Conformational change of an amylose derivative in chiral solvents: amylose tris(n-butylcarbamate) in ethyl lactates

Abstract

The z-average radius of gyration, the particle scattering function and the intrinsic viscosity have been determined for amylose tris(n-butylcarbamate) (ATBC) in D-, DL- and L-ethyl lactates, all at 25 °C, by light and small-angle X-ray scattering and viscometry as functions of the weight-average molecular weight ranging from 1.7 × 10⁴ to 1.7 × 10⁶ to investigate the chiral solvent dependence of the helical conformation of the amylose derivative. The data were analyzed in terms of the wormlike chain model to determine the Kuhn segment length λ⁻¹ (the stiffness parameter) and the helix pitch per residue h. The λ⁻¹ value of 49 nm in D-EL is 52% larger than 32 nm in L-ethyl lactate, an unmistakable chiral solvent effect to the helical conformation of the amylose derivative, and the relation between h and λ⁻¹ is consistent with that obtained previously in nine different solvents [Polymer, 2010, 51, 4243]. The content of intramolecularly hydrogen bonding CO groups in D-ethyl lactate is estimated to be 15% more than that in L-ethyl lactate, confirmed by heats of dilution for ethyl lactate solutions of ATBC estimated by isothermal titration calorimetry.