Temperature and Concentration Dependence of the Electrical Conductance,Diffusion, and Kinetics Parameters of the Ions in Aqueous Solutions of Sulfuric Acid,Selenic Acid,and Potassium Tellurate

The temperature and concentration dependences of the electrical conductance of aqueous solutions of sulfuric acid, selenic acid, and potassium tellurate were studied. The coefficients of the corresponding empirical equations were determined, and the values of equivalent conductances of the anions were evaluated at infinite dilution at the experimental temperatures. The values of the coefficients in the Fuoss and Onsager equation were evaluated for the three electrolytes at 298 K. The values of the molecular and ionic coefficients of self-diffusion at infinite dilution were calculated in the temperature range 288–318 K. The change of the translational energy Δ E∘_tr. of water molecules in the ionic hydration sphere was determined. The number of water molecules participating in the ionic hydration sphere at 298 K and the changes of Gibbs free energy, enthalpy, and entropy of activation of ionic conductance were calculated. The results obtained were interpreted according to the Samoylov’s theory of positive and negative hydration of ions. The differences observed in the temperature dependences of the mentioned parameters were explained in terms of the different radii and hydration numbers of the ions.     

Low-temperature heterogeneous oxidation of sulfide ions on a higher Co oxide system in aqueous medium

Low-temperature heterogenous oxidation of sulfide ions on a higher Co oxide system in aqueous medium has been studied. The effects of pH, temperature and catalyst amount on the kinetic parameters as well as on the selectivity of the oxidation process were investigated. An oxidation mechanism has been proposed based on the results of kinetic investigations and on the data obtained by IR and XPS spectroscopic studies of Co oxide before and after sulfide ion oxidation.     

Acid—base equilibria in the mixed solvent 80% dimethyl sulfoxide—20% water: Part 3. Determination of Acid—Base Indicator Constants

The acid—base constants of ten nitrophenol, sulfonphthalein and phthalein indicators in 80% dimethyl sulfoxide—20% water are reported. The indicators were selected so that their transitional intervals cover a large part of the pH-scale. The relationship between the constants in the mixed solvent and in water is linear: (pK_HI)_SH = 1.48 (pK_HI)_H2O— 1.68.     

Products and kinetics of non-isothermal decomposition of vanadium(IV) oxide compounds

The kinetics of dehydration and decomposition of VOSO₄·2H₂O, VOSO₄ and VOSeO₃·H₂O was studied under non-isothermal heating on a derivatograph. The stages and products of the thermal decomposition were determined. It was proved that VOSO₄·2H₂O decomposes to V₂O₅ while VOSeO₃·H₂O − to V₂O₄. A number of kinetic models and calculation procedures were used to determine the values of the kinetic parameters characterizing the process. The parameters calculated were compared and analyzed. IR-spectra of the initial substances and the solid residue after decomposition are presented.     

Extension of the ladder model of self-assembly from cylindrical to disclike surfactant micelles

The ladder model of growth of cylindrical micelles gives expressions for the micellar size distribution and for the mean aggregation number, which are in good agreement with the experiment. Here, we consider this model and its extension to the case of disclike micelles. In analogy with the modeling of elongated micelles as sphero-cylinders, the disclike micelles can be modeled as toro-discs. Upon micelle growth, the hemispherical caps of a cylindrical aggregate remain unchanged, whereas the semitoroidal periphery of a disclike micelle expands. This effect can be taken into account in the expression for the size distribution of the disclike micelles, which predicts the dependence of the micelle mean aggregation number on the surfactant concentration. It turns out that disclike micelles could form in a limited range of surfactant concentrations, and that their mean aggregation number cannot exceed a certain maximal value. Large disclike micelles can exist only near the border with the domain of cylindrical micelles. Then, small variations in the experimental conditions could induce a transformation of the disclike micelles into cylindrical ones.     

Molecular structure and spectroscopic studies on novel complexes of coumarin-3-carboxylic acid with Ni(II), Co(II), Zn(II) and Mn(II) ions based on density functional theory

Novel Ni(II), Co(II), Zn(II) and Mn(II) complexes of coumarin-3-carboxylic acid (HCCA) were studied at experimental and theoretical levels. The complexes were characterised by elemental analyses, FT-IR, (1)H NMR, (13)C NMR and UV-Vis spectroscopy and by magnetic susceptibility measurements. The binding modes of the ligand and the spin states of the metal complexes were established by means of molecular modelling of the complexes studied and calculation of their IR, NMR and absorption spectra at DFT(TDDFT)/B3LYP level. The experimental and calculated data verified high spin Ni(II), Co(II) and Mn(II) complexes and a bidentate binding through the carboxylic oxygen atoms (CCA2). The model calculations predicted pseudo octahedral trans-[M(CCA2)(2)(H(2)O)(2)] structures for the Zn(II), Ni(II) and Co(II) complexes and a binuclear [Mn(2)(CCA2)(4)(H(2)O)(2)] structure. Experimental and calculated (1)H, (13)C NMR, IR and UV-Vis data were used to distinguish the two possible bidentate binding modes (CCA1 and CCA2) as well as mononuclear and binuclear structures of the metal complexes.     

