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Molecular Modeling of Saccharides, Part XXIV.
The Hydrophobic Topographies of Amylose and its Blue Iodine Complex.
S. Immel and F. W. Lichtenthaler, Starch/Stärke 2000, 52, 1-8.
Abstract / Fulltext PDF
Starch, the biologically most important carbohydrate energy reservoir in plant cells, is contained in the "non-living", but metabolism-associated granules of these cells. Amylose, the unbranched fraction of native starch, is a polymer of several hundred α(1→4)-linked glucose units, which in contrast to the linear chain polymer cellulose composed of β(1→4)-linked glucoses adopts a helical conformation. On the basis of characteristic X-ray diffraction patterns obtained for different samples of starch, the individual polymorphs were termed A-, B-, C-, and V- ("Verkleisterung") amylose.
Molecular lipophilicity patterns (MLPs) were calculated for structural models of two polymorphs of amylose. The native double helical and parallel-stranded A-form represents a rather compact structure with an irregular distribution of hydrophilic and hydrophobic regions over the entire outer surface, the interior of the helix is inaccessible even for small molecules. Denaturation yields V-type amylose, which consists out of single-helices with a central channel passing through the molecular axis. In relation to the outside surface the channel is decisively hydrophobic. The hydrophobicity patterns explain the capability of V-amylose to form inclusion complexes with fatty acids. In the well-known dark-blue stained amylose-iodine complex, the channel structure serves as a well-ordered matrix to accommodate nearly linear polyiodide chains with an almost perfect steric fit.