An efficient synthesis of aziridines from ephedrines

The reaction of chlorodeoxyephedrine hydrochlorides with one, two, and three molar equivalents of base was studied. Isochlorodeoxypseudoepherines were identified and assigned by ¹H and ¹³C NMR data as intermediate compounds in the formation of cis-aziridines. Erythro and threo ephedrinethylethers were isolated as new compounds and analyzed by spectroscopic data. In addition, the erythro isomer was studied by X-ray diffraction.     

Electrochemical determination of p-cresol concentration using zeolite-modified electrodes

Carbon paste electrodes modified with different zeolites (MFI and FAU) were studied in order to evidence the electro-oxidation of p-cresol. Cyclovoltammetric experiments were applied by direct measurement in p-cresol-containing aqueous solution, or during release in solution without p-cresol after impregnation. In both cases, the electro-oxidation signal of p-cresol led to two oxidation peaks. Different concentrations of p-cresol were studied. Influences of charge compensating cations, electrode impregnation time and zeolite type were investigated. It was shown that electrochemical measurements could be used as a detection method for p-cresol in aqueous solution with a high sensitivity.     

Imino- and bis-imino-pyridines with N-ter-butyl-N-aminoxyl group: synthesis, oxidation and use as ligand towards M ( Mn, Ni, Zn) and Gd

Imino- and bis-iminopyridine ligands bearing N-ter-butylhydroxy groups were synthesized by the condensation reaction between a N-ter-butylhydroxy substituted aniline and 2-formylpyridine, 2-acetylpyridine and 2,6-bis-acetylpyridine. The N-ter-butylaminoxy radicals obtained after oxidation using PbO₂ or Ag₂O were studied by EPR spectroscopy in solution. Indeed, complete decomposition was observed during isolation of these radical derivatives. The N-ter-butylhydroxy substituted ligands obtained were complexed with Mn²⁺, Ni²⁺, Zn²⁺ and Gd³⁺ salts; the obtained complexes were characterized and oxidized to give the aminoxy analogs, which were studied using IR, UV and EPR spectroscopies.     

Measurements and modeling of cloud point behavior for polypropylene/n-pentane and polypropylene/n-pentane/carbon dioxide mixtures at high pressure

The phase behavior of polypropylene (PP) in n-pentane and n-pentane/carbon dioxide solvent mixtures has been studied using a high-pressure variable volume view cell. Cloud point pressures for polypropylene (M_w=50,400) in near-critical n-pentane were studied at temperatures ranging from 432 to 470 K for polymer concentrations of 1 to 15 mass%. Furthermore, cloud point pressures for polypropylene (M_w=95,400) in near-critical n-pentane were studied at temperatures ranging from 450 to 465 K for polymer concentrations of 1 to 8 mass%. Cloud point pressures were also measured for PP (M_w=200,000, 3 mass%) in n-pentane at temperatures ranging from 450 K to 465 K. The cloud point pressures for PP (M_w=50,400) in n-pentane/CO₂ mixtures were determined for PP concentrations of 3.0 mass% and 9.7 mass% with CO₂ solvent concentrations ranging from 12.6 mass% to 42.0 mass% at temperatures ranging from 405 K to 450 K. All of the experimental cloud point isopleths were relatively linear with approximately the same positive slope indicating LCST behavior. The experimental cloud point pressures were relatively insensitive to the concentration and molecular weight of polypropylene. At a given temperature, the cloud point pressure of the PP/n-pentane/carbon dioxide system increased almost linearly with increasing carbon dioxide solvent concentration (for carbon dioxide concentrations less than 30 mass%). The Sanchez–Lacombe (SL) equation of state was used to model the experimental data.     

Thermodynamics of fluorinated derivatives of carbosilane dendrimers of high generations

The temperature dependences of the heat capacities of fluorinated derivatives of carbosilane dendrimers of high (4.5 and 7.5) generations were studied by adiabatic vacuum calorimetry in the range from 6 to 340 K for the first time. The standard thermodynamic characteristics of devitrification were estimated. The experimental results were used to calculate the standard thermodynamic functions C _p °(T), H°(T)?H°(0), S°(T)?S°(0), and G°(T)-H°(0) over the range from T??0 to 340 K and standard entropies of formation of dendrimers at T = 298.15 K. The low-temperature (T ?? 50 K) heat capacity was analyzed by using Debye??s heat capacity theory of solids and the multifractal model. The values of fractal dimensionality D were determined, and some conclusions about topology of the studied structures were made. The standard thermodynamic characteristics of the studied fluorinated derivatives of carbosilane dendrimers were compared.     

The thermodynamic characteristics of complex formation between vanadium(V) and malonic acid

Coordination and protolytic equilibria in the system vanadium(V)-malonic acid were studied calorimetrically at 298.15 K and I = 1.0(NaClO₄). The heat effects of formation of the VO₂CH₂(COO) ₂ ^? complex and step protonation of the malonate ion were determined for the first time. The data obtained were used to calculate the thermodynamic characteristics (logK, ΔG, ΔH, and ΔS) of the equilibria studied.     

