THE PHYSICAL PROPERTIES OF INULIN SOLUTIONS

Abstract

Carefully recrystallized samples of inulin have been analysed chromatographically for low-molecular-weight contaminants. The analysis of the samples revealed amounts of low-molecular-weight polyfructosans amounting to 5-10% of the inulin. The possible polymorphism of inulin, its solubility behavior and suggestions of association to solution are discussed. Physical techniques suggest considerable polydispersity. Ultracentrifugation gives a weight-average molecular weight (Mw) 7250, whereas osmotic-pressure measurements suggest a number-average molecular weight (Mn) 5600. A probable steric model is suggested of a helix repeating every four residues, of diameter 12A and axial ratio 7. 5-10. Fractionation of the inulin on columns of Sephadex G-25 show a pronounced polydispersity. Some doubt is cast on the reliability of inulin as an indicator of physiological volumes of distribution in body fluids.