Ultrasonic absorption studies in aqueous solutions of modified β-cyclodextrins

Ultrasonic absorption studies over the frequency range 0.6–210 MHz were conducted in aqueous solutions of the following modified β-cyclodextrins (β-CD): 2,6-O-dimethyl-β-CD (DMβCD), 2,3,6-O-trimethyl-β-CD(TMβCD), and hydroxypropyl-β-CD (HPβCD). Anomalous ultrasonic absorption found in the three systems was attributed to three relaxations in the DMβCD and HPβCD systems and two in the TMβCD 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 DMβCD/decyltrimethylammonium bromide system was also investigated ultrasonically in solution. Keywords: ultrasonic absorption, modified β-cyclodextrins, surfactant inclusion, relaxation frequency.