Effect of the ratio R = [Na2O]/[B2O3] on the structure of glass in the Na2O-B2O3-SiO2 system

Sodium borosilicate glass, with the ratio R = [Na₂O]/[B₂O₃] varied from 0.31 to 1, were studied by IR spectroscopy and Raman scattering techniques. The dependence of the structure of borosilicate glasses on their composition was studied also for the section with a constant value R = 1. The main borate and silicate groups in the system, and especially changes in the structure of glasses depending on the ratio R were identified.     

Fatty acid composition of wild edible mushrooms species: A comparative study

A comparative study was developed on the total fatty acids composition of twelve wild edible mushroom species (Suillus bellini, Suillus luteus, Suillus granulatus, Hygrophorus agathosmus, Amanita rubescens, Russula cyanoxantha, Boletus edulis, Tricholoma equestre, Fistulina hepatica, Cantharellus cibarius, Amanita caesarea and Hydnum rufescens). In order to define qualitative and quantitative profiles, combined fatty acids were hydrolyzed with potassium hydroxide/methanol and all free compounds were derived to their methyl ester forms with methanolic boron trifluoride, followed by analysis by GC-MS. Thirty fatty acids were determined. As far as we know, the fatty acid profiles of A. caesarea and H. rufescens are described for the first time. As for the remaining species, a high number of new compounds were identified, which much improved the knowledge about their fatty acids profiles. In general, oleic, linoleic, palmitic and stearic acids were present in highest contents. Polyunsaturated and monounsaturated fatty acids, valuable healthy compounds for humans, predominated over saturated fatty acids for all the studied mushroom species. R. cyanoxantha presented the highest fatty acids amounts, while B. edulis was the poorest species. By Agglomerative Hierarchic Cluster Analysis the studied species were gathered in 5 groups, based in their fatty acid patterns.     

Specifics of chemical etching of PbTe and Pb1 − x Sn x Te single crystals with I2-DMF solutions

The physicochemical interactions of Pb_{1 ? x} Sn _x Te solid solution and PbTe single crystals with I₂-DMF solutions were studied under reproducible hydrodynamic conditions for the first time. Their dissolution rates were investigated as dependent on the etchant components ratio and the temperature and stirring of etching blends, and the effect of the composition of solid solutions on the parameters of chemical etching was studied. Etchant compositions and the chemicodynamical polishing regimes for the studied single crystals were optimized.     

Cross-mixing study of a poisonous Cestrum species,Cestrum diurnum in herbal raw material by chemical fingerprinting using LC-ESI-QTOF-MS/MS

Poisonous plants are widely distributed and may have risk of phytotoxicity upon mixing with medicinal plants. Several species of Cestrum genus are poisonous and linked with many serious health issues. In the present study, cross-mixing of a toxic plant, Cestrum diurnum with morphologically resembling medicinal plant, Adhatoda vasica was studied using chemical fingerprinting approach. LC-ESI-MS/MS tool was used to develop the chemical fingerprints of three toxic species of Cestrum, including, C. diurnum, C. nocturnum and C. parqui. Total forty-three compounds were identified using high-resolution LC-ESI-MS/MS data comparison. Chemometric analyses were done to compare the distribution of identified compounds present in these Cestrum species. One of the identified compounds, nornicotine (a toxic compound) was also quantified using LC-IT-MS/MS. Adulteration study was conducted by mixing toxic C. diurnum in A. vasica with various ratios (w/w) and five differentiable compounds were identified to detect the adulteration. The method was able to detect up to the limit of 5% mixing of toxic C. diurnum. Moreover, cytotoxicity of the methanolic extracts of these three species were also studied on normal human PBMC (peripheral blood mononuclear cells) and all found to be toxic, while the C. nocturnum showed the highest level of toxicity with the IC₅₀ 12.5 μg/mL.     

Chromatographic properties of fullerene modified with liquid crystal p, p′-azoxyphenetol

Stationary phases for gas chromatography based on liquid crystal p,p′-azoxyphenetol applied onto Chromaton N-AW bearing a layer of C₆₀ fullerene were studied. The thermodynamic properties of the adsorption of n-alkanes and n-alcohols on the mesogen surface were studied at low occupancies. Test mixtures of structural isomers of substituted benzene and polycyclic aromatic hydrocarbons were analyzed in a wide temperature range from 100 to 240°C.     

Cyclic voltammetry of FAD adsorbed on graphite,glassy carbon,platinum and gold electrodes

The electrochemical properties of FAD adsorbed on graphite were studied with cyclic voltammetry. A film with a surface coverage of up to 2×10^?8 mol cm^?2 was formed after 4 h. The film-covered electrodes were stable for long times and they were investigated in buffers without any FAD. A single well-behaved wave was observed, k⁰≌1 s^?1. The pH dependence of E_1/2 was studied. On glassy carbon, platinum and gold much less FAD was adsorbed and it was removed with one rinse.     

