The use of recurrent equations in chromatography

Recurrent equations A(x + k) = aA(x) + b were shown to be applicable to the approximation not only of virtually arbitrary properties of organic compounds (A) in homologous series (A = n _C, k = 1 or 2) but also of the dependences of chromatographic retention parameters on the number of carbon atoms in homologue molecules (A = t _R). The same equations described the temperature dependences of retention times of arbitrary compounds under isothermal separation conditions in gas chromatography (x = T, k = ΔT = const) and the dependences of retention times on the concentration of an organic solvent as an eluent component (x = C, k = ΔC = const) under isocratic separation conditions in high performance liquid chromatography.     

Thermodynamic properties and functions of condensed Bi<Subscript>8</Subscript>O<Subscript>11</Subscript>

The values of ΔH°₂₉₈, S°₂₉₈, H°₂₉₈–H°₀, T, ΔH _fus, and C _p(T), as well as the temperature dependences of the Gibbs energy function, are calculated for Bi₈O₁₁ oxide by proven computational methods.     

The assignment of signals in the EPR spectra of axially symmetrical quintet dinitrenes

Fine structure levels in an external magnetic field and angular dependences of resonance magnetic fields on the direction of an external magnetic field were calculated for two axially symmetrical quintet dinitrenes with the zero-field splitting parameters D _q = 0.260 cm^?1, E _q = 0.000 and D _q = 0.243 cm^?1, E _q = 0.003 cm^?1. The EPR spectra of such dinitrenes contained lines of only three xy transitions (xy ₁, xy ₂, and xy ₄), two Δm _s = ±2 transition lines between the W _?2 and W ₀ sublevels, and three additional lines from noncanonically oriented molecules whose magnetic axis Z made an angle of 12°–16° or 52°–54° with an external magnetic field.     

Viscosities and Surface Tensions of Phenetole with <Emphasis Type="Italic">N</Emphasis>-Methyl-2-pyrrolidone, <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylformamide and Tetrahydrofuran Binary Systems at Three Temperatures

Viscosities, η, and surface tensions, σ, of binary systems of phenetole (ethoxy benzene or ethyl phenyl ether) with N-methyl-2-pyrrolidone, N,N-dimethylformamide or with tetrahydrofuran were measured over the entire mole fraction range and at (298, 303 and 308) K. The experimental data was used to compute the deviations in viscosity, Δη, and surface tension, Δσ. Values of the excess Gibbs energy of activation G*^E, surface entropy S _σ and surface enthalpy H _σ were calculated. Viscosity data of the binary systems were calculated using the Grunberg and Nissan and the three-body and four-body McAllister correlations. The Redlich–Kister method was used for evaluation of coefficients and standard deviations for Δη, Δσ and G*^E. The results were interpreted in terms of the probable effect of molecular interactions between components as well as polarity.     

Volumetric,Viscometric and Speed of Sound Studies of Binary Mixtures of <Emphasis Type="Italic">Tert</Emphasis>-butyl Acetate with Fluorobenzene,Chlorobenzene and Bromobenzene at (298.15 and 308.15) K and at Atmospheric Pressure 0.087 MPa

Volumetric, viscometric and speed of sound studies of binary mixtures of tert-butyl acetate with fluorobenzene, chlorobenzene and bromobenzene have been made over the entire range of composition, at (298.15 and 308.15) K and at atmospheric pressure (p?=?0.089 MPa). From the experimental values of density, viscosity, and speed of sound, the excess molar volumes V^E, deviations in viscosity ?η and deviation in isentropic compressibility ΔK _S have been calculated. The V^E and ΔK _S values are negative while the ?η the values are positive over the entire composition range for the binary mixtures. The derived parameters have been fitted with the Redlich–Kister polynomial equation. The interaction parameters of McAllister model are used to correlate the experimental values of density, viscosity and speed of sound.     

New approaches to the calculation and interpretation of asymmetry factors of chromatographic peaks

The suitability of the determination of the asymmetry factor of chromatographic peaks by the ratio of areas of two components separated by a perpendicular dropped from the maximum of the peak to the base-line, A _s * = S _b /S _a , where symbol a corresponds to the leading edge of the peak and b is for its tailing slope, is discussed. It is demonstrated that this method enables the estimation of the asymmetry of even partially separated chromatographic signals, including those eluted “in the tail” of intense peaks of solvents. The concepts of the asymmetry index I(A _s *) and its increment ΔI(A _s *) = (A _s *)–I(A _s *) are introduced, which ensures the characterization of the asymmetry of peaks of polar analytes with respect to the asymmetry of nonpolar reference components, that is, the separation of the effects of the polarity of analytes and their quantities injected into the chromatographic column on this parameter. For the first time we revealed a correlation of the asymmetry factors of compounds of different chemical nature with such a characteristic of their polarity as the difference in chromatographic separation temperature and the normal boiling point of analytes.     

