Influence of the interaction between adsorbed organic ions and supporting electrolyte ions on the kinetic current of protonation reaction

The paper presents an ionite model of a mercury electrode covered with adsorbed organic ions, and points out that the kinetic current of protonation in the presence of ionic surfactants depends on the process of ion exchange with the participation of the so-called ionite layer formed during the adsorption of organic ions, which have long carbon chains (C10).     

Direct or indirect influence of triphenyl‐lead on activity of Na+/K+‐ATPase

We have studied the effect of triphenyl‐lead chloride on the lipid phase of erythrocyte membranes, on lipid monomolecular layers and Na⁺/K⁺‐ATPase of the microsomal fraction of rat brain. It was found that the haemolytic effect induced by this compound occurs when its concentration exceeds 30 µM . The minimal lead concentration inducing measurable effects in monomolecular lecithin layers is about 1 µM . Inhibition of Na⁺/K⁺‐ATPase activity begins at a concentration exceeding 0.5 µM . Maximum inhibition is observed at around 40 µM —a concentration at which haemolysis also occurs. It can thus be thought that at very low lead concentrations the main (or exclusive) role in modifying membrane function is played by direct interaction between lead and the sulphydryl groups of ATPase, whereas at higher concentrations two effects seem to overlap: direct interaction between lead and enzymic proteins via their sulphydryl groups and as indirect influence on the proteins via changes in the organization of the lipid phase of the membrane. Copyright © 2000 John Wiley & Sons, Ltd.     

Formation and stabilization of persistent free radicals

We demonstrate that stable and relatively unreactive “environmentally persistent free radicals (PFRs)” can be readily formed in the post-flame and cool-zone regions of combustion systems and other thermal processes. These resonance-stabilized radicals, including semiquinones, phenoxyls, and cyclopentadienyls, can be formed by the thermal decomposition of molecular precursors including catechols, hydroquinones and phenols. Association with the surfaces of fine particles imparts additional stabilization to these radicals such that they can persist almost indefinitely in the environment. A mechanism of chemisorption and electron transfer from the molecular adsorbate to a redox-active transition metal or other receptor is shown through experiment, and supported by molecular orbital calculations, to result in PFR formation. Both oxygen-centered and carbon-centered PFRs are possible that can significantly affect their environmental and biological reactivity.     

Novel sample treatment procedures for the determination of phosphorus in Cu‐based alloys using X‐ray fluorescence spectrometry to solve the microstructural effect issue

The accurate analysis of hard CuP and CuPAg‐type solders using X‐ray fluorescence spectrometry is a difficult task. Surface milling, the most common sample preparation method for calibration materials, results in poor accuracy for the phosphorus analysis, as evidenced by the unacceptable values of the root mean square error. Meanwhile, the analysis of real samples provides incorrect results, and microstructural effects are the main source of error. Thus, this effect was negated by considering the information depth of the phosphorus Kα line and the microstructure size of the alloys. Phosphorus was measured using a thin layer of the sample (a thickness of several micrometers). As a result, the analyzed layer was a poor representative of the sample. Two different approaches for solving the microstructural effect issue were proposed. In the first method, the alloy was remelted under controlled conditions to obtain fine‐grain samples, which successfully limited the microstructural effects. The second solution used specially prepared thin layer samples, and the sample dissolution eliminated the microstructural effect. Using the developed sample treatment methods resulted in an improvement in the accuracy of the phosphorus calibration curves. This allowed for the correct determination of phosphorus and other alloying elements in the Cu‐based alloys with low uncertainties.     

TG study on real role of active carbon support in propane dehydrogenation with CO2

Active carbon was used as a support for chromium(III) oxide phase. The synthesized materials appeared to be very active catalysts of the propane dehydrogenation in the presence of CO₂. An influence of the Cr content on the catalytic activity and selectivity was observed. The best results were achieved over the sample containing about 5 wt.% of Cr. A negative effect of activity decay with time-on-stream was found. The reasons of the observed deactivation were explained using the thermal analysis method. A behavior of the fresh and used samples was tested in a temperature range of 25–1000 °C in different atmospheres (inert gas, air or CO₂). It was found that the catalytic runs resulted in a partial decomposition of surface O-containing groups, which together with CrO_x species play a role of active centers. Moreover, a formation of inactive carbonaceous deposit on the catalyst surface was observed.     

350 MHz 1H NMR spectra,dipole moments and preferred conformation of 8,9-epoxy-6,7-dihydro-5H-benzocyclohepten-5-ones

350 MHz ¹H NMR spectra and dipole moments showed that in the preferred conformation of 8,9-epoxy-6,7-dihydro-5H-benzocyclohepten-5-one and its 1,4-dimethoxy derivative the oxirane ring takes a pseudo-axial position.     

1H NMR studies of solvent effects on hydrogen bonding in some pyridine trifluoroacetates

The chemical shifts of hydrogen bonded protons in complexes of 11 substituted pyridines with trifluoroacetic acid were examined, in five dry solvents of different activity, with respect to proton transfer and aggregation effects. The results were correlated with ΔpK_a, the Kirkwood function and E _T parameters. The solvent effect on the intersection point obtained from the plot of the chemical shift of the hydrogen bonded protons against ΔpK_a can be used, similar to an isotopic effect, to differentiate strong hydrogen bonds. The aggregation of acid–base complexes can lead to downfield or upfield shifts; the variation of chemical shift with aggregation depends on the position of the proton in the hydrogen bridge.     

The protonation of ortho-methoxy- and hydroxy-benzaldehydes in FSO3H?SbF5?SO2 solution

The protonation of o-methoxy- and o-hydroxy-benzaldehydes in FSO₃H? SbF₅? SO₂ solution was investigated by ¹H NMR spectroscopy. The formation of the Z-carbonyl protonated molecule is explained by intramolecular hydrogen bonding.     

Studies on Pyrazine Derivatives,XLIII: Synthesis and Antituberculosis Activity of 6-(1,2,3,4-Tetrahydroisoquinolino) and 6-(1,3,3-Trimethyl-6-azabicyclo-[3, 2, 1]-octano)-pyrazinocarboxylic Acid Derivatives

The reactivity of the chloride atom of 2-cyano-6-chloropyrazine was used in the reactions with amines, 1,2,3,4-tetrahydroisoquinoline and 1,3,3-trimethyl-6-azabicyclo-[3,2,1]-octane, which yielded the substrates for the syntheses of a series of new derivatives. The bulk of them were tested for their tuberculostatic activity. MIC values of the most active ones ( 2a , b , 5b , 7a , 9b , and 11b ) were within 3.1–50 μ g/mL.