Structure cristalline d'une deuxième forme de mélézitose monohydrate. Effet de l'environnement sur la géométrie d'un oligosaccharide

Abstract Melezitose [ O -α- d -glucopyranosyl-(1→3)-β- d -fructofuranosyl α- d -glucopyranoside] monohydrate crystallizes in two polymorphic forms (I and II). The structure of form II, studied by X-ray crystallography, shows an orthorhombic cell having a 7.135 (4), b 15.362 (8), c 19.134 (8) A, space group P2 1 2 1 2 1 , and Z 4. The structure, solved by direct methods, was refined to a final value of R 0.045. The molecule of form II seems to be more constrained by its crystalline environment than that of form I. These constraints imply not only little variations in glycosidic bonds, but also a change of conformation for the furanose ring, and a perceptible deformation of the sucrose pyranose ring. This study gives an example of estimation of oligosaccharide molecular-flexibility.