ULTRASONIC-ABSORPTION STUDIES IN AQUEOUS-SOLUTIONS OF MODIFIED BETA-CYCLODEXTRINS

Ultrasonic absorption studies over the frequency range 0.6-210 MHz were conducted in aqueous solutions of the following modified beta-cyclodextrins (beta-CD): 2,6-O-dimethyl-beta-CD(DM-beta-CD), 2,3,6-O-trimethyl-beta-CD (TM-beta-CD), and hydroxypropyl-beta-CD (HP-beta-CD). Anomalous ultrasonic absorption found in the three systems was attributed to three relaxations in the DM-beta-CD and HP-beta-CD systems and two in the TM-beta-CD system. These relaxations were assigned to hydrogen bond "wig-wagging", to CD cavity water exchange, and to bond rotation within the CD units. The 1:1 DM-beta-CD/decyltrimethylammonium bromide system was also investigated ultrasonically in solution.