The osmotic second virial coefficient and the Gibbs–McMillan–Mayer framework

The osmotic second virial coefficient is a key parameter in light scattering, protein crystallisation, self-interaction chromatography, and osmometry. The interpretation of the osmotic second virial coefficient depends on the set of independent variables. This commonly includes the independent variables associated with the Kirkwood–Buff, the McMillan–Mayer, and the Lewis–Randall solution theories. In this paper we analyse the osmotic second virial coefficient using a Gibbs–McMillan–Mayer framework which is similar to the McMillan–Mayer framework with the exception that pressure rather than volume is an independent variable. A Taylor expansion is applied to the osmotic pressure of a solution where one of the solutes is a small molecule, a salt for instance, that equilibrates between the two phases. Other solutes are retained. Solvents are small molecules that equilibrate between the two phases. The independent variables of the solvents are temperature, pressure, and chemical potentials. The derivatives in the Gibbs–McMillan–Mayer framework are transformed into derivatives in the Gibbs framework. This offers the possibility for an interpretation and correlation of the osmotic second virial coefficient using activity coefficient models.     

Development of a new form for the alpha function of the Redlich–Kwong cubic equation of state

The dependence on temperature and acentric factor of the attractive term of the Redlich–Kwong equation of state has been modified. A new alpha function is expressed in a generalized form. The new equation allows a good representation of vapor pressure data of a great variety of compounds, as well as thermodynamic properties such as the enthalpy of vaporization and the entropy of vaporization.     

On the Nature of the Cherdyntsev–Chalov Effect

It is shown that the Cherdyntsev–Chalov effect, usually presented as the separation of even isotopes of uranium upon their transition from the solid to the liquid phase, can include initiated acceleration of the radioactive decay of uranium-238 nuclei during the formation of cracks in geologically (seismic and volcanically) active zones of the Earth’s crust. The fissuring of the solid-phase medium leads to an increase in mechanical tensile stress and the emergence of strong local electric fields, resulting in the injection of chemical-scale high-energy electrons into the aqueous phase of the cracks. Under these conditions, the e^? catalytic decay of uranium-238 nucleus studied earlier can occur during the formation of metastable protactinium-238 nuclei with locally distorted nucleon structure, which subequently undergo β^–decay with the formation of thorium-234 and helium-4 nuclei as products of the fission of the initial uranium-238 nucleus with a characteristic period of several years. The observed increased activity of uranium-234 nuclei that form during the subsequent β-decay of thorium and then protactinium is associated with the initiated fission of uranium-238. The possibility is discussed of developing thermal power by using existing wastes from uranium production that contain uranium-238 to activate this isotope through the mechanochemical processing of these wastes in aqueous media with the formation of ₉₁ ²³⁸ Pa _isu , the half-life of which is several years.     

An effective modification of the Benedict–Webb–Rubin equation of state

A modification of the BWR equation of state is proposed, which is a simplified form of a previously proposed one. It applies to systems formed by hydrocarbons and related compounds, with particular attention to the critical conditions. The range of treatable compounds was extended to a value 0.9 of the acentric factor, corresponding to C₂₀ hydrocarbons. The critical compressibility factor Z_c was made independent of the acentric factor, for a more accurate prediction of pure-component properties (the previous equation did not give the same improvement). Mixing rules require one binary interaction constant for each component pair. Zero binary constants can be used for methane–alkane and alkane–alkane pairs. Examples of applications to pure hydrocarbons and their mixtures are given.     

Simple modification of the temperature dependence of the Sanchez–Lacombe equation of state

In this work, the interaction energy term of the Sanchez–Lacombe equation of state (SL EOS) was modified to take into account the temperature dependence of hydrogen bonding and ionic interactions. A simple function was used in the form of the Langmuir equation that reduces to the original SL EOS at high temperature. Comparisons are shown between the ?*-modified SL EOS and the original SL EOS. The ?*-modified SL EOS could represent volumetric data for the group of non-polar fluids, polar fluids and ionic liquids to within an absolute average deviation (AAD) of 0.85%, 0.51%, and 0.054%, respectively whereas, the original Sanchez–Lacombe EOS gave AAD values of 0.99%, 1.2%, and 0.21%, respectively. The ?*-modified SL EOS provides remarkably better PVT representation and can be readily applied to mixtures.     

