Preparation Of Sulfhydryl Chitosan Derivatives And The Nature Research

Chitosan, as a kind of natural polymer materials, has attracted much attention in recentyears. Because of the effect of intramolecular hydrogen bonds, it is difficult to dissolve inwater, so the study of the modification is being paid more and more attention. Sulfhydrylchitosan is widely used in the biological medicine as wound dressing and drug carrier for itsstrong adhesion and non-bio toxicity. Deoxycholic acid, derived from organisms, has uniquebiological characteristics. It can be reacted with chitosan as the hydrophobic group to givesnew applications of chitosan. In this study, N-acetyl-L-cysteine (NAC) was used as thesulfhydryl groups to hydrophilic modification of chitosan, deoxycholic acid (DCA) was usedto hydrophobic modification, to synthesis a new type of amphiphilic chitosan derivatives thioldeoxycholic acid (DCA-NAC-CHS). The corresponding applications were studied, such assulfhydryl chitosan derivatives in biosensor; bovine serum albumin (BSA) coating and oilsoluble CdSe QDS modification effect.Sulfhydryl chitosan Derivatives：The best condition was investigated of synthesizesulfhydryl chitosan (NAC-CHS), with N-acetyl-L-cysteine (NAC) as reagent, HOBt andEDAC as condensing agent, by the method of Ellman’s reagent measurement of sulfhydrylcontent. Deoxycholic acid was used to hydrophobic modification of chitosan in the presenceof activating reagent EDAC and NHS, then connected with NAC, with EDAC as acondensing agent in the presence of HOBt environment. IR and NMR were used tocharacterize the structure of NAC-CHS and DCA-NAC-CHS, indicating that DCA and NACwere grafted onto the chitosan molecules with amide bond. The aggregate formation ofDCA-NAC-CHS was studied by fluorescence probe method. Results showed that,DCA-NAC-CHS can form aggregation with the hydrophobic interaction.NAC-CHS modified electrode: Glassy carbon electrode was modified with NAC-CHS,gold nanoparticles, cytochrome C, respectively, through the way of layers of layers adsorbedto the surface of the electrode. The modification status was characterized by cyclicvoltammetry, AC impedance, and scanning electron microscopy. Results showed that after theblank electrode was modified by sulfhydryl chitosan, the charging current is significantly reduced, and the impedance increases because sulfhydryl chitosan hindered the electrontransfer; further modified with gold nanoparticles, the charging current increased slightly,indicating that the gold nanoparticles can increase the electrode conductive. But theimpedance increase more. That may because the negatively charged gold nanoparticles cangenerate electrostatic repulsion with the probe in solution, resulting in electron exchangereactions of the electrode more difficulties, so that electrochemical impedance increasesignificantly. After the modification of cytochrome C, the charging current was furtherreduced, and appeared a quasi-reversible redox peaks, indicating that cytochrome C has beensuccessfully modified glassy carbon electrode. But the cytochrome C with a positive chargewas able to attract negatively charged probe solution so that the resistance value was clearlyreduced. In this part, the results showed that the fixed sulfhydryl chitosan-gold nanoparticlecomposite membrane cytochrome C can not only direct effective electron transfer, but alsomaintain the Cytochrome C hydrogen peroxide and kept its electrocatalytic reduction activity.The coated effect of deoxycholic acid sulfhydryl chitosan on oil-soluble CdSe quantumdot: Oil-soluble CdSe quantum dots were synthesized, and were coated into the hydrophobiccore by taking use of the amphipathy of the deoxycholate sulfhydryl chitosan. Nanoparticlesof oil-soluble CdSe quantum dots that were coated by deoxycholic acid sulfhydryl chitosanwere characterized by fluorescence spectroscopy, UV-visible spectroscopy, X-ray diffractionand transmission electron microscopy. The results showed that different sizes of CdSequantum dots can be obtained by changing the growth time of the quantum dots.DCA-NAC-CHS has a good modification effect on the oil-soluble CdSe QDs. It can reducethe toxicity of CdSe, and maintains the strong fluorescence intensity at the same time.The slow-release effect of deoxycholic acid sulfhydryl chitosan coated BSAnanoparticles: Sodium tripolyphosphate (TPP) was used as polymerization agent to prepareDCA-NAC-CHS and loaded BSA nanoparticles. They were observed with microscope andTransmission Electron Microscope (TEM).Results showed that the nano-particles had adiameter of about200-300nm.The drug loading and encapsulation efficiency were12.51%-45.72%and38.05%-69.41%. Both the drug loading and encapsulation efficiencywere the highest when the feed ratio of BSA: DCA-NAC-CHS was1:4. The release time grew with the increase of thiol substitution degree. The best controlled release effect lasted24h, cumulative release was89.75%.In conclusion, the sulfhydryl chitosan derivatives have good water solubility; theadhesion of NAC-CHS can be applied to the sensor research. DCA-NAC-CHS can beself-assembled to form aggregate in solution, can also coat the oil-soluble quantum dots andhas a good effect on the protection and sustained release of BSA. The novel chitosanderivatives have good prospects for the development in basic research and applications.