CHEMICAL MODIFICATION OF PULULAN .1. PERIODATE-OXIDATION

The present paper describes the periodate oxidation of pullulan. Special attention is paid to the structures and characteristics of the activated products. Pullulan contains three different anhydroglucoside moieties in the repeating unit. Therefore, periodate oxidation of pullulan results in different types of dialdehyde structures. From titrimetric analysis of the formic acid generated during the oxidation of pullulan, the numbers of singly and doubly oxidized anhydroglucoside units can be calculated. The aldehyde content in completely periodate-oxidized pullulan as determined by reaction with hydroxylamine hydrochloride is only 67%. A plausible explanation is the presence of a stable, six-membered hemiacetal. The presence of aldehyde groups with different reactivities is also evidenced by the data collected from reduction experiments and by C-13 n.m.r. Finally, the hydrolytic stability of the polysaccharide backbone was studied.