Correlation between conformational feature in solution and chiral separation ability of linear and nonlinear amylose tris(alkylcarbamate)s

Five immobilized-type chiral columns were prepared from linear, cyclic, and hyperbranched amylose tris(n- octadecylcarbamate) (ATODC) and amylose tris(n-butylcarbamate) (ATBC). A small amount of the linker site, 3(triethoxysilyl)propylcarbamate, significantly reduced the chain dimensions of ATBC for which high chain stiffness is attained by intramolecular hydrogen bonding between butylcarbamate groups located on the neighboring glycosidic residue. This phenomenon was not found for ATODC, which is mainly stiffened by bulky side groups. While both columns have appreciable chiral recognition ability, number of separated racemates decreased with decreasing side group bulkiness. The bulkiness of the side groups thus plays a definite role in the chiral separation ability. Furthermore, chain linearity on the silica surface is an important factor for the chiral separation because no substantial chiral separation was found for the chiral columns consisting of cyclic ATODC and cyclic ATBC. The chiral column made of hyperbranched ATODC has an intermediate chiral separation ability between linear and cyclic ATODC, supporting this suggestion.