The applicability of the “straight-line method” of asmus in the determination of the composition of polynuclear complexes

The straight-line method of Asmus was originally developed for the determination of n in mononuclear complexes of the general form AB_n (n≧ 1). In the present investigation it is demonstrated that the method also can be used for determining the value of n in polynuclear complexes of the form A[_mB_n (m > 1). The method as suggested by Asmus, is, however, not capable of distinguishing between mono- and polynuclear species. It is further shown, that the straight-line method can be applied for the determination of the value of m.     

Hydrochloride method for the determination of monomer in the polycondensation of esters of α-amino acids

Summary A method is proposed for determining the monomer in the polycondensation of esters of-amino acids. The accuracy of the method was to within 1–1.5%.     

Diffusion of linear paraffins in silicalite studied by the ZLC method in the presence of CO2

The diffusion behavior of C₄–C₁₀ n-alkanes in silicalite-1 has been investigated by using the Zero Length Column method. The diffusivities derived from measurements at different purge rates with different purge gases confirming intracrystalline diffusion control. Data are compared with results reported in the literature for MFI zeolites. The diffusivities were found to be consistent and agree well with data previous obtained by ZLC. However, these data showed a remarkable disagreement with other reported techniques (PFG-NMR, QENS and Permeation). The eventual influence of carbon dioxide (CO₂) adsorption on diffusion properties of n-alkanes in silicalite was also investigated. For this purpose, a series of experiments was performed involving hydrocarbons mixed with CO₂. Data were obtained at 303 K and flow rates between 20 and 80 mL/min. The presence of CO₂ does not seem to influence the intracrystalline transport rate of the investigated light hydrocarbons (n-C₄ and n-C₆). On the other hand, the situation for n-C₈ and n-C₁₀ is more complex. The diffusivity values are higher compared to the previously reported values.     

Validation of the RP–HPLC method for analysis of hydrochlorothiazide and captopril in tablets

A rapid and sensitive reverse-phase high performance liquid chromatography (RP–HPLC) method with ultra-violet (UV) detection for a routine control of hydrochlorothiazide and captopril in tablets was developed. The chromatographic system Hewlet Packard 1100 consisted of a HP 1100 pump, HP 1100 UV–VIS detector and HP ChemStation integrator. The samples were introduced through a Rheodyne injector valve with a 20-L sample loop. The isocratic system consisted of a Beckman Ultrasphere ODS 4.6 mm x 15 cm, 5-m-particle column and a mobile phase containing methanol/water (45:55 v/v). The pH of the mobile phase was adjusted to 3.8 with 85% ortophosphoric acid. Quantitation was accomplished using the internal standard method. At the selected conditions, the other excipients of the tablets did not interfere in the assay of active substances. The developed RP–HPLC method was validated, so linearity, precision, accuracy, robustness, limit of quantitation and limit of detection were investigated. For the robustness test, three factors were considered: the composition of the mobile phase , the pH of the mobile phase, and temperature. With the aid of response surface metodology (RSM), it was possible to precisely define the robustness of the method.     

Development of a gas chromatography — mass spectrometry method for the determination of carbon disulfide in the atmosphere

Carbon disulfide (CS₂), a relevant reduced sulfur compound in air, is well-known for its malodor and its significant effect on global atmospheric chemistry. Therefore, a reliable method for determining CS₂ in atmospheric samples has been developed based on solid-phase sampling and gas chromatography–mass spectrometry (GC–MS). Two types of solid-phase sampling supports (Orbo-32 and SKC) and the elution with organic solvents — hexane and toluene — were evaluated for low-volume outdoor sampling. Recovery studies and the standard addition method were carried out to demonstrate the proper determination of CS₂ in the absence of the influence of interferences such as ozone, hydrogen sulfide or water — important atmospheric pollutants —. The proposed methodology was validated by performing experiments in a high-volume smog chamber and by comparison with two reference optical methods, Fourier Transform Infrared (FTIR) and Differential Optical Absorption Spectroscopy (DOAS) installed in these facilities. Satisfactory analytical parameters were reported: fast analysis, a correct repeatability of 6 ± 1% and reproducibility of 14 ± 3%, and low detection limits of 0.3–0.9 pg m^? 3. Finally, the method was successfully applied to industrial samples near a pulp factory area, where a high correlation between industrial emissions and reported carbon disulfide concentrations were observed.     