Thermophoto-emf of hot carriers in <Emphasis Type="Italic">γ</Emphasis>-irradiated single crystals of Cadmium Mercury Tellurides

The effect of γ-irradiation on thermophoto-emf of hot carriers in n-Cd_0.94Hg_0.06Тe and р-Cd_0.82Hg_0.18Тe single crystals has been studied. The dependence of the pattern of |U_tp| curves on E in the test Cd_xHg_1—хTe crystals is explained by the change in the degree of spatial heterogeneity of these crystals resulted from the accumulation of point radiation defects at relatively low D_γ and their spatial ordering caused by the introduction of a large number of point radiation defects at higher exposures. The proposed mechanism for the effect of γ-irradiation on the thermophoto-emf of hot carriers explains satisfactorily the dependence of |U_tp| kinetics on radiation dose, sample composition, temperature, and field strength.     

Substituted benzotriazoles as inhibitors of copper corrosion in borate buffer solutions

The adsorption of substituted 1,2,3-benzotriazoles (R-BTAs) onto copper is measured via ellipsometry in a pure borate buffer (pH 7.4) and satisfactorily described by Temkin’s isotherm. The adsorption free energy (?ΔG _a ⁰ ) values of these azoles are determined. The (?ΔG _a ⁰ ) values are found to rise as their hydrophobicity, characterized by the logarithm of the partition coefficient of a substituted BTA in a model octanol–water system (logP), grows. The minimum concentration sufficient for the spontaneous passivation of copper (C _min) and a shift in the potential of local copper depassivation with chlorides (E _pt) after an azole is added to the solution (i.e., ΔE = E _pt ⁱⁿ ? E _pt ^backgr characterizing the ability of its adsorption to stabilize passivation) are determined in the same solution containing a corrosion additive (0.01М NaCl) for each azole under study. Both criteria of the passivating properties of azoles (logC _min and ΔE) are shown to correlate linearly with logP, testifying to the role played by surface activity of this family of organic inhibitors in protecting copper in an aqueous solution.     

Micromechanism of Cu and Fe alloying process on the martensitic phase transformation of NiTi-based alloys: First-principles calculation

Using first-principles pseudo-potential plane wave method, the formation enthalpy ΔH, binding energy ΔE, elastic constants, and electronic structure were calculated and analyzed carefully for NiTiX (X = Cu, Fe) shape memory alloy. The results show that the Cu or Fe element prefers to occupy the Ni site in the NiTi matrix phase respectively. Compared with the NiTi matrix phase, the ΔH, ΔE, c ₄₄ and c′ of NiTi (Cu) are similar to each other. However, the structural stability of the NiTi phase is improved obviously by the Fe alloying process. Simultaneously, the shear modulus c ₄₄ and c′ of NiTi (Fe) are larger than those of the NiTi matrix phase. Furthermore, Milliken population results indicate that Q _Cu–Ti is smaller than Q _Ni–Ti after the Cu alloying process, but Q _Fe–Ti is larger than Q _Ni–Ti. The electron density difference shows that some covalent bonding exists between Fe and Ti elements. Based on the upward analysis, the difference in the phase stability and elastic constants of NiTiX (X = Cu, Fe) is the substantial mechanism for the different M _s of NiTiX (X = Cu, Fe) although Cu or Fe substitutes for the same atom Ni elements in the NiTi matrix phase.     

A quantum-chemical study of the thermodynamic properties of the CNOH<Subscript>3</Subscript> isomers

The B3LYP/6-311++G(3df,3pd) DFT method was used to determine the geometry and vibrational frequencies for the formamide, formaldoxime, nitrosomethane, oxaziridine, and formimide. The potential energy functions of the hindered internal rotations were calculated. The conformers of formaldoxime and formimide were determined. For all the molecules, including the conformers, the thermodynamic characteristics Δ_f H° (298 K), S°(298 K), C _p(298 K), and Δ_f G° (298 K) were determined. The temperature dependences C _p(T) within 298–1500 K were represented in the form of cubic polynomials.     

Molecular orientation ordering in surface layers of polymer films

The spontaneous ordering of fragments of chain molecules near the surface in polymer films is described in terms of the multichain model that allows for local intra-and interchain orientational interactions of chain segments and for transverse fluctuation of their orientation in the approximation of strong planar-orientation order in the layers. Chain packing in the plane-ordered state is impossible unless the interchain interaction parameter has a value of b = 2K ₂/k _B T > b _c. The value of b _c decreases with a growth in chain rigidity (parameter a = 2K ₁/k _B T). The calculated dependence of the limiting values of the quadrupole orientation order parameter S ₀ on the length of the Kuhn statistical segment A = 2a reasonably well describes the experimental data obtained in a study of polymer-homolog (polysaccharide) films by means of the tilted polarized-beam technique at an interchain interaction parameter of b = 1.75. The monolayer thickness (d ? 10 mn) is films of some polysaccharides was calculated from the fit of the theoretical to the experimental dependences of the orientational order parameter and the birefringence on the number of layers.     

