Adsorption behavior of water molecules onto alpha-, beta-, and gamma-cyclodextrins and branched alpha-cyclodextrins

Moisture adsorption properties of alpha-, beta-, and gamma-cyclodextrin (CD) and branched alpha-CDs were investigated to elucidate the basis of the results of adsorption isotherms of water at 10, 20, and 30 degrees C, the differential heat of adsorption, the entropy of the adsorbed water, and the heat of immersion in water, It is concluded that the water molecules were adsorbed on the hydroxyl groups of the glucose molecule of alpha-CD, were first adsorbed on that of beta-CD and then were included in the pore structure of beta-CD, and were only included in the pare structure of gamma-CD. Branched alpha-CDs were developed and produced to increase the interaction with water molecules. However, the interaction between the branched alpha-CDs and the water was smaller than that between the virgin alpha-CD and the water, The solubility of branched, alpha-CD required a long time because the heat of immersion was larger in the order G(2)-alpha-CD and G(1)-alpha-CD or alpha-CD, It is considered that the side chain, glucosyl and maltosyl groups, decreased the interaction between the water molecule and the surface of the CD because of steric hindrance. Therefore, it is concluded that the side chain inhibited the melter adsorption of the inner molecule of CD. (C) 1996 Academic Press, Inc.