The protonation thermodynamics of ferulic acid/γ-cyclodextrin inclusion compounds

• Published in: Thermochimica acta 2005-01, Vol.425 (1), p.143-147
• Main Authors: Casolaro, Mario, Anselmi, Cecilia, Picciocchi, Giuliana
• Format: Article
• Language: English
• Subjects: Enthalpy and entropy changes; Ferulic acid; Inclusion compounds; Titration calorimetry; γ-Cyclodextrin
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2004.06.016

The physico-chemical properties of ferulic acid (FA) and its inclusion compounds with the γ-cyclodextrin (γ-CD) have been studied at 25 °C in aqueous solution (0.15 M NaCl) by potentiometry and solution calorimetry. The two basicity constants of the ionized FA, log K 1 8.94 and log K 2 4.48, in agreement with those of compounds of similar structure, were attributed to the protonation of hydroxyl and carboxyl ionized groups, respectively. Unlike log K 2, the first basicity constant showed a slight decreasing pattern on increasing the amount of γ-CD. On the other hand, calorimetric data showed greater exothermicity during the protonation of the COO − group in FA when in the presence of the γ-CD. Any increase of the latter led to greater enthalpy (–Δ H°) and lower entropy (Δ S°) changes. The increase of –Δ H° and the decrease of Δ S° values reached a constancy only beyond γ-CD/FA molar ratios of 1. Thermodynamic data were consistent with the hypothesis of the inclusion complexation obtained by the penetration of the neutralized guest FA into the γ-CD host cavity.