Gas chromatographic properties of two thermotropic Poly(L-glutamates) with long alkyl side chains

Summary Comparative gas chromatographic properties of two thermotropic Poly(L-glutamates) with long alkyl side chains (10 and 16 carbons called Poly 10 and Poly 16 respectively) are studied.Their thermal properties were established with differential scanning calorimetry (DSC) and gas chromatography. They present a cholesteric liquid crystal in a large temperature range.The chromatographic separation abilities of the two polymers in the liquid crystal state were studied using capillary glass columns. Interesting analytical performances were obtained in different fields: isomeric separation of alkanes, aromatics, polyaromatics, volatile aroma compounds and cis and trans isomers. Some differences were noticed in their behaviours; 2 and 3-methyloctane and xylene isomers are separated only on Poly 10 while limonene and eucalyptol are separated only on Poly 16.     

On the elucidation of the mechanism of Vinca alkaloid fluorination in superacidic medium

Detailed investigations on one of the key steps of the superacidic fluorination of Vinca alkaloids that is the origin of C20' activation are reported. While two different pathways can be envisioned for the emergence of the transient secondary carbocationic intermediate, isotopic labeling experiments unambiguously revealed the involvement of a 1,2-hydride shift mechanism.     

Enantioselective intramolecular hydroamination catalyzed by lanthanide ate complexes coordinated by N-substituted (R)-1,1'-binaphthyl-2,2'-diamido ligands

Ytterbium and lutetium ionic complexes derived from enantiopure substituted (R)-binaphthylamine ligands, of the general formula [Li(THF)n][Ln[(R)-C20H12(NR)2]2], have been investigated for the hydroamination/cyclization of several aminopentenes and an aminohexene. Complexes with isopropyl or cyclohexyl substituents on nitrogen atoms were found to be efficient catalysts under mild conditions for the formation of N-containing heterocycles with enantiomeric excesses up to 78%.     

First-principles study of structural, electronic and magnetic properties in Cd1−xFexS diluted magnetic semiconductors

In this paper, we report theoretical investigations of structural, electronic and magnetic properties of ordered dilute ferromagnetic semiconductors Cd_1−xFe_xS with x=0.25, 0.5 and 0.75 in zinc blende (B3) phase using all-electron full-potential linear muffin tin orbital (FP-LMTO) calculations within the density functional theory and the generalized gradient approximation. The analysis of band structures, density of states, total energy, exchange interactions and magnetic moments reveals that both the alloys may exhibit a half-metallic ferromagnetism character. The value of calculated magnetic moment per Fe impurity atom is found to be 4 μ_B. Moreover, we found that p-d hybridization reduces the local magnetic moment of Fe from its free space charge value of 4 μ_B and produces small local magnetic moments on Cd and S sites.     

Enantiodivergence in alkylation of 1-(6-methoxynaphth-2-yl)ethyl acetate by potassium dimethyl malonate catalyzed by chiral palladium-DUPHOS complex

Alkylation of racemic 1-(6-methoxynaphth-2-yl)ethyl acetate by potassium dimethyl malonate catalyzed by a chiral palladium-DUPHOS complex afforded the substitution product with 87% ee, along with 6-methoxy-2-vinylnaphthalene that arose from an elimination process, in a 43/57 substitution/elimination ratio. The reaction performed on a mixture of quasi-enantiomeric substrates provided insight into the stereochemical course of the reaction, establishing that—for a given enantiomer of the catalyst, one enantiomer of the substrate afforded mainly the substitution product whereas the other enantiomer underwent elimination.     

Assay for the enantiomeric analysis of [2H1]-fluoroacetic acid: insight into the stereochemical course of fluorination during fluorometabolite biosynthesis in streptomyces cattleya

A sensitive method for the configurational analysis of (R)- and (S)-[2H1]-fluoroacetate has been developed using 2H[1H]-NMR in a chiral liquid crystalline solvent. This has enabled biosynthetic experiments to be conducted which reveal stereochemical details on biological fluorination occurring during the biosynthesis of fluoroacetate and 4-fluorothreonine in the bacterium Streptomyces cattleya. In particular, feeding experiments to S. cattleya with isotopically labeled (1R, 2R)- and (1S, 2R)-[1-2H1]-glycerol 3d and 3e and [2,3-2H(4)]-succinate 4a gave rise to samples of enantiomerically enriched [2-2H1]-fluoroacetates 1a. The predominant enantiomer resulting from each experiment suggests that the stereochemical course of biological fluorination takes place with an overall retention of configuration between a glycolytic intermediate and fluoroacetate 1. Consequently, this outcome suggests that the stereochemical course of the recently identified fluorinase enzyme which mediates a reaction between fluoride ion and S-adenosyl-l-methionine (SAM), occurs with an inversion of configuration.     

Empirical determination of the absolute configuration of small chiral molecules using natural abundance 2H NMR in chiral liquid crystals

Natural abundance deuterium 2D NMR spectroscopy in polypeptide liquid crystals is used for empirically determining the absolute configuration of small chiral molecules.     

Solvent-free condensation of arylacetonitrile with aldehydes

The condensation of a series of arylacetonitriles with aldehydes can be carried out by mixing equivalent amounts of reagents with neat powdered KOH at room temperature for 3-60 min depending on the aldehyde steric hindrance. At higher temperature (110 °C), yields were generally higher and purity increased within very short reaction times (1-5 min). With pentamethylphenylacetonitrile, a phase transfer agent was necessary to give a satisfactory yield.     

Host-guest complex of nabumetone: β-cyclodextrin: quantum chemical study and QTAIM analysis

The aim of the present work is the investigation of the inclusion complex of nabumetone (NAB) and β-cyclodextrin (β-CD) using PM3, DFT, DFT-D and ONIOM2 methods. The results indicate that the most energetically favorable structure predicts a preference of the methoxy group to enter the cavity of β-CD from its wide rim. Consequently, the butanone moiety is positioned outside the cavity on the side of the secondary hydroxyls, with a total insertion of naphthalene group. The semi-empirical PM3 results are in good agreement with those obtained by the DFT optimization (with and without dispersion correction). The donor–acceptor interactions between drug and the cavity wall of the host, studied on the basis of natural bonding orbital (NBO) analysis, show the presence of weak intermolecular hydrogen bonds in addition to the most important van der Waals interactions. Furthermore, it is revealed that among the DFT and DFT-D techniques selected to quantify these interactions, WB97X-D functional provides the greatest values of stabilization energies E⁽²⁾. Finally, a detailed topological charge density analysis based on the quantum theory of atoms in molecules (QTAIM), developed by Bader and co-workers, has been accomplished using the WB97X-D and B3LYP methods on the most favorable complexes. A good correlation between the structural parameters and the electronic density is found.