Voltammetric determination of α-tocopherol in the presence of surfactants

As established, α-tocopherol is electrochemically active on glassy carbon electrode in the available range of anodic potentials in acetonitrile and its aqueous mixtures. However, an increase in the water percentage up to 50% and beyond leads to a substantial decrease and then the total disappearance of the analytical signal. A scheme of electrode reaction responsible for the signal formation is proposed. The effect of surfactants on the oxidation of α-tocopherol in aqueous acetonitrile is estimated. As found, surfactants (N-dodecylpyridinium bromide, Triton X-100 and N-cetylpyridinium bromide) enhance the current of α-tocopherol oxidation. The surfactants reduce the detection limit and extend the analytical range. Analytical methods for the voltammetric quantification of α-tocopherol in drugs in the presence of surfactants are elaborated and may be recommended for the control of pharmaceuticals.     

A Cholinesterase Sensor Based on a Graphite Electrode Modified with 1,3-Disubstituted Calixarenes

New cholinesterase sensors based on screen-printed graphite and graphite/epoxy electrodes modified with 1,3-disubstituted calix[4]arenes were developed for the detection of compounds that form host–guest complexes (using copper(II) and oxalate ions as an example). The effect of calix[4]arenes on the biosensor signal was studied under homogeneous and heterogeneous conditions. It was found that the effect of the studied compounds was due to changes in the electrostatic interactions and mobility of enzyme effectors in the electrode layer. Procedures were developed for the determination of Cu(II) by its activating effect in the concentration range 0.05–4.0 mM and of oxalate ions by their inhibiting effect in the concentration range 0.5–20 mM.     

Mechanism of the antitumor action of complex compounds of copper(II) with α-amino acids

It is shown theoretically and experimentally that the high superoxide dismutase-like activity of certain amino acids and their CuA₂ and CuAB complexes does not correlate with antitumor activity. It was found that the difference in activity is connected with the electronic structure, which explains the dependence of activity on the structure of the complex and the nature of its ligands.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 3, pp. 233–238, May–June, 1993.     

Determination of Ionol by Voltammetry and Coulometric Titration

Procedures were developed for determining ionol by voltammetry and by coulometric titration with electrogenerated chlorine using the amperometric indication of the titration end point. Possible mechanisms of ionol oxidation with electrogenerated chlorine and its electrochemical oxidation at a glassy carbon and a gold electrode were discussed. Procedures were developed for determining ionol in mineral oil in analytical ranges from 1.0 × 10^–4 to 1.0 × 10^–2 M (RSD = 9%) and from 3.0 × 10^–5 to 4.0 × 10^–3 M (RSD = 9%) using a glassy carbon and a gold electrode, respectively. The detection limits for ionol at the glassy carbon and gold electrode were 2.8 × 10^–4 and 1.0 × 10^–5 M, respectively. The detection limit in coulometric titration was 20 g/mL.     

The mechanism of formation of light-scattering centers in sapphire crystals grown in gas atmospheres

The mechanism of the formation of light-scattering centers in sapphire crystals grown by horizontal directed crystallization in gas atmospheres reducing with respect to the Al₂O₃ melt was studied. The experimental regularities here significantly differ from those observed upon formation of other conventional defects in sapphire crystals (vacancy pores, gas bubbles, and so on). It is shown that the known formation mechanisms of macroscopic ≥1 mm) inclusions in crystals are not acceptable in this case. Using the model of bulk crystallization is proposed to describe the obtained regularities.     

Study of tautomerism and geometrical isomerism of nitrogen-containing derivatives of carbonyl compounds Report 12. Polarographic study of semi- and thiosemicarbazones of aliphatic aldehydes

Conclusions The polarographic behavior and semi- and thiosemicarbazones of acetic, butyric, isobutyric, and isovaleric aldehydes and the thiosemicarbazone of propionaldehyde was studied.Translated from Izvestiya Akademii Nauk SSSR, Setiya Khimicheskaya, No. 6, pp. 978–984, June, 1964