Electrocatalytic oxidation of 2-thiouracil and 2-thiobarbituric acid at a carbon-paste electrode modified with cobalt phthalocyanine

Voltammetric behavior of two mercaptopyrimidine derivatives (2-thiouracil and 2-thiobarbituric acid) has been studied by cyclic voltammetry at a cobalt phthalocyanine (CoPc)-modified carbon-paste electrode. The results of voltammetric determinations showed that the CoPc in the matrix of modified electrode acts as catalyst for electrooxidation of these thiols (RSH), lowering the overpotential of the reaction and significantly increasing the sensitivity for detection of thiols in neutral conditions. The results of voltammetric and polarization measurements in solutions with various pHs were used for prediction of the mechanism of electrocatalytic oxidation at the surface of modified electrode. These results showed that at the modified electrode, electrochemical oxidation of thiolate anion (RS-) is the rate-determining step. It was found that the modified electrode exhibits good selectivity for catalytic oxidation of mercaptopyrimidines over other biologically important mercaptans such as cysteine, glutathione and thioglycolic acid. The results demonstrate that the peak current for thiol oxidation has a linear variation with the concentration in the range of 1 x 10(-2)-1 x 10(-5) M. This system can be used for sensitive and selective voltammetric detection of mercaptopyrimidine derivatives.