Etude par RMN d'une inversion de cycle de quelques benzodiazépinones

The NMR spectra of five benzodiazepinones are determined over a range of temperature. They indicate that the seven ring has a twist-boat shape, which inverts more or less rapidly according to the nature of substituents. The activation parameters and the rates of inversion are determined and the substituent effects are discussed.     

Evidence of secondary structure by high-resolution magic angle spinning NMR spectroscopy of a bioactive peptide bound to different solid supports.

The structure of the 19-amino acid peptide epitope, corresponding to the 141-159 sequence of capsid viral protein VP1 of foot-and-mouth disease virus (FMDV), bound to three different resins, namely, polystyrene-MBHA, PEGA, and POEPOP, has been determined by high-resolution magic angle spinning (HRMAS) NMR spectroscopy. A combination of homonuclear and heteronuclear bidimensional experiments was used for the complete peptide resonance assignment and the qualitative characterization of the peptide folding. The influence of the chemicophysical nature of the different polymers on the secondary structure of the covalently attached FMDV peptide was studied in detail. In the case of polystyrene-MBHA and polyacrylamide-PEGA resins, the analysis of the 2D spectra was hampered by missing signals and extensive overlaps, and only a propensity toward a peptide secondary structure could be derived from the assigned NOE correlations. When the FMDV peptide was linked to the polyoxyethylene-based POEPOP resin, it was found to adopt in dimethylformamide a helical conformation encompassing the C-terminal domain from residues 152 to 159. This conformation is very close to that of the free peptide previously analyzed in 2,2,2-trifluoroethanol. Our study clearly demonstrates that a regular helical structure can be adopted by a resin-bound bioactive peptide. Moreover, a change in the folding was observed when the same peptide-POEPOP conjugate was swollen in aqueous solution, displaying the same conformational features as the free peptide in water. The possibility of studying solid-supported ordered secondary structures by the HRMAS NMR technique in a wide range of solvents can be extended either to other biologically relevant peptides and proteins or to new synthetic oligomers.     

Synthese de molecules encombrees : Recherche des conditions optimales de condensation dbs composes organolithiens cage sur differents substrats organiques

La réactivité des organolithiens á structure-cage vis-à-vis de trois cétones non énolisables (hexaméthyl acétone, adamantanone et benzophénone) a été testée dans différents milieux.

L'utilisation de solvants mutes (pentane-éther ou pentane-THF) est nécessaire pour que ces réactions de condensation aient lieu, mais provoque la formation de produits secondaires d'attaque sur le solvant. L'alkylation du groupe “structure-cage”, en augmentant le caractére lipophyle de la molécule, permet de solubiliser ces organolithiens dans les hydrocarbures et de mener les condensations dans ces milieux.

Les réactions de condensations avec l'hexaméthylacétone, l'adamantanone et la benzophénone conduisent respectivement à des rendements en alcool de 72, 95 et 60%, avec le triméthyl-3,5,7 adamantyl-1 lithium dans le pentane alors qu'ils ne sont que de 40, 42 et 47%, pour l'adamantyl-1 lithium dans les solvants mixtes. Les rendements optima en produit de condensation peuvent être obtenus selon les cas par la réaction de Grignard (Two-step Reaction) ou par la synthése de Barbier (One-step Alternative Grignard Reaction). Le choix entre ces deux protocoles expérimentaux dépend essentiellement de la nature de la cage dans le dérivé halogéné.

Abstract

The reactivity of bridgehead organo-lithium compounds with three nonenolisable ketones (hexamethylacetone, adamantanone and benzophenone) has been examined in various media. The condensations require use of mixed solvents (pentane-ether or pentane-THF), but secondary products are formed by solvent-attack. The alkylation of the bridgehead structure, by increasing the lipophilicity of the molecule, makes it possible to solubilise organolithium compounds in hydrocarbons and to perform condensations therein.

Condensations with hexamethylacetone, adamantanone and benzophenone lead to alcohols in yields of 72, 95 and 60%, respectively, with 3,5,7-trimethyl-l-adamanty-lithium in pentane, but only 40, 42 and 47%, for 1-adamanty-lithium in mixed solvents. The best yields of condensation product are obtained either by the Grignard reaction (two-step reaction) or by the Barbier synthesis (one-step alternative Grignard reaction). The choice between these two methods depends essentially on the nature of the cage-radical in the halide.     

Study of longitudinal distributions in the fragmentation regions,using the quark-parton model,in K−p interactions at 70 GeV/c

The study of π^±, π⁰, K⁰ and Λ production in the fragmentation regions (|x|0.2) of K^?p interactions at 70 GeV/c shows that the x-dependence of each invariant cross section is well described by the power law (1?|x|)ⁿ suggested by the dimensional counting rule. Furthermore, pion production is found, both in K^? and proton fragmentation regions, to be very similar to their production in $\text{ν(}\text{ν}\text{)}\text{p}$ interactions as expected from quark-parton models. The quark and diquark fragmentation functions D_u^π, D_uu^π and D_ud^π are extracted from our data.     

