Network formation in dilute amylose and amylopectin studied by TEM

The retrogradation, or reprecipitation, of dilute amylose and amylopectin a queous solutions was investigated by transmission electron microscopy (TEM) . Negative staining, shadowing, and cryo-TEM were combined to study the mor phology of the molecular assemblies at different stages of precipitation. A mylose fractal-like networks formed within a few days. They are described a s clusters of elementary semicrystalline 10-15 nm units, formed by associat ions of molecules into parallel double helices, linked by amorphous section s containing loosely organized chains. These networks subsequently condense d, yielding thick aggregates. Amylopectin was found to form similar network s whose branches also had a 10-15 nm lateral width. The elementary units ar e thought to be clusters of nanocrystals formed by association of the short side branches of the molecule into parallel double helices. As the amylope ctin networks were stable in solution at this concentration during several months and did not undergo any further aggregation, the branched configurat ion of the molecule is believed to hinder the long-scale rearrangement of t he crystallites.