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The electrosorption behavior of cytosine at the mercury electrode/acetic buffer of pH 4 and 5 interfaces was determined from the double-layer differential capacity measurements extrapolated to zero frequency. Solutions of cytosine were prepared to cover the range from 1 × 10-4 to 6 × 10-3 mol dm-3. Adsorption of cytosine was described by the adsorption isotherms constants derived from the surface pressure data as a function of electrode charge density and bulk concentration. The obtained values of the relative surface excesses Γ′ were higher in the acetic buffer of pH 4 than of pH 5. Maximum of cytosine adsorption in the mentioned buffers was at -581 and -551 mV, respectively. The values of the standard Gibbs energy ∆G° obtained from the Frumkin isotherm were higher in the buffer of pH 4 than of pH 5. The values of the interaction parameter A indicated weaker repulsive interaction between adsorbed molecules of cytosine in the former buffer. The adsorption parameters obtained from the virial isotherm confirmed corresponding parameters obtained from the Frumkin isotherm. The dependences of ΦM-2 on the relative surface excess at a constant charge density were analyzed in order to calculate the electrostatic parameters of the inner layer.

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Studies of mixed adsorption layers with respect to their influence on kinetics of Zn 2 ions reduction indicate dynamics of this process in the presence of inhibitor and accelerating substances. This effect can be seen as a much greater increase of standard constant rates compared with a similar increase without the inhibitor. 1-Butanol was used as an inhibitor in the studies and p-toluidine and m-toluidine as accelerating substances. The adsorption measurements show that in the range of Zn 2 ion reduction potentials in the solutions containing 1-butanol and the definite isomer of toluidine, toluidine plays a dominant role in establishing equilibrium in the mixed adsorption layer. The obtained values of the true standard constant rates of the transfer of the first electron k s1 t and the second electron k s2 t indicate that in each of the studied systems the stage of the first electron transfer is more strongly accelerated compared with the stage of the second electron transfer. The linear character of the dependence k s1 t and k s2 t in the function of the surface excess and in the function of 1-butanol concentration indicates that active complexes are formed for each case of the mixed adsorption layer.

The dependence of the two-step reduction of Zn2+ ions on NaClO4 and TMTU concentration at the dropping mercury electrode was examined. The catalytic activity of TMTU is related to both electron transfer steps and decreases in the order: 1 M NaClO4 > 0.5 M NaClO4 > 0.1 M NaClO4. In each of the studied systems there was observed a much larger increase in the (kts2) values compared to the (kts1) values when the concentration of TMTU was increased. A linear relationship between the rate constant of the electroreduction of Zn2+ and the relative surface excess of TMTU indicates the formation of a bridge between Zn2+ and TMTU which facilitates the transfer of electrons across the inner layer.