New approaches to the calculation and interpretation of asymmetry factors of chromatographic peaks

The suitability of the determination of the asymmetry factor of chromatographic peaks by the ratio of areas of two components separated by a perpendicular dropped from the maximum of the peak to the base-line, A _s * = S _b /S _a , where symbol a corresponds to the leading edge of the peak and b is for its tailing slope, is discussed. It is demonstrated that this method enables the estimation of the asymmetry of even partially separated chromatographic signals, including those eluted “in the tail” of intense peaks of solvents. The concepts of the asymmetry index I(A _s *) and its increment ΔI(A _s *) = (A _s *)–I(A _s *) are introduced, which ensures the characterization of the asymmetry of peaks of polar analytes with respect to the asymmetry of nonpolar reference components, that is, the separation of the effects of the polarity of analytes and their quantities injected into the chromatographic column on this parameter. For the first time we revealed a correlation of the asymmetry factors of compounds of different chemical nature with such a characteristic of their polarity as the difference in chromatographic separation temperature and the normal boiling point of analytes.     

Primary photophysical and photochemical processes for Pt(SCN)<Subscript>6</Subscript><Superscript>2–</Superscript> complex

Photosolvation of a Pt^IV hexathiocyanate complex Pt(SCN)₆ ^2– in water and ethanol was studied by steady-state photolysis, nanosecond laser flash photolysis, and ultrafast kinetic spectroscopy. Complexes Pt(SCN)₅(H₂O)^– and Pt(SCN)₅(C₂H₅OH)^– were found to be the only reaction products. The quantum yields of photosolvation are independent of the excitation wavelength, being equal to 0.25 and 0.5 for the solutions of the complex in water and ethanol, respectively. Photosolvation proceeds by the mechanism of heterolytic metal—ligand bond dissociation without involvement of redox processes. The characteristic time of formation of the end products for both solvents is about 10 ps. Three successive intermediates detected on the picosecond time scale were interpreted as Pt^IV complexes. The nature of the intermediates and possible mechanisms of photosolvation are discussed.     

Solution state and complexing ability of 1,4-bis(amidomethylsulfinyl)butane toward iron(III), copper(II), cobalt(II), nickel(II), and manganese(II)

The solution state and thermodynamic stability of complexes of the new antituberculosis agent 1,4-bis(amidomethylsulfinyl)butane (L) with iron(III), copper(II), cobalt(II), nickel(II), and manganese(II) in an aqueous solution in the presence and in the absence of the nonionic surfactant Brij 35 were studied by spectrophotometry, pH potentiometry, NMR relaxation technique (T = 25 °C; variable ionic strength), and mathematical simulation. The geometry optimization of all structures was carried out by the molecular mechanics method MM2 in order to obtain data on coordination modes. In addition, the structure of 1,4-bis(amidomethylsulfinyl)butane was refined by the DFT/B3LYP/6-311++G(d,p) quantum chemical method using the IEFPCM model to take into account solvent effects. In an aqueous solution (in the concentration range of 1.3?10^–5—1?10^–3 mol L–1) and in the presence of Brij 35, 1,4-bis(amidomethylsulfinyl)butane exists as a neutral monomer. The Beer—Lambert—Bouguer law is obeyed in a wide concentration range for compound L in an aqueous solution, as well as in the presence of the surfactant, which can be used for the quantification of compound L. Iron(III), cobalt(II), and nickel(II) were shown to form 1: 1 mononuclear complexes with L; and copper(II) forms, 1: 1 and 2: 2 complexes. The presence of Brij 35 in the Cu²⁺—L system at a micellar concentration promotes the formation of a dinuclear complex.     

Alkylation of phenol with olefins in the presence of catalysts based on mesoporous aromatic frameworks

Mesoporous polyaromatic frameworks (PAFs) based on tetraphenylmethane were obtained and modified with sulfonic acid groups. The compounds were characterized by solid-state ¹³C NMR and IR spectroscopy, low-temperature nitrogen adsorption-desorption, and transmission electron microscopy. The acidities of the PAF-1-SO₃H and PAF-2-SO₃H samples determined by titration were 3.99 mmol g^–1 and 0.91 mmol g^–1, respectively. The catalytic activity of PAF-SO₃H for alkylation of phenol with linear terminal olefins was investigated. The reaction products were isomeric monoalkylphenols (C-alkylates), and alkyl phenyl ethers (O-alkylates).     