On the Aqueous Chemistry of the UIV–DOTA Complex

The 1,4,7,10-tetrazacyclodecane-1,4,7,10-tetraacetic acid (DOTA) aqueous complex of U^IV with H₂O, OH⁻, and F⁻ as axial ligands was studied by using UV/Vis spectrophotometry, ESI-MS, NMR spectroscopy, X-ray crystallography, and electrochemistry. The U^IV–DOTA complex with either water or fluoride as axial ligands was found to be inert to oxidation by molecular oxygen, whereas the complex with hydroxide as an axial ligand slowly hydrolyzed and was oxidized by dioxygen to a diuranate precipitate. The combined data set acquired shows that, although axial substitution of fluoride and hydroxide ligands instead of water does not seem to significantly change the aqueous DOTA complex structure, it has an important effect on the electronic configuration of the complex. The U^IV/U^III redox couple was found to be quasi-reversible for the complex with both axially bonded H₂O and hydroxide, but irreversible for the complex with axially bonded fluoride. Intriguingly, binding of the axial fluoride renders the irreversible one-electron U^V/U^IV oxidation of the [U^IV(DOTA)(H₂O)] complex quasi-reversible, which suggests the formation of the short-lived pentavalent form of the complex, an aqueous non-uranyl chelated U^V cation.     

On the Mechanism of the Initial Stage of Titanium–Carbon Interaction

High-speed micro video recording and electron and atomic force microscopy have been used to obtain new experimental data at the initial stage of the titanium melt spreading along a carbon material (oriented pyrolytic graphite) and the formation of a reaction product. It has been shown that the melt spreading at the initial stages takes place along a framework of flat submicron crystalline grains of TiC with an open porosity. The grains form an island structure at the reagent contact boundary with gaps of about 100 nm in width between them, and these gaps are connected to each other to give a continuous network of channels along which the melt spreads. Thus, at the initial stage of the interaction, despite the formation of a solid product, direct contact of the reagents is retained, which ensures a high process speed.     

On approximate mathematical modeling of the vapor–liquid coexistence curves by the Van der Waals equation of state and non-classical value of the critical exponent

Van der Waals equation of state as well as power laws and critical exponent theories are prototypes to study the cubic shape, asymmetries and “flatness” of the vapor–liquid equilibrium curves near the critical point. In this work we study two similar methods to determine the phase curves in analytical form, which differ from each other by simplicity of mathematical calculation. We analyze temperature dependence of the coexistence curves asymptotically close to the vapor–liquid critical point. We explain the novelty of our method with respect to the standard thermodynamic limit discussed in the literature. Therefore we show that the shape of the coexistence curves can strongly influence the accepted value of the critical exponent. The results of theoretical studies have been compared with the ones obtained by experimental methods.     

On the accuracy of numerical Hartree–Fock energies

It is demonstrated that numerical Hartree–Fock (HF) energies reported in the literature in some cases have errors in the milliHartree range. The main cause of these errors is due to the use of too small a value for the practical infinity parameter in the finite difference method for generating the results. By systematically investigating the convergence with respect to the computational parameters, HF energies accurate to at least 1 microHartree are generated for 42 diatomic systems containing first and second row elements, encompassing both cationic, neutral and anionic systems.     

Preparation of the Ca–diclofenac complex in solid state

Two ONNO type naphtaldehyde derivative Schiff base compounds were reduced and two symmetric phenol-amine ligands containing naphthalene groups were obtained; bis-N,N′[(2-hydroxy-1-naphtyl) methyl]-1,3-propanediamine (NAFL^H) and bis-N,N′[(2-hydroxy-1-naphtyl) methyl]-2,2′-dimetyhyl-1,3-propanediamine (NAFLDM^H). Homotrinuclear Ni(II) complexes of these ligands were prepared. The solid-state molecular structures of representative nickel complex of NAFLDM^H were determined using single crystal X-ray diffraction analysis. The terminal Ni(II) ions were found to be situated in between the donor atoms of the organic ligand. The central Ni(II) ion was observed to be bonded via two different μ-bridges. The phenolic oxygens and carboxylate ion were seen to form two different μ-bridges. TG analysis proved that the compounds have different thermal characteristics than those cited in literature. The complexes showed extreme exothermic degradation reactions in inert atmosphere. The complexes are ruptured with a two stepped exothermic reaction which appears huge heat over 300 °C. The heat appeared in O₂ atmosphere is observed to be higher than the heat appeared in inert atmosphere. Revealed heat is observed to be higher than the conventional explosive materials.     

