Fine structure of (1→3)-β-d-glucans: curdlan and paramylon

Paramylon, a natural (1→3)-β-d-glucan found in Euglena gracilis, and curdlan, a “regenerated” (1→3)-β-d-glucan found in Alcaligenes faecalis, have been studied. Differences in chemical and physical properties are compared to each other and it is concluded that this system is a “native-regenerated” pair just as the well known “native cellulose-regenerated cellulose” system. X-Ray diffraction and density measurements indicate for paramylon a very high level of crystallinity, approaching 90%, whereas curdlan powder is only 30% crystalline. The effect of hydrolytic treatment on the crystallinity of the different samples shows the same trends as for cellulosic materials. From the negative birefringence of annealed fibers and positive birefringence of the paramylon granules, a tangential disposition of the chains in the granules may be concluded. Microfibril formation from curdlan precipitated from solution is in line with a proposed triple-helical structure for the crystalline form of this polysaccharide.