Photoelectron spectra andab initio calculations of the electronic structure of amino-n-sulfenyl chlorides

The electronic structure of some amino-N-sulfenyl chlorides and related compounds is studied by photoelectron spectroscopy and ab initio calculations. Similar values of IP(n _S ) and IP(n _N ) and the total energy minimum indicate that in stable conformations the n _S and n _N orbitals are orthogonal. These conformers are characterized by an effective n_N-σ _S-Cl ^* interaction. The relationship between the intramolecular shift of charge and ionization potential values and the spatial structure of amino-N-sulfenyl chlorides is analyzed. A. E. Arbuzov Institute of Organic and Physical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 2, pp. 69–73, March–April, 1994. Translated by L. Smolina     

Heat capacity of niobium chlorides in the range 6–320 K

The heat capacities of NbCl₅ and Nb₃Cl₈ samples with less than 1·10^–3 mass-% of impurities were determined over the range 6–320 K by an adiabatic calorimeter. An anomaly was found in Nb₃Cl₈ within the 7–13 K range. Comparisons ofC _p values of Nb₃Cl₈ are made with the theoretical works of Tarassov. The qualitative fit is quite good.

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Zusammenfassung Die Wärmekapazitäten von NbCl₅- und Nb₃Cl₈-Proben mit Verunreinigungsgehalten 10^–3 Masse-% wurden mit einem adiabatischen Kalorimeter bei 6 bis 320 K bestimmt. Am Nb₃Cl₈ wurde eine Anomalie bei 7 bis 13 K nachgewiesen. Die C_p-Werte von Nb₃Cl₈ werden mit theorischen Ergebnissen von Tarassov verglichen, die qualitative Übereinstimmung ist gut.

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6–320 NbCl₅ Nb₃Cl₈ , 1· 10^–3 . Nb₃Cl₃ 7–13 . _p Nb₃Cl₈ , .

     

Potentiometric sensors based on organic ion exchangers for determining tetraalkylammonium salts

Potentiometric sensors with plasticized polymer membranes based on organic ion exchangers, tetraalkylammonium dodecyl sulfates (benzyldimethyldodecylammonium, benzyldimethyltetradecylammonium, dimethyldistearylammonium), have been proposed for the determination of quaternary ammonium salts in model solutions and KATAPAV technical solutions. The thermal stability, composition, and solubility product have been estimated. It has been shown that ion associates are stable to 60?C70°C, K _S varies in the range from 2 × 10^?8 to 5 × 10^?10. The basic electrochemical parameters of the sensors have been determined as well, such as linearity ranges of the electrode function (5 × 10^?5 (5 × 10^?6)?1 × 10^?2 (1 × 10^?3) M) and slopes of the electrode functions (47?C59 mV/pc), response time (60?C90 sec), potential drift (2?C3 mV/day), operation period (3?C4 months), limits of detection for tetramethylammonium salts (1 × 10^?5?4 × 10^?7 M).     

Quantum-chemical study of the structure of copper(I) acetate and trifluoroacetate oligomers

The results of B3LYP quantum-chemical calculations of the equilibrium structures of [(CX₃COOCu)₂]₃, [(CX₃COOCu)₂]₂, and (CX₃COOCu)₂ oligomers (X = H, F) using the cc-pVTZ correlation-consistent basis for C, O, and F atoms and the Stuttgart 1997 RSC basis and relativistic effective core potential for Cu(I) atoms are presented. The differences in the structures of the free dimer and dimer units in oligomers were studied. The hexamer structure was chosen as the model of a fragment of the crystalline phase. Good agreement was obtained between the experimental and calculated differences between the geometrical parameters of the structures in the “gas phase-crystal” and “acetate-trifluoroacetate” series. Based on the calculated data, the increase in the Cu(I)-Cu(I) bond length in the silver acetate crystal compared with the gas phase can be explained by the effect of the neighboring dimer units of the polymer ribbon, while the increase in the Cu(I)-Cu(I) bond length in gaseous trifluoroacetate compared with acetate, by the acceptor effect of fluorine atoms.     

