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

The interaction of β-cyclodextrin (β-CD) with palmitoleate, linolenate, caprinate and caprylate was studied by the displacement of phenolphthalein (PHP) from the β-CD cavity. Absorbance values of β-CD–PHP solutions at 550 nm in 0.020 mol L-1 Na2CO3 buffer, pH 10.5, at 21.0 ± 0.5 °C, increased as the fatty acid anion was added. The concentration range of fatty acid anion used was 0.390–32.1 × 10-4 mol L-1 in the study of palmitoleate and linolenate, 1.92–80.0 × 10-4 mol L-1 in the study of caprinate and 0.770–32.0 × 10-3mol L-1 in the study of caprylate. Concentrations of β-CD and PHP were 1.00 × 10-3 mol L-1 and 1.00–3.00 × 10-4 mol L-1 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 : β-CD complex were: (1.2 ± 0.2) × 104 and (2.9 ± 0.2) × 102 mol-1 L for palmitoleate, (9.3 ± 0.9) × 103 and (1.1 ± 0.1) × 102 mol-1 L for linolenate, (4.1 ± 0.2) × 103 and 81 ± 8 mol-1 L for caprinate, and (5.2 ± 0.7) × 102 and 27 ± 5 mol-1 L for caprylate respectively. The PHP–β-CD complex was also evaluated as a spectrophotometric sensor for the determination of olive oil acidity.