文摘
Eight amylose tris(ethylcarbamate) (ATEC) samples ranging in the weight-average molar mass Mw from 1.0 脳 104 to 1.1 脳 106 g mol鈥? and five amylose tris(n-hexylcarbamate) (ATHC) samples of which Mw varies from 4.9 脳 104 to 2.2 脳 106 g mol鈥? have been prepared from enzymatically synthesized amylose samples having narrow dispersity indices and no branching. Small-angle angle X-ray scattering (SAXS), light scattering, viscometry, and infrared (IR) absorption measurements were carried out for their dilute solutions, that is, ATEC in tetrahydrofuran (THF), 2-methoxyethanol (2ME), methanol (MeOH), and ATHC in THF and 1-propanol (1PrOH) to determine Mw, particle scattering functions, intrinsic viscosities, and IR spectra. SAXS and viscosity measurements were also made on ATEC in d- and l-ethyl lactates. The data were analyzed in terms of the wormlike cylinder model to estimate the helix pitch (or contour length) per residue h and the Kuhn segment length 位鈥? (stiffness parameter, twice the persistence length). Both ATEC and ATHC have large 位鈥? in THF, that is, 33 and 75 nm, respectively, and smaller 位鈥? were obtained in alcohols, indicating that they have rigid helical conformation stabilized by intramolecular hydrogen bonds in THF. On the contrary, the helical structure estimated from the h value significantly depends on the alkyl side groups in a complex fashion, that is, h = 0.36 nm for ATEC, h = 0.29 nm for ATHC, and h = 0.26 nm for amylose tris(n-butylcarbamate) (ATBC). This is likely related to the bulkiness of side groups packed inside the amylosic helices. The solvent dependence of h, 位鈥?, and the fraction fhyd of intramolecular hydrogen bonds for ATEC can be explained by a current model as is the case with ATBC [Terao, K.; Macromolecules 2010, 43, 1061], in which each contour point along the chain takes loose helical and rigid helical sequences independently.