The thermodynamic and structural rules governing the solubilization of anthracene in aqueous solutions of polyethylene oxide

The influence of the temperature and concentration of aqueous solutions of polyethylene oxide (PEO) on the UV absorption spectrum of anthracene (Ant) was studied. The enthalpy and entropy factors of dynamic equilibrium of Ant molecules between the aqueous phase, in which Ant molecules form hydration capsules around them, and polymer-chain capsule structures responsible for bonding between Ant and macromolecules were determined. It was shown by the method of molecular mechanics that the solubilization of Ant molecules by dissolved PEO involves the formation of capsules of polymer chain units around Ant molecules. A phenomenological equation of equilibrium solubilization was obtained and theoretically substantiated. At low PEO concentrations, this equation transformed into the Sechenov solubility law, which described the equilibrium solubilization of Ant molecules no less successfully than the well-known equation for the solubilization of such hydrophobic hydrocarbons as naphthalene and diphenyl.     

A few simple rules governing hydrogenation of graphene dots

We investigated binding of hydrogen atoms to small polycyclic aromatic hydrocarbons (PAHs)--i.e., graphene dots with hydrogen-terminated edges--using density functional theory and correlated wavefunction techniques. We considered a number of PAHs with three to seven hexagonal rings and computed binding energies for most of the symmetry unique sites, along with the minimum energy paths for significant cases. The chosen PAHs are small enough to not present radical character at their edges, yet show a clear preference for adsorption at the edge sites which can be attributed to electronic effects. We show how the results, as obtained at different levels of theory, can be rationalized in detail with the help of a few simple concepts derivable from a tight-binding model of the π electrons.     

Structural kinetic rules governing the thermal decomposition of pyridine N-oxides

The Arrhenius parameters of the thermal composition of pyridine N-oxides in the liquid phase have been determined. The conclusion has been reached that the formation of an oxaziridine activated complex can be considered as the initial act of the thermolysis. A correlation has been found to exist between the rate constants of the thermal decomposition and the calculated values of the fractional electron charge at the oxygen of the N-oxide, and the length of the N- O bonds.Kazan' State Technological University, Kazan' 420015. Biisk Liceum of the Altai Region, Biisk 659322. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 644–646, May, 1994. Original article submitted April 4, 1994.     

Separation and spectrophotometric determination of trace quantities of lithium in high-purity beryllium and beryllium oxide

A spectrophotometric method is described for the determination of trace quantities of lithium in beryllium metal and its oxide. Lithium is selectively separated from beryllium by extraction from 1M potassium hydroxide solution into 0.1M dipivaloylmethane in diethyl ether. Fluoride, added before the extraction, successfully masks the beryllium; as little as 3 microg of lithium can be separated from as much as 1 g of beryllium. The lithium is then back-extracted into 0.1M hydrochloric acid and is determined spectrophotometrically with o-(2-hydroxy-3,6-disulpho-1-naphthylazo) benzene arsonic acid, Thoron. In an acetone-water medium Beer's law is obeyed over the range 0.1-1.0 microg ml. The method has been applied successfully to the determination of lithium in concentrations as low as 3 ppm; the relative standard deviation for the determination of 200 ppm is 3%.     

Gas chromatographic determination of helium in neutron-irradiated beryllium oxide

A method has been developed for the determination of helium produced during neutron irradiation of beryllium oxide ((9)Be + n --> (8)Be + 2n; (8)Be --> 2(4)He). The sample is dissolved by refluxing in a sulphuric acid-phosphoric acid mixture in an argon atmosphere. After the sample has completely dissolved, the released helium is transferred to a gas sampling bulb by means of a Toepler pump. An activated charcoal trap cooled by liquid nitrogen is used to separate helium from argon. The helium is determined by gas chromatography using a 20-ft Linde 5A molecular sieve column.     

Cluster model for the surface OH groups of beryllium oxide

Cluster models calculated by a semiempirical CNDO method are used to describe properties of the surface hydroxy groups of beryllium oxide. The results are compared with those obtained from IR studeies and with data on BeO energy bands.

---

- , . , BeO.

     

Relationships governing the heterogeneous-catalytic reduction of nitric oxide by methane

The relationships governing the reduction of NO by methane at supported catalysts containing palladium and the oxides of transition metals of the fourth period were investigated. Ways of improving the process are discussed. It was shown that NO can be reduced under nonstationary conditions with separation of the stages of the thermocatalytic process in time.L. V. Pisarzhevskii Institute of Physical Chemistry, Ukrainian Academy of Sciences, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 5, pp. 553–560, September–October, 1991. Original article submitted June 28, 1991.     

