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|Title:||The protonation thermodynamics of ferulic acid/gamma-cyclodextrin inclusion compounds.||Authors:||Casolaro, Mario
|Keywords:||Ferulic acid; gamma-Cyclodextrin; Inclusion compounds; Titration calorimetry; Enthalpy and entropy changes||Issue Date:||2005||Project:||None||Journal:||THERMOCHIMICA ACTA||Abstract:||
The physico-chemical properties of ferulic acid (FA) and its inclusion compounds with the -cyclodextrin (-CD) have been studied at25 ◦C in aqueous solution (0.15M NaCl) by potentiometry and solution calorimetry. The two basicity constants of the ionized FA, log K18.94 and logK2 4.48, in agreement with those of compounds of similar structure, were attributed to the protonation of hydroxyl and carboxylionized groups, respectively. Unlike log K2, the first basicity constant showed a slight decreasing pattern on increasing the amount of -CD.On the other hand, calorimetric data showed greater exothermicity during the protonation of the COO− group in FA when in the presence ofthe -CD. Any increase of the latter led to greater enthalpy (–H◦) and lower entropy (S◦) changes. The increase of –H◦ and the decreaseof S◦ values reached a constancy only beyond -CD/FA molar ratios of 1. Thermodynamic data were consistent with the hypothesis of theinclusion complexation obtained by the penetration of the neutralized guest FA into the -CD host cavity.
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