The thermal expansion of mannan I obtained from ivory nuts

We have investigated the thermal expansion of mannan I crystals obtained from the endosperm of ivory nuts using X-ray diffraction in the temperature range of from room temperature to 250 degrees C on heating. Seven major diffractions were observed, and all the d-spacings gradually increased with increasing temperature. However, discontinuities indicating a phase transition were observed at a temperature of 130 degrees C. The unit cell parameters showed an anisotropic thermal expansion between the intermolecular hydrogen bonded direction and the covalently bonded direction, where the a and b axes lengths increased, but the c-axis length decreased with increasing temperature. Although the reason for the contraction of the c-axis length on heating is not clear, the thermal behavior should be related to the crystal structure and hydrogen bonding system of mannan ID. (c) 2007 Elsevier Ltd. All rights reserved.