Portably parallel construction of a configuration-interaction wave function from a matrix–product state using the Charm++ framework

The construction of configuration-interaction (CI) expansions from a matrix product state (MPS) involves numerous matrix operations and the skillful sampling of important configurations in a large Hilbert space. In this work, we present an efficient procedure for constructing CI expansions from MPS employing the parallel object-oriented Charm++ programming framework, upon which automatic load-balancing and object migrating facilities can be employed. This procedure was employed in the MPS-to-CI utility (Moritz et al., J. Chem. Phys. 2007, 126, 224109), the sampling-reconstructed complete active-space algorithm (SR-CAS, Boguslawski et al., J. Chem. Phys. 2011, 134, 224101), and the entanglement-driven genetic algorithm (EDGA, Luo et al., J. Chem. Theory Comput. 2017, 13, 4699). It enhances productivity and allows the sampling programs to evolve to their population-expansion versions, for example, EDGA with population expansion (PE-EDGA). Further, examples of 1,2-dioxetanone and firefly dioxetanone anion (FDO⁻) molecules demonstrated the following: (a) parallel efficiencies can be persistently improved by simply by increasing the proportions of the asynchronous executions and (b) a sampled CAS-type CI wave function of a bi-radical-state FDO⁻ molecule utilizing the full valence (30e,26o) active space can be constructed within a few hours with using thousands of cores.     

On the kinetics of pozzolanic reaction in the system kaolin–lime–water

The kinetics of the pozzolanic reaction of enriched kaolin from the “Senovo” deposit (Bulgaria) with lime is the object of this article. The kaolin contains kaolinite as a major clay mineral as well as admixtures of quartz and illite. The experimental data of pozzolanic activity at temperatures of 100 and 23 °C are obtained for different reaction times. The reaction degrees of kaolinite and lime at 100 °C are determined from the pozzolanic activity data using a powder X-ray diffraction analysis. The kinetic analysis is performed by joint presentation of theoretical and experimental data in dimensionless coordinates having in mind the influence of particle size distribution on the reaction rate. It is found by the kinetic analysis that the rate of entire reaction is limited by the rate of chemical reaction on the reaction surface up to degree of reaction near to 0.4. The rate of penetration of the chemical reaction into the kaolinite particles for this area—from the beginning to degree of reaction 0.4, is determined to be equal to 2.10⁻¹¹ m/s.     

Simulation of double retrograde vaporization using the Peng–Robinson equation of state

Double retrograde vaporization is a phenomenon characterized by an unexpected retrograde dew point curve at compositions approaching nearly the pure volatile component (component A) and at temperatures very close to the critical temperature of the more volatile component (Tc_A). On the p–x–y diagram, instead of the single-domed dew point curve in the familiar “single” retrograde vaporization, double retrograde vaporization shows two “domes” at temperatures above but close to Tc_A. At temperatures below but close to Tc_A, the dew point curve has an “S”-shape. This results respectively in quadruple- or triple-valued dew points at a specific composition. In this work, the phenomenon of double retrograde vaporization has been simulated using a cubic equation of state. Both the “double-dome” and the “S”-shape curves for the binary systems (ethane+linalool) and (ethane+d-limonene) were successfully modelled, even without the use of binary interaction parameters. Results are also obtained by optimizing interaction parameters using experimental bubble point data. Even though double retrograde vaporization has rarely been observed in literature, we believe that it is the normal behaviour that always occurs in binary mixtures in which the two components differ largely enough in molecular symmetry to produce a very steep dew point curve. To further verify this generality, simulations were performed on a number of binary mixtures of different families. Double retrograde vaporization was estimated in every system with a steep dew point curve.     

Influence of phosphorus concentration on the state of the surface layer of Pd–P hydrogenation catalysts

Phase composition and surface layer state of the Pd–P hydrogenation catalyst formed at various P/Pd ratios from Pd(acac)₂ and white phosphorus in a hydrogen atmosphere were determined. Palladium on the catalyst surface is mainly in two chemical states: as Pd(0) clusters and as palladium phosphides. As the P/Pd ratio increases, the fraction and size of palladium clusters decrease, and also the phase composition of formed palladium phosphides changes: Pd₃P_0.8 → Pd₅P₂ → PdP₂. The causes of the modifying action of phosphorus on the properties of palladium catalysts for hydrogenation of unsaturated compounds were considered.     

On the microelectrode behaviour of graphite–epoxy composite electrodes

Electrodes fashioned from conducting particles embedded in insulating binder show some properties commonly associated with arrays of microelectrodes, viz. independence of current from convective flow and sigmoidal current–voltage curves. We have systematically investigated the electrochemical behaviour of a range of composite formulations. The fraction of the surface area that is conducting and the size of the conducting features have been quantified using the novel technique of conducting atomic force microscopy (C-AFM). We have shown that flow sensitivity and voltammetric behaviour are correlated with results from the C-AFM. The more dilute formulations behave like arrays of microelectrodes, though exhibiting large time constants. The origin of this behaviour is discussed.     

