S.aureus, while the antibacterial activity against E.coli increase as the DS of nanoparticles increased. The antibacterial activities of QCS nanoparticles increase with the increment of the pH value, while OA-OCS nanoparticles have the best antibacterial activities under neutral condition.