The molecular packing in native starch

A remarkable feature of this structure is that the van der Waals packing distance between double heUces is in agreement witft the glucoside lirik. This is a direct consequence of the IPMS character of the structure. The position of the polyglucan chain in relation to diis surface is illustrated in Fig. 8.5. Just as in quartz, there is a packing distance between the double helices that is related to the helical units. These links correspond to the labyrinths joining the double helices. The nature of these labyrinths of the Q surface space group 6422 is considered further below. 

This extraordinary structure leads to an understanding of some important mechanisms in the biosynthesis of starch. There is evidence for formation of a so-called coacervate , in other words a phase separation. The tendency of imits like those shown in Fig. 8.4 to crystallise is obvious - the possibility of close-packing of adjacent units exists, as well as close packing within each imit. A direct consequence of lateral packing of such units is that the enzyme 

If amylose and amylopectin are mixed in water, an amylose-rich upper phase and an amylopectin-rich bottom phase are formed. We can regard the starch gelatinisation itself as such a phase separation, where amylopectin remains in the water-swollen granules and amylose forms the outside solution. It is interesting to see how the shape of the granules changes successively during this process, which is illustrated in the case of wheat starch in Fig. 8.6. Thus there is a clear tendency of deformation so as to obtain an outer surface with 

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