Cinchona based squaramide catalysed enantioselective Michael addition of α-nitrophosphonates to aryl acrylates: enantioselective synthesis of quaternary α-aminophosphonates

Several cinchona based squaramide catalysts were applied to the asymmetric Michael addition of α-nitroethylphosphonates to acrylic acid aryl esters, resulting in high yields and enantioselectivities. The absolute configuration of one of the quaternary α-nitrophosphonate adducts was deduced from its experimental and calculated CD spectra. The adducts were reduced to their cyclic aminophosphonates by catalytic hydrogenation.     

Sensitivity- and Gradient-Enhanced Hetero (ω1) Half-Filtered TOCSY Experiment for Measuring Long-Range Heteronuclear Coupling Constants

An enhanced version of the X(ω₁) half-filtered TOCSY experiment for measurement of long-range heteronuclear coupling constants is proposed which yields high-quality spectra with substantially increased sensitivity and resolution. The modified method features gradient-enhanced X filtering sequences, broadband homonuclear decoupling duringt₁, optional¹J_XHscaling in theF₁domain, and gradient coherence selection in combination with the sensitivity-enhanced protocol for the TOCSY transfer. These modifications extend the applicability of the method—coupling constants can be measured accurately for natural abundance samples at low concentrations and for compounds yielding complex spectra. Computer-aided analysis of E.COSY-type multiplets is applied for the determination of heteronuclear long-range coupling constants.     

The effect of Schwarzschild field on spin 1/2 particles compared to the effect of a uniformly accelerating frame

The Dirac Hamiltonian is calculated in the Schwarzschild space and compared to the analogous one in a uniformly accelerating Minkowski frame yielding a test of the equivalence principle. Comparing these Hamiltonians, we see that the flat-space energy-mass terms and their redshifted forms are the same in the two cases, but the coefficient of the spin-orbit coupling term is different and an additional term appears in the gravitational case.     

Binding affinity studies of 1,2,3-triazole copper(II) complexes to human serum albumin

Abstract

Two copper(II) complexes with tetradentate 1,4-disubstituted-1,2,3-triazole ligands, [CuL(MeCN)](ClO₄)₂ (1) and [CuL′](ClO₄)₂ (2), have been prepared and characterized by different techniques, including X-ray structure determination, spectroscopic, and electrochemical measurements, as reported elsewhere. Herein, we report the interactions of these complexes, and corresponding free ligands, with human serum albumin (HSA) verifying their relative thermodynamic stability and differences in binding to this protein. Interactions with HSA were verified by CD measurements monitored at 564?nm, up to stoichiometric ratio 2:1 [Complex]:[protein], according to competitive equilibria involving the insertion of copper at the selective N-terminal metal binding site in HSA, and additionally at a secondary nonselective site. Further interactions of these complexes with L-tryptophan residues, and probable supplementary site(s) for the binding, were followed by fluorescence measurements. Analogous experiments with the free L and L′ indicated much weaker interactions. Protein oxidation damage was observed for both complexes, monitored by carbonyl groups formation in the presence of H₂O₂, probably with the participation of reactive oxygen species. Density functional theory calculations exhibit metal-ligand binding interaction energies similar to [Cu(HSA-N_terminal)]⁺, and reinforced the experimental results, showing clearly that such triazole ligands are competitive toward copper(II) in biological medium.     

Recent Studies on the Decomposition of n-Hexane and Toluene in RF Thermal Plasma

Thermal decomposition of volatile organic compounds (VOCs) such as n-hexane and toluene has been studied in an inductively coupled thermal plasma reactor, at atmospheric pressure, in neutral and oxidative conditions, respectively. Thermodynamic calculations were performed for predicting the product distribution due to thermal decomposition. Based on these calculations formation of the products observed in the gas phase and in the extract of soot could be interpreted. In neutral conditions formation of soot and PAH was detected to different extent for the different models. The presence of oxygen in the plasma reactor depresses both soot and PAH formation. GC-MS analyses of the gaseous products and the extract of the soot, respectively, refer to as complex decomposition and recombination mechanism in given conditions.     

Racemic compound formation-conglomerate formation

The phenomena of conglomerate formation-racemic compound formation were investigated in a series of five (N-alkyl)-2,6-pipecoloxylidides. The optically active enantiomers were prepared by optical resolution of the racemates using 2R,3R-tartaric acid and 0,0-dibenzoyl-2R,3R-tartaric acid as resolving agent. By DSC measurement of the racemates and the enantiomer the binary phase diagrams were determined.Among the four racemic molecular compounds the N-methyl derivative is the more stable. By increasing the length of the alkyl chain the stability of the racemic compound decreased, and in case of the longest -butyl-chain conglomerate formation was observed.Part 3. D. Kozma, Zs. Böcskei, Cs. Kassai, K. Simon and E. Fogassy: Racemic Compound Formation-Conglomerate Formation. Part 3. Investigation of the Acidic Salts of -phenylethylamine by Achiral Dicarboxylic Acids. Optical Resolution by Preferential Crystallization and a Structural Study of R--phenylethylammonium hydrogen ithaconate, J. Chem. Soc. Perkin Trans. 2 (1996) 1511.The authors are grateful for financial support to OTKA foundation (grant numbers: F14851 (D. K.), T14887 (E. F.)) and for the Z. Magyary award for D. K.     

Thin-Layer Chromatographic Characterization of Metabolites Formed from an AMPA Antagonist Drug Candidate

JPC – Journal of Planar Chromatography – Modern TLC - A pilot study has been conducted to develop sample preparation procedure and TLC separation of radiolabeled metabolites of an AMPA...     

Structural and thermal characterization of Fe(III) and Fe(II) complexes with tridentate ONO pyridoxal semicarbazone

In the scope of design and optimise the equipment for alcoholic distillate beverages production, a sufficient knowledge of physical properties and phase equilibria is necessary. In this paper we present the temperature dependence of excess molar volumes of the ternary system ethanol+water+1-propanol at the range 288.15–323.15 K and atmospheric pressure, due to the importance of the 1-propanol among the flavour compounds contained into this type of beverages. Derived properties were computed due to its importance in the study of specific molecular interactions.     

The effect of K+ ion exchange on the structure and thermal reduction of hexagonal ammonium tungsten bronze

This paper discusses the changes in the structure and thermal reduction of nanosize hexagonal ammonium tungsten bronze (HATB), (NH₄)_0.33−xWO_3−y, which were caused by K⁺ ion exchange (doping) and studied by XRD, XPS, ¹H-MAS NMR, FTIR, SEM and TG/DTA-MS. Comparison of the cell parameters of undoped and doped HATB revealed that both a and c cell parameters decreased after the ion exchange reaction, which showed that smaller K⁺ ions partly replaced the larger NH₄⁺ ions in the hexagonal channels of HATB. After the reaction, from the hexagonal channels less NH₃ evolved, which also supported the incorporation of K⁺ ions into the hexagonal channels.