Abstract
The interaction of octanoic acid and its conjugate base sodium octanoate with α-cyclodextrin was studied by 1H NMR and isothermal titration calorimetry, respectively, at 298.15 K. The results are in agreement with a 1:1 stoichiometry in the complex. The binding of octanoate with α-cyclodextrin is characterized by a positive entropy, stressing the relevance of hydrophobic interactions. Based on the host-guest complex formation, the effect of α-cyclodextrin on the acidity behavior of the acid was evaluated by potentiometric titration. The results are interpreted in terms of the Henderson-Hasselbalch equation and by using an analytical equation for the titration curve. The apparent ionization constants of the complexes are higher than those obtained in water, indicating that octanoic acid becomes a weaker acid after complexation.
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