Structure-performance Relationship Of Chiral Separation Materials From Acylated Chitosan Derivatives

Among coated-type polysaccharide derivatives based chiral stationary phases(CSPs),the ones prepared from cellulose/amylose derivatives possess high chiral separation ability and thus widely are used for enantiomeric separation of chiral compounds.However,since cellulose and amylose derivatives may be dissolved or highly swollen in some common organic solvents,and the corresponding coated-type CSPs exhibit poor solvent tolerance in mobile phases and as a result,the application of the CSPs is limited.Chitin/chitosan derivatives based CSPs can work in mobile phases containing organic solvents,thereby broadening mobile phase range.In recent years,some chitosan derivative based CSPs have been reported,which showed powerful chiral separation performance and good organic solvent tolerance.However,the relationship between structure and property of the chitosan derivatives which work as a chiral selector(CS)is very complicated and still unclear.Therefore,this thesis aims at investigating the relationship between structure and property of chitosan derivatives based CSP,clarifying influence of molecular weight and source of chitosan on enantioseparation performance,as well as developing enantioseparation materials hopefully with powerful separation performance and high eluent tolerance.Hence,in this thesis,a variety of chitosan derivatives were prepared with molecular-weight-different and source-different chitosans.The relationship between the structure of the chitosan derivatives and the performance of the corresponding CSPs was discussed.Specifically,the works in this thesis are summarized as follows:(1)N-Isobutyryl and N-benozyl chitosans were prepared by selective derivatization of the amino group at C2 in glucose unit of chitosan.The hydroxyl groups at C3/C6within N-isobutyryl and N-benozyl chitosans were then modified with 4-methylphenyl isocyanate or cyclohexyl isocyanate to provide a series of chitosan3,6-bis(carbamate)-2-(amide)derivatives which are similar in structure but contain different numbers of benzene ring.The swelling capacity of the CSs and the enantioseparation capability of CSPs were evaluated.The results showed that the trend in chiral recognition ability of the CSP follows this order:the CSP with two benzene rings>the CSP with three benzene rings>the CSP with one benzene ring.The fact reveals that benzene ring in a CS is necessary for enantioseparation.However,more benzene rings do not definitely cause better enantioseparation performance.Generally,two benzene rings are needed at minimum when constructing a chitosan-type CS.(2)Four chitosan bis(4-methylphenylcarbamate)-(2-methylpropylamide)derivatives were prepared from shrimp shell chitosan and crab shell chitosan with viscosity-average molecular weights of 2.8×10~5 and 1.4×10~5.Enantioseparation performances of the chitosan derivatives based CSPs were evaluated.The CSPs prepared from shrimp shell chitosan were found to be slightly better in enantioseparation performance than the CSPs prepared from crab shell chitosan when the CSs were prepared from the two kinds of chitosan with the same molecular weights.This observation implies the CSs prepared from shrimp shell and crab shell chitosans should be similar in suprastructure.When the CSs were prepared with chitosans of the same source,the CSP derived from a chitosan with higher molecular weight showed slightly better enantioseparation performance than the one with lower molecular weight.The enantioseparation results showed that the CSPs derived from chitosans with the same source but different molecular weights or with the same molecular weight but different sources are very similar in enantioseparation feature.Therefore,shrimp shell chitosan and crab shell chitosan with appropriate molecular weight are both practicable to be used as material for development of new CSPs.(3)Chitosan derivatives with different substituents at C2 and C3/C6 were prepared by derivatizing N-benzoyl and N-(2-methylpropylamide)chitosans with benzoyl chloride containing different substituents.The chitosan bis(4-chlorobenzoate)-(2-methylpropylamide)was observed to be soluble in alcohol and therefore could not be applied to prepare CSPs.Among the other three chitosan derivative based CSPs,chitosan bis(3,5-dimethylbenzoate)-(benzamide)CSP showed relatively better chiral recognition ability.Comparing the structure and the performance of the prepared chitosan derivatives,it was found that the property,position and number of substituents on the phenyl group in the chitosan derivative significantly affected chiral recognition ability.In summary,the dependence of performance on structure of some chitosan derivative based enantioseparation materials was observed in this thesis,which made chiral recognition of polysaccharide-type CSPs to be understood more deeply.The trends found in thesis might be helpful for developing new enantioseparation materials of polysaccharide derivatives.