Fine steps of electrocatalytic oxidation and sensitive detection of some amino acids on copper nanoparticles.

The electrocatalytic oxidation of five amino acids-glycine, aspartic acid, cysteine, glutamic acid, and tyrosine-on two copper-based electrodes comprising copper microparticle-modified carbon paste electrode (m-CPE) and copper nanoparticle-modified CPE (n-CPE) was investigated. In the voltammograms recorded using m-CPE, a single anodic peak related to the oxidation of amino acids appeared and was related to the electrocatalytic oxidation of the amino acids via the electrogenerated Cu(III) species. Using n-CPE, however, two overlapped anodic peaks in the voltammograms appeared and were related to two fine tunable steps of the oxidation process. The currents of the two peaks were controlled by diffusion and were confirmed by chronoamperometric measurements. The amino acids were oxidized on n-CPE at higher rates and at lower potentials compared with m-CPE. This was attributed to the nanosize of copper nanoparticles. Some primary linear-chain amines and primary branched-chain amines were oxidized on the copper-based electrodes as markers. The catalytic rate constants, the transfer coefficients, and the diffusion coefficients for the amino acids are reported. Simple, sensitive, and time-saving sensing procedures in both batch and flow systems were developed for the analysis of the amino acids, and the corresponding analytical parameters are reported.

Copper nanoparticles-modified carbon paste transducer as a biosensor for determination of acetylcholine.

The electrocatalytic oxidation of acetylcholine (Ach) on two different copper-based transducers, copper microparticles-modified carbon paste electrode (m-CPE) and copper nanoparticles-modified carbon paste electrode (n-CPE), was investigated. In the voltammograms recorded using m-CPE, a single anodic oxidation peak related to the oxidation of ACh was appeared which was related to the electrocatalytic oxidation of ACh via the electrogenerated Cu(III) species in an EC' mechanism. Using n-CPE, however, two overlapped anodic peaks appeared which were related to two fine tunable steps of oxidation. ACh oxidized on n-CPE with higher rates at low potentials with respect to m-CPE. The kinetic of the reaction was formulated and the charge-transfer resistance of the system was obtained both theoretically and experimentally. The catalytic rate constant, the transfer coefficient for the electrocatalytic oxidation and the diffusion coefficients for ACh were reported using chronoamperometry, pseudo-steady-state polarization measurement and electrochemical impedance spectroscopy. Sensitive and time-saving sensing procedures in both batch and flow systems were developed for the analysis of ACh, and the corresponding analytical parameters were reported.

Electrocatalytic oxidation and determination of deferasirox and deferiprone on a nickel oxyhydroxide-modified electrode.

The electrocatalytic oxidation of two orally administered iron chelator drugs (deferiprone, CP20, and deferasirox, ICL670) was investigated on a nickel oxyhydroxide-modified nickel electrode in alkaline solution. The oxidation process involved and its kinetics were investigated using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy techniques, as well as steady-state polarization measurements. Voltammetric studies indicated that in the presence of the drugs under study, the anodic peak current of low-valence nickel species increased, followed by a decrease in the corresponding cathodic current. This result indicates that the drugs were oxidized via oxyhydroxide species immobilized on the electrode surface via an EC' mechanism. A mechanism based on the electrochemical generation of Ni(III) active sites and their subsequent consumption by the drugs in question was also investigated. The corresponding rate law under the control of charge transfer was developed, and kinetic parameters were derived. In this context, the charge-transfer resistance accessible both theoretically and through impedancemetry was used as a criterion. The rate constants of the catalytic oxidation of the drugs and the electron-transfer coefficients are reported. A sensitive, simple, and time-saving amperometric procedure was developed for the analysis of deferasirox and deferiprone, with detection limits of 28 and 19 microM, respectively. The electrode was used for the direct assay of deferasirox and deferiprone tablets.