The double-helical nature of the crystalline part of A-starch

Structural studies of starches with different water contents

“…[1][2][3] The short-range order structures have been found to consist of parallel-stranded double helices, and the long-range order arrangements of these double helices give rise to two types of crystalline, or polymorph, structures, A and B. A-type polymorphs are formed from the orthogonal packing of double helices with a small amount of tightly bound structural water. [3][4][5][6][7][8] It has been suggested that either four 5 or eight 6 water molecules per unit cell are present within A-type polymorphs. B-type polymorphs are formed by a more open hexagonal packing of the double helices, with 36 water molecules per unit cell, some of which are located in channels formed by the hexagonal packing.…”

Why should polymer physicists study biopolymers?

“…Surprisingly, to a polymer physicist's mind, it is not the linear amylose molecule which is involved in the crystals present in the granule, but the side-chain branches of the amylopectin which form double helices which align to give small crystals a few nanometer in thickness. 24 For systems in which the amylopectin side chain branch distribution contains a significant number of very short branches, crystallinity is significantly impeded, and here we see an example of where the biological route of production can affect the end products. The granules of many genetically modified starches are found to be misshapen and cracked (compared with the equivalent native species), and changes in the molecular composition are clearly a key ingredient in these changes.…”

Characterization Methods for Starch-Based Materials: State of the Art and Perspectives

“…V-type crystallites involve lipid complexes. [99,102] A-type crystallites have a monoclinic unit cell [103,104] and B-type crystallites are formed by a hexagonal unit cell which contains a large water channel. [105,106] C-type crystallinity is a mixture of both A-and B-type crystallites, with A-type crystallites typically localized at the granule periphery and B-type closer to the centre.…”