B-amylose

Fig. 1. (a) The glucopyranosyl basic unit, where e = equatorial and a = axial bond (b) amylose with equatorial—axial intemnit bonding (the C—H axial... 

Fig. 11. — Parallel packing arrangement of 6-fold, B-amylose (9) molecules, (a) Stereo side view of slightly less than 2 turns of a pair of double helices 10.7 A apart along the long diagonal of the ab-plane. The two strands in each helix are distinguished by open and filled bonds, and the helix axis is also drawn, for convenience. Notice that atom 0-6 mediates both intra- and inter-double helix hydrogen bonds.

With regard to molecular morphology, whether it is A- or B-amylose, there is no room for a water or similar molecule to enter the cavity in the interior of the... 

KOH-amylose complex, 346-347 A-Amylose, 340-342, 407-408 B-Amylose, 342-344, 409 V-Amylose, 345-346, 410 Analytical chemistry, 18 Anhydrides... 

Fig. 16. Projection view of B-amylose showing the large central canal occupied by guest water molecules (black dots). The helical double strands of amylose are repesented as rings. The arrows illustrate the antiparallel nature of the packing...

Figure 3.25 CD spectra of (a) arylalkylcarbamates of cellulose (25) and (b) amylose (26) cast from THF solution. (Reprinted with permission from Ref. 188. Copyright 1993 by Elsevier Science.)...

FIGURE 2 The chemical structures of (a) cellulose and (b) amylose polymers. 

The unit cell dimensions of all crystalline amyloses that have been determined in some detail, are listed in Table I. Also included are some intermediate forms between the va and Vjj amyloses (Ji.) and some V-amylose complexes with n-butanol, which, although not yet completely determined, have been added to illustrate the range of variability in unit cell dimensions. In the case of the Va-BuOH complex, a doubling of one unit cell axis was detected after a careful study of electron diffraction diagrams of single crystals ClO). A consequence of the doubling is that the unit cell now contains four chains, instead of the two normally found in amylose structures. Cln a strict sense, the A- and B-amyloses should also be considered as four-chain unit cells, but their double-helical structure still results in only two helices per cell) (13,1 ). 

Almost all unit cells shown in Table I are either orthorhombic or pseudo-orthorhombic, with a majority of space groups P2] 2] 2] and P2. Only a few structures exhibit higher symmetry and none shows lower symmetry. All structures have an antiparallel packing of chains (however, see A- and B-amyloses). On the other hand, a large variety of helix characteristics are evident, in addition to the variability in the unit cell dimensions. Some of the features useful for classifying amylose structures are shown in Table II. The distance between the two nearest antiparallel-... 

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...

Unit cell dimensions of different polymorphs of amylose and amylose derivatives. All unit cells contain 2 chains except Va-BuOH and A- and B-amyloses, which contain 1+ chains. 

The double-helical structures of native A- and B-amyloses are found in the fourth group. It is interesting that in both h as well as the d and dyg spacings, they are comparable with the structure of amylose triacetate I (ATAI). In part, this may arise because the packing of the bulky acetate substituents in ATAI is similar to the close-packing of two amylose chains into a double helix. In the latter, one chain may act as the "substituent" for the other chain. At any rate, all three structures contain similar, cylindrical-shaped helices. Somewhat unexpectedly, the distances cL and d-yo are very close for the two native polymorphs, even though their unit cells and packing are... 

The molecular conformation and interstrand hydrogen bonding of the A- and B-amyloses are shown in Figd 9 Both strandg of the duplex are relatively extended (h - 3. 7 A for B and 3.51 A for A), although not nearly as extended as the alkali or salt amyloses, or some of the derivative structures. The extension of the helix prevents the formation of the intramolecular 0-2...0-3(2) hydrogen bond that occurs in V-amyloses. Conversely, the extended conformation permits the formation of the interstrand hydrogen bonds that appear instrumental in the stabilization of the structure. 

Figure 9. Side view of the double helix of A- and B-amyloses. Interstrand hydrogen bonds are shown by dashed lines (38).

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)...

Wu H-CH, Sarko A (1978) The double-helical molecular structure of crystalline A-amylose. Carbohydr Res 61 27 -40 The double-helical molecular structure of crystalline B-amylose. Carbohydr Res 61 7-25... 

Fig. 8.2 Carbohydrate structures (a) cellulose, (b) amylose and amylopectin, (c) chitin.

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