Showing papers in "Russian Journal of Physical Chemistry A in 2009"

The specific surface area and porous structure of graphite materials

Abstract: Transformations of the specific surface area and porous structure of carbon materials based on graphite were studied by low-temperature adsorption of nitrogen. Exfoliated graphite and graphite foil were found to have a developed (compared with the initial graphite) surface (up to 90 m2/g) and a porous structure formed by slit-like mesopores with a characteristic radius of ∼20 A. The determining influence of the method of synthesis on the adsorption properties of materials was demonstrated for the first time.

The kinetics of ozone decomposition in water, the influence of pH and temperature

Abstract: The influence of pH on the kinetics of ozone decomposition in water was studied. Over the pH range 1–8, the kinetics was well described by a second-order reaction equation. Starting with approximately pH 3, the pH dependence of the logarithm of the constant at 19°C corresponded to the equation logk= −2.66 + (0.49 ± 0.03)pH. The activation energy of ozone decomposition was found to be 76.0 ± 8.3 kJ/mol.

Effects of the degree of substitution on the physicochemical properties and photodynamic activity of zinc and aluminum phthalocyanine polycations

Abstract: A series of zinc and aluminum phthalocyanines containing 3–8 pyridiniomethyl or cholinyl substituents on average were synthesized. As the number of cation substituents increased, in aqueous solutions, the aggregation ability of phthalocyanines decreased, while the quantum yields of fluorescence and singlet oxygen generation increased. The photodynamic inactivation of coliform bacteria sensitized by zinc and aluminum phthalocyanine polycations with an increase in the substitution degree became more effective.

The hydrodechlorination of chlorobenzene in the vapor phase in the presence of metal-carbon nanocomposites based on nickel, palladium, and iron

Abstract: Metal-carbon nanocomposites based on nickel, palladium, and iron and bimetallic palladium-nickel-carbon nanocomposites were for the first time used as catalysts of hydrodechlorination of chlorobenzene in the vapor phase in the atmosphere of hydrogen. Nickel and Pd-Ni nanoparticles completely coated by a carbon layer not only were stable to oxidation and agglomeration but also exhibited considerable activity in hydrodechlorination of chlorobenzene at temperatures much lower than those at which dechlorination on carbon carriers occurred. The dependence of catalytic properties (activity, selectivity, and stability) on temperature and nanocomposite composition was studied. Depending on the nature of the metal, the composition of bimetallic particles and temperature the selectivity could be changed, and the reaction could be directed toward the formation of benzene or cyclohexane. Carbon coating was stable under reaction conditions at least up to 350°C and did not hinder hydrodechlorination. Substrate adsorption likely occurred on the outside carbon surface of composite particles. The activity and structure of Ni@C composite remained almost unchanged after triple cycling over the temperature range from 50 to 350°C in a flow system.

Investigation of single wall carbon nanotubes electrical properties and normal mode analysis: Dielectric effects

Abstract: Besides thermodynamic information, vibration can identify modes of a molecule by comparison of the spectroscopy and parameterize force field. By the application of group theory with the state of projection operators, a systematic method for getting the vibrational model of molecules such as the (3, 0), (4, 0), (5, 0) nanotubes was proposed. The U matrix from the combination of primitive’s harmonic vibrations was calculated and the effect of dielectric constants on the mechanism of these vibrations in nanotubes was studied. We found that in the high dielectrics the frequency of vibration has alternative behavior, however by the decreasing of the dielectrics, this behavior change to stable situation of geometry. The calculated data shown in Tables and Figures are in correspondence with some behavior of nanotubes.

The bulk properties of the water-dimethylsulfoxide system at 278–323.15 K and atmospheric pressure

Abstract: The densities of water-dimethylsulfoxide (DMSO) mixtures were measured over the temperature range 278–323.15 K and over the whole range of compositions at atmospheric pressure. The partial molar volumes of water and dimethylsulfoxide, mixture volumetric thermal expansion coefficients, and partial molar volumetric thermal expansion coefficients of the components were calculated. The composition dependences of the density of the mixture passed a maximum at x ∼ 0.6 at all temperatures (x is the mole fraction of dimethylsulfoxide). The composition dependences of the partial molar volumes of water and DMSO also passed extrema.

