The crystal structure of (t-maltose [4-O-qt-D-glucopyranosyl)-~vD-glucopyranose] has been determined by single-crystal X-ray techniques. The unit cell is orthorhombic, space group P2z2~2 ~, with dimensions a = 12.667 (3), b = 13.830 (5) and c = 8.400 (2) A. The structure was solved using a direct method and refined by full-matrix least-squares procedures. Difference syntheses showed all H atoms and also indicated a partial (18%) random substitution of tt-maltose molecules by the fl anomer. The final discrepancy factor, R, is 0.043 for 1379 observed reflections. Bond lengths and angles are in good agreement with those of other disaccharides. The pyranosyl rings are slightly distorted from the C1 chair form and the O(1)-O(4) distance of 4.052 A is shorter than found previously. The primary alcohol groups have gauche-trans orientations. All the O atoms in both the t~ and fl anomers, except the bridge O atoms, take part in a hydrogen-bonding network.
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Introduction ExperimentalIn connection with X-ray diffraction studies of selected carbohydrates in this laboratory (James, French & Rundle, 1959;Hybl, Rundle & Williams, 1965;Jacobson, Wunderlich & Lipscomb, 1961;Hackert & Jacobson, 1971), we have determined the crystal and molecular structure of st-maltose. Maltose is obtained, along with other products, from the partial hydrolysis of starch in aqueous acidic solution. Maltose is also formed in the fermentation of starch to ethyl alcohol, when catalyzed by the enzyme diastase, which is present in malt. The i.mportance of the molecular conformations of carbohydrates has long been recognized, and therefore a number of crystal investigations of monosaccharides, disaccharides, polysaccharides and their derivatives have been carried out using X-ray and neutron diffraction techniques. Just as the molecular structure of cellobiose is important in order to better understand the properties and reactions of cellulose, the molecular conformation of maltose is important in basic studies of starch. The crystal structures of fl-maltose monohydrate (Quigley, Sarko & Marchessault, 1970), methyl fl-maltopyranoside monohydrate , and isomaltose monohydrate (Dreissig & Luger, 1973) have been determined by other workers. We decided to carry out a molecular structure investigation of a-maltose in order to elucidate its molecular conformation and to compare the st and fl forms and the corresponding hydrogen bonding in these solids. Crystalline samples of it-maltose containing approximately 20% of the fl anomer and whose preparation has been described by Hodge, Rendleman & Nelson (1972) were kindly supplied by J. E. Hodge and D. French. The unit-ceU parameters and their estimated standard deviations were obtained by a leastsquares fit to the +20 values of 12 independent highangle reflections.For data collection a crystal in the shape of a parallelepiped formed with the (100), (010) and (001) planes as faces and of dimensions 0.3 × 0.3 × 0.5 mm was selected. Data were collected at room temperature using an automated four-circle diffracto...