Adsorption of 2-thiouracil on mercury from ethylene glycol and ethanol solutions

Differential-capacitance curves of the Hg electrode are measured with an ac bridge at 400 Hz and 20 degrees C in ethanol and ethylene glycol solutions of 2-thiouracil in 0.5 M NaClO4. The data suggest that 2-thiouracil is adsorbed at the Hg/C2H5OH and Hg/C2H4(OH)(2) interfaces at the expense of a donor-acceptor interaction through the sulfur atom. The increase in the interaction, caused by a potential shift in the positive direction, makes the adsorption state alter from noncondensed to condensed. The former is characterized by a linear potential dependence of the adsorption energy. In the latter case, according to the model of two parallel capacitors, the dependence becomes quadratic.