Dielectric Relaxation Study of Some Solutions Containing β-Cyclodextrin and Dimethylsulfoxide

Dielectric spectra have been measured up to 72 GHz at 20°C for solutions of β-cyclodextrin (CD) in the following solvents over the whole solubility range of CD: dimethylsulfoxide (DMSO), DMSO/ 1,4-dioxane mixture (2:1 molar ratio), DMSO/water mixtures (2:1 and 1:2). The spectra are analyzed into a sum of Debye type spectral components. These are likely to be caused by different physical pro-cesses. The discussion shows (i) that there is a preferential CD-DMSO interaction, by far exceeding the CD-water interaction, and (») that, concerning CD-DMSO, a loose interaction can be distinguished from the formation of an inclusion complex.

Studies of the role of water on some imine–acid complexes by means of Raman spectroscopy

The percentages of protonation were determined for a conjugated Schiff base trans, trans-2,4-heptadienylidene tert-butylamine in the presence of 3-chloropropionic acid (CPR) and dichloroacetic acid (DCA) in three solvents of different polarities. In dioxane, a solvent of low polarity, protonation is only important for the strong acid DCA (50–60%). By using solvents of higher polarities, protonation is seen to increase and is almost complete for DCA in ethanol. When water molecules are added to these systems, hydrolysis of the Schiff base, measured inside the time span of the experiments (10 min), occurs readily in dioxane, is very slow in a chloroform–dioxane mixture (9:1), and is totally absent in a mixture of ethanol–dioxane (1:9). Results indicate that water does not mediate protonation in all three sets of solvent combinations. The results are also discussed in terms of the possible role that water molecules could have in the visual and bacterial pigments.