Heterocyclisation de diols βγ′-alleniques.

The silver nitrate assisted cyclization of the entitled diols $\text{3}$ leads, depending on the substitution of the allenic linkage, specifically to dihydropyranes $\text{4}$, when R is alkyl or to an equimolecular mixture of $\text{4}$ and its tetrahydrofuranyl isomer $\text{5}$ when R is hydrogen.     

Plant drug analysis by planar chromatography

Optimal performance laminar chromatography and automated multiple development chromatography are relatively recent techniques of planar chromatography that can be applied with success in plant material analysis. Therefore, these methods are used to study plant extracts and constituents belonging to different chemical classes of secondary metabolism: heterocyclic oxygen compounds (coumarins, flavonoids, and anthocyanins), alkaloids and quaternary ammonium salts, cannabinoids, essential oils, ginsenosides, and cardiac heterosides. Generally, the results obtained with these methods are good, and in most cases they compare with those of thin-layer chromatography.     

THE REACTION BETWEEN SUPEROXIDE ANION AND HYDROGEN PEROXIDE

Abstract— In order to obtain a better understanding of the kinetics of the Haber-Weiss reaction

often proposed as a source of OH radicals, we have measured the decomposition rate of H₂O₂ in aqueous solutions by y rays and for different pH values. This decomposition proceeds by a chain reaction involving the preceding one as the propagating step.
The rate constant found is to be
     

Structural basis for thrombin activation of a protease-activated receptor: inhibition of intramolecular liganding

Protease-activated G protein-coupled receptors (PAR1-4) are tethered-ligand receptors that are activated by proteolytic cleavage of the extracellular domain (exodomain) of the receptor. PAR1, the prototypic member of the PAR family, is the high-affinity thrombin receptor of platelets and vascular endothelium and plays a critical role in blood coagulation, thrombosis, and inflammation. Here, we describe the solution structure of the thrombin-cleaved exodomain of PAR1. The side chains of a hydrophobic hirudin-like (Hir) sequence and adjacent anionic motif project into solution. Docking of the exodomain Hir sequence to exosite I of thrombin reveals that the tethered ligand in the cleaved exodomain bends away from thrombin, leaving its active site available to another large macromolecular substrate. The N-terminal ligand is longer than anticipated and forms an intramolecular complex with a region located in the C terminus of the exodomain. Mutational analysis confirmed that this C-terminal region is a ligand binding site for both intra- and intermolecular ligands. A lipidated-ligand binding site peptide was found to be an effective inhibitor of thrombin-induced platelet aggregation.     

Kinetics of solvolysis of 1-acetyl-4-(1-ethoxycarbonyl-1-cyano) methylene-1,4-dihydroquinoline in undried DMSO-d6· formation of Acetic Anhydride as an intermediate

The kinetics of solvolysis of the title compound (QAc) in undried DMSO-d₆ to give 4-(1-ethoxycarbonyl-1-cyano)methylquinoline (QH) and HOAc at ambient temperature were investigated by ¹H nmr spectrometry. With a limited excess of water the solvolysis follows a three-step process of $ {\rm QAc} + {\rm H}_2 {\rm O}\mathop \to \limits^{k_1} {\rm QH} + {\rm HOAc}, $ , and $ {\rm Ac}_{\rm 2} {\rm O} + {\rm H}_2 {\rm O}\mathop \to \limits^{k_3} {\rm 2\,HOAc}, $ where k₂ > k₁ and k₃ < k₁. Addition of pyridine-d₅ to the reaction mixture markedly catalyzes the overall solvolysis, while addition of CF₃CO₂D to the reaction mixture simplifies the kinetics to pseudo first-order in [QAc] with k = 4.3 × 10^?3 min^?1.     

Investigation of U(VI) extraction with calixarene: Application to analysis of urine sample

A macrocyclic molecule, the calix[6]arene 4₆, functionalized with carboxy groups, has been studied and its extraction efficiency towards uranium determined in a two phases solvent-extraction system. Two solvents, dichloromethane and benzene were used to follow uranium extraction from media containing sodium ions. The study of the extraction parameters allowed proposing an extraction scheme with each solvent. The extraction efficiency was found to increase with pH, with an optimal efficiency of nearly 100%. No decrease of uranium extraction was observed in synthetic solutions containing sodium ions (spiked with²²Na) and/or²³⁹Pu. Under specific conditions, almost 100% of uranium have been extracted by the calixarene from real urine samples.     

Titanates de cuivre substitués à structure bixbyite: Les composés Cu1−xTi1−xFe2xO3 (0.15 ≤ x ≤ 0.33)

A new bixbyite family, Cu_1?xTi_1?xFe_2xO₃ (0.15 ≤ x ≤ 0.33) has been synthesized and characterized. The unit cell is cubic: a ～ 9.40Å. The X-ray powder diffraction study shows up an isotypism with the (Fe, Mn)₂O₃ compounds. There is a disordered distribution of Cu^II, Ti^IV, and Fe^III over the two cyrstallographic sites: P_I and P_II. P_II is highly distorted (two long MO distances) by the Jahn-Teller effect of Cu^II. The bixbyite structure is described in terms of polyhedra arrangement, as a particular case of the CM₂O₃ family. The cation packing is discussed in relation with the existence of the bixbyite structure for the Cu_1?xTi_1?xFe_2xO₃ compounds. The electrical properties (σ ～ 10^?5(Ω cm)^?1 for x = 0.286 at room temperature) show an electron conduction with probably a hopping mechanism.     

