Rigid helical conformation of curdlan tris(phenylcarbamate) in solution

Light and small-angle X-ray scattering and viscosity measurements were made for four curdlan tris(phenylcarbamate) (CdTPC) samples having quite narrow dispersity indices (DI) and ranging in the molecular weight between 6 × 104 and 2 × 106, to determine weight-average molecular weights Mw, radii of gyration 〈 S 2 〉 , particle scattering functions P(q), and intrinsic viscosities [η] in tetrahydrofuran (THF) and 4-methyl-2-pentanone (MIBK). Size-exclusion chromatography equipped with light scattering and/or viscosity detectors was performed for some broad DI samples in THF also to determine 〈 S 2 〉 and [η] as a function of Mw. The solution data were analyzed in terms of the wormlike-chain model to estimate the Kuhn segment length of 57 nm in THF and 17 nm in MIBK and the helix pitch per residue h of 0.39 nm in THF and 0.51 nm in MIBK. Since the former h value is almost equivalent to that for single helical curdlan and its acetate derivative in crystal, it is reasonably suggested that the local conformation of CdTPC in THF is close to the tightly wound helix stabilized by the intramolecular hydrogen bonding, which was detected from the solution IR spectra.