Investigation of NH–π (Ph) interaction in the 1:1[α:α-N-amino]mers using 1H NMR and FTIR absorption spectroscopy

¹H NMR and FTIR experiments performed on the 1:1[α:α-N-amino]mers series let us to point out a rare NH–π interaction between the carbamidic NH of the i residue and the phenyl group of a phenylalanine residue located at i+2.     

Critical Evaluation of Kinetic Method Measurements: Possible Origins of Nonlinear Effects

The kinetic method is a widely used approach for the determination of thermochemical data such as proton affinities (PA) and gas-phase acidities (ΔH° _acid ). These data are easily obtained from decompositions of noncovalent heterodimers if care is taken in the choice of the method, references used, and experimental conditions. Previously, several papers have focused on theoretical considerations concerning the nature of the references. Few investigations have been devoted to conditions required to validate the quality of the experimental results. In the present work, we are interested in rationalizing the origin of nonlinear effects that can be obtained with the kinetic method. It is shown that such deviations result from intrinsic properties of the systems investigated but can also be enhanced by artifacts resulting from experimental issues. Overall, it is shown that orthogonal distance regression (ODR) analysis of kinetic method data provides the optimum way of acquiring accurate thermodynamic information.      

Stereospecific Synthesis and Acylation of cis 1-Halo 2-Trimethylsilyl Ethylenes

Several routes to 1-halo 2-trimethylsilyl ethylenes have been previously proposed ^1-6: from ethyn7yltrimethylilane (addition of HBr^1,2), ethyltrichlorosilane (addition H by C1, followed by dehydrohalogenation and further methylation of th Si-C1 bonds)³ or by other ways ^4,5, especially by reaction of (2-trimethylsilyl) vinyl lithium with dibromoethane⁶.     

The refocused INADEQUATE MAS NMR experiment in multiple spin-systems: interpreting observed correlation peaks and optimising lineshapes

The robustness of the refocused INADEQUATE MAS NMR pulse sequence for probing through-bond connectivities has been demonstrated in a large range of solid-state applications. This pulse sequence nevertheless suffers from artifacts when applied to multispin systems, e.g. uniformly labeled (13)C solids, which distort the lineshapes and can potentially result in misleading correlation peaks. In this paper, we present a detailed account that combines product-operator analysis, numerical simulations and experiments of the behavior of a three-spin system during the refocused INADEQUATE pulse sequence. The origin of undesired anti-phase contributions to the spectral lineshapes are described, and we show that they do not interfere with the observation of long-range correlations (e.g. two-bond (13)C-(13)C correlations). The suppression of undesired contributions to the refocused INADEQUATE spectra is shown to require the removal of zero-quantum coherences within a z-filter. A method is proposed to eliminate zero-quantum coherences through dephasing by heteronuclear dipolar couplings, which leads to pure in-phase spectra.     

The sense of smell,its signalling pathways,and the dichotomy of cilia and microvilli in olfactory sensory cells

Smell is often regarded as an ancillary perception in primates, who seem so dominated by their sense of vision. In this paper, we will portray some aspects of the significance of olfaction to human life and speculate on what evolutionary factors contribute to keeping it alive. We then outline the functional architecture of olfactory sensory neurons and their signal transduction pathways, which are the primary detectors that render olfactory perception possible. Throughout the phylogenetic tree, olfactory neurons, at their apical tip, are either decorated with cilia or with microvilli. The significance of this dichotomy is unknown. It is generally assumed that mammalian olfactory neurons are of the ciliary type only. The existence of so-called olfactory microvillar cells in mammals, however, is well documented, but their nature remains unclear and their function orphaned. This paper discusses the possibility, that in the main olfactory epithelium of mammals ciliated and microvillar sensory cells exist concurrently. We review evidence related to this hypothesis and ask, what function olfactory microvillar cells might have and what signalling mechanisms they use.     

Analytic modeling of the angular sensitivity function and modulation transfer function of ultrathin multichannel imaging systems

We propose what we believe to be a novel, refined model of the angular sensitivity function of artificial apposition compound eyes. Compared with the formerly used Gaussian approximation that was derived for natural compound eyes, our model is better suited to describe the resolution capacity of artificial compound eyes accounting for the cylindrical sensitivity function of technical receptors. It is shown that this analytic model is valid over a broad range of parameters of the optical system, which was not fulfilled by one of the previous models. Finally, an analytic approach is used to derive the modulation transfer function of these multichannel imaging systems.     

Reactive polymers incorporating silyl enol ether groups. I. synthesis by radical polymerization of 2-(trimethylsiloxy)-butadiene and 2-(tert)-butyldimethylsiloxy butadiene

2-(Trimethylsiloxy)butadiene (TMSBD) and 2-(tert-butyldimethylsiloxy)butadiene (TBMSBD) were copolymerized with styrene (St) and methyl methacrylate (MMA) under free-radical conditions. The obtained polymers were found to contain reactive silyl enol ether groups in a ratio identical to the TMSBD or TBMSBD molar fraction in the copolymer. All investigated samples displayed only 1,4- and 3,4-microstructures. The influence of several experimental factors on the yields, rates of polymerization, microstructures, and copolymer compositions were examined. Monomer reactivity ratios r₁ and r₂ at 60°C were determined from copolymer composition curves at low conversions. The homopolymerization of TBMSBD was also investigated and results were compared with those previously obtained for TMSBD. A slight increase in rates was observed and was rationalized on the basis of the higher viscosity resulting from the structural change in the monomer. Thermal stabilities of the synthesized polymers were investigated by TGA and their glass transition temperatures were determined by DSC. All measurements are compatible with a possible use of TMSBD and TBMSBD copolymers as reactive polymers. © 1996 John Wiley & Sons, Inc.     

GC-MS headspace analysis of the volatile components of soya oil without heating the sample

The analysis of volatile compounds, and particularly of certain hydrocarbons, e.g. pentane, and some aldehydes, e.g. hexanal, has been used to estimate the degree of oxidation of vegetable oil. We have tested a dynamic headspace technique without heating the sample during the purge time of the analysis. Some tests have been performed after heating the sample at 180°C for a specified time before the analysis, to compare the results of analysis with and without heating. The best results were obtained at room temperature.     

Estimation of the surface energetic heterogeneity of fillers by inverse gas chromatography

The surface properties of the fillers are determining for obtaining high performance filled polymers. Yet, their determination is most difficult. This paper proposes to use inverse gas chromatography, either at infinite dilution or finite concentration conditions, to estimate surface energy and nanomorphological characteristics, but also surface heterogeneity of different clays, talcs of various origins and ground muscovites.