A New Polysaccharide Selenylation System Based On Solubilization And Synergistic Catalytic Effects

In the polysaccharide modification,the insolubility of substrate polysaccharide and low substitution efficiency of the modified group hindered the in-depth study of the structure-activity relationship of polysaccharide derivatives.Among them,the polysaccharides solubility is limited in conventional and aprotic solvents,due to the different structure of the polysaccharide chain including glycosidic bond form,bond angle and short-range interaction.Meanwhile,several drawbacks such as insufficient protonation degree and weak nucleophilic offensive ability of selenide reagent,which reduces the substitution efficiency.The non-covalent interaction between the polysaccharide chains can be destroyed by DES through the synergistic effect of H-bonds,and new H-bonds are formed between polysaccharides and DES,which promotes the polysaccharide solubilize.While overcoming the drawbacks of traditional reagent contamination,it is expected to become a powerful tool for efficient pretreatment of polysaccharide structures.In terms of improving reaction efficiency,while the Lewis acid site in the magnetic solid acid forms a coordination effect with the substituent,the Br(?)nsted acid site promotes the protonation of the substituent,which significantly enhances the nucleophilic offensive ability of the substituent.1.Research on the synergistic effect of DES H-bond on the solubilization effect of polysaccharidesWith[Ch]Cl as HBA,EG and Urea as HBD,different DESs are synthesized respectively.Among them,[Ch]CI1-EG4 and[Ch]CI1-Urea2 show significant solubilization performance to PAS.Characterization by FT-IR,1H NMR and polar parameters reflects that[Ch]Cl1-EG4 has greater polarity and more complex non-covalent interactions.Further QC calculation on DES has shown that[Ch]Cl1-Urea2 forms a stable cyclic DES structure with HBD interaction.The solubilization of[Ch]Cl1-EG4 on PAS is attributed to the formation of DES complex with Cl-as the center of the EG molecule,which achieves the solubilization of the substrate polysaccharide by virtue of the synergistic effect of H-bonds.2.Preparation and structure analysis of magnetic solid acidFe3O4/TiO2/SO42-and Fe3O4/SiO2-SO3H are prepared by sol-gel method.Among them,through structural characterization,it is found that the prepared magnetic solid acid presents a spherical morphology with a standard crystal form and significant paramagnetism.Meanwhile,Ti-based magnetic solid acid shows stronger acidity,while Si-based solid acid has more excellent apparent parameters.3.Construction of a new polysaccharide selenylation system based on magnetic solid acid-DESA new polysaccharide selenylation system is constructed based on the DES and magnetic solid acid,and the effect of different solvent systems on PAS selenylation is evaluated.It is showed that DMSO has low solubility to PAS,the selenide reagent is reduced by Fm and the selenylation is inhibited by H2O.Above results show a lower efficiency of the selenylation.Comparing different acidic catalysts,it is found that polysaccharide chains are severely damaged by homogeneous catalysts due to better penetration.However,SePASs are prepared according to DES-magnetic solid acid selenylation system.It is showed an excellent reaction efficiency(Se contentmax=5666.20 ?g/g),which is significantly higher than the conventional selenylation method(1026.71 ?g/g).Combining the results of FT-IR,XPS and NMR show that the seleno-group has an incomplete O-6 substitution reaction in the Man-C6 position of PAS in the form of selenite.Meanwhile,the residual elements involved in solvents and catalysts are not observed in the elemental residual analysis of selenized products.In addition,the evaluation of magnetic solid acid reusability showed that the catalyst still has great catalytic performance after 4 cycles.In summary,the substrate polysaccharide can be solubilized in the DES-magnetic solid acid system,which significantly promotes the polysaccharide selenylation efficiency.It has a certain reference for the rational design of polysaccharide modification and the investigation of the structure-activity relationship of Se-polysaccharide derivatives in the later stage.