Composants volatils de la «mousse de chêne» (Evernia Prunastri (L.) ACH.) 3e communication

Volatiles constituents of “Oakmoss”(Evernia Prunastri (L .) ACH .) The chemical consititution of different fractions of two oakmoss oleoresines were investigated by GC./MS. using SCOT. and capillary columns. Besides many known compounds, over 52 (sesquiterpenes, aliphatic and aromatic hydrocarbons) have not yet been reported as constituents of oakmoss.     

Synthesis,Characterization and Photocatalytic Activity of TiO<Subscript>2</Subscript> Powders Prepared Under Different Gelling and Pressure Conditions

Homogeneous TiO₂ gel powders were prepared by hydrolysis and condensation of titanium(IV) isopropoxide with HCl or SnCl₂ catalysts, by working under reduced pressure or in air. Ti(IV) alkoxide was previously modified by reaction with formic or acetic acid, used as chelating ligands, when gelation was performed in acidic catalysis. Crude TiO₂ xerogels were purified by water reflux treatment in order to induce a low temperature crystallisation to the anatase phase. Both crude and purified TiO₂ samples were characterised by XRD, FT-IR, SEM, and N₂ adsorption analysis. Thermoanalyses (TG, DTA, DTG, TG-MS, TG-GC-MS) were carried out to quantify the residual organic components in the crude TiO₂ gels and to obtain stoichiometric formulas to describe their chemical compositions. XRD data of purified TiO₂ powders were processed by means of a Rietveld refinement procedure to determine TiO₂ polymorphs, crystallite sizes and cell parameters, before their use in photocatalytic tests. The photoactivity of the purified TiO₂ anatase powders was studied by using 4-nitrophenol degradation as probe reaction carried out in a batch and/or a membrane photoreactor. Samples prepared by using formic acid or SnCl₂ were the most photoactive, whereas specimens gelled under vacuum treatment showed detrimental effects.     

Intermolecular dynamical charge fluctuations in water: a signature of the H-bond network

We report a simulation of deuterated water using a Car-Parrinello approach based on maximally localized Wannier functions. This provides local information on the dynamics of the hydrogen-bond network and on the origin of the low-frequency infrared activity. The oscillator strength of the translational modes, peaked around approximately 200 cm-1, is anisotropic and originates from intermolecular--not intramolecular--charge fluctuations. These fluctuations are a signature of a tetrahedral hydrogen-bonding environment.     

MD simulation of the Na+-phenylalanine complex in water: competition between cation-pi interaction and aqueous solvation

The competition between cation-pi interaction and aqueous solvation for the Na+ ion has been investigated by molecular dynamics simulations, using the phenylalanine amino acid as the test pi system. Starting from one of the best standard force fields, we have developed new parameters that significantly improve the agreement with experimental and high quality quantum mechanical results for the complexes of Na+ with phenylalanine, benzene, and water. The modified force field performs very well in forecasting energy and geometry of cation coordination for the complexes. Next, analysis of MD trajectories and steered MD simulations indicate that the Na+-phenylalanine complex survives for a significant time in aqueous solution and that the free energy barrier opposing dissociation of the complex is sizable. Finally, we analyze the role of different intermolecular interactions in determining the preference for cation-pi bonding with respect to aqueous solvation. We thus confirm that the Na+-phenylalanine stabilization energy may overcome the interactions with water.     

Etude de la réactivité de la fonction carbonyle avec le cétène en présence d'un alcoxyde de titane. 2e communication. A propos de l'interprétation de quelques spectres RMN de β-hydroxyesters formés

The NMR. spectra of a serie of β-hydroxyesters have been studied. It has been found that the methylene protons are magnetically nonequivalent only when the substituents on the center of asymmetry of I or II are very different. The magnetically non-equivalence of the isopropylmethylprotons arise when the β-hydroxyesters contain an aromatic or aromatic conjugated group directly bonded to the asymmetric carbon. The interpretation of this finding is proposed.     

Silver(I) complexes ofN-ethylthiourea. An infrared study

Summary The following silver(I) complexes ofN-ethylthiourea, L, have been isolated in the solid state: AgLX (X = Cl, Br, ClO₄, BF₄, and CF₃CO₂), Ag₂L₃X₂ (X=ClO₄, BF₄ and CF₃CO₂), AgL₂ClO₄, AgL₃X (X = Cl, Br, I, ClO₄, BF₄ and CF₃CO₂). The decrease of the(CS) and (SCN₂) frequencies in the i.r. spectra of the complexes indicates S-coordination of the ligands. The(AgS) frequencies lie in the 267–252 cm^–1 range for terminal and 240-210 cm^–1 range for bridged or long Ag-S bonds. The following structures may be proposed for the complexes. AgLX (X = Cl and Br), polymeric trigonal coordination with bridging halide ions; Ag₂L₃A₂ (A = ClO₄ and BF₄), polymeric trigonal coordination with three bridging sulphur atoms; AgL₂ClO₄, polymeric tetrahedral coordination with four bridging sulphur atoms; AgL₃A (A = ClO₄ and BF₄), dimeric tetrahedral coordination with two terminal and two bridging sulphur atoms; AgLO₂CCF₃ and Ag₂L₃(O₂CCF₃)₂, trigonal and/or tetrahedral coordination with terminal sulphur bonds and bridging CO₂ groups; AgL₃O₂CCF₃, tetrahedral coordination with terminal sulphur bonds and a monodentate CO₂ group. In the trifluoroacetato complexes, a(AgO) band is observed at 185–209 cm^–1. The AgL₃X complexes (X = Cl, Br and I) show two(AgX) and two(AgS) bands with rather low frequencies corresponding to long metal-ligand bond distances.     

The Synthesis of a Novel Epoxycyclohexane from the Fungus Eutypa lata (Pers: F.) TUL

The synthesis of the novel (1′R*,2′S*,3′R*, 4′S*,5′R*)-1-(3′,4′-epxoy-2′, 5′-dihydroxycyclohexyl)-3-methyl-but-2-enone ( 2 ), recently isolated from the culture medium of the fungus Eutypa lata, is described.     

The inactivation of phospholipase A2 by scalaradial: a biomimetic study by electrospray mass spectrometry

A biomimetic approach was employed to shed light on the nature of chemical reactions occurring in the covalent inactivation of phospholipase A(2) (PLA(2)) by scalaradial (1), a marine dialdehyde terpenoid endowed with potent anti-inflammatory activity. To this end, a detailed study of the reaction profile between the nitrogenous nucleophile isopropylamine and scalaradial was performed under biologically relevant conditions.     

Unusual sulfated marine steroids from the ophiuroid ophioderma longicaudum

Polar extracts of the ophiuroid Ophioderma longicaudun contain unusual sterol sulfates together with a mixture of common 3β-hydroxysterol sulfates. The more polar compound has been shown to be 5β-cholestane-3, 4,11β,12β,21-pentol 3,21-disulfate 1. A second group of unusual compounds are disulfated 3,21-dihydroxysteroids. After solvolysis to remove the sulfate groups they have been identified as : (20R)-5-cholestane-3, 21-diol 4a, (20R)-cholest-5-ene-3,21-diol 5a, (20R22E)-cholest-5,22-diene-3,21-diol 6a and (20R)-24-methylcholest-5,24(28)-diene-3,21-diol 7a. Analysis of the “non-sulfated” sterol fractions has shown the presence of common 3β-hydroxy sterols.