Catalytic asymmetric 5-enolexo aldolizations. A computational study

The diastereo- and enantioselectivity obtained experimentally by Enders et all. (Enders, D.; Niemeier, O.; Straver, S. Synlett 2006, 3399-3402) in the amine-catalyzed intramolecular 5-enolexo aldolization of 1,6-dicarbonyl compounds were fully rationalized using density functional theory methods. A polarizable continuum model was used to describe solvent effects. While 6-enolexo aldolizations are well described by Houk's model on the basis of steric and electrostatic contacts, the main factors conditioning the final selectivity in 5-enolexo processes are calculated to be quite different. Thus, the selectivity results from the summation of several small electrostatic contacts with an unexpected HOMO electronic overlapping plus the ring strain of the five-membered ring, whereas steric effects seem to be unimportant. Our results indicate, in contrast with 6-enolexo processes, that high selectivities are not expected in this type of reaction and that the experimental selectivity shall be very dependent on the reaction conditions, as known experimental results seem to suggest. 7-enolendo products are not expected, as they are predicted to be formed by higher energetic transition states. Variable reaction rates, experimentally observed with different catalysts, are suggested to be mainly a result of different catalyst solubilities.     

NMR,IR and DFT studies of phenylplatinum complexes with O-monodentate coordinated silsesquioxanate and auxiliary phosphine ligands

The molecular structure and spectroscopic properties of a series of phenylplatinum complexes containing silsesquioxanate and phosphine ligands with general formula trans-[Pt{O₁₀Si₇(R)₇(OH)₂}(Ph)(L)₂] (1: R = cyclo-C₅H₉, L = PEt₃; 2: R = iso-C₄H₉, L = PEt₃; 3: R = CH₃, L = PEt₃; 4: R = cyclo-C₅H₉, L = PMe₃; 5: R = cyclo-C₅H₉, L = PMe₂Ph; 6: R = cyclo-C₅H₉, L = PPh₂Me; 7: R = cyclo-C₅H₉, L = PPh₃) have been investigated by DFT/OPW91/6-31G(d) calculations, ¹H, ¹³C, ²⁹Si and ³¹P NMR and IR spectroscopy. DFT molecular modeling based on available X-ray and NMR data for complexes 1 and 2 allowed deriving structure-NMR spectra correlations. It was found that the alkyl substituents (R) attached to Si atoms, cyclo-C₅H₉, iso-C₄H₉ and CH₃, slightly influence the geometry and multinuclear NMR parameters of the complexes in the series studied. The molecular structures of the Pt(II) complexes with R = cyclo-C₅H₉ (4–7) were predicted by DFT calculations of their simplified models with R = CH₃ (4′?7′). The geometry optimizations of 4′?7′ showed square-planar configuration of Pt(II) center bonded to two trans phosphine ligands, a phenyl group and an O-monocoordinated silsesquioxanate. The structures 4′?6′ are stabilized by two intramolecular hydrogen bonds similar to 1 and 2. A fast conformer exchange process A?B and switching of H-bonds in solution of 1–6 were suggested based on (i) the calculated conformer energies and small barrier of the process, and (ii) the observed single ¹H NMR signal at low magnetic field. The stability of the Pt(II) complexes depends on the nature of the phosphine ligands and decreases in the order PMe₂Ph > PMe₃ > PPh₂Me > PEt₃ > PPh₃. The PPh₃ ligands attached to Pt(II) in 7 cause the largest geometry changes and a new set of weaker hydrogen bonds. The comparison of the calculated NMR and IR parameters with the experimental spectroscopic data reveals good coincidence and thus confirmed the suggested molecular structures.     

EPR and UV spectral study of gamma-irradiated white and burned sugar, fructose and glucose

The EPR and UV spectral properties of gamma-irradiated white and burned sugar, fructose and glucose are studied with the accent on their suitability as dosimetric materials. It is shown that gamma-irradiation of solid samples of white sugar and fructose yields stable EPR spectra whereas glucose signal remains time-dependent even 11 months later. Sugar and glucose exhibit linear EPR dose response in the region 0.44-21 kGy and fructose only up to ca. 10 kGy. The relative radiation sensitivity obtained for sugar and fructose is up to 10 kGy and slightly lower for glucose. Burned saccharides provide 2-3 orders of magnitude lower EPR radiation sensitivity making them not suitable for the proposed designation. According to the UV spectra water solutions of gamma-irradiated solid white saccharides show well pronounced absorption bands at 267 and 286 nm for sugar and fructose with time-dependent intensities reaching steady values ca. 11 days after dissolution. The intensities of these absorption bands are in linear relation with the absorbed dose of gamma-radiation. Glucose shows low sensitively because irradiation with 5.5 kGy yields only a shoulder at about 260-280 nm with decreasing to ca. 40% intensity in the first few days after dissolution. Excellent correlation between the intensities of the EPR- and UV-absorbed dose response is found for sugar and fructose in the region 0.44-10 kGy. This opens new possibilities for independent calibration the EPR dose response. Finally, the comparison suggests sugar as the best, universal material for EPR- and/or UV-dosimetry in the region 0.44-160 kGy.