Flexibility of solid-phase microextraction for passive sampling of atmospheric pesticides

For low volatile pesticides, the applications of solid-phase microextraction (SPME) as an air sampler were reported with sampling time chosen in the linear stage of the sorption kinetics because of long equilibrium time. In these pre-equilibrium conditions, sampling rates (SRs) expressed as the volume of air sampled by the SPME sampler per unit of time, were used to estimate analytes concentrations in air. In the present study, to achieve good extraction performance and accurate calibration, the sorption kinetics of several pesticides with SPME were investigated in detail, with a focus on parameters influencing SRs. Linear air velocity was found to be the main parameter affecting SRs. For exposed fibers, with air velocities below 20–25 cm s⁻¹, SRs increased with increasing air velocity. When linear air velocity was equal to or greater than 25–30 cm s⁻¹, it had little effect on SRs. To improve the flexibility of SPME, different configurations of SPME were compared, i.e. different lengths of fibers exposed, retracted fibers, exposed fibers with grids. SRs were linearly proportional to exposed lengths of fibers. Using grids, lower SRs and wider calibration time range were achieved. SRs for retracted fibers were the lowest among the different experimented configurations. The accuracy of calibration was improved and more flexibility of SPME was provided.     

Synthesis and structures of the first bismuth-ester complexes using heterobifunctional thiolate anchored ligands and mass spectrometric identification of ligand-bridged derivatives

The first systematic series of bismuth complexes involving ester donors, Bi(SCH(2)C(O)OCH(2)CH(3))Cl(2), Bi(SCH(2)C(O)OCH(3))(2)Cl, and Bi(SCH(2)COOCH(3))(3), has been isolated and characterized by spectroscopic (IR, Raman) and X-ray crystallographic data. In addition, these and other species have been identified by electron-impact, electrospray, and atmospheric pressure chemical ionization mass spectometry. The generally applicable synthetic methodology involves the use of heterobifunctional ligands containing a thiolate moiety as an anchor to facilitate coordinate interactions between weak donors (carbonyls) and weak acids (bismuth). The bifunctional nature of the ligands is manifested in both chelating and bridging roles. Important comparisons can be made with the pharmaceutical agent "colloidal bismuth subcitrate" (CBS). The observations allow for a new appreciation of bioactive bismuth compounds, by providing an approach to study the interaction of biorelevant functional groups with bismuth.     

Monomeric, one- and two-dimensional networks incorporating (2,6-Me2C6H3S)2Pb building blocks

The amine coordination of lead(II) has been examined through the preparation and structural analysis of Lewis base adducts of bis(thiolato)lead(II) complexes. Reaction of Pb(OAc)(2) with 2,6-dimethylbenzenethiol affords (2,6-Me(2)C(6)H(3)S)(2)Pb (6) in high yield. The solubility of 6 in organic solvents allows for the preparation of the 1:2 Lewis acid-base adduct [(2,6-Me(2)C(6)H(3)S)(2)Pb(py)(2)](7), and 1:1 adducts [(2,6-Me(2)C(6)H(3)S)(2)Pb(micro(2)-bipy)](infinity](8) and [(2,6-Me(2)C(6)H(3)S)(2)Pb(micro(2)-pyr)](infinity)(9)(where py = pyridine, bipy = 4,4'-bipyridyl and pyr = pyrazine) from reaction with an excess of the appropriate amine. In contrast to 7, reaction of (C(6)H(5)S)(2)Pb (1) with pyridine afforded the 2:1 adduct [(C(6)H(5)S)(4)Pb(2)(py)](infinity)(10). Compounds were characterized via elemental analysis, FT-IR, solution (1)H and (13)C[(1)H](6) NMR spectroscopy, and X-ray crystallography (7-10). The structures of 7-9 show the thiolate groups occupying two equatorial positions and two amine nitrogen atoms occupying axial coordination sites, yielding distorted see-saw coordination geometries, or distorted trigonal bipyramids if an equatorial lone pair on lead is considered. The absence of intermolecular contacts in 7 and 8 result in monomeric and one-dimensional polymeric structures, respectively. Weak Pb...S intermolecular contacts in 9 result in the formation of a two-dimensional macrostructure. In contrast, the structure of , shows extensive intermolecular Pb...S interactions, resulting in five- and six-coordinate bonding environments for lead(II), and a complex polymeric structure in the solid state. This demonstrates the ability of the 2,6-dimethylphenylthiolate ligand to limit intermolecular lead-sulfur interactions, while allowing the axial coordination of amine Lewis base ligands.     

Assessing the transfer of pesticides to the atmosphere during and after application. Development of a multiresidue method using adsorption on Tenax and thermal desorption-GC/MS

An air sampling and analytical method based on adsorption on porous polymer (Tenax TA) followed by automatic thermal desorption (ATD) and GC/MS analysis was developed for ten pesticides commonly used on major crops in Britanny and some of their metabolites in air (from spray drift and volatilisation transfer processes): alachlor, atrazine (and two major degradation products: deethylatrazine and deisopropylatrazine), carbofuran, cyprodinil, epoxyconazole, iprodione (and 3,5-dichloroaniline), lindane (and -HCH, its isomer), metolachlor, terbuconazole and trifluralin. This method was established with special consideration for optimal thermal desorption conditions, linear ranges, limits of detection and quantification. Moreover, collection efficiencies of Tenax TA at room temperature were examined. This method was then applied to the determination of ambient pesticide levels during the spraying season at a rural area. The method was also applied to determine the vertical gradient of alachlor concentrations on a treated maize parcel to evaluate volatilisation fluxes.