The physico-chemical properties of ferulic acid (FA) and its inclusion compounds with the gamma-cyclodextrin (gamma-CD) have been studied at 25degreesC in aqueous solution (0.15 M NaCl) by potentiometry and solution calorimetry. The two basicity constants of the ionized FA, log K, 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 gamma-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 gamma-CD. Any increase of the latter led to greater enthalpy (-DeltaHdegrees) and lower entropy (DeltaSdegrees) changes. The increase of -DeltaHdegrees and the decrease of AS' values reached a constancy only beyond gamma-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 gamma-CD host cavity. (C) 2004 Elsevier B.V. All rights reserved.