Intramolecular changes during polymorphic transformations of amylose

Abstract

A survey of small saccharide crystal structures indicates that there is substantial variability in the shape of the α-D-glucose residue and in the conformation angles at the glycosidic linkage. Both factors appear to be altered primarily by hydrogen bonding and crystal packing forces. For the purposes of building computer models of cyclodextrins and amyloses, the residues from different crystals may be characterized in terms of the virtual angles, O(1)-C(1)-C(4) and C(1)-C(4)-O(4). Computer models of six-, seven-, and eight-residue cyclodextrins require residues having different such angular values because of the role played by the parameter n (number of residues per cycle). In computer models of amyloses, a similar role is also played by the helical parameter h (rise per residue). It is therefore concluded that polymorphic transformations often involve alterations in monomeric geometry as well as rotations about valence bonds to the linkage oxygen atoms. Finally, it is proposed that the entire space of accessible conformations be represented on a grid of h vs. n with consideration given to the full range of residue geometries at each grid point.