The thermochemical characteristics of solution of DL-α-alanylglycine and DL-α-alanylalanine in water-alcohol mixtures at 298.15 K

The integral enthalpies of solution of DL-α-alanylglycine and DL-α-alanylalanine in water-ethanol, water-n-propanol, and water-isopropanol mixtures were measured calorimetrically at alcohol concentrations x ₂ = 0?0.4 mole fractions. The standard enthalpies of solution (Δ_sol H°) of the peptides and their transfer (Δ_tr H°) from water into the mixed solvents were calculated. The influence of the structure and properties of the solutes and mixture composition on the enthalpy characteristics were considered. The Δ_sol H° = f(x ₂) and Δ_tr H° = f(x ₂) dependences were found to have extrema. The enthalpy coefficients of pair interactions (h _xy ) between the peptide and alcohol molecules were calculated. The coefficients were positive and increased in the series ethanol, n-propanol, isopropanol.     

Bulk properties of a liquid phase mixture {ethylene glycol+<Emphasis Type="Italic">tert</Emphasis>-butanol} in the temperature range 278.15–348.15 K and pressures of 0.1–100 MPa. II. Molar isothermal compressibility,molar isobaric expansibility,thermal pressure coefficient,and internal pressure

Based on the experimental data, the molar isothermal compressibilities, molar isobaric expansibilities, thermal pressure coefficients, internal pressures of a liquid phase mixture {ethylene glycol (1) + tert-butanol (2)} are calculated for a wide spectrum of compositions in the range of pressures of 0.1–100 MPa and temperatures of 278.15–323.15 K. Shown that the dependences of molar isothermal compressibilities K _{T, m} , molar isobaric expansibilities E _{P, m} , and isochoric thermal pressure coefficients β on the mole fraction of tert-butanol in the mixture are characterized by the absence of extrema typical of aqueous systems. The manifestation of negative partial expansibility and negative partial expansibility of ethylene glycol in the mixture is found. The thermal pressure coefficients decrease with an increase in the mole fraction of tert-butanol at all pressures and temperatures. A rise in the pressure increases the thermal pressure coefficient, while a rise in the temperature decreases its value due to a decrease of free space in the mixture. An increase in the concentration of tert-butanol leads to an increase in the negative temperature coefficient of internal pressure ΔP _int/ΔT, which indicates a weakening of intermolecular interaction at these compositions.     

The thermodynamic properties of 5-vinyltetrazole and poly-5-vinyltetrazole over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 350 K

The temperature dependences of the heat capacities of 5-vinyltetrazole and poly-5-vinyltetrazole were measured by adiabatic vacuum calorimetry over the temperature range 6-(350–370) K with errors of ～0.2%. The results were used to calculate the thermodynamic functions of the compounds, C _p ^° , H ^°(T) - H ^°(0), S ^°(T), and G ^°(T) - H ^°(0), over the temperature range from T → 0 to 350–370 K. The energy of combustion of 5-vinyltetrazole and poly-5-vinyltetrazole was measured in an isothermic-shell static bomb calorimeter. The standard enthalpies of combustion Δ _c H ^° and thermodynamic characteristics of formation Δ_f H ^°, Δ_f S ^°, and Δ_f G ^° at 298.15 K and p = 0.1 MPa were calculated. The results were used to determine the thermodynamic characteristics of polymerization of 5-vinyltetrazole over the temperature range from T → 0 to 350 K.     

Magnetocaloric effect and the heat capacity of ferrimagnetic nanosystems in magnetic fluids

The specific heat capacity of a magnetite-based magnetic fluid and changes in the magnetic part of the molar heat capacity of its magnetic phase in magnetic fields of 0–0.7 T were determined calorimetrically over the temperature range 288–353 K. The temperature dependence of changes in the magnetic part of entropy in an applied magnetic field was calculated. It was found that the field dependence of heat capacity had a maximum in fields of 0.3–0.4 T, and the temperature dependences of changes in the magnetic part of heat capacity ΔC _p (H) and entropy ΔS _m(H) had maxima at the magnetic phase transition temperature.     