The synthesis, structure, and properties of carbon-containing nanocomposites based on nickel, palladium, and iron

Abstract: Nickel, iron, palladium, and bimetallic nickel-palladium nanoparticles encapsulated in carbon were synthesized by contactless levitation fusion of metals in a magnetic field in a flow of an inert gas containing a hydrocarbon. The products were characterized by X-ray diffraction, differential thermal analysis, thermogravimetry, high-resolution transmission electron microscopy, and adsorption. A layered carbon shell preventing agglomeration and oxidation formed on the surface of nickel- and iron-containing particles. The size of particles depended on preparation conditions and could be of 5–15 nm.

Nonpair Interactions in Na + (H 2 O) n Clusters under Thermal Fluctuation Conditions

Abstract: The influence of many-particle interactions on the structure of Na + (H 2 O) n clusters at 298 K was studied by the Monte Carlo method. The interaction parameters were reproduced from the experimental data on the Gibbs energy of hydration in water vapor. The interaction of induced dipoles results in the displacement of part of molecules through large distances from the ion. Covalent interactions strengthen the bond with the first attached molecule and weaken bonds with the other molecules.

Copper, iron, and zinc interactions with chlorophyll in extracts of photosynthetic pigments studied by VIS spectroscopy

Abstract: Interactions of copper, iron and zinc with chlorophyll, the major photosynthesis pigment, were studied by VIS spectrophotometry in extracts of photosynthetic pigments (in vitro). Copper predominantly forms Cu-Chl complexes in all studied systems (Cu-, Cu/Fe-, Cu/Zn- and Cu/Fe/Zn-incubated pigment solutions). It is not clear whether iron forms Fe-Chl complexes or produces pheophytin. It’s effect is dominant over zinc (Fe/Zn-system) but highly minor compared to Cu-effect when all three metals are present (Cu/Fe/Zn-Chl system) in the same concentrations.

Thermochemistry and NBO analysis of peptide bond: Investigation of basis sets and binding energy

Abstract: Ab initio methods were used to analyze the structure, energetic and binding energy of the five began dipeptides with methionine, Met-Gly, Met-Ala, Met-Ser, Met-Cys, and Met-Thr dipeptides, in gas phase. The structures of the dipetides and involved amino acids in them were optimized by using Hartree-Fock and DFT methods and 3-21G(d), 6-31G(d), 6-311G, 6-311G(d), and 6-311+G(d) basis sets. The effect of basis sets and electron correlations were analyzed with special emphasis on the calculated binding energies and thermodynamic functions. All used methods revealed that Met-Thr has the highest binding energy among all of the five dipeptide molecules. These numerical results suggest that Thr donates the proton easier than other four amino acids and it has the most tendency to join with methionine and it forms the most strong bond with methionine. This fact may be the reason behind the obtained high binding energies for Met-Thr at all levels. From comparison of the values of binding energy for dipeptides in different levels of theory, we could identify that the order of tendency for joint with methionine is Thr > Gly > Ala > Cys > Ser. Also, these data represented that the highest binding energy provide in HF/6-311G level for all of the dipeptides (14.4202, 11.2387, 8.3267, 9.8853, 17.3362 kcal mol−1 for dipeptides 1–5, respectively). Moreover, natural bond orbital (NBO) analysis demonstrated that the effect of basis sets and electron correlations on σN1-C2 bonding orbital occupancy is the same as the basis set and electron correlation effects on binding energy of dipeptides in all cases. The obtained results from studying the effect of basis sets and electron correlations on binding energy, NMR and NBO properties showed that the effect of basis sets is almost independent of molecular structure and computational method, while electron correlation effects are relatively dependent to molecular structure and basis set type. In investigating the effect of basis sets and electron correlations on binding properties, the NBO results are in good agreement with the energetic and thermochemistry data at all levels of calculations.

Dissociation constants of phosphoric acid in dimethylformamide-water mixtures at 298.15 K

Abstract: The dissociation constants of phosphoric acid (pK 1 and pK 2) in water-dimethylformamide (DMFA) mixtures (0–0.65 mole fractions of DMFA) were determined at 298.15 K by potentiometric titration. The extrapolation of these data to pure DMFA and the comparative calculation method were used to estimate the dissociation constants of the acid in DMFA.

IR Spectra of N,N′-Ethylene-Bis(salicylaldiminates) and N,N′-ethylene-Bis(acetylacetoniminates) of Ni(II), Cu(II), and Zn(II)

Abstract: Vibrational spectra of N,N′-ethylene-Bis(salicylaldiminaates) and N,N′-ethylene-Bis(acetylacetoniminates) of nickel (II), copper (II), and zinc (II) are studied experimentally (IR spectroscopy, 400–4000 cm−1) and theoretically (B3LYP), band assignment is given, and the distribution of potential energy of normal vibrations in internal coordinates is studied. Differences between vibrational spectra of the complexes are discussed. Thermodynamic functions of gas-phase complexes corresponding to temperatures of 298 and 800 K are calculated.

