Reduction of an Ensemble of Chloride Aquacomplexes of Platinum(II): An Analysis in the Framework of Phenomenological Approach

A general approach is offered to a phenomenological analysis of experimental data on the kinetics of an electrode reaction complicated by chemical stages. The approach is based on a consideration of the way the process rate depends on the supporting-electrolyte concentration at a constant electrode charge. The possibilities of the approach are illustrated by the example of the reduction of chloride complexes of Pt(II) in the presence of chloride, indifferent (in the sense of inner-sphere substitution), and mixed supporting electrolytes. The performed analysis generalizes the Frumkin–Petrii relationship, which determines the average charge of the single reactant in the solution bulk. A system may contain an ensemble of reactants. In this case, in addition to the bulk properties of the system, similar relationships take into account the interface structure and the balance between partial rate constants for parallel reactions involving reactants of different chargeness.     

Speciation in strongly acidic metastable solutions of oxotungstate(vi) compounds

The ionic composition of long-lived metastable aqueous solutions of oxo compounds of tungsten(IV) with pH ≤ 1 was studied by spectrophotometry. The nature of some isopolytung-states formed in these solutions in the presence of various inorganic acids (HCl, HClO₄, HNO₃, H₂SO₄, and H₂SeO₄) was established.     

Comparison of the Possibilities of Thermal-Lens Detection in Capillaries and Microchips

The conditions of thermal-lens detection are compared for samples with small path lengths: capillaries and microchannels of chemical microchips. The optimum parameters of the optical configuration of a thermal lens spectrometer (beam diameters and their in-sample ratios, and the detector position) were calculated from the theory and confirmed experimentally. The limits of detection of a model chemical substance (ferroin) are estimated at 1 × 10^–8 M for microchips and 5 × 10^–8 M for capillaries. The absolute limits of detection are the same and equal to 3 × 10^–17 M. The advantages and disadvantages of thermal lens detection in capillaries and microchips are discussed.     

On the Most Powerful Chemical Traps for Bis(methoxycarbonyl)carbene (=2‐Methoxy‐1‐(methoxycarbonyl)‐2‐oxoethylidene)

The efficiency and validity of different chemical substrates for trapping bis(methoxycarbonyl)carbene (=2‐methoxy‐1‐(methoxycarbonyl)‐2‐oxoethylidene; 1 ) is dependent on the conditions of carbene generation. On conventional photolysis of dimethyldiazomalonate (=2‐diazopropanedioic acid dimethyl ester; 2 ) by long‐wave UV light (through a Pyrex filter, λ>290 nm), the most powerful trap for carbene 1 in the series of substrates Me₂S, MeOH, cyclohexane, and pyridine is Me₂S (with an efficiency ratio of ca. 6 : 4 : 2 : 1, resp.). When short‐wave decomposition of diazomalonate 2 is employed (through a quartz filter, λ>210 nm), more reliable and useful chemical traps for bis(methoxycarbonyl)carbene ( 1 ) are pyridine and cyclohexane, whose adducts with 1 are rather stable under short‐wave‐irradiation conditions. Application of alcohols for the trapping of 1 proves to be preferential when simultaneous monitoring of carbene and oxoketene formation during photolysis is necessary.     

Free-surface non-Newtonian fluid flow in a round pipe

Free-surface pseudoplastic and viscoplastic fluid flows in a round pipe were studied for the case where the direction of motion coincides with the direction of gravity. Numerical modeling was performed using a technique based on a combination of the SIMPLE algorithm and the method of invariants. Three characteristic filling regimes were found to exist: a complete filling regime, a regime characterized by air-cavity formation on the solid wall, and a jet regime. Critical parameter values separating the regions of existence of these regimes were calculated. The evolution of quasisolid cores was studied for flow of a fluid with an yield point.     

Exciton-photon interaction in low-dimensional semiconductor microcavities

The structure of the photon states and dispersion of cavity polaritons in semiconductor microcavities with two-dimensional optical confinement (photon wires), fabricated from planar Bragg structures with a quantum well in the active layer, are investigated by measuring the angular dependence of the photoluminescence spectra. The size quantization of light due to the wavelength-commensurate lateral dimension of the cavity causes additional photon modes to appear. The dispersion of polaritons in photon wires is found to agree qualitatively with the prediction for wires having an ideal quantum well, for which the spectrum is formed by pairwise interaction between exciton and photon modes of like spatial symmetry. The weak influence of the exciton symmetry-breaking random potential in the quantum well indicates a mechanism of polariton production through light-induced collective exciton states. This phenomenon is possible because the light wavelength is large in comparison with the exciton radius and the dephasing time of the collective exciton state is long. Zh. éksp. Teor. Fiz. 114, 1329–1345 (October 1998)     

Effect of Filler Aggregation on Properties of a Composite Based on Epoxy Polymer

The plasticity of a composite based on epoxy polymer was studied as influenced by the concentration of the filler, nanosized powders containing aggregates of strongly bound ZrO₂ particles.     

Effect of Ammonium Ions on the Electroreduction of Anions at a Mercury Electrode

The effect of ammonium ions on the electroreduction of peroxodisulfate (S₂O^2- ₈) and perbromate (BrO^- ₄) anions is found to be commensurate with that of potassium ions. Ammonium ions accelerate the reduction of iodate (IO^- ₃), bromate (BrO^- ₃), and chromate (CrO^2- ₄) anions in nonbuffered solutions and does not, in buffered ones. In the former case, the effect is connected with the pH change in the near-electrode layer during the reaction and with the participation of ammonium ions in hydrolytic equilibriums, rather than with a simultaneous transfer of ammonium ions and electrons in an elementary act. The conclusions in the literature in favor of a simultaneous transfer of the proton and electron in the proton-consuming reactions of reduction of anions is shown to be ambiguous.     

HPTLC Determination of Polyaromatic Hydrocarbons in Smokers’ Hair

JPC – Journal of Planar Chromatography – Modern TLC - A method developed for quantitative determination of the total amount of polyaromatic hydrocarbons (PAH) in human hair has been...