title: Side-chain-dependent helical conformation of amylose alkylcarbamates: amylose tris(ethylcarbamate) and amylose tris(n-hexylcarbamate).
abstract: Eight amylose tris(ethylcarbamate) (ATEC) samples ranging in the weight-average molar mass M(w) from 1.0 × 10(4) to 1.1 × 10(6) g mol(-1) and five amylose tris(n-hexylcarbamate) (ATHC) samples of which M(w) varies from 4.9 × 10(4) to 2.2 × 10(6) g mol(-1) 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 M(w), 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 λ(-1) (stiffness parameter, twice the persistence length). Both ATEC and ATHC have large λ(-1) in THF, that is, 33 and 75 nm, respectively, and smaller λ(-1) 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, λ(-1), and the fraction f(hyd) 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.
authors.affiliation: Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan. kterao@chem.sci.osaka-u.ac.jp
authors.forename: Ken
authors.initials: K
authors.lastname: Terao
authors.forename: Fumihiro
authors.initials: F
authors.lastname: Maeda
authors.forename: Keiko
authors.initials: K
authors.lastname: Oyamada
authors.forename: Takaaki
authors.initials: T
authors.lastname: Ochiai
authors.forename: Shinichi
authors.initials: S
authors.lastname: Kitamura
authors.forename: Takahiro
authors.initials: T
authors.lastname: Sato
mesh_terms: D000688:Amylose / Q000031:analogs & derivatives* / Q000737:chemistry*; D002219:Carbamates / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D013237:Stereoisomerism
chemical_list: D002219:Carbamates; C579296:amylose tris(ethylcarbamate); C579297:amylose tris(n-hexylcarbamate); D000688:Amylose