Real‐space crystal structure solution. Crystal and molecular structure of laminarabiose octaacetate, C28H38O19

Abstract

The elucidation of a crystal structure on the basis of complete minimization of intramolecular and intermolecular energy of packing has been applied to laminarabiose octaacetate. [Crystal data: Mr = 678.6, orthorhombic, P212~21, a = 10.379 (2), b = 22.943 (7), c=14.599 (4) A, Z=4, V=3476.4~ 3, Din= 1.30 (1), Dx = 1.297 Mgm -3, h(Cu Ka)= 1.54178 A, /z(Cu Ka)=0.91 mm -~, F(000)= 1432, room temperature, final R = 0.095 for 1660 observed independent reflexions.] The two D-glucose residues have the 4C~ pyranose conformation and are fl-(1 ~ 3) linked. The conformational angles ~p and ~ at the glycosidic linkage have the values -81.1 and 134.8 ° respectively. The present work establishes in an unambiguous manner the foundation of conformational analysis theory applied to the elucidation of crystal structures. It appears that intermolecular interactions in the crystal can be treated in good approximation with the intramolecular potential functions. When coupled with appropriate X-ray data, crystalline conformations may be deduced without highly refined potential functions. As compared to what is faced in polymer crystallography, where the number of packing parameters is reduced, finding a good starting point may represent the essential difficulty associated with the proposed methodology. Once a reasonable location * Laboratoire Propre du CNRS, associ6 ~ l'Universit6 Scientifique et M6dicale de Grenoble, France. f Present address: Laboratoire de Stockage et de Conservation des Denr6es Alimentaires, INRA, Centre de Recherche de Nantes, Chemin de la G6raudi6re, 44072 Nantes, France. has been found for the molecule, the minimization procedure allows one to handle a reasonable number of parameters and yet yields only a few possible structural models. At this stage, the best packing models have to be checked against X-ray structure amplitudes.