Mojtaba Bagherzadeh

Voltammetric oxidation of 2-oxo-1,2,3,4-tetrahydropyrimidin-5-carboxamides: substituent effects.

Electrochemical oxidation of a series of 20 substituted 2-oxo-1,2,3,4-tetrahydropyrimidin-5-carboxamides (THPMs) in acetonitrile has been studied using voltammetric methods at a glassy carbon electrode to investigate the influence of the substituents on the 4- and 5-positions of the heterocyclic ring. Analysis of the results shows that the electronic nature and steric hindrance of the substituents, especially their orientations toward the heterocyclic ring, determine their effects on the oxidation potential. Analysis of the computational results obtained at the DFT-B3LYP/6-31++G** level of theory suggests a mechanism in which the first electron removal occurs from either the N(1) of the heterocyclic ring or N(17) of the amide substitution. This process is followed by a fast proton removal resulting in the formation of stable allylic and/or benzylic radicals which then undergo further oxidation to the 2-oxo-1,2-dihydropyrimidin-5-carboxamides (DHPMs).

A Dopamine Sensor Based on Pre-Concentration by Magnetic Nanoparticles

Herein, Fe3O4 magnetic nanoparticles (MNPs) were synthesized and characterized. Afterward, a magnetic carbon paste electrode (MCPE) was modified with MNPs via casting and drying MNPs on top of the MCPE (MCPE/MNP). Electrochemical behavior of the MCPE/MNP was studied by cyclic voltammetry in the presence of [Fe(CN)6]3−/4− as a redox probe, and surface of MNPs was evaluated as . The behavior of MCPE/MNP towards dopamine (DA) and ascorbic acid (AA) has been investigated by electrochemical methods, and the obtained results showed that the MCPE/MNP has adsorption behavior towards only DA. Based on this behavior, the DA molecules were pre-concentrated on top of the MCPE/MNP and followed with stripping in DA free solution. Subsequent to experimental and instrumental optimization, a calibration curve from to  M DA with , DL =  M DA, and RSD = 4.6%, was obtained in the presence of  M AA. Performance of the MCPE/MNP was successfully tested in a pharmaceutical sample.

ELECTROCATALYTIC DETERMINATION OF HYDROQUINONE WITH MN+ MODIFIED GOLD-5-AMINO-2-MERCAPTOBENZIMIDAZOLE SELF-ASSEMBLED MONOLAYER ELECTRODES

Application of immobilized metal cations on the topside of gold-5-amino-2-mercaptobenzimidazole self-assembled monolayer (Au-5A2MBI-Mn+ SAM, Mn+:Cu2+ or Ag+) for electrocatalytic determination of hydroquinone (H2Q) is described by voltammetric method. Several parameters were investigated to evaluate the performance of the sensors. Calibration curves for H2Q concentrations were linear from 1.0 × 10-5 to 4.0 × 10-4 M (r = 0.998) for Au-5A2MBI, from 1.0 × 10-5 to 6.0 × 10-4 M (r = 0.998) for Au-5A2MBI-Cu2+, and from 2.0 × 10-6 to 2.0 × 10-5 M (r = 0.996) and 1.0 × 10-4 to 1.0 × 10-3 M (r = 0.991) for Au-5A2MBI-Ag+ SAM modified electrode. The respective detection limits were found as 6.5 × 10-6, 4.6 × 10-6 and 1.8 × 10-7 M. Both Cu2+ and Ag+ ions were found to have a good electrocatalytic effect on the oxidation of H2Q; however, Ag+ was a more effective catalyst and showed better sensitivity and lower detection limit than all other tested electrodes. Au-5A2MBI-Ag+ SAM electrode was used as a suitable sensor for determination of H2Q in a radiolysis developing agent as real sample. The results obtained by using proposed sensor and that obtained by an ASTM reference method were in good agreement at the 95% confidence level.