Calcium interactions with D-glucans: crystal structure of alpha, alpha-trehalose-calcium bromide monohydrate

Three-dimensional X-ray diffraction data were used to determine the crystal structure of α,α-trehalose-calcium bromide monohydrate, a model system for investigation of factors involved in the binding of calcium ions to d-glucans of dental plaques. Crystals of C₁₂H₂₂O₁₁ ·CaBr₂·H₂O are orthorhombic, space group C222₁, with a  11.058(1) b  11.537(1), c  15.101(1) Å, and Z  4. Intensity data for 925 independent reflections were measured with an automated diffractometer. A trial structure, obtained by the heavy-atom method, was refined by least-squares to R  0.03. An outstanding feature of the crystal packing is the interaction of trehalose molecules with calcium ions. Each calcium is coordinated to hydroxyl groups from four symmetry-related d-glucose moieties, thereby cross-linking the trehalose molecules. Similar interactions between calcium ions and the d-glucose residues of extracellular d-glucans may be of importance in the agglutination processes involved in dental-plaque formation.