The beryllium dimer potential

The convergence of ab initio calculations of the beryllium dimer potential is examined with several basis sets orders of perturbation theory. When the atomic pair natural orbital basis set calculations are extrapolated to the complete basis set and full CI limits, the calculated parameters: R_e=2.447 Å, D_e=827 cm⁻¹, ν₀₁=212.7 cm⁻¹, ν₁₂=167.2 cm⁻¹, ν₂₃=121.5 cm⁻¹ and ν₃₄=77.7 cm⁻¹ are in good agreement with the experimental parameters: R_e=2.45 Å, D_e=839±10 cm⁻¹, ν₀₁=223.2 cm⁻¹, ν₁₂=169.7 cm⁻¹, ν₂₃=122.5 cm⁻¹, and ν₃₄=79 cm⁻¹.     

The rules governing hydrogen combustion close to the lower ignition limit in the kinetic region of chain termination

The kinetic scheme of hydrogen combustion near the lower self-ignition limit in the kinetic region can be augmented by the reactions of bimolecular nonlinear termination O + OH → H + O₂ and heterogeneous propagation of chains with the participation of adsorbed hydrogen atoms H_s. The literature data on the experimental determination of the probability of hydrogen atom trapping by the surface of quartz were analyzed.     

The fermi surface of beryllium

The Fermi surface (FS ) of beryllium has been calculated using the augmented plane wave energy bands for the material. The extremum area and the FS caliper distances are in excellent agreement with the de Haas–van Alphen measurements, and are better than existing ab initio calculations.     

The analysis of beryllium and beryllium oxide—IV The determination of cobalt

A method is described for the determination of cobalt in beryllium or beryllium oxide by extraction of the cobalt thiocyanate complex with acetylacetone (2:4-pentanedione). The method is accurate to ±2% or 2 μg of cobalt, whichever is greater. Of the 68 elements investigated only manganese and chromium interfere in 10 mg amounts. No interference was observed when 1g of each had been removed by ion-exchange or volatilisation (of chromium only) before extraction.     

The dependence of the rules governing gas-phase combustion on the competition between chain propagation and chain termination reactions

The competition between chain propagation and chain termination reactions was shown to play an important role in gas-phase combustion. Conditions under which this competition to a substantial extent determined the critical ignition conditions and the rate of the process were analyzed. Examples that showed that ignoring the role played by chain propagation, chain termination, and chain branching reactions in branched-chain processes led to conclusions that contradicted experimental data were considered.     

Configurational rules governing the stereochemical control of chiral initiators in ring-opening polymerizations of heterocyclic monomers

Configuration rules were established for the polymerization of cyclic monomers with chiral initiators. The latter recognize in the monomer an asymmetric carbon of homochiral configuration. The chirality of the initiator is defined by the “local” asymmetry of the ligand and by the overall asymmetry of the particular arrangement of catalytic aggregates. Two types of process called “homosteric” and “antisteric,” which apply to the polymerization of resolvable monomers and achiral monomers of meso structure, are defined. These configurational rules have a general character and are verified in many examples of differently substituted three- or four-membered cyclic monomers (oxiranes, thiiranes, β-lactones). Stereoelective polymerization appears to be an original method for the determination of the absolute configuration of some monomers of unknown chirality.     

Biosorption of beryllium from aqueous solutions onto modified chitosan resin: Equilibrium,kinetic and thermodynamic study

The goal of the present work is the recovery of beryllium ion from their solution by modified chitosan hydrogel. Chitosan was chemically cross-linked with glutaraldehyde to prevent its dissolution in aqueous acidic solutions. The obtained chitosan/glutaraldehyde adsorbent was reacted with chloroacetic acid to produce carboxymethyl chitosan (CMC), which was converted into sodium form by reaction with sodium hydroxide solution to increase its hydrophilic properties. The chemically synthesized chitosan adsorbent contains carboxylate group that expected to have a strong affinity to beryllium ions according to the hard-soft acid-base concept by Pearson because that beryllium ion is a hard acid and has smaller ionic radii. The synthesized adsorbent was characterized and its affinity towards beryllium ions was tested. The different experimental parameters including pH, beryllium concentration, agitation period and temperature were studied to optimize the biosorption process. The maximum biosorption values of beryllium species on the investigated biosorbent are 44.96 and 36.72?mg/g at pH 1 and 5, respectively. Kinetics and thermodynamic parameters of the biosorption process were evaluated from kinetic and biosorption experiments. The adsorbed beryllium species were eluted with a 3?M H₂SO₄ solution.     

