Proton-deuteron and H2O-D2O exchange in polysaccharides by X-ray and small-angle neutron scattering

Rodlike fragments of the polysaccharide cinerean were examined in H 2 O and D 2 O with small-angle X-ray and neutron scattering (SAXS and SANS). From measurements of the macroscopic scattering cross section on an absolute scale the mass per length of the rods has been determined. The SANS measurements in D 2 O yield a value very different from those obtained by other measurements (SAXS with H 2 O and D 2 O; SANS with H 2 O). This effect has been used to determine the exchange of protons and bound H 2 O from the polysaccharide against deuterons and D 2 O. The number of H 2 O molecules per repeating unit is determined to be about 17.