Determination of Binding Constants for Inclusion Complexes of Cyclodextrins with Organic Solvents, Ethylene Glycol, and Its Related Compounds by Means of 1H NMR Spectroscopy

Abstract

Abstract The binding constants (Ka’s) for the complexation of α- and β-cyclodextrins (α- and β-CDs) with some hydrophilic organic solvents such as methanol, dimethyl sulfoxide, acetone, etc., were successfully determined in D2O by following changes in the 1H NMR chemical shift of the C(3)–H signal of CD, using the C(1)–H signal as an internal reference. The Ka value obtained for a β-CD–methanol complex was 0.088 mol−1 dm3 at 298 K, which is, as we know, the smallest among Ka’s measured thus far for CD complexes. The same method was also applied to the determination of Ka’s for the complexation of α-CD with ethylene glycol and some related compounds. It was revealed that these molecules were certainly included within the cavity of α-CD, though the Ka values are fairly small.