Anomeric exchange and the structure of n-alkyl D-glucopyranosides. A study of binary phase behavior.
X-Ray diffraction and calorimetric data from the alpha and beta anomers of n-alkyl D-glucopyranosides are analyzed to describe the molecular packing and co-solubility in the crystalline and liquid-crystalline phases. In the smectogenic chain-length series, the beta-glucosides are co-soluble, with almost ideal mixing in the crystalline and meso-phases for chain-length differences of two carbon atoms. The smectic phases of octyl alpha- and beta-glucosides are also co-soluble and a time sequence of phase diagrams (as well as lamellar X-ray data), as the solid obtained from the cooled melt is equilibrated, indicate that a metastable co-crystalline phase may exist until the respective hydrogen-bonding schemes are established. Lamellar spacings from a homologous series of the beta anomers indicate that both the crystal structure and smectic-layer packings involve bilayer stacking of the molecules, a result that is difficult to reconcile with the respective surface-area requirements of the molecular acyl chain and sugar moieties.
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Electron Diffraction Department, Medical Foundation of Buffalo, Inc., NY 14203.
D002152:Calorimetry, Differential Scanning; D005960:Glucosides / Q000737:chemistry*; D015394:Molecular Structure; D013816:Thermodynamics; D014961:X-Ray Diffraction
D005960:Glucosides