Reversed-Phase TLC Study of the Lipophilicity of Fourteen 1,3-Benzoxazol-2(3H)-one Derivatives and Comparison with Isomeric 1,2-Benzisoxazol-3(2H)-one Analogs

JPC – Journal of Planar Chromatography – Modern TLC - The lipophilicity and specific hydrophobic surface area of fourteen 1,3-benzoxazol-2(3 H)-ones substituted in the benzene ring...     

Nonlinear screening in multilayer graphene systems

Electrostatic screening in multilayer graphene is highly nonlinear due to the vanishing density of states at the Fermi level. Using a discrete model we study the charge screening normal to the layers. Our model shows a strong charge and temperature dependence and has a simple continuum limit at T=0 for undoped systems. Doped systems can exhibit more complex behavior due to minority-carrier screening. Most importantly we find that the screening length can vary more than an order of magnitude depending on the experimental conditions, reconciling the large range of screening lengths reported in previous experiments. This has important consequences for technological applications of multilayer graphene used in electrodes or transistor channels.     

Classification of amino acids and oligopeptides with the use of multi-mode chemical images obtained with ion selective electrode array

The analysis of amino acids and oligopeptides as important bioanalytes is a significant task in medical diagnostics and proteomic research and currently it is based on chromatographic and electrophoretic methods. In this paper, an approach based on sensor array coupled with titration is proposed for effective recognition of 5 amino acids and 4 oligopeptides. It is shown, that the increase of information gained during measurements of sensors’ signals in various pH allows for capturing more data on interaction of amino acids and oligopeptides with various polymeric membranes of potentiometric electrodes used in the array, and that leads to the lowering of classification errors in partial least squares analysis.     

Electroreduction of Bi(III) Ions at a Cyclically Renewable Liquid Silver Amalgam Film Electrode in the Presence of Methionine

The catalytic influence of methionine (Mt) on the electroreduction of Bi(III) ions on the novel, cyclically renewable liquid silver amalgam film electrode (R–AgLAFE) in a non-complexing electrolyte solution was examined. The presence of methionine leads to a multistep reaction mechanism, where the transfer of the first electron is the rate limiting step, which is the subject of catalytic augmentation. The catalytic activity of methionine is a consequence of its ability to remove water molecules from the bismuth ion coordination sphere, as well as to form active complexes on the electrode surface, facilitating the electron transfer process.     

The kinetics of CO2 gasification of coal chars

The gasification reactivities of three char samples derived from coals of varying ranks (“Turów” lignite, “Piast”, and “Wieczorek” sub-bituminous coals) toward CO₂ were investigated isothermally using thermogravimetric analysis. Kinetic behavior was studied at temperatures of 900, 950, and 1,000 °C under atmospheric pressure. Conditions for the chemical-controlled regime were established at these temperatures and pressure. In this paper, four kinetic models were applied to describe the varying conversion rate: volumetric model, grain model, modified volumetric model, and random pore model. From these models, only the random pore and the volumetric models positively corresponded to nearly the entire range of experimental results. Calculated values of activation energy for study samples were in the range of 180–250 kJ mol^?1, which is in accordance with other reported data. Moreover, the obtained results confirmed the significant impact of parent coal rank on its char reactivity, offering possibilities in the approximation of coal char kinetic behavior after further more detailed studies with a larger number of samples.     

Magnetic Properties of Ball-Milled Nanocrystalline Alloys Fe78B13Si9

Summary.  Magnetic properties of nanocrystalline Fe₇₈B₁₃Si₉ alloys are studied for three series prepared by ball milling starting from amorphous ribbons, crystallized ribbons, and elemental powders. Temperature variation of static magnetization results in strong ferromagnetic interaction which is weakly dependent on the initial material. Magnetic hysteresis loops show that saturation magnetization, magnetic remanence, and coercive field increase with frequency for both series of ribbon samples, whereas they decrease for alloys prepared from elemental powders. Power losses raise faster for the alloys prepared from elemental powders than for the two other alloys. Received October 5, 2001. Accepted (revised) November 12, 2001     

Application of a likelihood ratio approach in solving a comparison problem of Raman spectra recorded for blue automotive paints

Evidential values of Raman spectra recorded for solid and metallic blue car paints were evaluated using visual comparison as well as a statistical approach, i.e. likelihood ratio (LR) test supported by Empirical Cross Entropy (ECE) results. Raman spectra were obtained using a Renishaw inVia spectrometer equipped with a confocal Leica microscope and a near infrared semiconductor laser (785 nm) as an excitation source. When a visual comparison was performed for solid paints, in 17.7% of comparisons (53 pairs out of 300) the samples were indistinguishable, whereas for metallic paints this value was 8.5% of such comparisons (37 pairs out of 435). Comparing the spectra using an LR approach was based on variables being the areas under the most significant Raman spectra bands of pigments present in the analysed samples. Proposed LR models delivered low false positive and false negative rates (for many models lower than 10%), and the ECE plots confirmed that their performance was much better than visual comparison. Copyright © 2015 John Wiley & Sons, Ltd.     

Pomegranate Seed Oil and Bitter Melon Extract Affect Fatty Acids Composition and Metabolism in Hepatic Tissue in Rats

Pomegranate seed oil (PSO) and bitter melon dried fruits (BME) are used as natural remedies in folk medicine and as dietary supplements. However, the exact mechanism of their beneficial action is not known. The aim of study was to assess how the diet supplementation with PSO and/or with an aqueous solution of Momordica charantia affects the metabolism of fatty acids, fatty acids composition and the level of prostaglandin E₂ (PGE₂) in rat liver. Animals (Sprague-Dawley female rats, n = 48) were divide into four equinumerous groups and fed as a control diet or experimental diets supplemented with PSO, BME or both PSO and BME for 21 weeks. Fatty acids were determined using gas chromatography with flame ionization detection. PSO added to the diet increased the rumenic acid content (p < 0.0001) and increased accumulation of n-6 fatty acids (p = 0.0001) in hepatic tissue. Enrichment of the diet either with PSO or with BME reduced the activity of Δ⁶-desaturase (D6D) (p = 0.0019), whereas the combination of those dietary factors only slightly increased the effect. Applied dietary supplements significantly reduced the PGE₂ level (p = 0.0021). No significant intensification of the influence on the investigated parameters resulted from combined application of PSO and BME. PSO and BME have potential health-promoting properties because they influence fatty acids composition and exhibit an inhibiting effect on the activity of desaturases and thus they contribute to the reduction in the metabolites of arachidonic acid (especially PGE₂).     

Solution structure of the aqueous model peptide N-methylacetamide

Classical molecular dynamics simulations of aqueous N-methylacetamide (NMA) have been performed across a concentration range at 308 K. This peptidic fragment molecule is a useful model for investigating water/peptide hydrogen bond competition. The simulations predict considerable NMA self-association even at low concentrations with a concentration-dependent increase in the ratio of branched to linear clusters. Water-mediated NMA contacts are a feature of this regime, manifested by an unexpected increase in the number of short NMA oxygen contacts arising from water bridge motifs. In contrast, bulk water structure is significantly disrupted by the addition of even small quantities of NMA. With increases in NMA concentration water molecules become progressively more isolated, forming dimers and trimers hydrogen-bonded to NMA. The mixture in this concentration regime may therefore offer a minimal model system for certain structural properties of interior water buried in protein cavities and hydrogen-bonded to mainchain peptide groups.