Conformational isomorphism in crystalline 1,4-cis-polyisoprene

The possibility that the statistical structure of 1,4-cis-polyisoprene (natural rubber), proposed by Nyburg, could be interpreted with a statistical succession of different conformations along the polymer chain has been investigated. The X-ray data can be interpreted on the basis of a statistical succession of conformations S₊ TS_? or S_? TS₊ of each triplet of consecutive single bonds along the chain.     

Sensitive procedure for the determination of reboxetine enantiomers in human plasma by reversed-phase high-performance liquid chromatography with fluorimetric detection after chiral derivatization with (+)-1-(9-fluorenyl)ethyl chloroformate

A sensitive and selective high-performance liquid chromatographic method for the determination of reboxetine enantiomers in human plasma was developed. Although two chiral centres are present in reboxetine, its stereospecific synthesis leads to two rather than four possible enantiomers. After extraction from plasma and reaction with (+)-1-(9-fluorenyl)ethyl chloroformate, reboxetine enantiomers were separated as diastereoisomeric derivatives by reversed-phase high-performance liquid chromatography (HPLC) and determined by fluorimetric detection. The HPLC analysis time was about 90 min. The linearity, precision, accuracy and limit of quantification of the method were evaluated. No interference from blank plasma sample was observed. The suitability of the method for in vivo samples was assessed by the analysis of plasma samples obtained from a healthy male volunteer who had received a single oral dose of 4 mg of reboxetine in tablet form.     

1,4-Benzodiazepines as ligands. Synthesis,characterization and crystal and molecular structure ofbis(8-chloro-6-(o-chlorophenyl)-1-methyl-4H-s-triazolo[4,3-a]1,4-benzodiazepine (triazolam)) cadmium (II) dichloride

The compound C₃₄H₂₄CdN₈Cl₆ was prepared and characterized by means of X-ray, IR, and Raman measurements. The crystals are monoclinic, space groupC2/c, (No. 14) witha=22.284(3),b=14.501(2),c=14.595(2) Å=129.77(1)° andZ=4. The structure was solved by the heavy-atom method, and least-squares refinement of structural parameters led to a conventionalR factor of 0.040 for 2379 independent reflections. The structure consists of discrete molecules, in which the Cd atom is coordinated in a distorted tetrahedral geometry by two chlorine atoms and by two nitrogens of two triazolic rings of triazolam molecules. Infrared and Raman bands are assigned on the basis of the known structure. An electronic charge calculation has been performed on the unbonded ligand.     

Microscopic FT-IR analysis of blends from functionalized polyolefins and poly(vinyl chloride) or polystyrene

Binary mixtures consisting of ethylene-propylene copolymer functionalized with diethyl maleate (FEP) and poly(vinyl chloride) or polystyrene have been studied by means of the microscope-FT-IR system. Parallel DSC measurements have been carried out on the functionalized ethylene-propylene copolymer/poly(vinyl chloride) mixtures. Intermolecular interactions involving the carbonyl of the ester groups of the copolymer and the methin hydrogen of poly(vinyl chloride), through hydrogen bonding, have been evidenced in the various microareas of the samples. Intensity of these effects depends on composition in different domains of the blends. An increase of the gauche sequences with respect to the long and short trans sequences of poly-(vinyl chloride) chains has been detected with increasing the content of FEP. The partial compatibility of FEP/poly (vinyl chloride) blends has been confirmed by DSC measurements.     

Thermal Shift Assay as a Tool to Evaluate the Release of Breakdown Peptides from Cowpea β-Vignin during Seed Germination

The present work aimed to characterize the molecular relationships between structure and function of the seed storage protein β-vignin, the vicilin storage protein of cowpea (Vigna unguiculata, l. Walp) seeds. The molecular characterization of β-vignin was carried out firstly by assessing its thermal stability, under different conditions of pH and ionic strength, by thermal shift assay (TSA) using SYPRO Orange fluorescent dye. Secondly, its aggregation propensity was evaluated using a combination of chromatographic and electrophoretic techniques. Two forms of β-vignin were considered: the native form purified from mature quiescent seeds, and a stable breakdown intermediate of 27 kDa produced while seeds germinate. TSA is a useful tool for determining and following over time the structural changes that occur to the protein during germination. The main result was the molecular characterization of the 27 kDa intermediate breakdown polypeptide, which, to the best of our knowledge, has never been described before. β-vignin seems to retain its trimeric conformation despite the evident degradation of its polypeptides.     

Textilindustrie

Ohne Zusammenfassung     

Nucleophilic addition to styryl sulphones. part II. Regio- and stereochemistry of the addition of enamines from 4-substituted cyclohexanones

Formation of β- and α-adducts in the reactions of styryl sulphones with enamines from 4-alkylcyclohexanones is reexamined. Steric effects, electrostatic interactions between the nitrogen atom of the enamine and the oxygen atoms of the sulphone group, and medium effects contribute to the regioselectivity of the reaction.     

Déchirures de variétés de dimension trois et la conjecture de Nash de rationalité en dimension trois

Sans résumé Dédié à Heisuke Hironaka     

Unexpected spin-off from quantum gravity

We propose a novel way of investigating the universal properties of spin systems by coupling them to an ensemble of causal dynamically triangulated lattices, instead of studying them on a fixed regular or random lattice. Somewhat surprisingly, graph-counting methods to extract high- or low-temperature series expansions can be adapted to this case. For the two-dimensional Ising model, we present evidence that this ameliorates the singularity structure of thermodynamic functions in the complex plane, and improves the convergence of the power series.