Thermodynamic study of sodium decyl sulfate solutions in the region of second critical micelle concentration: 2. Thermodynamic functions of polymorphic micellar transition and components of its Gibbs energy

Temperature dependences of the thermodynamic functions of polymorphic micellar transition in the region of second critical micelle concentration are calculated based on data on heat capacities of sodium decyl sulfate solutions obtained previously by scanning calorimetry. Equilibrium constants and fractions of surfactant molecules aggregated into spheroidal and cylindrical micelles are calculated. Using the models of the ellipsoid of revolution and cylinder, components of the equilibrium Gibbs energy of intermicellar transition are calculated.     

Evaluation of the reliability of maize reference assays for GMO quantification

A reliable PCR reference assay for relative genetically modified organism (GMO) quantification must be specific for the target taxon and amplify uniformly along the commercialised varieties within the considered taxon. Different reference assays for maize (Zea mays L.) are used in official methods for GMO quantification. In this study, we evaluated the reliability of eight existing maize reference assays, four of which are used in combination with an event-specific polymerase chain reaction (PCR) assay validated and published by the Community Reference Laboratory (CRL). We analysed the nucleotide sequence variation in the target genomic regions in a broad range of transgenic and conventional varieties and lines: MON 810 varieties cultivated in Spain and conventional varieties from various geographical origins and breeding history. In addition, the reliability of the assays was evaluated based on their PCR amplification performance. A single base pair substitution, corresponding to a single nucleotide polymorphism (SNP) reported in an earlier study, was observed in the forward primer of one of the studied alcohol dehydrogenase 1 (Adh1) (70) assays in a large number of varieties. The SNP presence is consistent with a poor PCR performance observed for this assay along the tested varieties. The obtained data show that the Adh1 (70) assay used in the official CRL NK603 assay is unreliable. Based on our results from both the nucleotide stability study and the PCR performance test, we can conclude that the Adh1 (136) reference assay (T25 and Bt11 assays) as well as the tested high mobility group protein gene assay, which also form parts of CRL methods for quantification, are highly reliable. Despite the observed uniformity in the nucleotide sequence of the invertase gene assay, the PCR performance test reveals that this target sequence might occur in more than one copy. Finally, although currently not forming a part of official quantification methods, zein and SSIIb assays are found to be highly reliable in terms of nucleotide stability and PCR performance and are proposed as good alternative targets for a reference assay for maize.     

Dispersion of the dielectric function real part for Mg:LiNbO3 crystals at terahertz frequencies

We study dispersion of the dielectric function real part ε′ in the terahertz-frequency range for bulk and periodically poled congruent LiNbO₃ and Mg:LiNbO₃ crystals. The concentration of Mg in Mg:LiNbO₃ samples was close to 5 mol%, which is the photorefractive threshold. Approximate expressions for extraordinary polariton dispersion dependence were obtained in the range 0.5–6.5 THz. The influence of Mg-dopant on the optical properties of crystals in the terahertz range is revealed. Changes of the defect structure of lithium niobate crystals are discussed.     

Molecular structure of N-chlorosuccinimide studied by gas-phase electron diffraction and quantum-chemical methods

The molecular structure of N-chlorosuccinimide has been studied by GED method at the nozzle temperature of 116 °C. Vibrational corrections to the r _a parameters, Δ(r _a − r _e), have been calculated using the scaled quadratic and cubic force constants from B3LYP/6-31G(df,p) calculations. The force field scaling has been carried out using the IR and Raman spectra of the solid N-chlorosuccinimide. The molecular skeleton and the bond conformation around nitrogen were found to be planar within large experimental errors. The equilibrium geometrical parameters derived from the experimental data assuming C _2v molecular symmetry and those from MP2(fc)/6-311G(3df,2pd) calculations are in a good agreement.     

Thermodynamic study of sodium decyl sulfate solutions in the region the second critical micellization concentration: 1. Volumetric and heat capacity properties

Densitometry and precision adiabatic scanning calorimetry are used to reveal a number of volumetric and heat capacity properties of sodium decyl sulfate in the region of the second critical micelle concentration. Heat capacities are established in a wide temperature range. The coefficients of thermal expansion, apparent and partial mole expandabilities, volume, heat capacities, and excess partial mole heat capacities are calculated. The analysis of variations in these thermodynamic properties occurring upon variations in concentration and temperature makes it possible to identify the structural variations in sodium decyl sulfate micelles that are relevant to the transition of micelles from globular to cylindrical forms.     

Conformational analysis of six-membered cyclic carbonates

The conformational isomerization of 2-oxo-1,3-dioxane and its methyl analogs was investigated by means of ab initio RHF//6-31G(d,p) and MP2//6-31G(d,p) quantum-chemical methods. It is shown that in comparison with 1,3-dioxanes the potential energy surface of the mentioned compounds has a fewer number of stationary points and includes two minima corresponding to conformers of sofa or distorted sofa configuration and one maximum corresponding to 2,5-twist form. The value of potential barrier of interconversion of cyclic carbonates is significantly lower than that of the analogously substituted 1,3-dioxanes.     

Conformational isomerization of 4-methyl-1,3-dioxane

The whole possible course of conformational isomerization of 4-methyl-1,3-dioxane has been established using empirical (MM+) and nonempirical [STO-3G, 3-21G, 6-31G(d) and 6-31G(d,p)] approximations within the limits of the Hartree-Fock method. It was shown that the potential energy surface of this compound contains a principal (equatorial chair conformer) and local minima corresponding to the axial chair conformer and series flexible forms.     

Calcium phosphate powders synthesized from solutions with [Ca2+]/[PO 4 3− ]=1 for bioresorbable ceramics

Calcium phosphate powders for manufacturing bioceramics were synthesized via precipitation from stock solutions of (NH₄)₂HPO₄ and Ca(NO₃)₂, or CaCl₂ or Ca(CH₃COO)₂ with [Ca²⁺]/[PO₄³⁻] = 1, without pH regulation. Properties of powdered samples, including density and microstructure of ceramics sintered at 900, 1000, 1100°C, were studied. The following pairs of precursors such as Ca(NO₃)₂/(NH₄)₂HPO₄, CaCl₂/(NH₄)₂HPO₄, Ca(CH₃COO)₂/(NH₄)₂HPO₄ gave both insoluble calcium phosphates and the corresponding by-products of synthesis — NH₄NO₃, NH₄Cl, NH₄CH₃COO. These by-products were released from the calcium phosphate precipitates in the course of heating to the temperature of sintering. Owing to specific buffer properties of the solutions being formed during synthesis, the pH value varied in a wide range during the precipitation process leading to different final values of pH and, thus, to different target phase(s) after annealing at 900–1100°C. After sintering, the samples based on the powders synthesized from Ca(NO₃)₂/(NH₄)₂HPO₄ consisted of β-Ca₂P₂O₇, whereas the samples based on the powders derived from CaCl₂/(NH₄)₂HPO₄ were composed of β-Ca₂P₂O₇ and β-Ca₃(PO₄)₂, and the samples based on the powders synthesized from Ca(CH₃COO)₂/(NH₄)₂HPO₄ contained only β-Ca₃(PO₄)₂. All the powders can be considered as the precursors for fabrication of bioceramics with enhanced resorption.      

On global solutions of the radial p-Laplace equation

We obtain blow-up conditions for solutions of the radial p$p$-Laplace equation.