A theoretical study of conformational flexibility,magnetic properties,and polarizabilities of trimethylnaphthalenes

For almost all trimethylnaphthalenes (TMNs), the transition from a planar equilibrium ring conformation to a nonplanar conformation characterized by the torsional angle of 20° results in an energy increase of less than 2.5 kcal/mol. For some of them, it is less than 1.6 kcal/mol, which indicates that these molecules can change their conformation easily through intermolecular interactions. The results of the calculations reveal a linear relationship between the averaged rigidity constant and the relative energy for all planar TMNs. The changes of rings deformational energy imposed on π‐electron systems of TMNs by medium polarity are negligible (less than 0.05 kcal/mol). The aromaticity indices, based on nucleus‐independent chemical shifts, indicate aromatic character of TMNs. The α substitution increases the ring area more than the β substitution. The increase of anisotropy of dipole polarizabilities with the decrease of the area of rings for all planar TMNs, dimethylnaphthalenes and methylnaphthalenes is noticed. © 2013 Wiley Periodicals, Inc.     

Densitometric Determination of Omeprazole,Pantoprazole, and their Impurities in Pharmaceuticals

JPC – Journal of Planar Chromatography – Modern TLC - A method has been developed for separation of omeprazole and pantoprazole, and their impurities omeprazole sulfone and...     

Photochemical transformation of β,β′-dithienyl substituted o-divinylbenzenes leading to 1,2-dihydronaphthalenes or fused pentacyclic compounds: first evidence of electrocyclization process via 2,3-dihydronaphthalene intermediates

The photochemical behaviour of 2,2′-(o-phenylenedivinylene)dithiophenes (7a–c), 3,3′-(o-phenylenedivinylene)dithiophene (8a) and 3,3′-(o-phenylenedivinylene)dibenzothiophene (8b) was studied under the low concentrations. An intramolecular reaction via the 2,3-dihydronaphthalene intermediate has been observed in all studied examples accompanied by dimerization and polymerization. The 1,2-dihydro-2,3-dithienylnaphthalenes (9a–c) were isolated (7–9%) from the 2-thiophene derivatives while the 3-thiophene derivatives gave polycyclic structures (13–44% yield).     

On coefficients of Kapteyn-type series

Quite recently Jankov and Pogány [JANKOV, D.—POGÁNY, T. K.: Integral representation of Schlömilch series, J. Classical Anal. 1 (2012) 75–84] derived a double integral representation of the Kapteyn-type series of Bessel functions. Here we completely describe the class of functions Λ = {α}, which generate the mentioned integral representation in the sense that the restrictions $\alpha |_\mathbb{N} = (\alpha _n )_{n \in \mathbb{N}} $ is the sequence of coefficients of the input Kapteyn-type series.     

Determination of the soil-to-grass transfer of 137Cs and its relation to several soil properties at various locations in Serbia

Transfer coefficients of ¹³⁷Cs from soil to grass were determined for the terrain around the city of Kragujevac in central Serbia. Mass activity concentrations of ¹³⁷Cs in soil and grass samples were determined with a high-purity Ge-detector (HPGe). The activity concentration at the depth of 20 cm was found to be in the range of 14.92–124.05 Bq kg^?1, whereas the activity in grass for the same location was in the range of 4.60–84.95 Bq kg^?1. Transfer factors (TFs) were in the range of 0.07 up to 1.94.

Dependences of TFs on different soil characteristics were presented graphically. Weak dependences were determined between them. Absalom's model was used to predict TFs based on soil characteristics: pH value, contents of clay, exchangeable potassium and humus.

A comparison of measured and predicted values from Absalom's model is shown graphically. It has been found that Absalom's model might be carefully used for the prediction of ¹³⁷Cs in grass for specific regions.     

Onset of glassy dynamics in a two-dimensional electron system in silicon

The fluctuations of conductivity sigma with time have been studied in a two-dimensional electron system in low-mobility Si inversion layers. The noise power spectrum is approximately 1/f(alpha) with alpha exhibiting a sharp jump at an electron density n(s) = n(g). A huge increase in the relative variance of sigma is observed as n(s) is reduced below n(g), reflecting a dramatic slowing down of the electron dynamics. This is attributed to the freezing of the electron glass. The data strongly suggest that glassy dynamics persists in the metallic phase.     

Thermodynamic and phase diagram investigation of Pb-BiIn section in Pb-Bi-In ternary system

The results of thermodynamic study of Pb-BiIn section of Pb-Bi-In system done experimentally by Oelsen calorimetry and calculated by general solution model, as well as measurements performed by DTA and optic microscopy in order to investigate phase diagram of the given section, are presented in this paper. Thermodynamic properties, such as integral molar enthalpies of mixing, activities, activity coefficients, partial and integral excess Gibbs energies at 600 and 650 K were determined and comparison between obtained experimental and calculated values were done. Also, based on cooling curves, DTA recordings and optic microscopy results phase diagram was constructed and compared with literature data.     

Summations of Schlömilch series containing some Lommel functions of the first kind terms

The main aim of this article is to establish certain closed expressions for the Schlömilch series which members contain some Lommel functions of the first kind.     

Multivariate Curve Resolution - Alternate Least Square Analysis of Excitation-Emission Matrices for Maize Flour Contaminated with Aflatoxin B1

In this preliminary study, we used the Multivariate Curve Resolution- Alternating Least Squares (MCR-ALS) algorithm to analyze the excitation-emission matrix for different samples of maize flour contaminated with aflatoxin B1 (AFB1) - uncontaminated, low-contaminated, high-contaminated and flour from the local market. We intended to see if there are differences in emission spectral parameters that depend on degree of contamination. The analysis used genuine emission of the fluorophores in the flour, in absence and presence of AFB1, which enables fast screening of the samples, without sample pre-processing. As a result of the analysis, two fluorescence components were derived from the emission spectra for all analyzed samples. The components’ positions were the same for the uncontaminated reference sample and the commercial flour sample from the local market, whereas for the samples contaminated with the aflatoxin B1, the emitted peaks’ positions were red-shifted. We found that the ratio of the areas of these two components is proportional to the intensity of contamination: 0.071 for uncontaminated sample, 0.090 for the sample from local market, 0.192 for low-contaminated sample and 1.431 for high-contaminated sample. These results indicate that fluorescence EEM coupled with MCR-ALS could be used for rapid and simple estimation of the degree AFB1 contamination in maize flour.     

Experimental study and thermodynamic calculation of Au–Bi–Sb system phase equilibria

Phase equilibria in the Au–Bi–Sb ternary system have been studied experimentally and calculated by the CALPHAD method. Three calculated isopleths with molar ratios Au:Bi=1, Bi:Sb=1 and Au:Sb=1 were compared with the DTA results from this work. The liquidus projection has been calculated. Two ternary invariant reactions were noted. Calculated phase diagram of isothermal section at 573 K was compared with the results of SEM/EDX analysis.