PHYSICOCHEMICAL PROPERTIES AND INCLUSION COMPLEX-FORMATION OF DELTA-CYCLODEXTRIN

delta-Cyclodextrin (CD) is a cyclic oligosaccharide composed of nine alpha-1,4-linked D-glucose units. Its physicochemical properties have been characterized only in terms of its X-ray crystal structure (Fujiwara et al., 1990). A method for the purification of delta-CD was examined, and its physicochemical properties and complexation abilities were elucidated and compared with those of alpha-, beta-, and gamma-CD (Kobayashi et al., 1986; Miyazawa et al., 1993). Purification of delta-CD from the commercially available CD powder was mainly carried out with the combined treatment of HPLC and column chromatographies. The molecular weight of delta-CD was determined by FAB-MS, and the cyclic structure of delta-CD was identified by H-1-NMR and C-13-NMR. The aqueous solubility of delta-CD was greater than that of beta-CD but less than that of alpha-CD or gamma-CD. No surface activity of delta-CD was observed. delta-CD did not exhibit any hemolytic activity at 4.0 x 10(-2) M 6-CD, which was close to its saturated solution. The acid-catalyzed hydrolysis increased in the following order: alpha-CD < beta-CD < gamma-CD < delta-CD. delta-CD did not show any significant solubilization effect on most of the slightly soluble or insoluble drugs in water. However, in the case of a large guest molecule such as spironolactone (SP) and digitoxin, which have a steroidal framework, the enhancement of solubility of the guest molecule by delta-CD was greater than that by alpha-CD. The solubility of SP increased about 30-fold in the presence of delta-CD (4.5 x 10(-2) M), showing the features of an AL type phase diagram.