other reports (8, 9), the progressive substitution of the proton The results of ultrasonic absorption and conductance studies of of the hydroxyl groups of the pyranose rings of b-CD with 1:1 complexes of 2,6-O-dimethyl-b-cyclodextrin (b-DMCD) and alkyl groups increased the sound absorption in the frequency cetyltrimetylammonium bromide (CTAB) at 25ЊC are reported. range investigated. However, upon complete substitution of CTAB was chosen as a guest species to eliminate any contribution all of the hydroxyl groups of the pyranose rings, there was to the experimental sound absorption from the monomer surfaca sharp decrease in the ultrasonic absorption. From these tant-micelle exchange process. The resulting sound absorption is results it was concluded that the intramolecular hydrogen considered to be primarily due to the 1:1 complex of b-DMCD:surbonding network of the unsubstituted b-CD formed a rigid factant, and its amplitude is observed to be smaller than that of b-DMCD in aqueous solution. This suggests that the intermolecular framework that allowed little flexibility of motion within interaction between the host and the guest species makes the structhe pyranose rings and, hence, produced little evidence of ture of the 1:1 complex more rigid than that of b-DMCD and, nonclassical sound absorption. Upon substitution of alkyl consequently, the degrees of freedom contributing to sound absorpgroups into b-CD, the degree of intramolecular hydrogen tion are reduced. This is in contrast to the results observed for bbonding was diminished and a loose ''wig-wag'' motion of CD:surfactant 1:1 complexes, for which it appears that the interthe pyranose rings was enhanced, consistent with the obmolecular guest/host interactions in the complex loosen the more served increase in the nonclassical sound absorption relative rigid structure of b-CD, which exists because of the presence of to b-CD. However, in the case of permethylated b-CD, the more intramolecular hydrogen bonding sites in b-CD than in modincreased flexibility expected from the complete elimination ified b-CD. This increases the sound absorption of the complex of the intramolecular hydrogen bonding network was offset relative to b-CD.