Résonance magnétique nucléaire du noyau 14N par Transformée de Fourier

¹⁴N-NMR. measurements using the Fourier Transform technique are presented and compared to C. W. experiments. The F. T. technique is especially advantageous for relaxation time measurements. However, since ¹⁴N-nuclei may have widely different relaxation times, it is often not possible to have optimal gain in sensitivity (as compared to C. W. measurements) in a single F. T. experiment for different ¹⁴N-nuclei contained in the same sample. Different experiments have to be performed, optimizing the spectrometer parameters for each ¹⁴N-resonance of appreciably different linewidth. The technique is applied to three different problems. ¹⁴N-relaxation in symmetrical ammonium salts is shown to arise from reorientation of the water dipoles. The use of a double spin-probe, ¹³C-¹⁴N, allows the determination of the electric field gradients in cyclic ammonium salts. The electronic distribution is especially distorted from tetrahedral symmetry in the highly strained N, N-dimethyl-aziridinium cation. Finally, electric and dynamic effects in ion pairing may be studied as shown on the case of tetrabutylammonium iodide in water and in benzene.     

沸石表面有机金属化学ZSM-5外表面上——Ge(n-C4H9)x基团的接枝及其性质研究

用气体分析及IR,NMR和元素分析等方法研究了真空系统中230℃和280℃下四丁基锗在ZSM-5沸石表面上的接枝反应,并对所得沸石的热稳定性和吸附性质进行了表征,与作者曾报道的硅胶及丝光沸石上的反应类似,四丁基锗也能与ZSM-5沸石表面上的硅羟基发生缩合反应,在其外表面或孔口生成组成为(=Si-O)xGe(n-C4H9)4-x(x=2~3)的表面有机锗化合物,在２３０℃接枝丁基锗基团不影响沸石的结构和表面积,仅改变它的孔口大小,在改性后的沸石上,Ｎ２的吸附性质没有改变,而不同分子尺寸的烃,加正已烷,２-甲基戊烷,２,３-二甲基丁烷却呈现出完全不同于起始ＺＳＭ-５沸石的择形吸附效应.     

Optimisation of wort volatile analysis by headspace solid-phase microextraction in combination with gas chromatography and mass spectrometry

The aim of this study was to create a simple, solventless technique without derivatisation in order to analyze a broad range of volatiles in beer wort. A method was developed using headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry. The procedure was optimised by selection of the appropriate fibre and optimisation of extraction temperature, extraction time, and salting-out. The detection limits were well below the actual wort concentrations of the selected volatiles, ranging from 12 ng/l for linalool to 0.53 microg/l for furfural. Moreover, the procedure showed a good linearity and was applied to the analysis of wort samples taken from a wort boiling process in an industrial brewery.     

Helical self-organization and hierarchical self-assembly of an oligoheterocyclic pyridine-pyridazine strand into extended supramolecular fibers

The synthesis and characterization of an alternating pyridine-pyridazine strand comprising thirteen heterocycles are described. Spontaneous folding into a helical secondary structure is based on a general molecular self-organization process enforced by the conformational information encoded within the primary structure of the molecular strand itself. Conformational control based on heterocyclic "helicity codons" illustrates a strategy for designing folding properties into synthetic oligomers (foldamers). Strong intermolecular interactions of the highly ordered lock-washer subunits of compound 3 results in hierarchical supramolecular self-assembly into protofibrils and fibrils. Compound 3 also forms mechanically stable two-dimensional Langmuir-Blodgett and cast thin films.     

Separation and structural analysis by 1H-NMR of the telomers of methyl methacrylate with thiophenol

The stereoselectivity of the addition step and the transfer step of the radical telomerization of methyl methacrylate with thiophenol has been studied by determining the structure and the amount of each isomer by ¹H-NMR. We found, in this case, that the addition step gave preferentially a diad r and that the transfer step gave preferentially a diad m. On the other hand, the tacticity observed for higher telomers is preferentially syndiotactic, similar to that of the poly(methyl methacrylate) prepared by radical initiation. The propagation process for radical telomerization obeys, as for the radical polymerization, Bernoulli's statistics.     

Sequencing of Oligourea Foldamers by Tandem Mass Spectrometry

This study is focused on sequence analysis of peptidomimetic helical oligoureas by means of tandem mass spectrometry, to build a basis for de novo sequencing for future high-throughput combinatorial library screening of oligourea foldamers. After the evaluation of MS/MS spectra obtained for model compounds with either MALDI or ESI sources, we found that the MALDI-TOF-TOF instrument gave more satisfactory results. MS/MS spectra of oligoureas generated by decay of singly charged precursor ions show major ion series corresponding to fragmentation across both CO-NH and N′H-CO urea bonds. Oligourea backbones fragment to produce a pattern of a, x, b, and y type fragment ions. De novo decoding of spectral information is facilitated by the occurrence of low mass reporter ions, representative of constitutive monomers, in an analogous manner to the use of immonium ions for peptide sequencing.      

An approach to channel type molecular structures. 1. Synthesis ofBouquet-shaped molecules based on an [18]-O6 polyether macrocycle

An approach to a transmembrane cation channel is described. It is based on the grafting of oxygen bearing side-chains on a macrocyclic polyether unit that constitutes the organizing core. The resulting species has a structure of overall bouquet shape. The synthesis of such a molecule . _M ⁰ ,14a is described, together with that of its analogue bearing polymethylene side-chains _M ^C ,14b. The physicochemical properties of these molecules indicate that they possess the features expected on the basis of their structure.This paper is dedicated to the memory of the late Dr C. J. Pedersen.