Acid-base properties of the surface of the α-Al2O3 suspension

Abstract: The distribution of the acid-base centers on the surface of α-Al2O3 suspension particles was studied by potentiometric titration, and the corresponding pK spectra were constructed. It was inferred that the double electric layer created by the supporting electrolyte substantially affected the screening of the acid-base centers on the particle surface of the suspension.

The nanoheterogeneous structure of aqueous solutions of n-propanol

Abstract: The results of positron spectroscopy and molecular light scattering studies, the data on radiationchemical yields and optical absorption spectra of solvated electrons formed under the action of ionizing radiation, and the data on the concentration dependences of viscosity, adiabatic compressibility, the velocity of sound, and partial molar volume were used to determine the structure of water-n-propanol mixtures. The conclusion was drawn that the insertion of alcohol molecules into water network voids over the range of alcohol mole fractions 0 x2 > 0.9), its molecules combined into nanodrops.

Apparent molar volume, viscosity, and adiabatic compressibility of some mineral sulfates in aqueous binary mixtures of formamide at 298.15, 308.15, and 318.15 K

Abstract: The densities and viscosities of several sulfates, viz, ammonium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, zinc sulfate and cadmium sulfate in aqueous binary mixtures of formamide (FA) have been determined at 29815, 30815, and 31815 K and at atmospheric pressure The ultrasonic speeds of the electrolytic solutions have also been measured at 29815 K Apparent molar volumes (ϕ V ), viscosity B-coefficients and adiabatic compressibilities (K S) of these electrolytic solutions were calculated from the experimental densitiy, viscosity and acoustic data The density and viscosity data were evaluated by using Masson’s and Jones-Dole equation respectively; the derived parameters have been analyzed in terms of ion-ion and ion-solvent interactions The structure making/breaking capacities of the electrolytes have been inferred from the sign of (∂2ϕ 0 /∂T 2) P The results showed that all the electrolytes act as structure-makers in these media Also the compressibility data indicated electrostriction of the solvent molecules around the cations The activation parameters of viscous flow were also determined and discussed by the application of transition state theory

Electrochemistry of nitronyl and imino nitroxides

Abstract: Redox potentials of a wide group of azolyl-substituted nitronyl and imino nitroxides were determined by classic cyclic voltammetry (CV). Conclusions have been made for this group of compounds, and their peculiarities were emphasized in comparison with methyl-, phenyl-, iodo-, and cyano-substituted nitroxides.

Ion-solvent and ion-ion interactions of phosphomolybdic acid in aqueous solution of catechol at 298.15, 308.15, and 318.15 K

Abstract: Apparent molar volume (VO) and viscosity B-coefficients were measured for phosphomolybdicacid in aqueous solution of catechol from solution density (ρ) and viscosity (η) at 298.15, 308.15, and 318.15 K at various solute concentrations. The experimental density data were evaluated by Masson equation and the derived data were interpreted in terms of ion-solvent and ion-ion interactions. The viscosity data have been analyzed using Jones-Dole equation and the derived parameters, B and A, have been interpreted in terms of ion-solvent and ion-ion interactions respectively. The structure-making or breaking capacity of the solute under investigation has been discussed in terms of sign of (δ2VOo/δT2)P. The activation parameters of viscous flow were determined and discussed by application of transition state theory.

Charge recombination in excited donor-acceptor complexes with two absorption bands

Abstract: The dynamics of charge recombination in a photoexcited donor-acceptor complex comprising 1,2,4-trimethoxybenzene (electron donor) and tetracyanoethylene (electron acceptor) in several polar solvents (acetonitrile, valeronitrile, and octanonitrile) was studied in terms of the stochastic approach. The Gibbs energy of charge recombination and the reorganization energies of the medium and quantum and vibrational degrees of freedom were found by fitting the stationary absorption spectrum. The electronic couplings were determined by analyzing the time dependences of the population of the ionic state in acetonitrile. A comparison of the numerical simulation results with the experimental data showed that the nonstationary model under consideration quantitatively described the dynamics of charge recombination and its dependence on the carrier frequency of excitation pulses and the relaxation properties of solvents.

