Raman spectroscopic evidence for the inclusion of decanoate ion in trimethyl-β-cyclodextrin

A method for calibrating Raman intensities of diluted aqueous solutions, based on the integrated intensity of the OH stretching bands of liquid water as an external intensity standard, is described and used to obtain a difference spectrum that reveals intensity changes mainly due to the intermolecular interaction between two solutes. The method is applied to trimethyl-β-cyclodextrin in sodium decanoate aqueous solutions. The difference between the interaction spectra above and below the critical micellar concentration of sodium decanoate, in the CH stretching region between 2700 and 3100 cm−1, shows an intensity increase of the CH stretching bands for trimethyl-β-cyclodextrin above the critical micellar concentration of sodium decanoate, whereas β-cyclodextrin is relatively insensitive to the presence of decanoate ion micelles in aqueous solution.