The Inclusion Properties of a New Watersoluble Sulfonated Calix[4]resorcinarene towards Alkylammonium and N-Methylpyridinium Cations

The inclusion behaviour of a new water-soluble sulfonated calix[4]resorcinarene towards alkylammonium and N-methylpyridinium cations has been investigated on the basis of ¹H NMR spectroscopy and pH-potentiometry data. The inclusion of the N-methylpyridinium cation has been found to be dependent on pH with the preferable inclusion of the methyl substituent in alkaline and the aromatic ring in neutral aqueous media.     

Fissile radionuclides in thyroid of the inhabitants of the gomel region in belarus and peculiarities of their distribution

Severe radiation damages with the following substitution of connective tissue are the effect of high doses in microvolumes of the thyroid. Calcium, strontium and uranium deposited into these sections was more as compared to a normal tissue of the thyroid. An estimation of the microdistribution of fissile radionuclides was carried out using the method of fragmental radiography. The analysis of tracks done visually using a microscope magnification of 300 revealed the local density of fission fragments up to 10³ mm⁻². The irradiation of the surrounded cells which contain the hidden genetic damages, initiated by radioiodine, does not exclude their possible promoter role in thyroid cancerogenesis.     

Activation of molecular hydrogen on platinum nanoparticles: Quantum-chemical modeling

The interaction of molecular hydrogen with platinum clusters of different size has been modeled by the density functional theory method within the generalized gradient approximation (GGA). The cluster size turns out to have little effect on the interaction energy, whereas the effect of the cluster structure is rather significant. The most efficient interaction with hydrogen is observed for clusters with a structure resembling the crystal structure of platinum metal. In such clusters, the hydrogen molecule is attached to its surface without a barrier. Configurations with the bidentate hydrogen coordination are the most stable ones. The H atoms can migrate over the cluster surface, overcoming moderate potential barriers of ∼0.3–0.4 eV.     

Determination of copper by its catalytic effect on the oxidation of hydroquinone by hydrogen peroxide on supports

The reaction of oxidation of hydroquinone by hydrogen peroxide catalyzed by copper(II) in the presence of 2,2’-dipyridyl is activated by hexamethylenediamino groups that are bonded to the surface of filter paper; additional activating effect is produced by 2,2′-dipyridyl. The introduction of malonic acid dinitrile into the indicator reaction improves the sensitivity of the determination of copper and the contrast of the reaction in solution because of the formation of a blue product. Differently colored compounds are formed on a paper support at different concentrations of copper, which makes it possible to visually distinguish the quantities of copper that differ by an order of magnitude in the range 1 × 10^-5-0.5 μg. Quantitative detection is possible in the range 5 × 10^-6-0.1 μg (c_min = 3 × 10^-6 μg). The concentration of copper (0.2-1.5 μg/mL) is determined in blood serum; the consumption of the sample per one determination is 3 μL     

Synchronization in a Network of Spiking Neural Oscillators with Plastic Connectivity

Radiophysics and Quantum Electronics - Synchronization of neural activity plays an important role for processing of information in the brain. In this work, we study the dynamics of a neural network...     

Internal Rotation and Equilibrium Structure of the Bromonitromethane Molecule According to Gas Electron Diffraction Data and Quantum Chemical Calculations

The structure and internal rotation of the bromonitromethane molecule are studied using electron diffraction analysis and quantum chemical calculations. The electron diffraction data are analyzed within the models of a general intramolecular anharmonic force field and quantum chemical pseudoconformers to account for the adiabatic separation of a large amplitude motion associated with the internal rotation of the NO₂ group. The following experimental bond lengths and valence angles are obtained for the equilibrium orthogonal configuration of the molecule with C_s symmetry: r_e(N=O) = 1.217(5) Å, r_e(C–N) = 1.48(2) Å, r_e(C–Br) = 1.919(5) Å, ∠_еBr–C–N = 109.6(9)°, ∠_еO=N=O = 125.9(9)°. The equilibrium geometry parameters are in good agreement with CCSD(T)/cc-pVTZ calculations. Thermally averaged parameters are calculated using the equilibrium geometry and quadratic and cubic quantum chemical force constants. The barrier to internal rotation cannot be determined reliably based on the electron diffraction data used in this work. There is a 82% probability that the equilibrium configuration with orthogonal C–Br and N=O bonds is most preferable, and internal rotation barrier does not exceed 280 cm^-1, which agrees with CCSD(T)/cc-pVTZ calculations.