Interfacial thermodynamics of gallic acid adsorption on a chargeable hydrophobic surface

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, ΔGADS, enthalpy, ΔΗADS and entropy, ΔSADS, 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.

Graphical abstractΔG of interfacial adsorption of Gallic Acid on hydrophobic chargeable surface e.g. modeling cell membranes, shows a non-linear temperature dependence.Figure optionsDownload full-size imageDownload high-quality image (93 K)Download as PowerPoint slideHighlights► The thermodynamics of adsorption of gallic acid on HMDE was studied by SW-CSV. ► ΔGADS, ΔΗADS, ΔSADS, have been determined at physiological temperatures 2–40 °C. ► Chemisorption of species ≡[GA(OH)2(O−)] is the energetically important reaction. ► A mechanism is proposed for interfacial adsorption of polyphenols on cell membranes.