CONFORMATION OF (2-]1)-BETA-D-FRUCTAN IN AQUEOUS-SOLUTION

The conformation and dilute solution properties of (2 --> 1)-beta-D-fructan in agueous solution were studied by gel permeation chromatography, low-angle laser light-scattering photometry, viscometry, small-angle X-ray scattering and electron microscopy. Fractions covering a broad range of weight-average molecular weights (M(w)) from 1.49 x 10(4) to 5.29 x 10(6) were obtained from a native sample by ultrasonic degradation and fractional precipitation. For M(w) < 4 x 10(4), the intrinsic viscosity [eta] varies with M(w)(0.71), indicating that the fructan chain behaves as a random coil expanded by an excluded-volume effect in this molecular weight region. For M(w) > 10(5), [eta] exhibits an unusually weak dependence on M(w) and finally becomes almost independent of molecular weight. This behaviour is interpreted in terms of a globular conformation of the high-molecular-weight fructan molecules. Small-angle X-ray-scattering measurements and electron microscopic observations support this interpretation of the values of [eta] observed.