The Crystalline Structure of Poly-β,D(1→4′)mannose: Mannan I

The crystallographic structure of mannan I has been examined by X-ray fiber diffraction, polarized i.r. spectroscopy, and computer chain-packing methods. The combination of X-ray intensity data and the chain packing analyses have shown that the overall number of permissible structures is very limited so that van der Waals' forces play a major role in packing. It was concluded that the chain senses are anti-parallel. The interpretation of the polarized i.r. spectra in the OH stretching region is in line with the presence of an intra-molecular hydrogen-bond between O(3)… O(5′). The awkward "knobby" shape of the mannan molecule, largely a result of the axial disposition of O(2)—H, lends itself to a close packing mainly determined by van der Waals' forces. The considerable similarity between X-ray and i.r. data from mannans and glucomannans would indicate that structural conclusions about the former might relate to the latter.