Preparation And Property Of Chitosan Derivatives

Chitosan(CS),the only alkaline polysaccharide in nature,attracts wide attention owing to its characteristic properties,including biocompatibility,sources extensively and innocuous,as well as anti-oxidant activity and anti-bacterial activity.Unfortunately,due to the strong intramolecular and intermolecular hydrogen bonds,CS is insoluble in common solvents except acidic solution and has a low anti-oxidant and anti-bacterial activity,which have severely limited its application in food,medicine and biology field.So in this study,chemical modifications have been used to introduce other functional groups to improve the properties of CS.In this study,three new CS derivatives were prepared,the derivatives were characterized by fourier transform infrared spectrometer(FTIR),nuclear magnetic resonance spectrum(NMR),X-ray diffraction(XRD)and elemental analysis(EA)techniques.Then we studied the thermal stability,water solubility,anti-oxidant and anti-bacterial activity of CS derivatives,the major findings and results were listed as follows:1.Firstly C6 hydroxyl groups of CS were oxidized into carboxyl groups by TEMPO catalytic system,then C2 amino groups were replaced by 3-chloropropionic acid,after separation and purification,we obtained the derivative assigned as N,O-carbonylated chitosan(NTCS),which was confirmed by FTIR,1H NMR and XRD.The results of the physical experiment showed that thermal stability of NTCS decreased compared with CS,water solubility of NTCS was 15.005 g/100 m L H2 O,which was 20-fold of CS,meanwhile the viscosity of NTCS was significantly lower than that of CS,total content of carboxyl was 2.833 mmol/g.Particularly the results of the anti-oxidant experiment showed that NTCS put up significantly higher anti-oxidant activity compared with CS in DPPH radical,OH radical and reducing power,the in vitro bile acid binding capacity reached 17.209 mg/g,which was 3.5-fold higher than that of CS(3.810 mg/g).2.The C6 hydroxyl groups of CS were modified into amino groups to improve the anti-bacterial activity of CS.After C2 amino phthalylation,C6 hydroxyl toluene sulfonylation,azidation,reduction,and C2 amino deprotection,we obtained 6-amino chitosan(NCS).The structures were identified by FTIR,XRD and EA.After modification,the thermal stability was decreased,the degree of substitution of NCS obtained by different reactant molar ratio(CS:Ts Cl=1:5,1:10,1:15)was 0.190,0.335,0.487,respectively.Anti-oxidation experiment showed that NCS has a higher anti-oxidant activity,at 1.2 mg/m L,the scavenging effect of DPPH radical,OH radical and reducing power was 92.19%,62.81%,0.611,respectively.The anti-bacterial activity against Escherichia coli and Staphylococcus aureus showed that the introduction of amino groups promoted the anti-bacterial activity of CS.3.We took water-soluble chitosan oligosaccharide(COS)as the raw material,and grafted vanillic acid(VA)onto its hydroxyl groups.Me SO3 H could act as both sulfonate to protect amino groups of COS and reaction solvent.Firstly the carboxy group of VA was chlorinated,then esterification reaction was proceeded between COS and chlorovanillic acid,after deprotection,the vanillic acid-O-chitosan oligosaccharide(VA-O-COS)was obtained,then COS was characterized by FTIR,13 C NMR and XRD.The study of VA-O-COS showed that the structure became more ordered and the thermal stability was enhanced.The degree of substitution of derivative at different substrate molar ratio(VA:COS=1:2,1:3,1:5)was 0.750,0.912,1.064,respectively.The anti-oxidation experiment results showed that scavenging activity of the derivatives,including the DPPH radical,OH radical and reducing power had different degrees of enhancement,scavenging effect was 85.46%,58.52%,0.733 at 1.2 mg/m L.The bacteriostatic test showed that anti-bacterial activity of VA-O-COS on Escherichia coli and Staphylococcus aureus activity was higher than that of COS.The study showed that,after modification,the three derivatives had better anti-oxidant activity,in vitro bile acid binding capacity or anti-bacterial activity.The paper will provide a new thinking and method for the development of CS on more efficient and safe anti-oxidant and anti-microbial preservatives.