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-gl ucopyranosyl-(1 --> 4)-O-beta-D-glucopyranosyl-(1 --> 4)-beta-D-glucop yranoside) complexed with water and ethanol, C19H34O16. H2O . 0.25[C2H 6O] was determined by combining Cu K alpha X-ray and synchrotron data collected at room temperature. The crystals have the monoclinic space group P2(1) with Z = 8 and unit cell parameters a = 7.9978(11), b = 76 .38(4), c = 8.9908(6) Angstrom and beta = 116.40(1)degrees. The struct ure, which was solved by direct methods and refined to a final R-facto r of 0.067, contains four independent molecules of methyl beta-cellotr ioside with an extended conformation. They are arranged parallel to th e long b axis of the unit cell, and organized in two pairs of antipara llel molecules. Each beta-D-glucopyranosyl residue of the four indepen dent molecules is in the C-4(1) pyranose conformation, and each (0-6) primary hydroxyl group has the gt conformation. The crystal structure of methyl beta-cellotrioside has many points in common with that of ce llotetraose hemihydrate as well as with the structure of cellulose II. Thus, it is likely that the precise atomic coordinates obtained in th is study can be directly transposed to give an improved structure for cellulose II where, in particular, only the gt conformation would be p resent at the primary hydroxyl groups of both polysaccharide chains.