Solution thermodynamics of Lanthanide–Cryptand 222 complexation processes

The thermodynamics of trivalent cations (Y³⁺, La³⁺, Pr³⁺, Nd³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Ho³⁺, Er³⁺, Yb³⁺) and cryptand 222 in acetonitrile at 298.15?K is discussed. Recent reports regarding the behavior of lanthanide(III) trifluoromethane sulfonate salts in acetonitrile are considered. Thus, the experimental work was carried out under conditions in which ions (M³⁺) are predominantly in solution. Therefore, conductiometric titrations were carried out to establish the composition of the cation–cryptand 222 complexes and their ionic behavior in solution. Stability constants and derived standard Gibbs energies, enthalpies and entropies were determined by competitive titration microcalorimetry. Previously reported thermodynamic data for the complexation of cryptand 222 and a few lanthanide cations (La³⁺, Pr³⁺ and Nd³⁺) in acetonitrile are revisited. The medium effect on the stability of complex formation in acetonitrile relative to N,N-dimethylformamide is demonstrated. Thus, a drop in stability by a factor of 8 × 10¹⁰ is observed for the latter relative to the former solvent. The selectivity of cryptand 222 for these cations relative to La³⁺ in acetonitrile is discussed.     

The thermodynamics of ionization of α-alanine in methanol + water mixtures and the determination of single ion thermodynamics

In order to understand the effect of solvents on the thermodynamic parameters of amino acids, the thermodynamic dissociation constants, k₁ and K₂, for the reactions

and

(where RH^± = α-alanine) have been determined pH-metrically in methanol + water mixtures. The measurements were carried out in dilute solutions and in the absence of neutral electrolytes to minimize the “salt effect” as far as practicable so that the “medium effects” on the dissociation constants of the α-alanine can be properly understood.The enthalpy values for reactions (1) and (2) (up to 44.14 wt% of methanol) have been determined calorimetrically. It has been observed that the conversion of α-alanine into cations and anions is favourable both from enthalpic and entropic considerations, so that the reverse reactions of (1) and (2) are spontaneous. Attempts have been made to interpret the thermodynamics properties of α-alanine in terms of hydrophilic and hydrophobic interactions and other structural changes of the solvent molecules.In order to get a better insight into the nature of specific solute-solvent interactions, we have analysed the results in terms of single ion values using the thermodynamic values from the present work and other relevant data from previous work in our laboratory.     

Melt–gas phase equilibria and state diagrams of the selenium–tellurium system

The partial pressures of saturated vapor of the components in the Se–Te system are determined and presented in the form of temperature–concentration dependences from which the boundaries of the melt–gas phase transition are calculated at atmospheric pressure and vacuums of 2000 and 100 Pa. The existence of azeotropic mixtures is revealed. It is found that the points of inseparably boiling melts correspond to 7.5 at % of Se and 995°C at 101325 Pa, 10.9 at % at 673°C and 19.5 at % at 522°C in vacuums of 2000 and 100 Pa, respectively. A complete state diagram is constructed, including the fields of gas-liquid equilibria at atmospheric and low pressures, the boundaries of which allow us to assess the behavior of selenium and tellurium upon distillation fractionation.     

On the kinetics of pozzolanic reaction in metakaolin–lime–water system

The kinetics of pozzolanic reaction metakaolin–lime is studied in the present work. Metakaolin is prepared by calcination of enriched kaolin (deposit “Senovo”, Bulgaria) at temperature of 830 ± 10 °C in a labscale muffle oven. The reaction is performed in intensively stirred water suspension at different temperatures in the range 20–100 °C. The kinetics is analyzed by comparing the experimental data with theoretical curves, derived according to appropriate kinetic and diffusion models taking into account the grain size distribution of metakaolin. The macroscopic mechanism and activation energy of the reaction are determined. It is found, that the activation energy decreases gradually from 71 to 45 kJ/mol[Ca(OH)₂] with the increase of the reaction degree from 0.2 up to 0.6, respectively, which is a characteristic for transition regime reactions.     

On the possibility of homolytic addition of N-bromohexamethyldisilazane to the triple carbon–carbon bond

Russian Journal of General Chemistry - By an example of a reaction of N-bromohexamethyldisilazane with phenylacetylene the possibility of its homolytic addition to the triple carbon-carbon bond...