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The crystal structures of the A-, B-and C-polymorphs of amylose have been determined through a combination of fiber x-ray diffraction analysis and computer-based structure refinement. The three structures correspond to the naturally occurring A-, B-and Cstarches. A-and B-structures differ in the crystalline packing of the helices and the water content. The C-structure is a mixture of Aand B-unit cells and, therefore, intermediate between the A-and B-forms in packing density. Die Kristallstrukturen der polymorphen FormenA, B und C von Amylose und Starke. Die Kristallstrukturen der polymorphen Formen A, B und C von Amylose wurden mit Hilfe einer Kombination der Faser-Rontgenbeugungsanalyse und der Struktur-Raffinierung auf Computerbasis untersucht. Die drei Strukturen entsprechen dennaturlich vorkommenden A-, Bund C-Starken. Die A-und B-Strukturen unterscheiden sich hinsichtlich der kristallinen Packungsdichte der Helices und des Wassergehaltes. Die C-Struktur ist eine Mischung aus A-und B-Elementarzellen und steht somit hinsichtlich ihrer Packungsdichte zwischen der A-und B-Form.

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SynopsisContinued study of the five crystalline Na-celluloses, previously shown to occur as intermediates during the mercerization of cellulose and exhibiting two types of crystallographic fiber repeats, further indicates that they fall into three classes based on their unit cells and NaOH contents. In one class are Na-celluloses I and 111, both containing up to 34% NaOH; in the second class are Na-celluloses IIA and IIB, marked by ca.15 8, fiber repeat and containing up to 65% NaOH and in the third class is Na-cellulose IV which is likely to be a hydrated form of cellulose 11. Na-cellulose I was found to be the common first alkali-cellulose structure produced in the NaOH treatment of both cellulose I and cellulose 11. Further study of this conversion step suggested a mercerization mechanism in which the alkali begins the conversion of cellulose to Na-cellulose I in the amorphous parts of the fiber. The conversion of the parallelchain cellulose I structure to an antiparallel one is likely to occur already in this first step.