528
A. Nosal-Wierci´ nska and W. Kaliszczak
leading to the formation of a more or less compact structure of adsorption layers
should not be ruled out [29–34].
Table 1a, b presents the values of the potentials of zero charge E z and the values of
the surface tension γ z at the zero charge potential for the studied systems. As follows
from tables the addition of 6-mercaptopurine, 6-thioguanine, and azathioprine to the
2 mol · dm chlorates(VII) solution causes a shift of E z potentials. Further increase
in the 6-mercaptopurine, 6-thioguanine, and azathioprine concentrations causes a
significant shift of the E z values towards more positive values of potentials [29–32].
The linear dependence points out to the specific adsorption of thiopurine derivatives
on the mercury surface [35–37].
The presence of surfactants in the 2 mol · dm chlorates(VII) solution also affects
the changes in the E z values (Tables 1a, b). The addition of TritonX-100 and Tween
80 causes a shift of E z towards more positive potentials. The biggest changes were
observed for thioguanine. However, in the case of azathioprine, after a very significant
shift of the zero charge potential (by about 0.2 V), the addition of surfactants does
not cause significant changes.
Such changes E z with an increase in the concentration of tested surfactants confirm
the suggestions related to the reorganization and formation of mixed adsorption layers
[29–34].
The surface tension values (Tables 1a, b) at the potential of zero charge γ z decrease
which also confirms the phenomenon of adsorption [35–37] on the mercury electrode.
Introduction of thiopurine derivatives to the solutions of Bi(III) ions in
2 mol : dm
−3 chlorates(VII) causes an increase in the SWV peak current for the
Bi(III) ion electroreduction and a shift towards positive potentials (Fig. 2), as well
as a simultaneous reduction in the width of SWV peaks at half of their height. This
indicates an increase in the reversibility of Bi(III) electroreduction in the presence of
the studied substances [10, 38, 39]. As can be seen from Fig. 2, the greatest catalytic
effect was obtained in the presence of 6-thioguanine.
The effect of the studied surfactants on the picture of the SWV peaks Bi(III)
ions electroreduction in 2 mol · dm
−3 chlorates(VII) at the constant concentration
of accelerating substance (1 : 10
−3 mol : dm
−3 6TG, 6MP, AZA) depends on the
change of electrode process reversibility towards inhibition (Figs. 2, 3, and 4). The
pictures of peaks are still well defined and no drastic change of the width at half of
their height is observed. That may point out compensation of the inhibiting process
due to the presence of the catalyzing substance in the basic electrolyte solution [38,
39].
Only for azathioprine in the presence of Tween 80 the peak becomes not so well
defined.
Similar changes in the reversibility of Bi(III) electroreduction due to the presence
of thiopurine derivatives or surfactants are indicated by the CV voltammograms
(Fig. 5).
A. Nosal-Wierci´ nska and W. Kaliszczak
leading to the formation of a more or less compact structure of adsorption layers
should not be ruled out [29–34].
Table 1a, b presents the values of the potentials of zero charge E z and the values of
the surface tension γ z at the zero charge potential for the studied systems. As follows
from tables the addition of 6-mercaptopurine, 6-thioguanine, and azathioprine to the
2 mol · dm chlorates(VII) solution causes a shift of E z potentials. Further increase
in the 6-mercaptopurine, 6-thioguanine, and azathioprine concentrations causes a
significant shift of the E z values towards more positive values of potentials [29–32].
The linear dependence points out to the specific adsorption of thiopurine derivatives
on the mercury surface [35–37].
The presence of surfactants in the 2 mol · dm chlorates(VII) solution also affects
the changes in the E z values (Tables 1a, b). The addition of TritonX-100 and Tween
80 causes a shift of E z towards more positive potentials. The biggest changes were
observed for thioguanine. However, in the case of azathioprine, after a very significant
shift of the zero charge potential (by about 0.2 V), the addition of surfactants does
not cause significant changes.
Such changes E z with an increase in the concentration of tested surfactants confirm
the suggestions related to the reorganization and formation of mixed adsorption layers
[29–34].
The surface tension values (Tables 1a, b) at the potential of zero charge γ z decrease
which also confirms the phenomenon of adsorption [35–37] on the mercury electrode.
Introduction of thiopurine derivatives to the solutions of Bi(III) ions in
2 mol : dm
−3 chlorates(VII) causes an increase in the SWV peak current for the
Bi(III) ion electroreduction and a shift towards positive potentials (Fig. 2), as well
as a simultaneous reduction in the width of SWV peaks at half of their height. This
indicates an increase in the reversibility of Bi(III) electroreduction in the presence of
the studied substances [10, 38, 39]. As can be seen from Fig. 2, the greatest catalytic
effect was obtained in the presence of 6-thioguanine.
The effect of the studied surfactants on the picture of the SWV peaks Bi(III)
ions electroreduction in 2 mol · dm
−3 chlorates(VII) at the constant concentration
of accelerating substance (1 : 10
−3 mol : dm
−3 6TG, 6MP, AZA) depends on the
change of electrode process reversibility towards inhibition (Figs. 2, 3, and 4). The
pictures of peaks are still well defined and no drastic change of the width at half of
their height is observed. That may point out compensation of the inhibiting process
due to the presence of the catalyzing substance in the basic electrolyte solution [38,
39].
Only for azathioprine in the presence of Tween 80 the peak becomes not so well
defined.
Similar changes in the reversibility of Bi(III) electroreduction due to the presence
of thiopurine derivatives or surfactants are indicated by the CV voltammograms
(Fig. 5).