MS/MS in structural analysis of an oviposition-deterring pheromone

A recently characterized oviposition-deterring pheromone (ODP, structure 1) of the European cherry fruit fly was used as a test case for probing the potential of tandem mass spectrometry (MS/MS) in structure elucidation as a stand-alone technique. The glycolipid-taurinate 1 was subjected to MS/MS analyses under a variety of conditions with and without preceding chemical degradation. Acidic methanolysis of 1 and subsequent in-batch derivatization (trideuterioacetylation) yielded methyl 2,3,4,6-tetrakis-O-trideuterioacetyl-glucopyranoside (2), methyl 8,15-bis-trideuterioacetoxy-palmitate (3), and taurine (4) as suitable target compounds for direct mixture analysis.Low energy collision induced dissociation (CID) on selected precursor ions (MS/MS on [M + H – CH₃OH]⁺ and [M + H]⁺ produced by fast atom bombardment (FAB)) allowed direct identification of 2 and 4, respectively, by comparison with appropriate reference ions. In the case of 3, low energy CID (desorption chemical ionization (DCI) instead of FAB, MS/MS on [M + H]⁺) permitted deduction of gross molecular structure, but failed to provide positional detail. In sharp contrast,high energy CID of trideuterioacetylated intact 1 (FAB-MS/MS on [M – H]^– ions of la) clearly revealed a linear 8,15-hydroxylated palmitic acid backbone. Less certain was assignment of 15-O-glucosylation by this approach.     

Synthesis and characterization of maleimide polymers with pendant pyrazole groups. IV. Copolymerization of pyrazole-modified maleimides with vinyl ethers

The synthesis of maleimides that have pyrazolic or bipyrazolic pendant groups is described. Their homopolymerization and their copolymerization with 2-chloroethyl vinyl ether (CEVE) is reported. The homopolymerizations of such maleimides were performed under various conditions and led to low molecular-weight polymers. However, alternating copolymers were obtained from CEVE as comonomers whatever the monomers feed compositions. A similar behavior was also observed for maleimides that do not exhibit any spacer, whereas for bulky vinyl ethers, random copolymers were produced. A comparison of the thermal behavior between these copolymers (glass transition temperatures, T_g, and decomposition temperatures) and other copolymers having different spacers between the nitrogenated cycles and the chain are related. Thus, an important decrease of T_g, was observed when C₃H₆CO₂CH₂ groups were used as the spacer instead of methylene groups. Moreover, the thermal weakness of these copolymers may come from the substituents of the vinyl ether and is discussed. © 1994 John Wiley & Sons, Inc.     

The thioketone–enethiol tautomerism of aliphatic thiocarbonyls: An ab initio study

Approximate minimum energy reaction paths have been calculated for two thioketone–enethiol tautomeric systems using an ab initio SCF–MO method. The calculations indicate nearly equal stabil ties of the isolated tautomers in both systems and an energy barrier of ca. 85 kcal/mol for their interconversion. This barrier is expected to be significantly lower in solution as a result of solvent–solute interactions.     

Fluorescent, Siderophore-Based Chelators. Design and Synthesis of a Trispyrenyl Trishydroxamate Ligand, an Intramolecular Excimer-Forming Sensing Molecule Which Responds to Iron(III) and Gallium(III) Metal Cations

Two pyrene-labeled hydroxylamines, 5-Bn and 5-Bz, O-protected with the benzyl and the benzoyl group, respectively, have been prepared for the generation of siderophore-based new chelators incorporating both the pyrene chromophore and the hydroxamic acid functionality. 5-Bz formed the starting point toward the synthesis of the tripod-shaped trishydroxamate, 1. That trichromophoric ligand displays remarkable fluorescence emission properties (dual emission: "monomer" and excimer type) which are markedly and selectively modified by binding Fe(NO(3))(3) and Ga(NO(3))(3). Ferric ions induce a quasi total quenching of the pyrene fluorescence, whereas the nonquenching Ga(III) cations are observed to affect the value of the excimer-to-monomer fluorescence intensity ratio. Ethylenediaminetetraacetic acid (EDTA) competition reactions yielded an estimated value of 3.8 for log K of the complex LFe in methanol/water (80/20 v/v), where K = ([LFe][H(+)](3))/([LH(3)][Fe(3+)]) and L is the ligand in its totally deprotonated form. Compound 1 is the prototype of a new class of photoresponsive molecular systems which could act as sensitive probes for metal cation detection and recognition.     

