Synthesis,Characterization And Biological Evaluation Of Biomimetic Phosphoryldiserine Chitosan Derivatives

Novel biomimetic zwitterionic chitosan derivatives,phosphoryldiserine-chitosan conjugate（PdSCs）was synthesized by coupling phosphoryldiserine（PdS）mimicking phosphatidylserine of cell membrane phospholipid to chitosan using a phosphorus chemistry method.And we systematically investigated the synthesis mechanism,structure,self-assembly and biological properties of PdSCs.In order to obtain PdSCs,chitosan was firstly modified to be the oil-soluble chitosan derivative（6-O-triphenylmethyl ether chitosan）,then PdS groups were coupled to acquire PdSCs based on the Antherton-Todd reaction,which was characterized by ¹H and ³¹P NMR spectra.For the purpose of explaining the synthesis mechanism of PdSCs,we also coupled the groups of phosphoryldithreonine（PdThr）,phosphoryldihydroxypivalate（PdH）and phosphoryldi-tert-butoxycarbonyl-serine to chitosan and investigated their structure.The results of ¹H,³¹P and ³¹P CPD NMR spectra revealed that the phosphoramide bond formed via the Antherton-Todd reaction migrated to the hydroxyl group of C3 in chitosan in the presence of free carboxyl groups.Conductometric titration and plasma emission spectrometer（ICP）results confirmed that the coupled group to chitosan was the phosphoryldiserine group.We also investigated and compared the performance of PdSCs,PdThrCs,and PdHCs.XRD,TGA and DSC results exhibited that the modified chitosan derivatives reduced the crystallization of chitosan,resulting in the reduction of the thermal stability,but the introduction of the PdS,PdThr and PdH groups can improve the hydrophilicity of the material.Thermal analysis revealed that there existed some freezing bound water restrained by branched dizwitterionic PdSCs,but almost not by branched dizwitterionic PdThrCs,while a little freezing bound water also existed for dianionically charged PdHCs.The self-assembly behaviors of PdSCs was also investigated by DLS,TEM and AFM,which can form pH-responsive nanoparticles with surface electrical transition at pH=9.6.It was found that the self-assembly behaviors of PdSCs could be adjusted by Cu（II）ions.As biological materials,materials should be required to be non-toxic.Therefore,a series of biological evaluations of PdSCs,PdThrCs,and PdHCs were performed.Compared with PdThrCs and PdHCs,PdSCs had almost no effect on the conformation of the BSA and improved its thermal stability,according to the results of UV adsorption and fluorescence spectra.Coagulation time experiments exhibited that PdSCs had a certain anticoagulant effect.Hemolysis rate and erythrocyte morphology showed that PdSCs had good blood compatibility.The cytotoxicity test showed that PdSCs was non-toxic and beneficial to cell proliferation.Therefore PdSCs can be used in biomedical applications.In summary,the biomimetic zwitterionic chitosan derivatives（PdSCs）prepared via the Atherton-Todd reaction can restrain some freezing bound water,which has excellent compatibility in protein,blood and cells.It can be predicted that PdSCs can be applied to many aspects such as biomaterial coating and drug carrier.