The structural characteristics of Zn-Mn ferrite synthesized by spray pyrolysis

Abstract: The applicability of IR spectroscopy in studies of the structural characteristics of the ferrite spinel phase was shown for Zn0.5Mn0.5Fe2O4 samples prepared by the pyrolysis of aerosols of aqueous solutions of metal nitrates. The IR spectra of synthesized (ZnMn)Fe2O4 ferrites, Fe2O3, ZnO, MnO, and Mn2O3 pure oxides, and mixtures of these oxides in the region of characteristic M-O stretching vibration and M-O-H bending vibration frequencies were compared to determine the degree of concentration and structural uniformity of the ferrite spinel phase.

The chromatographic behavior and thermodynamic characteristics of adsorption of profen enantiomers on silica gel with grafted eremomycin antibiotic

Abstract: The chromatographic retention and thermodynamic characteristics of adsorption of several derivatives of 2-arylpropanoic acid on a chiral stationary phase with a grafted eremomycin antibiotic under the conditions of liquid chromatography with water-ethanol mobile phases were studied. The dependences of retention characteristics and selectivity on eluent pH were revealed. The difference between the adsorption mechanisms of acids with one and two benzene rings was demonstrated. Compensation effect manifestations in these systems are discussed.

The heat capacity and thermodynamic functions of EuPO4 over the temperature range 0–1600 K

Abstract: The heat capacity of EuPO4 was measured by adiabatic calorimetry over the temperature range 9.81–298.48 K. The experimental and literature data were generalized to obtain the temperature dependence of the heat capacity of europium orthophosphate from 0 to 1600 K. This dependence was used to calculate thermodynamic functions (entropy, enthalpy, and reduced Gibbs energy). The data on the heat capacity of europium orthophosphate and diamagnetic lanthanum orthophosphate were used to estimate the noncooperative magnetic transition (Schottky anomaly) value.

The thermodynamic properties of hydroxo compounds and the mechanism of ion flotation for cerium, europium, and yttrium

Abstract: The pH values of formation of hydroxo complexes and hydrates in solutions of cerium(III), europium(III), and yttrium salts were determined by conductometric titration. The instability constants of hydroxo complexes, solubility products of hydroxides, and Gibbs energies of formation of the compounds specified were calculated. Conclusions about the mechanism of extraction and ion flotation of these metal cations from aqueous solutions were drawn.

The dielectric properties of polyatomic alcohols: Asymmetric dispersion in butanediols

Abstract: Static permittivity ɛs, permittivity ɛ′, and dielectric loss ɛ″ were measured for 1,3-, 1,4-, and 2,3-butanediols over the frequency and temperature ranges 1 MHz-36 GHz and 293–423 K. These equilibrium properties of butanediols were analyzed using the Onsager-Kirkwood-Frohlich theory. The correlation factor g over the temperature range was calculated. The experimental permittivity ɛ′ and dielectric loss ɛ″ values were described by the Davidson-Cole equation. The relaxation times τD-C and parameter β of their distribution were calculated.

The pressure-induced spin transition in the Fe(phen) 2 (NCS) 2 model compound

Abstract: The influence of pressure on the high spin-low spin phase transition (HL transition) in a model Fe(phen)2(NCS)2 (polymorph II) compound at room temperature was studied by optical spectroscopy. An increase in pressure from atmospheric to 1.814 hPa caused the complete conversion of the low-spin to high-spin phase with the transition pressure p1/2 ↑ = 0.567 hPa at the equilibrium concentration of the high- and low-spin phases. Pressure drop caused the reverse HL transition with p1/2 ↓ = 0.543 hPa. The HL reversible transition took place with the transition pressure p1/2 = 0.555 hPa and hysteresis with width Δp1/2 = 0.024 hPa. The p1/2 value for the pressure-induced HL transition corresponded to the T1/2 value under pressure for the temperature-induced HL transition. The pressure dependences of the fraction of the high-spin phase determined from four independent measurements of the influence of pressure on the temperature-induced HL transition and the pressure-induced HL transition obtained in this work were compared. The experimental data were used to calculate the interaction and elastic energy parameters for temperature- and pressure-induced HL transitions. The qualitative coincidence of the interaction parameters for pressure- and temperature-induced HL transitions and the equality of the interaction parameter to elastic energy under pressure led us to conclude that the influence of pressure in two experiments well corresponds to the interaction energy and does not correspond the Gibbs potential.

