Effect of promotion of nickel sulfide catalyst with silver on kinetics of decarbonilation of stearic acid

Russian Chemical Bulletin - The kinetics of liquid-phase decarbonylation of stearic acid in n-dodecane on γ-Al2O3 supported nickel sulfide catalyst promoted with silver was experimentally...     

In silico optimization of merocyanine-spiropyran compounds as second-order nonlinear optical molecular switches

Time-dependent Hartree-Fock and M?ller-Plesset second-order calculations have been used to unravel the relationships between structure and first hyperpolarizability in spiropyran/merocyanine couples and therefore to design efficient second-order nonlinear optical switching compounds. Large first hyperpolarizabilities for the merocyanine form as well as large contrasts of first hyperpolarizability have been obtained when, on the same species, (i) substituents at R(1) and R(2) positions on the phenolate ring of the merocyanine form are strong acceptor and donor substituents, respectively, (ii) the ethylenic bridge is substituted by donor groups, (iii) the other aromatic part of the system is benzimidazolo rather than indolino or benzothiazolo, and (iv) strong donor substituents are placed on the benzimidazolo moiety.     

Phenylenediamine catalysis of "click glycosylations" in water: practical and direct access to unprotected neoglycoconjugates

Phenylenediamine-catalyzed click chemistry leads to the efficient, practical, and column-free preparation of neoglycoconjugates from unprotected glucosyl azide, in pure water when aglycon solubility permits.     

Online large volume sample staking preconcentration and separation of enantiomeric GHRH analogs by capillary electrophoresis

A capillary electrophoresis method is proposed to analyze the four most well-known growth hormone–releasing hormone (GHRH) analogs that are misused by athletes. Dimethyl-β-cyclodextrin used as a chiral selector allowed, for the first time, the separation of those basic peptide analogs, including enantiopeptides (sermorelin and CJC-1293) that differ by the chirality of only one amino acid. To increase the method sensitivity, electrokinetic preconcentration methods have been investigated. The large volume sample stacking with polarity switching (PS-LVSS) method with an injected sample volume corresponding to 80% of the capillary one was found superior to the sweeping in terms of signal enhancement factor (SEF). Acid and organic solvent addition to the sample (0.1 mM phosphoric acid with 30% methanol) led to a twofold signal improvement, when compared to water as a matrix. We increased capillary dimensions to provide a signal enhancement through the injection of a larger sample volume. Finally, using a combination of the optimized PS-LVSS preconcentration with the chiral capillary zone electrophoresis (CZE), the GHRH analogs were separated and limits of detection between 75 and 200 ng/mL were reached. This method was successfully applied to urine after a desalting step. An optimized C18 SPE was used for that purpose in order to provide low sample conductivity (<130 µS/cm) and preserve the efficiency of LVSS preconcentration. SEF of 640 was obtained with desalted urine spiked with sermorelin by comparison to the CZE (without preconcentration) method.     

Chiral Allenes via Alkynylogous Mukaiyama Aldol Reaction

Herein we describe the development of a catalytic enantioselective alkynylogous Mukaiyama aldol reaction. The reaction is catalyzed by a newly designed chiral disulfonimide and delivers chiral allenoates in high yields and with excellent regio‐, diastereo‐, and enantioselectivity. Our process tolerates a broad range of aldehydes in combination with diverse alkynyl‐substituted ketene acetals. The reaction products can be readily derivatized to furnish a variety of highly substituted enantiomerically enriched building blocks.     

[U(bipy)4]: A Mistaken Case of U0?

After more than 50 years, the synthesis and electronic structure of the first and only reported “U⁰ complex” [U(bipy)₄] ( 1 ) has been reinvestigated. Additionally, its one‐electron reduced product [Na(THF)₆][U(bipy)₄] ( 2 ) has been newly discovered. High resolution crystallographic analyses combined with magnetic and computational data show that 1 and its derivative 2 are best described as highly reduced species containing mid‐to‐high‐valent uranium ligated by redox non‐innocent ligands.     

Effect of medium acidity on the efficiency of oxidation of 2,4,6-trinitrotoluene to 2,4,6-trinitrobenzoic acid

An effect of boric acid additives on oxidation of 2,4,6-trinitrotoluene (TNT) to 2,4,6-trinitrobenzoic acid (TNBA) with chromic anhydride in concentrated (96—100%) H₂SO₄ has been studied. In the presence of tetrahydrosulfatoboric acid HB(HSO₄)₄ formed in situ (up to 5 mol.%) or added as a preliminary prepared solution (up to 1 mol. %), TNT is selectively oxidized to TNBA in the yields up to 95—99%. The mechanism including formation of TNT dication as a key step of its oxidation at the methyl group has been suggested.     

Rheological properties of sulfur-containing hyperbranched polycarbosilanes and related magnetic compositions

Russian Chemical Bulletin - The rheological properties of hyperbranched polycarbosilanes with butyl and decyl terminal groups and their sulfur-containing analogs were compared. The use of various...     

Relaxation and equilibrium properties of dilute aqueous solutions of alcohols

Regularities of equilibrium state establishment in dilute aqueous solutions of alcohols and the concentration and temperature dependences of the contraction, which is one of the simplest and important thermodynamic characteristics of solutions, were considered. The equilibrium state in aqueous solutions of the alcohols is established for days and even weeks after preparation. Such a slow relaxation process is directly related to the formation of the microheterogeneous state of the system and peculiarities of its time evolution. The character of the temperature and concentration dependences of the contraction is satisfactorily explained on the basis of the simplest virial equation of state assuming that its parameters are determined by the averaged potentials of intermolecular interaction. The physical nature of peculiar points of aqueous solutions of alcohols, i.e., intersection points of the contraction curves or points in the vicinity of which the intensity of molecular light scattering anomalously increases, was considered. The appearance of peculiar points depends on orientational correlations in water. The possibility of existence of peculiar points in other binary solutions is also discussed.