A comparative study of the reactions of fluorinated oxi- and thiiranes with acyl chlorides

The CoCl₂-catalyzed reactions of fluorinated 1,2-oxi- and thiiranes with acyl chlorides were studied. It was found that a regioselective heterocycle opening reaction resulted in two isomers having normal and abnormal structure in a ratio predetermined by the substituents in both the starting heterocycles and acyl chlorides.     

Synthesis of substituted 3-acyl-1-hydroxyindoles and azoles on their basis

A general approach to the synthesis of new 3-acetyl-substituted pyrrolo[3,4-f]indole-5,7-diones, 3-[3-(dimethylamino)acryloyl]-1-methoxypyrrolo[3,4-f]indole-5,7-diones and similar indole-5,6-dicarbonitriles has been developed. Dimethylaminoacryloyl derivatives synthesized on their basis regioselectively reacted with hydrazine hydrochlorides and hydroxylamine with the formation of the corresponding 5-substituted azoles.     

Conjugation of indole derivatives by copper-catalyzed alkyne-azide cycloaddition

An efficient synthetic procedure to combine biologically active indole derivatives by the triazole-containing spacer in a molecule has been proposed. The procedure was based on a copper-catalyzed alkyne-azide cycloaddition of azide-containing carbazoles and N-propargyl-containing carbazoles, tetrahydrocarbazoles, and tetrahydro-γ-carbolines.     

Synthesis and properties of 1-(R-adamant-1-yl)-3-(1-propionylpiperidin-4-yl)ureas and 4-({4-[3-(R-adamant-1-yl)ureido]cyclohexyl}oxy)benzoic acids,efficient target-oriented human soluble epoxide hydrolase inhibitors

A reaction of R-adamant-1-yl isocyanates with 4-[(4-aminocyclohexyl)oxy]benzoic acid and 1-(4-aminopiperidin-1-yl)propan-1-one in DMF afforded corresponding ureas in 90—95% yield, the target-oriented inhibitors of epoxide hydrolase sEH. The ureas are characterized by reduced melting points and increased solubility in water, as well as by inhibitory activity in the range of 0.5—4.0 nmol L^–1.     

The importance of glyceraldehyde radiolysis in chemical evolution

Studies in chemical evolution are intended to demonstrate how compounds of biological importance are generated from substances that could have been found in abiotic conditions on the primitive Earth or in extraterrestrial environments. In this context, the aim of the present work was to examine the behavior of dl-glyceraldehyde in both aqueous solution and solid samples under gamma irradiation. We irradiated dl-glyceraldehyde at different doses and temperatures with a gamma source; even at low doses and temperature (77 K), free radicals were detected. Among the products formed were ethylene glycol and glycolaldehyde. Some sugar-like compounds were also detected.

     

Sulphur content estimation of Venezuelan heavy oil by fast neutron and gamma transmission technique

A compact and modern equipment for implementing the fast neutron and γ-ray transmission technique (FNGT) has been developed in order to estimate the sulphur content of crude oil. FNGT is employed for non- destructive analysis of different kinds of samples. The compact system presented in this work represents an improvement of our previous experimental set-up [1, 2]. It makes use of a ²⁵²Cf source, an EJ-301 liquid scintillator detector (2″ × 2″) with excellent n/γ discrimination capabilities, and modern nuclear electronics based on fast digitizers. The fast neutron and gamma transmission technique was employed to study a system for on-line sulphur concentration measurement in Venezuelan heavy sour oil. The range of sulphur concentrations investigated is between 0.1 and 6.5 wt%. The equipment performances and limitations are compared with those predicted by a Monte Carlo model built in GEANT4 v10.01. The results show the possibility to implement a compact unit for on-line determination of sulphur concentration in crude oil.