Ion-exchange recovery of gold(I) and silver(I) from thiosulfate solutions

Abstract: The sorption recovery of gold(I) and silver(I) from model thiosulfate solutions (concentrations of gold, silver, and sodium thiosulfate were 0.1–1.6 mmol/l, 0.3–5.6 mmol/l, and 0.5 mol/l, respectively; pH was 8 to 12) by ion exchangers with different physical and chemical structure was studied. The anion exchanger Purolite A530 was shown to have the best sorption properties. By use of IR spectroscopy, it was ascertained that gold and silver are present within the phase of the sorbent in the form of [Au(S2O3)2]3− and [Ag(S2O3)2]3− particles, respectively

Cyclic voltammetry of nitronyl- and iminonitroxyls detected by electron spin resonance

Abstract: The combined cyclic voltammetry method (cyclic voltammetry detected by electron spin resonance, CVA-DESR CVA) was applied to study the electrochemical reactions of nitronyl- and iminonitroxyls (NN and IN) and to estimate the diffusion and absorption characteristics of their products. The ESR method yielded the hyperfine structure constants, including 13C. Even if exposed to lower temperature, all the studied NN were shown to spontaneously lose oxygen and to convert gradually into the relevant IN. For each specific NN, the combined CVA-DESR CVA experiments found the reduction potential value at which it can be virtually completely converted into the relevant IN.

The influence of fullerene additives on the structure of polystyrene films

Abstract: It was shown by electron microscopy and X-ray diffraction that a polystyrene solid with a three-level hierarchical structure was formed when the solvent was evaporated from a solution of polystyrene in o-xylene (polystyrene molecules stuck together united to form a framework). The kinetics of the transformation of formerly dissolved molecules into aggregates could be described by a Fokker-Planck-type equation. Fullerenes introduced into a solution of polystyrene in amounts less than 0.1 wt % transformed aggregated polystyrene molecules into nanocrystals and accelerated the formation of aggregates. The influence of fullerenes on the kinetics of the processes could be correctly described in the continuum approximation taking into account aggregation rate fluctuations.

Attenuated Total Reflectance-Fourier Transform Infrared Microspectroscopy of Copper(II) Complexes with Reduced Dextran Derivatives*

Abstract: Dextran is a water-soluble, extracellular neutral polysaccharide with a linear flexible chain of α-(1 → 6)-linked α-D-glucopyranose units, in a single compounds. In alkali solutions Cu(II) ion forms complexes with reduced low-molar dextran (RLMD). The metal content and the solution composition depended on pH. The complexing process begins in weak alkali solution (pH > 7), and involves OH groups in C2 and C3 dextran monomer units. Synthesized copper(II) complexes with RLMD, of average molar mass Mw = 5000 g/mol were investigated by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and FTIR imaging microscopy. ATR-FTIR microspectroscopic data of synthesized complexes are rare in literature. The changes in intensity and width of the IR bands in region 1500-1000 cm−1 were related to changes in conformation and short-range interactions of the ligand dextran. FTIR microscopy images shows more and less ordered structures of the Cu(II)-RLMD complexes. ATR-FTIR microspectroscopic data shows homogeneity of the Cu(II)-RLMD samples and green color of the samples confirm existence of Cu(II) ions.

The thermodynamic properties of DL- and L-lactides

Abstract: The enthalpies of formation of DL-lactide and L-lactide, cyclic esters of lactic acid, were determined by combustion calorimetry The transfer method was used to measure their vapor pressures and obtain the enthalpies of sublimation A conformational analysis of lactides was performed, and the most stable conformations were determined The equilibrium structures of lactides, sets of fundamental vibrations, moments of inertia, and total energies of the most stable conformers were calculated quantum-chemically at the B3LYP/6-311++G(3df,3pd) level The G3MP2 composite method was used to estimate the enthalpies of formation of lactides in the gas phase The thermodynamic properties of lactides in the ideal gas state were calculated over the temperature range 100–1500 K

The oxidative destruction of lignin in the ozonation of wood

Abstract: The oxidative destruction of lignin in the ozonation of aspen wood was studied The kinetic curves of ozone consumption for samples with different contents of water were obtained The consumption of ozone increased as the content of water grew The second derivatives of the UV absorption spectra of lignin were obtained to show that the principal direction of lignin transformations under the action of ozone was the destruction of its aromatic constituents with the formation of carboxyl- and carbonyl-containing compounds Measurements of the UV diffuse reflectance and EPR spectra of wood showed that the ozonation of wood caused the destruction of lignin quinoid structures Part of lignin remained unchanged under the action of ozone A key role in the destruction of wood lignin was played by ozone dissolved in water Varying the content of water in wood samples allows various lignin transformation products to be obtained through ozonation