Homodesmotic method of determining the O–H bond dissociation energies in phenols

The dissociation energy of the O–H bond has been calculated by the homodesmotic reaction method for phenolic compounds, which are well-known antioxidants, including for natural phenols. Use of moderately complex computational levels, such as B3LYP/6-31G(d), is sufficient for reliably estimating the D(O–H) value for phenols within the homodesmotic approach. The O–H bond dissociation energy for monosubstituted phenols has been calculated, and the additive character of the effect of methyl groups on D(O–H) in methylphenols has been demonstrated: the introduction of a CH₃ group into the aromatic ring decreases the D value by 7.8 kJ/mol (ortho position), 1.8 kJ/mol (meta position), and 7.6 kJ/mol (para position). The O–H bond strength has been calculated for a number of ubiquinols, selenophens, flavonoids, and chromanols. The D(O–H) value recommended for α-tocopherol is 328.0 ± 1.3 kJ/mol.     

Alkaloids of Nitraria komarovii. XI. Structure of komavicine and the products of the dehydrogenation of the nitrarine method of dehydrogenation in the quinolinyl-β-carboline series

The new alkaloid komavicine has been isolated from the epigeal part ofNitraria komarovii, and its structure has been established on the basis of spectral characteristics and chemical transformations. The products of the dehydrogenation of nitrarine with selenium and sulfur have been studied. A method has been developed for the dehydrogenation of dihydro and tetrahydro derivatives in the quinolinyl--carboline series.Institute of Chemistry of Plant Substances, Uzbekistan Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 33–39, January–February, 1993.     

Can the DFT-D method describe the full range of noncovalent interactions found in large biomolecules?

The DFT-D method is shown to yield interaction energies between biologically important groups to an accuracy comparable to that obtained using state-of-the-art ab initio methods.     

About the limits of regularization and the ansatz method

The well-known adsorption integral equation (AIE) for calculating pore size and adsorption energy distributions from adsorption isotherms on porous solids is, from the mathematical point of view, a linear Fredholm integral equation of the first kind and therefore an ill-posed problem. What can we realistically expect from the solution of such an ill-posed problem by regularization? Does it make sense to restrict the number of possible solutions by the so-called ansatz method? In this paper, the two methods for solving ill-posed problems are from scratch explained and illuminated by concrete examples. Their relevance and fundamental limitations are discussed.     

roposed method can effectively eliminate the effects of

大学区域光纤通信网国家重点实验室,上海交通大学区域光纤通信网国家重点实验室 上海200030 ,上海200030 ,上海200030 ,上海200030on-off源;;重尾分布;;自协方差以更新理论和拉普拉斯-司阶梯变换为数学工具推导出各种on/off周期持续时间尾分布情况下,on-off源的长程相关结构.证明了on-off源的长程相关结构主要取决于尾分布最重的那个周期的尾分布特性,并通过构造随机on-off样本序列对该结论的正确性进行了验证.Large-Timescale Autocovariance Structure of on-off Sources     

A peroxidase-based method for the determination of dopamine, adrenaline, and α-methyldopa in the presence of thyroid hormones in pharmaceutical forms

The analytical properties of two commercial plant peroxidases isolated from horseradish roots and soybean hulls in the catalysis of the transformation of some catecholamines were demonstrated in the absence and presence of thyroid hormones (l-thyroxine and 3,3′,5′-iodothyronine). For the first time the reactions of dopamine, adrenaline, and α-methyldopa oxidation with H₂O₂ catalysed by horseradish peroxidase with the addition of l-thyroxine as the amplification agent were studied and proposed as the indicator reactions for the simple and rapid enzymatic determination of the indicated catecholamines in their concentration ranges 0.5-300, 4-300, and 100-400 μM, respectively. The catalytic activity of the enzyme (characterized by the reaction rate) was controlled spectrophotometrically. The optimum conditions for the indicator reactions were thoroughly characterized. The mechanism of the stimulatory effect of l-thyroxine on the oxidation of the catecholamines was discussed. The developed enzymatic procedures were successfully applied for the determination of dopamine, adrenaline, and α-methyldopa in some pharmaceutical forms.     

