Ultrasonic Spectrometry of Triethylenediamine Aqueous Solutions. Protolysis and Supramolecular Structures

Dynamic Interaction between Alkylammonium Ions and β-Cyclodextrin by Means of Ultrasonic Relaxation

Ultrasonic absorption measurements in the frequency range from 0.8 to 220 MHz were carried out in aqueous solutions of pentylammonium chloride (PEACL) and hexylammonium chloride (HEACL) with beta-cyclodextrin (beta-CD) at pH approximately 7.2 and 25 degrees C. A single relaxational absorption was attributed to a perturbation of a chemical relaxation associated with the formation of a complex between beta-CD and the alkylammonium chlorides. The rate and equilibrium constants for the complexation reaction were determined from the concentration dependence of the relaxation frequency. Increasing the chain length of the alkylammonium ion led to an increase in the stability of the complex and slowed the exit rate of the ion from the beta-CD cavity. The standard volume change of the reaction was obtained from a maximum absorption per wavelength and was attributed to water molecules being expelled from the cavity with concomitant alkylammonium ion insertion.

Acoustic relaxation spectrometers for liquids

In this tutorial article methods of acoustic relaxation measurements of liquids are reviewed. The present performance of various techniques is described and desirable trends in future developments are shown. An account is given on standards in the optical monitoring of acoustic waves (Brillouin scattering), on time domain (jump) techniques, as well as on frequency domain (continuous and pulse modulated ultrasonic wave) methods. The merits and limitations of the different techniques of measurement, covering the frequency range from 10 kHz up to nearly 10 GHz now, corresponding with relaxation times between about 0.1 ms and 100 ps, are discussed. Efforts to further enhance the experimental accuracy and to reduce the required sample volume are indicated.