Thermal expansion behavior of hydrate paramylon in the low-temperature region

The thermal expansion behavior of hydrate paramylon between 100 and 300 K has been investigated using synchrotron X-ray powder diffraction. The X-ray diffraction profile at 300 K showed a typical pattern of the hydrate triple helical (1→3)-β-d-glucan with a hexagonal unit cell (a = 15.782 Å and c = 18.580 Å). On cooling, the hydrate paramylon had converted to a “low-temperature phase” around 270 K. On passing through the phase transition, the a-axis and c-axis values decreased and increased, respectively, and the low-temperature phase at 100 K exhibited a hexagonal unit cell (a = 15.586 Å and c = 18.619 Å). The phase transition took place reversibly. Below the transition point, both the a-axis and c-axis values decreased linearly. The thermal expansion coefficients are: αa = 1.50 × 10−5 K−1, αc = 0.33 × 10−5 K−1, and β = 3.08 × 10−5 K−1.