The crystal structure of methyl beta-cellotrioside monohydrate 0.25 ethanolate and its relationship to cellulose II

The crystal structure of methyl beta-cellotrioside (methyl O-beta-D-glucopyranosyl-(1-->4)-O-beta-d_guycopyranosyl-(1-->4)-be ta-D- glucopyranoside) complexed with water and ethanol, C19H34O16. H2O.0.25[C2H6O] was determined by combining Cu K alpha X-ray and synchrotron data collected at room temperature. The crystals have the monoclinic space group P21 with Z = 8 and unit cell parameters a = 7.9978(11), b = 76.38(4), c = 8.9908(6) A and beta = 116.40(1) degree. The structure, which was solved by direct methods and refined to a final R-factor of 0.067, contains four independent molecules of methyl beta-cellotrioside with an extended conformation. They are arranged parallel to the long b axis of the unit cell, and organized in two pairs of antiparallel molecules. Each beta-D-glucopyranosyl residue of the four independent molecules is in the 4C1 pyranose conformation, and each (O-6) primary hydroxyl group has the gt conformation. The crystal structure of methyl beta-cellotrioside has many points in common with that of cellotetraose hemihydrate as well as with the structure of cellulose II. Thus, it is likely that the precise atomic coordinates obtained in this study can be directly transposed to give an improved structure for cellulose II where, in particular, only the gt conformation would be present at the primary hydroxyl groups of both polysaccharide chains.