Curdlan three forms

Crystal data and a brief account for the structure of three forms of the curdlan are given in Table II. A schematic represen-... 

There are at least four crystalline forms of cellulose, based on different packing of the primary chain (Blackwell, 1982), and three forms of granular starch, based on the packing of double helices (Noel et al., 1993). The differences are largely in the unit-cell dimensions and the crystallization and precipitation temperatures. One form of starch, precipitated with alcohol, is in a symmetrical molecular arrangement and is readily dispersible in cold water (Kerr, 1950). Mannan and dextran yield different crystals at low and high temperatures, and there was not only a polymorphic difference, but a conformational difference in cellulose (Quenin and Chanzy, 1987). Curdlan appears to have three polymorphs—anhydrous, hydrated, and annealed. 

The dimensions of the xylan unit cell are slightly different a = b = 1.340 nm, (fibre axis) = 0.598 nm.) Atkins and Parker T6) were able to interpret such a diffraction pattern in terms of a triple-stranded structure. Three chains, of the same polarity, intertwine about a common axis to form a triple-strand molecular rope. The individual polysaccharide chains trace out a helix with six saccharide units per turn and are related to their neighbours by azimuthal rotations of 2ir/3 and 4ir/3 respectively, with zero relative translation. A similar model for curdlan is illustrated in Figure 6. Examinations of this model shows that each chain repeats at a distance 3 x 0.582 = 1.746 nm. Thus if for any reason the precise symmetrical arrangement between chains (or with their associated water of crystallization) is disrupted, we would expect reflections to occur on layer lines which are orders of 1.746 nm. Indeed such additional reflections have been observed via patterns obtained from specimens at different relative humidity (4) offering confirmation for the triple-stranded model. 

Another polysaccharide which displays interesting hydration phenomena is (l->-3 )-B-D-g 1 ucan, often called paramylon ( ), curdlan ( ) or laminaran (16). The molecular crystalline arrangement o P this polysaccharide consists of a triple helix formed by three intertwining 6j hel ices. (, 23) Two polymorphs... 

The beta-l,3-glucans are dramatically different from the glucans described so far. This polymer is extremely flexible, and occurs in many instances in nature. The polymer goes by the names of curdlan, pachyman, laricinan, schleroglucan, paramylon, lentinan, laminarin, callose and schizophylan. The prevalent form appears to be a triple helix, with n > 6 and b 0.3 nm for each of the three strands ( ). If triacetate derivatives are made, n > 6 and h = 0.31 to 0.36 nm (10). The acetate helices are single. Of some interest is the lack of allowed 2-fold conformations on the n-b map (Figure 5). The allowed zones close up when n = 20 or so, but some small adjustments in the monomer shape could allow an infinite number of monomeric units per helix repeat. 

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