1,8-Dihydroxyanthraquinone-Mg(II) complex: III. Spectrophotometric determination of Mg(II) by extraction in isoamyl alcohol

In this paper a direct spectrophotometric method is proposed to determine Mg(II). This new method is based on the extraction in isoamyl alcohol of the complex formed between Mg(II) and 1,8-dihydroxyanthraquinone. The method permits the determination between 1.25 and 12.5 γ (in aqueous phase). The error and the molar absorptivity are values of 2.22% and 10,114 liters mol^?1 cm^?1, respectively. Also studied were the values of the constant of exchange and the interference levels caused by foreign ions.     

Towards benchmark second-order correlation energies for large atoms: Zn2+ revisited

To provide very accurate reference results for the second-order M?ller-Plesset (MP2) energy and its various components for Zn(2+), which plays for 3d-electron systems a similar role as Ne for smaller atoms and molecules, we have performed extensive calculation by two completely different implementations of the MP2 method: the finite element method (FEM) and the variation-perturbation (VP) method. The FEM and VP calculations yield partial wave contributions up to l(max)=45 and 12, respectively. Detailed comparison of all FEM and VP energy components for l(max)=12 has disclosed an extraordinary similarity, which justifies using the present results as benchmarks. The present correlation energies are compared with other works. The dependability of an earlier version of FEM, already applied to very large closed-shell atoms, is confirmed. It has been found that for larger atoms the accuracy of the analytical Hartree-Fock results has an impact on the accuracy of the MP2 energies greater than for smaller atoms. Fields of applications of the present results in studies of various electron correlation effects in 3d-electron atoms and molecules are indicated.     

Haloacetylated enol ethers. 5 [5]. Heterocyclic ring closure reactions of β-alkoxyvinyl dichloromethyl ketones with hydroxylamine

The β-alkoxyvinyl dichloromethyl ketones 1a-d are cyclocondensed with hydroxylamine hydrochloride in pyridine to afford the 5-hydroxy-5-dichloromethyl-4,5-dihydroisoxazoles 2a-d in good yield. The cyclo-condensation of compound 1c gave, together with 2c , 3-cyano-2-hydroxy-2-dichloromethyltetrahydrofuran 5c. The dehydratation of compounds 2a,b , derived from acyclic enol ethers, with concentrated sulfuric acid at 30°, led the corresponding 5-dichloromethylisoxazoles 3a,b. The dehydratation of compounds 2c,d , derived from cyclic enol ethers, with concentrated sulfuric acid at 30°, led the bicyclic 4,5-dihydroisoxazoles 4c,d , and at 55°, a competitive rearrangement reaction gives the 3-cyano-2-hydroxy-2-dichloromethyl-2H-pyran 5d.     

Determination of sulphamethizole in the presence of nitrofurantoine by derivative spectrophotometry and ratio spectra derivative

Two methods for determining sulphamethizol in the presence of nitrofurantoine in mixtures by first-derivative spectrophotometry and by the first derivative of the ratio spectra are described. The procedures do not require any separation step. In the first method the measurements are obtained in the zero-crossing wavelengths and the calibration graphs were linear up to 32 mug/ml of sulphamethizole at 251 and 278.5 nm. In the second method, the calibration graphs were linear up to 43 mug/ml by measuring at the maximum (263 nm), at the minimum (244 nm) and peak to peak. The methods were applied for determining sulphamethizole in a pharmaceutical product containing nitrofurantoine.     

Appearance of flaws in layers of AlxGa1−xSb solid solutions during epitaxial growth from the liquid phase

Layers of Al_xGa_1–xSb (x0.7) solid solutions were grown epitaxially from the liquid phase on substrates of gallium antimonide. Aluminum was added to the melt during the buildup of an epitaxial layer. In these layers were found inclusions of the solvent as well as regions of localized chemical inhomogeneities. It is shown here that the appearance of such flaws is intimately related to the relief which the GaSb substrate has formed by the time aluminum enters into the solution. A mechanism of this flaw formation is suggested.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 75–80, June, 1976.     

