Collect. Czech. Chem. Commun. 1998, 63, 1977-1993

Adsorption and Condensation of Xanthine at the Mercury/Solution Interface

Viktor Dražana and Vladimír Vetterla,b

a Institute of Biophysics, Academy of Sciences of the Czech Republic, 612 65 Brno, Czech Republic
b Department of Physical Electronics, Faculty of Science, Masaryk University, 611 37 Brno, Czech Republic


The adsorption and two-dimensional condensation of xanthine at the mercury electrode in 0.2 and 2 M NaCl was studied by electrode double layer capacity measurements. The condensation of xanthine molecules adsorbed at the electrode was observed at pH 6.0 and 7.4, but not at 9.0. The standard Gibbs energy of adsorption, energy of lateral interactions and the surface occupied by one xanthine molecule in a compact layer were calculated from the temperature dependence of the capacity pit using the Frumkin and Ising lattice gas models. The orientation of xanthine molecules in a compact layer at the electrode surface was estimated. At higher bulk concentrations of xanthine, the double layer capacity decreases to a very low value of about 1.5 mF cm-2, which might be an indication of the formation of a xanthine multilayer at the electrode surface.

Keywords: Adsorption of purine bases; Frumkin adsorption isotherm; Electrochemical impedance; Ising model; Mercury/aqueous interface; Xanthine; Electrochemistry; Purines.