Conformation and packing analysis of polysaccharides and derivatives. I: Mannan

A previously described procedure for simultaneous optimization of bond lengths and angles was used to test different models for mannan I. Potential hydrogen bonds and the glycosidic angle were included in the optimization. A conformational model with bifurcated intramolecular hydrogen bonds of the type observed in the methyl cellobioside methanol complex showed the best agreement with available exprerimental data. The coordinates of this model were provided by computer calculations. The available X-ray data, however, were not sufficient for selecting this model; rather, ir data were necessary to furnish the needed information. The different conformational models tested all showed an almost constant virtual bond length O(1)–O(4) of the β-pyranose residue. This was in contrast to the previously obtained results for the α-pyranose residues.