The quest for beryllium peroxides

There is no experimental proof documented in the literature for the existence of any beryllium peroxide compound. All recent pertinent preparative attempts described in this work, using a range of beryllium salts with various peroxides as reagents under mild conditions, were equally unsuccessful. (1)H and (9)Be NMR investigations of aqueous solutions containing beryllium salts and hydrogen peroxide in a broad pH range also gave no definite evidence for the presence of peroxoberyllates as components of the manifold equilibria in such solutions. Quantum chemical calculations have therefore been carried out to delineate the energetics and structures of various beryllium peroxide model compounds. Standard Hartree-Fock and density functional methods were employed at various levels of sophistication. The series of prototypes considered consists of [BeOH](+), Be(OH)(2), Be(OH)(OOH), Be(OOH)(2), [Be(O(2))(2)](2-), [BeO(2)(OH(2))(2)], and [Be(2)(O(2))(2)(OH(2))(4)] (all in the gas phase). Surprisingly, the triatomic cation [BeOH](+) has been found to have a linear structure. All the Be-O(peroxide) bonds are found to be rather long, suggesting weaker bonding compared to the Be-O bonds in aquo, hydroxo, or oxo complexes. Hydrogen peroxide or anions derived therefrom are therefore not able to compete successfully with water (hydroxide anions) in aqueous solution. In the mononuclear beryllium peroxide molecules, the peroxide groups form chelating units at tetrahedrally 4-coordinate metal atoms. The binuclear compound [Be(2)(O(2))(2)(OH(2))(4)] has a puckered six-membered-ring structure, close to the standard chair conformation. A significant lengthening of the O-O bonds upon coordination to the Be(2+) centers has been calculated, but it is unlikely that the polarization of the peroxide group by the high positive charge density at Be(2+) is significant to cause an intrinsic instability of beryllium peroxides. All structures represent distinct local minima on the potential energy surface and are predicted to be (meta)stable species in nonaqueous media. The field of aluminum peroxides is a similar gray area on the map of metal and metalloid peroxides and is reminiscent of the well-established "diagonal-relation" of Be and Al in the periodic table of the elements.     

Mixing rules for van-der-Waals type equation of state based on thermodynamic perturbation theory

A concept based on the thermodynamic perturbation theory for a `simple fluid' has been applied to the attractive term of a van-der-Waals type equation of state (EOS) to derive a simple mixing rule for the a parameter. The new mixing rule is a small correction to the original one-fluid approximation to account for the influence of particles of j-type on the correlation function of ii-type in a mixture consisting of particles of i and j types. The importance of the correction has been shown by comparison of the calculated results for binary mixtures of Lennard–Jones fluids with the data obtained by numerical method (Monte-Carlo simulation). The new mixing rules can be considered as a flexible generalization of the conventional mixing rules and can be reduced to the original v-d-W mixing rules by defaulting the extra binary parameters to zero. In this way the binary parameters already available in the literature for many systems can be used without any additional regression work. Extension of the new mixing rules to a multicomponent system do not suffer from `Michelsen–Kistenmacher syndrome' and provide the correct limit for the composition dependence of second virial coefficients. Their applicability has been illustrated by various examples of vapor–liquid and liquid–liquid equilibria using a modified Patel–Teja EOS. The new mixing rules can be applied to any EOS of van-der-Waals type, i.e., EOS containing two terms which reflect the contributions of repulsive and attractive intermolecular forces.     

Intermolecular interactions governing solubilization in micelles of poly(alkylene oxide) surfactants

Partition coefficients for 39 low-molecular-mass compounds between water and micelles of an ethylene oxide-propylene oxide block copolymer (Pluronic P85) and the monolauryl ether of poly(ethylene oxide) (Brij 35) have been measured by the methods of fluorescence spectroscopy, fluorescence anisotropy, and dialysis kinetics. The tested compounds include aromatic hydrocarbons, phenols, naphthols, xanthene dyes, anthracycline antibiotics, and porphyrins. The multifactor analysis of the partition coefficients in terms of the linear free-energy relationships has been performed. It has been shown that the H-donating ability of compounds facilitates their solubilization in Pluronic micelles and has no effect on solubilization in micelles of monolauryl ether of poly(ethylene oxide). This difference indicates that, when solubilization occurs in Pluronic micelles, the compounds under study appear in a hydrophobic core composed of poly(propylene oxide) blocks.     

Thermodynamic characteristic calculations for oxide melts by complete thermodynamic modeling

The contents of substances and their activities as solution components at 1873 K were calculated for oxide melts of the binary and ternary systems FeO-SiO₂, CaO-SiO₂, Al₂O₃-CaO-SiO₂, and FeO-CaO-SiO₂ by the complete thermodynamic modeling method. The approach used was shown to be capable of describing the thermodynamic characteristics of oxide melts with strong intercomponent interactions.