Multi-technique surface characterization of bio-based films from sisal cellulose and its esters: a FE-SEM, μ-XPS and ToF-SIMS approach

Bio-based films were prepared from LiCl/DMAc solutions containing sisal cellulose esters (acetates, butyrates and hexanoates) with different degrees of substitution (DS 0.7–1.8) and solutions prepared with the cellulose esters and 20 wt% sisal cellulose. A novel approach for characterizing the surface morphology utilized field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and contact angle analysis. XPS and ToF-SIMS were a powerful combination while investigating both the ester group distribution on the surface and effects of cellulose content on the film. The surface coverage by ester aliphatic chains was estimated using XPS measurements. Fibrous structures were observed in the FE-SEM images of the cellulose and bio-based films, most likely because the sisal cellulose chains aggregated during dissolution in LiCl/DMAc. Therefore, the cellulose aggregates remained after the formation of the films and removal of the solvent. The XPS results indicated that the cellulose loading on the longer chain cellulose esters films (DS 1.8) increased the surface coverage by ester aliphatic chains (8.2 % for butyrate and 45 % for hexanoate). However, for the shortest ester chains, the surface coverage decreased (acetate, 42 %). The ToF-SIMS analyses of cellulose acetate and cellulose hexanoate films (DS 1.8) revealed that the cellulose ester groups were evenly distributed across the surface of the films.     

Ligated anionic polymerization: An innovative elf-atochem technology for the polymerization of (meth)acrylates

Admittedly performing materials, (meth)acrylic polymers, used in a wide variety of applications, are traditionally produced by radical polymerization processes. The extension of living polymerization, originally developed for dienes and vinyl-aromatics, to (meth)acrylic polymers, would be an interesting opening to a variety of products with a large scope of properties and applications. However, this method suffers from chemical and technical limitations when applied to (meth)acrylates under the usual conditions of solvent and temperature. We report how alkoxy alkoxides-based systems combined with a recent Elf Atochem process offer attractive conditions for ultra-fast anionic polymerization of (meth)acrylates at high solid content. Applications to cost effective syndiotactic poly(methyl methacrylate) and block copolymers syntheses are described.     

Carbocyclische Verbindungen aus Monosacchariden. I. Umsetzungen in der glucosereihe

Carbocyclic Compounds from Monosaccharides. 1. Transformations in the Glucose Series A method for the preparation of pentasubstituted cyclopentanes from monosaccharides is presented, involving two crucial steps, viz. the reductive fragmentation of 5-bromo-5-deoxyglucosides (such as 10, 17 and 23 , see Scheme 3) with Zn or butyl lithium yielding 5,6-dideoxy-hex-5-enoses (such as 11 and 24 , see Schemes 3 and 4), and the subsequent cyclization of these hexenoses with N-methyl- or N-(alkoxyalkyl)hydroxylamines (via the corresponding nitrones) to form cyclopentano-isoxazolidines (see Scheme 2). Thus, the glucosides 17 and 23 were converted diastereoselectively and in good yields into the cyclopentano-isoxazolidines 27 and 45 (Schemes 5 and 7), which were characterized by their transformation into various derivatives. 27 and 45 were correlated through the common derivative 62 . The configuration of the cyclization products were established by pyrolysis of the N-oxide 65 to the enol ether 67 (Scheme 10).