H-1-NMR RELAXATION STUDY OF A CHITOSAN-CYCLODEXTRIN NETWORK

The results of measurements of longitudinal and transverse proton rela xation times for a chemical network obtained by reacting chitosan with oxidized beta-cyclodextrin (beta-cyclodextrin polyaldehyde) are prese nted. The network was characterized by a 'two-component' transverse re laxation mechanism relative to structurally different environments exp erienced by water molecules. Different environments were also indicate d by the temperature of the spin-spin relaxation times (T-2) studied i n the range 4-50 degrees C. Between 4 and 18 degrees C, proton exchang e between the matrix and water prevails on the inter- and intra-molecu lar dipolar interactions of the water confined in the meshes of the ne twork, resulting in a marked change in the slope of T-2 With temperatu re. Stiffness of the matrix and reduced mobility of water in the gel m eshes are prerequisites for observing such relaxation phenomena. Possi ble mechanisms contributing to the activation energy in the case of ch itosan-cyclodextrin networks are discussed. The behaviour of the chito san-cyclodextrin hydrogel is compared with that of a gellan gel. (C) 1 997 Elsevier Science Ltd.