The conformation of amylose in solution. I

Abstract

The neutralization process of an alkalline solution of amylose was investigated by fluorescence depolarization and optical rotation to find the conformation of this polysaccharide in aqueous solution. The measurements showed that amylose existed in different conformations in alkaline and neutral solutions. The transition between these conformations appeared as a minimum in the 1/p and [α]405 vs. pH curves at pH 12.5. Here p is the degree of polarization and [α]405 is the specific optical rotation at 405 nm wavelength. In an alkalline solution, the reduced viscosity showed behavior characteristic of polyelectrolytes and the conformation of the polymer seemed to be a negatively charged expanded coil. But in a neutral solution, the polymer seemed to take on an ordered conformation. This ordered conformation disappeared when KSCN was added to the solution, implying that it was maintained by hydrogen bonds. This conformation also disappeared in two steps, at about 35 and 60°C on heating. One step, at the higher temperature, consists in the transition from helix to coil. This temperature agrees with the “gelatinization temperature” of amylose or starch. The other step, at the lower temperature, is a secondary change in the helical structure. The transition from coil to helix occurred in a pH range from 13 to 12. The salt produced by neutralization of the alkalline amylose solution seemed to allow the amylose molecules to shrink to compact coils before winding helical turns. © 1981 The Society of Polymer Science, Japan.