Amylose diffraction patterns

Although it has been found that the separated amylose component can be readily orientated to yield fiber patterns, amylopectin usually gives poor or amorphous patterns. In the granule, however, amylopectin does exhibit crystallinity, since waxy maize starch gives a diffraction pattern and other waxy starches behave similarly.193 -195 (This suggests that the branch points in the amylopectin molecule may be in the amorphous part of the granule.)... 

Bundle and coworkers196 first investigated the diffraction patterns obtained from stretched films of amylose obtained from maize starch ( B -modification). The dimensions of the orthorhombic unit cell were as follows. 

Figure 2. X-ray fiber diffraction patterns for ("top, left to right) V -amylose VrnlSo-amylose KOH-amylose (bottom, left to right) B-amylose, amylose triacetate I, triethylamylose I-nitromethane complex...

Because the varieties of starch that contain only amylopec-tin are also crystalline, exhibiting the same diffraction patterns as starches containing amylose, there is a strong likelihood that the extensively branched amylopectin molecule also crystallizes in a double-helical form. In turn, this implies that linear sequences in amylopectin remain sufficiently long to... 

Figure 5.4 X-ray powder diffractogram recorded for (a) A-type amylodextrins and (b) B-type amylodextrins grown as spherulites. X-ray fiber diffraction patterns (fiber axis vertical) for (c) A-amylose (fiber spacing 1.04 nm) and (d) B-amylose (fiber spacing 1.05 nm). (Reproduced with permission from references 30 and 31). Microcrystal of (e) A-starch and (f) B-starch observed by low dose electron microscopy. Inset the electron diffraction diagrams recorded under frozen wet conditions (e). (Reproduced with permission from references 32 and 34)...

Figure 16.4 X-ray diffraction patterns and relative crystallinities of normal, waxy and high-amylose starches. (Adapted from reference 42 with permission)...

The capacity of starch to stain blue-black with iodine suggests that some of the amylose is present in the starch in the V-form. The lipids present in cereal starch would bind to amylose if it were in the V-form, and yet X-ray analysis does not show the presence of the V-polymorph in cereal starches (i.e., most of the amylose would be in the amorphous form). The conclusion is that although a significant part of the amylose is probably in the helical form, the three-dimensional order necessary to give a crystalline diffraction pattern is absent. Indeed, the crystalline nature of starch is now attributed to the presence of amylopectin and not to amylose. Starch from waxy mutants contains only amylopectin (and no amylose), but this starch has the same degree of crystallinity and the same X-ray pattern as the regular starches that contain both components. 

Starch fractionation using 1-pentanol,657,705 cyclohexanol,706 2-butanol, and 2-propanol698 instead of 1-butanol have also been proposed. Amylose complexes with all of the normal-chain alcohols have essentially the same X-ray diffraction pattern, which differs from the patterns of amylose complexes with branched alcohols.707,708... 

Binding parameters and X-ray diffraction patterns of the complex of starch with 1-decanal do not differ significantly from corresponding analyses performed using 1-decanol.656,679 The temperatures of formation of the aldehyde complexes are likewise close to those for relevant starch-alcohol complexes.673,680 Analysis of the binding sites of the complex suggests that both amylose and amylopectin are involved in complexation, but these complexes are rather weak.717... 

Kooiman separated exocellular amylose formed in liquid media at pH < 5 by Cryptococcus albidus and Cryptococcus laurentii var. flavescens NRRL Y-1401 from a polysaccharide containing D-man-nose, D-xylose, and D-glucuronic acid. X-Ray diffraction patterns of the retrograded amyloses were identical with that of tuber starch (B modification). Periodate oxidation, optical rotational measurements, and hypoiodite oxidation data suggested a linear a-D-(l—>4)-linked structure having a chain length of about 44 units for the Cr. albidus amylose. Cryptococcus neoformans produces a crystalline amylose that was isolated by the method of Schoch. It has an iodine value and alpha- and hefa-amylase hydrolysis characteristics similar to those of corn amylose. 

Interpretation of the WAXS patterns of native starch is often difficult because of the low crystallinity, small size, defects and the multiple orientations of the amylopectin crystallites (Waigh et al, 1997). Two main types of X-ray scattering patterns have been commonly observed (A and B). Potato starch has been shown to crystallize in a hexagonal unit cell in which the amylopectin molecules twist in a double helix (the B structure) (Lin Jana Shen, 1993). Between adjacent helices a channel is formed in which 36 water molecules can be located within the crystal unit cell. By means of heat treatment this structure can be transformed into a more compact monoclinic unit cell (the A structure) (Shogren, 1992). Amylose (the linear and minor component of starch) can be crystallized from solution in the A and B structures (Buledn etal, 1984), yielding X-ray diffraction patterns similar to those of amylopectin but with higher orientation. 

Many other amylose complexes are water-insoluble, and the complexes with methanol, 1-propanol, acetone, and butanone may be precipitated from solutions of amylose in methyl sulfoxide, as well as from aqueous solution. As amylose frequently forms crystalline complexes. X-ray diffraction patterns have been obtained for a number of them. Amylose-methyl sulfoxide complexes have a structure almost identical to those of amylose-ethylenediamine complexes, in which the complexing ratio is one ethylenediamine molecule per two n-glucose residues. The helix packing-diameter of the complexes, at least for complexes with linear aliphatic ketones, is dependent upon the chain-length of the molecule complexed, although other factors are also involved. ... 

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