Preparation And Properties Of Polysaccharide-Based Chiral Recognition Materials

Polysaccharide derivatives are one of the most powerful functional polymer materials with great potentials for chiral separation.Especially,the phenylcarbamate derivatives of celluloseand amylose can achieve high-efficient chiral recognition and enantioseparation to varioustypes of racemates.Traditionally,polysaccharide derivatives were usually synthesized by introduction of small substituents,and the related research on these derivitation had been comprehensive.However,as far,the study on the development of synthetic procedures and functional performance of polysaccharide derivatives bearing bulky side groups has beens still rather limited,which greatly hindered the functionalization of natural polysaccharide-based macromolecules and their further development for various chiral recognition.The introduction of bulky side groups into polysaccharide derivatives is probably of great significance for expanding the function of polysaccharide materials and constructing novel series of chiral functional materials for high-efficient and broad-spectrum chiral recognition,enantioseparation and chiral sensing.Based on the above status.two kinds of bulky fluorescent chromophores（benzothiophene and benzofuran）were introduced into the main chains of cellulose and amylose,respectively.The synthesis,structure,chiral fluorescent sensing performance,chiral separation properties and metal ion recognition properties of the obtained polysaccharide derivatives with bulky side pendants were systematically studied,and the involved different recognition mechanisms were further explored in this paper.A series of novel cellulose and amylose derivatives bearing bulky fluorescent chromophore groups were successfully synthesized by carbamoylation reaction,Suzuki-Miyaura coupling reaction and esterification reaction using cellulose and amylose as matrix materials,and boric acid and formic acid derivatives bearing two bulky side groups of benzothiophene and benzofuran as derivatization reagents.The molecular structures and degree of substitution of the synthesized derivatives were characterized by ¹H NMR and FT-IR spectrum.The chiral fluorescence sensing properties of the synthesized polysaccharide derivatives bearing bulky side groups were characterized in detail by UV absorption spectroscopy and enantioselective fluorescence emission spectroscopy to eight chiral quenchers with different structures.The results showed that the polysaccharide-based chiral fluorescent sensing materials bearing bulky side groups possess excellent enantioselective fluorescence sensing properties to most chiral quenchers,especially to methylbenzylamine and aminoalcohol quenchers.Among them,the enantiomeric fluorescence difference ratio of amylose phenylcarbamate derivatives bearing benzofuran and benzothiophene groups toward chiral quenchers 3-amino-3-phenylpropan-1-ol（Q5）andα-1-phenylethylamine（Q1）reach 164.35and 115.90,respectively.Based on the synthesized polysaccharide derivatives bearing bulky side groups,the corresponding coated chiral stationary phases were prepared,and their chiral separation performance for 22 chiral compounds with typical structures was evaluated in detail by using thermogravimetric analysis and high performance liquid chromatography（HPLC）.The results showed that the chiral recognition performance of cellulose/amylose phenylcarbamate chiral stationary phase bearing benzothiophene group was significantly better than that of the same type of chiral stationary phase bearing benzofuran group.The cellulose phenylcarbamate chiral stationary phases bearing benzothiophene groups possess excellent chiral separation properties for metal complexes（cobalt acetylacetonate,chromium acetylacetonate and ruthenium acetylacetonate）,chiral drugs（amlodipine）,axially chiral compounds and chiral aromatic compounds.Their separation factors even exceed the commercial cellulose coated chiral column Chiralcel OD.In addition,the effects of the introduction of bulky side groups on the chiral fluorescence sensing properties and chiral separation properties of polysaccharide phenylcarbamate derivatives were further studied by fluorescence emission spectroscopy and circular dichroism spectroscopy.The different recognition mechanisms of chiral fluorescence sensing properties and chiral separation properties of these derivatives were further explored.The introduction of two bulky fluorescent chromophores（benzothiophene and benzofuran）effectively improved the chiral fluorescence sensing performance and chiral separation performance of cellulose and amylose phenylcarbamate derivatives under the premise of ensuring the regularity of the polymer main chain.It was found that the chiral fluorescence sensing performance of these materials mainly depended on the enantioselective interaction between polysaccharide derivatives and chiral quenchers in the excited state,while the chiral separation performance mainly depended on the enantioselective interaction between polysaccharide derivatives and chiral analysis substrates in the ground state.Polarizing microscope analysis showed that the synthesized polysaccharide derivatives bearing bulky side groups had obvious lyotropic liquid crystal phase structure,which proved again that the polysaccharide derivatives synthesized by this method had regular structure.To further expand the recognition performance of polysaccharide derivatives,the recognition performance of polysaccharide derivatives with bulky fluorescent chromophore for metal ions was evaluated by UV absorption spectroscopy and fluorescence emission spectroscopy.The results showed that the synthesized polysaccharide-based fluorescent sensing material possessed excellent selective recognition performance for Fe³⁺ions,and could achieve high selective recognition of Fe³⁺ions under low concentration conditions,and possessed excellent anti-interference and reversibility.In particular,the detection limit of amylose phenylcarbamate derivatives with benzofuran group for Fe³⁺ions were 3.0μM,which was lower than the maximum acceptable concentration of Fe³⁺ions in drinking water（5.4μM）stipulated by the US National Environmental Protection Agency（EPA）.The results showed that the polysaccharide-based fluorescent sensing materials synthesized in this paper had better Fe³⁺ions recognition performance than traditional metal ion sensors（small molecule and metal organic framework sensors）.This result is of great significance for further expanding the functional characteristics of polysaccharide-based chiral recognition materials.