The effect of pyridinecarboxylate chelating groups on the stability and electronic relaxation of gadolinium complexes

The ligand N,N'-bis[(6-carboxy-2-pyridylmethyl]ethylenediamine-N,N'-diacetic acid (H(4)bpeda) was synthesised using an improved procedure which requires a reduced number of steps and leads to a higher yield with respect to the published procedure. It was obtained in three steps from diethylpyridine-2,6-dicarboxylate and commercially available ethylenediamine-N,N[prime or minute]-diacetic acid with a total yield of approximately 20%. The crystal structure of the hexa-protonated form of the ligand which was determined by X-ray diffraction shows that the four carboxylates and the two amines are protonated. The crystal structure of the polynuclear complex [Gd(bpeda)(H(2)O)(2)](3)[Gd(H(2)O)(6)](2)Cl(3)(2), isolated by slow evaporation of a 1:1 mixture of GdCl(3) and H(4)bpeda at pH approximately 1, was determined by X-ray diffraction. In complex three [Gd(bpeda)(H(2)O)(2)] units, containing a Gd(III) ion ten-coordinated by the octadentate bpeda and two water molecules, are connected in a pentametallic structure by two hexa-aquo Gd(3+) cations through four carboxylato bridges. The protonation constants (pK(a1)= 2.9(1), pK(a2)= 3.5(1), pK(a3)= 5.2(2), and pK(a4)= 8.5(1)) and the stability constants of the complexes formed between Gd(III) and Ca(II) ions and H(4)bpeda (log beta(GdL)= 15.1(3); log beta(CaL)= 9.4(1)) were determined by potentiometric titration. The unexpected decrease in the stability of the gadolinium complex and of the calcium complex of the octadentate ligand bpeda(4-) with respect to the hexadentate ligand edta(4-) has been interpreted in terms of an overall lower contribution to stability of the metal-nitrogen interactions. The EPR spectra display very broad lines (apparent DeltaH(pp) approximately 800-1200 G at X-band and 90-110 G at Q-band depending on the temperature), indicating a rapid transverse electron spin relaxation. At X-band, Gd(bpeda) is among the fastest relaxing Gd(3+) complexes to date suggesting that the presence of pyridinecarboxylate chelating groups in itself does not lead to slow electron relaxation.     

Mass spectra of C-nucleosides II. An unusual fragmentation reaction of the heterocyclic moiety of pyrazomycin and some closely related compounds

The mass spectrum of pyrazomycin has been obtained and reveals a fragmentation pattern with several important peaks which are not normally found in the mass spectra of C-nucleosides. It has now been established, using model compounds, that these unusual fragment ions are a direct result of the juxtaposition of the exocyclic hydroxy and carboxamido groups of the aglycon. It appears that a facile elimination of ammonia and ethanol from o-hydroxycarboxamides and o-hydroxyethylesters, respectively, may be a general fragmentation reaction for aromatic heterocycles. A mass spectrum of the TMS derivative of pyrazomycin has also been obtained and factors which may result in exceptions to the empirical B+30 (M-103) rule for C-nucleosides are discussed.     

Phénylhalogénohydrodigermanes

The symmetric and unsymmetric phenylchlorohydrodigermanes can be isolated or characterized via partial halogenation of the Ge? H bonds of the symmetrical phenylhydrodigermanes Ph₂(H)GeGe(H)₂Ph, Ph(H)₂GeGe(H)₂Ph by chloromethyl methyl ether and carbontetrachloride. Some of these phenylchlorohydrodigermanes are formed by insertion of phenylchlorogermylene (PhGeCl) on the Ge? H or Ge? Cl bonds of the phenylchlorohydrogermanes. The hydrolysis of the monochloro phenylhydrodigermanes Ph₂(Cl)GeGe(H)₂ and Ph(Cl)(H)GeGe(H)₂Ph leads to the phenyl phenylhydrogermyl digermoxanes [Ph₂(H)GeGePh₂]₂O and [Ph(H)₂GeGe(H)Ph]₂O. Treatment of these oxides with the concentrated aqueous solutions of hydracides leads to the monofluorinated, brominated and iodinated phenylhydrodigermanes Ph₂(H)GeGe(X)Ph₂ and Ph(H)₂GeGe(H)(X)Ph (X) = F, Br, I). Phenylchlorohydrodigermanes decompose thermally by α-elimination on one germanium atom with formation of germylene and phenylchlorohydrogermane. The physico-chemical IR. and NMR. study of these phenylhalogenohydrodigermanes indicates that, if the vGe? H frequency variations are mostly linked to the inductive effects of the substituents on the same germanium, the variations of the chemical shifts of the Ge? H protons seem to be due to many factors and especially to the inductive effect of the substituents on the germanium and the magnetic anisotropy of the Ge? X bonds.