Helical conformation of amylose in aqueous solution. I. Viscosity measurements

Abstract

AbstractTwo amylose samples, amylose V (DPw = 2300) and amylose HE 15 (a low‐substituted hydroxyethylamylose, DPW = 1600) were studied. The intrinsic viscosity of the polymers in aqueous solution was measured with regard to its dependence on the alkalinity (0 to 5MNaOH), the ionic strength (0 to 5M), and the temperature (0 to 75°C). Additionally, the temperature dependence of the viscosity of the amylose‐iodine complex was measured. It was found that the two amylose samples show the same dependence on the studied parameters. Therefore, it was concluded that the conformation is unchanged by the hydroxyethylation in the present case. In a discussion, steric, hydrodynamic, and thermodynamic data on amylose in solution are compared with the corresponding data on cellulose and dextran. The comparison leads to the conclusion that amylose in a neutral solution must have a helical conformation, corresponding to the well‐accepted rod conformation of cellulose. The helical conformation also explains several viritual anomalies in the behavior of amylose. The results of the experiments support the helix model for amylose. The conclusion of the whole work, therefore, is that the amylose molecule in neutral aqueous solution can be regarded as a random coil, built up by helical segments. The average number of monomers per segment exceeds 100. This value decreases with increasing alkalinity.