EVIDENCE FOR A CONFORMATIONAL TRANSITION IN CURDLAN

Gelation occurred at a concentration of 0.3% curdlan solution at room temperature (25 degrees C). The curdlan showed a Newtonian behavior at 0.1%, but plastic behavior above 0.2% even at a temperature of 38 deg rees C. The dynamic modulus remained at a constant value with an incre ase of temperature up to 40 degrees C, which was estimated to be a tra nsition temperature, then it decreased rapidly with an increase of tem perature until 55 degrees C; however, it increased gradually with a fu rther increase of temperature. The dynamic viscoelasticity of curdlan solution remained at very low values on addition of urea (4 M) and dec reased with increasing temperature. The optical rotation of curdlan (0 .1%) increased with a decrease of temperature. Possible modes of intra -and intermolecular hydrogen bonding within and between curdlan molecu les were proposed. A hydrophobic interaction might take place at high temperatures (>55 degrees C), the mode of which was also proposed. (C) 1997 Elsevier Science Limited.