Inclusion Reaction of Some Fluorophores with β-Cyclodextrin and Its Effect on Their Reversed-Phase HPLC Retention

Abstract

The thermodynamics of the inclusion reaction of flavonol, 7-methoxyflavonol and 4-phenyl-7-hydroxycoumarin (L) with /8-cyclodextrin (CD) has been studied fluorometrically with special reference to the effect of organic solvents (S). The equilibrium constants for this reaction were determined in aqueous methanol, ethanol, acetonitrile, acetone, dimethyl sulfoxide, and A’.A-dimethylformamide. The dependence of the constants on the content of the respective S was attributable to the substitution of S included in CD with L as CD ·nS+L ⇌ CD · L+nS. Also, the inclusion constants of S with CD, βn=[CD · nS][CD]-1[S]-n, were found to be linearly correlated with the solubility parameter of S for both n=1 and 2. When aqueous methanol was employed as a mobile phase, the retention behavior of coumarins on a reversed-phase HPLC column was studied in the presence of j8-CD as a mobile-phase component. The change in the capacity factors could be reasonably explained by the same inclusion scheme as that mentioned above.