Synthesis of fluorinated imines and carbodiimides from azides via aza-Wittig reaction

The Staudinger reaction of fluoroalkylazides were studied. A series of N-fluoroalkylimines were synthesized via aza-Wittig reaction of N-fluoroalkyliminophosphoranes. The N,N′-difluoroalkylated carbodiimide was also synthesized via the reaction of N-fluoroalkyliminophosphoranes with carbon dioxide or carbon disulfide.     

Novel C 2-symmetric bis-oxazoline ligands

Two novel C ₂-symmetric bis-oxazoline ligands were synthesized and their complexes with Cu(OAc)₂ were studied as catalysts in the enantioselective Henry reaction of 4-nitrobenz-aldehyde with nitromethane giving high yield of nitro aldol with ee up to 40%.     

(Trifluoromethoxy)Phenylboronic Acids: Structures,Properties, and Antibacterial Activity

Three isomers of (trifluoromethoxy)phenylboronic acids were studied in the context of their physicochemical, structural, antimicrobial and spectroscopic properties. They were characterized by ¹H, ¹³C, ¹¹B and ¹⁹F NMR spectroscopy. The acidity of all the isomers was evaluated by both spectrophotometric and potentiometric titrations. The introduction of the -OCF₃ group influences the acidity, depending, however, on the position of a substituent, with the ortho isomer being the least acidic. Molecular and crystal structures of ortho and para isomers were determined by the single crystal XRD method. Hydrogen bonded dimers are the basic structural motives of the investigated molecules in the solid state. In the case of the ortho isomer, intramolecular hydrogen bond with the -OCF₃ group is additionally formed, weaker, however, than that in the analogous -OCH₃ derivative, which has been determined by both X-Ray measurements as well as theoretical DFT calculations. Docking studies showed possible interactions of the investigated compounds with LeuRS of Escherichia coli. Finally, the antibacterial potency of studied boronic acids in vitro were evaluated against Escherichia coli and Bacillus cereus.     

Chiral C2-symmetric ligands containing two binaphthyl units linked by 2,2′-bipyridyl bridge in asymmetric catalysis

The catalytic activities of new chiral C₂-symmetric ligands 1–4 in the asymmetric alkylation of aromatic aldehydes with diethylzinc to give 1-arylpropanols are studied. In most cases, the yields were good and enantioselectivities up to 87% were observed. Copper-catalyzed cyclopropanation proceeded with ⩽51% enantioselectivity and ∼3:1 trans/cis-diastereoselectivity.     

Enantioseparation of Novel Amino Analogs of Indole Phytoalexins on Macrocyclic Glycopeptide-Based Chiral Stationary Phase

Direct chiral separation of the enantiomers of spirobrassinin, 1-methoxyspirobrassinin and ten novel cis- and trans-diastereoisomers of 2-amino analogs of indole phytoalexin 1-methoxyspirobrassinol methyl ether on macrocyclic glycopeptide-based chiral stationary phase (CSP) with teicoplanin (Chirobiotic T) was studied. Normal phase eluents containing n-hexane with modifiers ethanol and 2-propanol were used. The effects of mobile phase composition, structure of the analytes and temperature were investigated. Chiral resolution on teicoplanin CSP was achieved only in the case of trans-diastereoisomers. The van??t Hoff plots were found to show linear behavior in all cases. It was found that studied normal phase enantioseparations were enthalpy driven. The elution order of the enantiomers was determined in some cases.     

Solid electrolytes with potassium cation conductivity in K1−2x M x AlO2 (M = Ba, Pb) systems

New solid electrolytes with high potassium cationic conductivity based on potassium monoaluminate were synthesized and studied in the K_1?2x Ba _x AlO₂ and K_1?2x Pb _x AlO₂ systems. A partial substitution of potassium cations with double charged positive cations results in a considerable increase in the conductivity of KAlO₂ in the whole studied range of temperatures. The electric characteristics are somewhat higher in the bariumcontaining system, which is in all probability connected with the effect of the size factor: the size of the Ba²⁺ ion is higher than that of Pb²⁺, which must correlate with the increase of the effective dimensions of the migration channels in the electrolyte structure. The main cause of the conductivity increase at the introduction of the studied additives is the formation of potassium vacancies at the substitution of 2K⁺ → Ba²⁺(Pb²⁺) + V′_K.     

New polymer-supported chiral phase-transfer catalysts in the asymmetric synthesis of α-amino acids: the role of a spacer

Polymer-supported cinchona alkaloid salts with different spacers were used as phase-transfer catalysts in the asymmetric C-alkylation of N-diphenyl methylene glycine tert-butyl ester. Various catalysts and alkylation conditions were studied, the best result being 81% e.e. with cinchoninium iodide bound to polystyrene with a four-carbon spacer.     

A study on the formation of N-tosyl-1,3,2-oxazaborolidin-5-one by electrospray mass spectrometry

The crude product generated in a reaction between N-tosyl valine and borane was studied by electrospray mass spectrometry (ESIMS). Intermediates in the formation of N-tosyl-1,3,2-oxazaborolidin-5-one 1a and further reactions of 1a were studied with negative ion mode. According to the results 1a may, as soon as it is generated, react with the starting amino acid.