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Influence of the HEPES buffer on the electrochemical reaction of the Cu(II)-salicylaldoxime complex

The effect of the 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) on the redox process of copper(II)-salicylaldoxime complex [Cu(II)-SA] was studied. The measurements were performed on a hanging mercury drop electrode (HMDE) using various electrochemical techniques. The presence of the HEPES buffer (pH 8.0) doubled the reduction current of the Cu(II)-SA complex, whereas the reduction potential shifted to more positive values (about 50 mV). The results obtained indicate that the presence of the HEPES buffer Facilitates the electron transfer between the mercury electrode and the adsorbed Cu(II)-SA complex during the reduction process. The experiments carried out using chronocoulometry with a double step potential revealed that the surface coverage of the Cu(II)-SA complex remained unchanged (in the range between 9 and 10.5 x 10(-11) mol cm(-2)), regardless of the presence of the HEPES buffer. Square-wave voltammetric measurements also indicate that the redox process of the Cu(II)-SA complex is electrochemically reversible with the reactant adsorption, in spite of the presence of the HEPES buffer.

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