Determination of stoichiometric coefficients and apparent formation constants for alpha- and beta-CD complexes of terpenes using reversed-phase liquid chromatography

The stoichiometric coefficients and apparent formation constants for (+/-)-alpha-pinene, (+/-)-beta-pinene, (+/-)-camphene and (+/-)-limonene with alpha- and beta-cyclodextrins were determined using high-performance liquid chromatography. These measurements were performed in 55:45 0.1% orthophosphoric acid in water-methanol using a Vydac C-4 column (15.0X0.46 cm I.D., 10 mu m, 300A). Using alpha-cyclodextrin (alpha-CD), 1:2 guest-CD complexes were found for the three bicyclic compounds, alpha- and beta-pinene and camphene; a 1:1 guest-CD complex was found for limonene. Using beta-cyclodextrin (beta-CD), 1:1 guest-CD complexes were found for all compounds. Recognition of the terpene enantiomers was only achieved for the bicyclic compounds using alpha-CD. For alpha- and beta-CD, the apparent formation constant for each terpene-CD complex was calculated.