Molecular structure,quantum chemical investigation,and thermal behavior of (DNAZ-CO)<Subscript>2</Subscript>

Bis-(3,3-dinitroazetidinyl)-oxamide ((DNAZ-CO)₂) is an acyl derivative of 3,3-dinitroazetidine (DNAZ). It is prepared and its crystal structure is determined. The crystal is orthorhombic, Fdd2 space group, a = 13.136(14) Å, b = 19.48(3) Å, c = 10.326(14) Å, V = 2642 (6) ų, Z = 8. A density functional theory (DFT) method of the Amsterdam Density Functional (ADF) package is used to calculate the geometry, frequencies, and properties. The optimized geometry, frontier orbital energy, and main atomic orbital percentage are obtained. The thermal behavior is studied under a non-isothermal condition by DSC and TG/DTG methods. The apparent activation energy (E _a) and pre-exponential factor (A) of the exothermic decomposition reaction of (DNAZ-CO)₂ are 164.10 kJmol^?1 and 10^13.38 s^?1 respectively. The critical temperature of thermal explosion is 272.20°C. The values of ΔS ^≠, ΔH ^≠, and ΔG ^≠ of this reaction are 6.44 Jmol^?1·K^?1, 163.76 kJmol^?1 and 160.34 kJmol^?1 respectively.     

The X<Superscript>−</Superscript>···benzohydrazide complexes: the interplay between anion-π and H-bond interactions

The compounds containing the benzohydrazide (BH) nucleus have a variety of biological activities because of various noncovalent intermolecular interactions. The interplay between anion-π and H-bond interactions, which can affect the activity of compounds, has been investigated in ten substituted BH exposed to the chloride ion using the quantum mechanical calculations. The total interaction energy is separated into the anion-π (ΔE _Aπ) and H-bond (ΔE _HB) contributions where both interactions are presented in the complexes. The electron-withdrawing substituents (EWSs) increase |ΔE _Aπ| and decrease |ΔE _HB|, while reversed changes are observed with the electron-donating substituents (EDSs). In addition, the total binding energy (ΔE) becomes more/less negative in the presence of EWSs/EDSs. The synergetic effects of mentioned interactions and substituent effects have also been investigated using the atoms in molecules (AIM), natural bond orbital (NBO) and molecular electrostatic potential (MEP) analyses. A good correlation is found between the energy data and the Hammett constants, the minimum of electrostatic potential (V _min) and the results of population analyses.     

Synthesis,crystal structure,and kinetics of thermal decomposition of the Zn(II) complex with vanillin

A complex [Zn(C₈H₇O₃)₂(H₂O)₂] (C₈H₈O₃ is vanillin) has been synthesized and characterized by IR, elemental analysis, and X-ray diffraction single-crystal analysis. The crystals are monoclinic, space group C2/c, a = 22.236(8) Å, b = 10.594(2) Å, c = 7.8190(16) Å, α = 89.90(3)°, β = 106.87(4)°, γ = 89.99(3)°, V = 1762.6(8) ų, Z = 4, F(000) = 832, S = 1.079, ρ _c = 1.521g cm^?3, R = 0.0221, R _w = 0.0604, μ = 1.433 mm^?1. The Zn²⁺ ion is six-coordinated with a distorted octahedron geometry. The complex forms a three-dimensional network through intermolecular hydrogen bonds. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal conditions by the TG and DTG methods. The kinetic equation can be expressed as dα/dt = Ae^?E/RT 2(1 ? α)[1 ? ln(1 ? α)]^1/2. The kinetic parameters (E, A), activation entropy ΔS ^≠, and activation free-energy ΔG ^≠ were also gained.     

Thermodynamic study of solid solutions in the SnTe–AgSbTe<Subscript>2</Subscript> system by means of EMF with solid electrolyte Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript>

The results from studying the SnTe–AgSbTe₂ system by means of EMF with the solid electrolyte Ag₄RbI₅ in the temperature range of 300–430 K are presented. The formation of a wide (≥80 mol % of AgSbTe₂) region of solid solutions based on SnTe is confirmed. Partial thermodynamic functions ΔG?, ΔH?, and ΔS? of silver in alloys are calculated from the equations for the EMF temperature dependences. Based on the literature data regarding solid-phase equilibria in the Ag₂Te–SnTe–Sb₂Te₃–Te system, potential-determining reactions are identified that allow us to calculate the standard thermodynamic formation functions and standard entropies of solid solutions (2SnTe) _x (AgSbTe₂)_1?x (х = 0.2, 0.4, 0.6, 0.8, and 0.9).     

2,6-Disubstituted 4-azidopyrimidines: synthesis,kinetic and thermodynamic studies of azide-tetrazole rearrangement by NMR spectroscopy

Thermodynamic and kinetic parameters of the tautomeric tetrazole-azide rearrangement for a series of 2,6-disubstituted 4-azidopyrimidines are determined by NOESY/EXSY and DNMR: ΔH = 15—28 kJ mol^–1; ΔS = 47—65 J mol^–1 К–1; Е _a = 93—117 kJ mol^–1; lgA = 15.1—18.9. They are dependent on electronic properties of the substituents and the polarity of solvent.