New method for the synthesis of α-chlorocinnamonitriles

A novel method for the preparation of nitriles of -chlorocinnamic acid from aldehydes and ketones was proposed. Transformation of carbonyl compounds into hydrazones followed by treatment of the reaction mixture with CCl₃CN in the presence of copper chloride(i) yields -chlorocinnamonitriles.     

New method for the synthesis of β-bromostyrenes

A new stereoselective method was developed for the synthesis of -bromostyrenes (E/Z > 5/1) starting from hydrazones of aromatic aldehydes and bromoform in the presence of CuCl.     

New method for the synthesis of γ-diketones

Summary Over platinized charcoal at 300° 1-(2-furyl)-3-alkanols, as a result of the hydrogenolysis of the furan ring, and 1-(tetrahydro-2-furyl)-3-alkanols, as a result of the isomerization of the tetrahydrofuran ring, give-diketones in yields of 35–50%.     

Evaluation of the protein concentration in enzymes via determination of sulfur by total reflection X-ray fluorescence spectrometry — limitations of the method

Total reflection X-ray fluorescence spectrometry (TXRF) offers many advantages for the identification of trace elements in biological samples like proteins, enzymes, tissues or plants. Because of difficult and time consuming isolations and cleaning procedures enzyme samples are often available in small amounts only. Using TXRF without any preliminary treatment, a ‘screening’ of such samples to determine the element composition is of interest and importance. Transition metals like Fe, Ni, Cu, Mo and the alkaline earth metal Ca may be determined with high accuracy. A further aspect of the investigation of enzymes is the simple and simultaneous determination of light elements. Sulfur, especially, is of interest. This element is a component of two amino acids, methionine and cysteine, and of iron–sulfur clusters and may be used for easy and simultaneous calculation of the protein concentration. Hence quantitative determination of sulfur by TXRF allows a cross-check regarding of conventional quantitative determination of protein concentration by, e.g. the Lowry method. On the basis of two selected enzymes of different origins and molecular weights this paper will demonstrate the influence of bio-organic matrix and different buffer media on sulfur determination by TXRF. The influence of layer thicknesses of the dry residues and absorption or scattering effects will be discussed. The results indicate that in enzymes with low molecular weights and minor amounts of buffer components a reliable determination of sulfur is possible. By contrast, for enzymes stored in higher buffer concentrations poorer results are given on account of the matrix effects described.     

Iron porphyrin-modified electrodes: influence of the method of modification on the stability and electroactivity in oxidation of sulfite or hydrogensulfite in ethanol–water solutions

The aim of this work is to study four types of modification of a glassy carbon electrode by Fe(III)-tetrakis(p-tetraaminophenyl)porphyrin and determine the influence of the method of immobilization of the complex on glassy carbon in electrocatalytic properties for the sulfite and hydrogensulfite oxidation in ethanol–water. The first modification was deposition of a drop of solution containing the porphyrin on a glassy carbon electrode and evaporation of the solvent (dry-drop method). The second method was immersion of the electrode at 54°C in a solution of dimethylformamide containing the porphyrin for 2 h. The third method consisted of the same heating treatment but after formation of a chemical bond of 4-aminopyridine on the glassy carbon surface, which acts as an axial ligand for the first layer of porphyrin. The fourth method involves electropolymerization of the porphyrin on the electrode surface. Important differences in stability, the potential where the oxidation wave begins and selectivity of the electrode to sulfite or hydrogensulfite were observed. The behavior of the polymer-modified electrode is different in water compared to ethanol–water.