JOURNAL OF INCLUSION PHENOMENA AND MOLECULAR RECOGNITION IN CHEMISTRY, 1999, VOL. 34, PP. 85-97

Interaction of  b-Cyclodextrin with Unsaturated and Saturated Straight Chain Fatty Acid Anions Studied by Phenolphthalein Displacement

Stavroula G. Skoulika, Constantinos A. Georgiou* and Moschos G. Polissiou
Chemistry Laboratory, Agricultural University of Athens, 75 Iera Odos, 118 55 Athens, Greece

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The interaction of b-cyclodextrin (b-CD) with palmitoleate, linolenate, caprinate and caprylate was studied by the displacement of phenolphthalein (PHP) from the b-CD cavity. Absorbance values of b-CD-PHP solutions at 550 nm in 0.020 M Na₂C0₃ buffer, pH 10.5, at 21.0 ± 0.5 ^oC, increased as the fatty acid anion was added. The concentration range of fatty acid anion used was 0.390-32.1 x 10^-4 M in the study of palmitoleate and linolenate, 1.92-80.0 x 10^-4 M in the study of caprinate and 0.770-32.0 x 10^-3 M in the study of caprylate. Concentrations of b-CD and PHP were 1.00 x 10^-3 M and 1.00-3.00 x 10^-4 M, respectively. Data were fitted by nonlinear regression to a two step complexation model. Complex formation constants thus determined for the 1:1 and 1:2, fatty acid anion: b-CD complex were: (1.2 ±0.2) x 10⁴ and (2.9 ± 0.2) x 10²  M^-1 for palmitoleate, (9.3 ± 0.9) x 10³ and (1.1 ± 0.1) x 10² M^-1 for linolenate, (4.1 ±  0.2) x 10³ and 81 ± 8 M^-1 for caprinate, and (5.2 ± 0.7) x 10² and 27 ± 5 M^-1 for caprylate respectively. The PHP-b-CD complex was also evaluated as a spectrophotometric sensor for the determination of olive oil acidity.

Key words: Palmitoleic acid; linolenic acid; capric acid; caprylic acid; linoleic acid; oleic acid; b-cyclodextrin; phenolphthalein; complex formation constants; olive oil; free fatty acid; spectrophotometric probe

*Corresponding author.
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Questions and comments to author: Dr C.A. Georgiou, cag@aua.gr
Phone: +3010-5294248, fax: +3010-5294265
Chemistry Laboratory, Agricultural University of Athens, Greece