title: Interfacial thermodynamics of gallic acid adsorption on a chargeable hydrophobic surface.
abstract: The thermodynamics of adsorption of gallic acid (GA, 3,4,5-trihydroxylbenzoic acid) on the hanging mercury drop electrode (HMDE) surface was studied by temperature-dependent stripping voltammetry (TD-SV), at physiological pH 7.4. The thermodynamic parameters, e.g., Gibbs free energy, ΔG(ADS), enthalpy, ΔΗ(ADS) and entropy, ΔS(ADS), of adsorption have been determined at physiological temperatures 2-40 °C. Chemisorption of the radical species ≡[GA(OH)(2)(O(-))]* is the energetically important reaction. The thermodynamic data show a complex mechanism of adsorption of GA on the electrode surface, which is strongly dependent on temperature. At low-temperatures T<12 °C, adsorption is controlled by enthalpy, while at T>22 °C, adsorption is entropy driven. In the temperature range 12 °C and 22 °C, a combined enthalpy-entropy stabilization occurs. A mechanism is proposed which analyses the implication of thermodynamics to the interfacial adsorption of polyphenols with cell membranes under physiological conditions.
authors.affiliation: Laboratory of Physical Chemistry, Department of Environmental and Natural Resources Management, University of Ioannina, Seferi 2, 30100 Agrinio, Greece.
authors.forename: Evangelos
authors.initials: E
authors.lastname: Giannakopoulos
authors.forename: Yiannis
authors.initials: Y
authors.lastname: Deligiannakis
mesh_terms: D000327:Adsorption; D002462:Cell Membrane; D005419:Flavonoids; D005707:Gallic Acid / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D010636:Phenols; D059808:Polyphenols; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D005419:Flavonoids; D010636:Phenols; D059808:Polyphenols; D005707:Gallic Acid