Dependence of the Structure and Properties of (M,Cu)Sr2(Ln,Ca)Cu2O8−δ (1212) and (M,Cu)Sr2(Ln,Ce4+)2Cu2O10−δ (1222) Phases on the Cation M

The composition and structure of (M,Cu)(Sr,Ln)₂(Ln,Ca,Sr)Cu₂O_8– phases, where M = B, Al, Cr, Pb, Bi, Ru, or Mo (1212 type), and (M,Cu)(Sr,Ln(₂(Ln,Ce⁴⁺)₂Cu₂O_10– phases, where M = V, Cr, Mn, Ru, or Mo (1222 type), have been determined. The role of the M cation in the formation of the crystal structures and the superconductivity phenomenon was analyzed. The relationship between the type of M cation and structural parameters was discovered.     

Righi-Leduc effect in a quantizing magnetic field

The Righi-Leduc effect in semiconductors with a Kane dispersion law in the presence of strong, quantizing, magnetic fields is studied theoretically. The explicit form of the dependence on the magnetic field, temperature, and concentration in arbitrary quantizing magnetic fields is established for semiconductors with a nondegenerate electron gas in the approximation of small nonparabolicity. A simple formula that is applicable for all strong magnetic fields, including quantizing fields, is derived for the Righi-Leduc coefficient in the case of strongly degenerate semiconductors with an arbitrary nonparabolic band. It is shown that in order to determine the photon part of the thermal conductivity ,ph directly from experiment it is best to employ samples with a nondegenerate electron gas in strong, but nonquantizing, magnetic fields.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 102–107, July, 1988.     

Dipolar addition of diazomethane to 5-methylene-1,3-dioxolan-4-one

The reactions of 1-pyrazoline-3-spiro-4-(1,3-dioxolan-5-one) were studied; this compound is the product of the 1,3-dipolar addition of diazomethane to 5-methylene-1,3-dioxolan-4-one. Depending on the conditions, thermolysis of the spiro compounds proceeds either with destruction of the pyrazoline ring, or with cleavage of the dioxolane ring, followed by rearrangement to give 1(2)-hydroxymethyl-3(5)-pyrazolecarboxylic acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1182–1184, September, 1985.     

A Quadratically Convergent Algorithm for Structured Low-Rank Approximation

Structured Low-Rank Approximation is a problem arising in a wide range of applications in Numerical Analysis and Engineering Sciences. Given an input matrix \(M\), the goal is to compute a matrix \(M'\) of given rank \(r\) in a linear or affine subspace \(E\) of matrices (usually encoding a specific structure) such that the Frobenius distance \(\left\| M-M' \right\| \) is small. We propose a Newton-like iteration for solving this problem, whose main feature is that it converges locally quadratically to such a matrix under mild transversality assumptions between the manifold of matrices of rank \(r\) and the linear/affine subspace \(E\). We also show that the distance between the limit of the iteration and the optimal solution of the problem is quadratic in the distance between the input matrix and the manifold of rank \(r\) matrices in \(E\). To illustrate the applicability of this algorithm, we propose a Maple implementation and give experimental results for several applicative problems that can be modeled by Structured Low-Rank Approximation: univariate approximate GCDs (Sylvester matrices), low-rank matrix completion (coordinate spaces) and denoising procedures (Hankel matrices).     

Improved Efficiency of Molecular‐Gel Formation by Adjusting Preorganization of Amino‐Acid‐Derived Flexible Molecules: A NMR and Thermodynamic study

The efficiency of the formation of molecular gels of simple derivatives of l ‐valine and l ‐isoleucine is greatly improved in different organic solvents when a hexyl fragment is replaced by a bulkier cyclohexyl one. A study using NMR and IR spectroscopy provides information on the preferred conformations of the molecules, indicating that the cyclohexyl moiety precludes intramolecular H bonding and preorganises the system for intermolecular interactions, which are responsible for fiber formation. NMR data of the gels provides thermodynamic data on fibrillization, revealing that the origin of this effect is mainly entropic. Electron microscopy (SEM and TEM) images show fibrillar and tape‐like objects, which are observed commonly in molecular gels. Rheological measurements reveal significant differences between cyclohexyl and hexyl appended gelators. These findings could contribute to the rational design of small, flexible, building blocks for self‐assembly.