X-RAY AND CONFORMATIONAL-ANALYSIS OF ARABINAN

Fibers prepared from the enzymically debranched plant polysaccharide a rabinan, containing (1 --> 5)-linked alpha-L-arabinofuranose residues, produce X-ray diffraction patterns containing concentric rings indica tive of a high degree of structural organization. The measured unit ce ll dimensions and fiber density are consistent with a 2-fold helix pas sing through each unit cell. According to model-building techniques an d energy calculations, a total of seven molecular structures (three wi th C2'-endo and four with C3'-endo sugars), all of pitch 8.74 Angstrom , and hence seven different crystal-packing arrangements are the most probable. While intrachain hydrogen bonds are only present in three ca ses, interhelix association is facilitated by hydrogen bonds in all al lomorphs. Small energy differences between them suggest that easy conf ormational transitions may be made from one form to another. This poly morphism and the tendency to form microcrystals in the solid state mig ht confer upon arabinan the observed fat mimetic properties. (C) 1997 Elsevier Science Ltd.