INFLUENCE OF THE WATER-CONTENT ON THE THERMAL-BEHAVIOR OF BETA-CYCLODEXTRIN AT LOW AND VERY-LOW TEMPERATURE

Heat capacities of beta-CD . 9.7H(2)O were measured by adiabatic calor imetry in the temperature range 10-300 K. Differential scanning calori metry was used to follow the evolution of the thermal behaviour versus hydration ratio between 170 and 300 K. At least three different behav iours were observed, according to the number, n, of water molecules: 0 < n < 7, 7 < n < 10, and n > 10. These macroscopic results are discus sed in terms of organization differences between the most or the least hydrated beta-CD. The structuring effect of the hydration water molec ules is emphasised. The existence of two energetically distinct beta-C D hydrates (n < 10 and n > 10) seems to be confirmed. This hypothesis is discussed in comparison with previous spectroscopic and structural studies.