Photochemical dehydration of acetamide in a cryogenic matrix

Vacuum ultraviolet (VUV) irradiation of acetamide has been monitored by Fourier transform infrared spectroscopy in argon matrix at 10 K. Several primary photoproducts, including HNCO ratio CH(4) and CO ratio CH(3)NH(2) molecular complexes, and acetimidic acid, which is reported for the first time, were characterized. The acetimidic acid identification was based on comparison between the experimental and theoretical (B3LYP) infrared spectra. Acetimidic acid is found in argon matrix in the (s-Z)-(E) and (s-Z)-(Z) configurations. It is also an intermediate in the VUV decomposition process, its dehydration leads to the formation of CH(3)CN ratio H(2)O molecular complex. The assignment of the complex was achieved by co-depositing the pairs of respective species and by ab initio calculation.     

Indium-mediated reduction of β-aminovinyl chloro-difluoromethylated ketones in the presence of heteroaryl aldehydes: A mild entry to novel difluoromethylene enaminone derivatives

The synthesis of new β-aminovinyl chloro-difluoromethylated ketones 1 and 2 is presented. In some of them the activation of the C-Cl bond was achieved, under mild conditions, using indium powder. The corresponding difluoro-enolates were trapped with a series of aromatic and heterocyclic aldehydes, to furnish the corresponding difluoromethylene aldol products 3 and 4, in moderate to good yields. The present synthetic methodology provides a convenient approach for the preparation of novel difluoromethylene functionalized enaminone derivatives.     

Automata and logics over finitely varying functions

We extend some of the classical connections between automata and logic due to Büchi (1960) [5] and McNaughton and Papert (1971) [12] to languages of finitely varying functions or “signals”. In particular, we introduce a natural class of automata for generating finitely varying functions called ’s, and show that it coincides in terms of language definability with a natural monadic second-order logic interpreted over finitely varying functions Rabinovich (2002) [15]. We also identify a “counter-free” subclass of ’s which characterise the first-order definable languages of finitely varying functions. Our proofs mainly factor through the classical results for word languages. These results have applications in automata characterisations for continuously interpreted real-time logics like Metric Temporal Logic (MTL) Chevalier et al. (2006, 2007) [6] and [7].     

Critical contribution of nonlinear chromatography to the understanding of retention mechanism in reversed-phase liquid chromatography

The retention of most compounds in RPLC proceeds through a combination of several independent mechanisms. We review a series of recent studies made on the behavior of several commercial C18-bonded stationary phases and of the complex, mixed retention mechanisms that were observed in RPLC. These studies are essentially based on the acquisition of adsorption isotherm data, on the modeling, and on the interpretation of these data. Because linear chromatography deals only with the initial slope of the global, overall, or apparent isotherm, it is unable fully to describe the complete adsorption mechanism. It cannot even afford clues as to the existence of several overlaid retention mechanisms. More specifically, it cannot account for the consequences of the surface heterogeneity of the packing material. The acquisition of equilibrium data in a wide concentration range is required for this purpose. Frontal analysis (FA) of selected probes gives data that can be modeled into equilibrium isotherms of these probes and that can also be used to calculate their adsorption or affinity energy distribution (AED). The combination of these data, the detailed study of the best constants of the isotherm model, the determination of the influence of experimental parameters (e.g., buffer pH and pI, temperature) on the isotherm constants provide important clues regarding the heterogeneity of the adsorbent surface and the main properties of the adsorption mechanisms. The comparison of similar data obtained for the adsorption of neutral and ionizable compounds, treated with the same approach, and the investigation of the influence on the thermodynamics of phase equilibrium of the experimental conditions (temperature, average pressure, mobile phase composition, nature of the organic modifier, and, for ionizable compounds, of the ionic strength, the nature, the concentration of the buffer, and its pH) brings further information. This review provides original conclusions regarding retention mechanisms in RPLC.     

Quasi-solitonic behavior of self-written waveguides created by photopolymerization

We investigated the condition of unique self-written channel and multichannel propagation inside bulk photopolymerizable materials. Light was introduced in the medium by a single-mode optical fiber. At a very low beam power of 5 muW , a unique uniform-channel waveguide without any broadening was obtained by polymerization. When the input power is increased to 100 muW , the guide becomes chaotic and multichannel. We connected two fibers separated by a 1-cm distance. The results open the door to studies of the optical and electro-optical properties of photopolymerized guides doped by nonlinear optical chromophores and to possible applications in integrated optical devices.     

Nonlinear acoustic wave equations with fractional loss operators

Fractional derivatives are well suited to describe wave propagation in complex media. When introduced in classical wave equations, they allow a modeling of attenuation and dispersion that better describes sound propagation in biological tissues. Traditional constitutive equations from solid mechanics and heat conduction are modified using fractional derivatives. They are used to derive a nonlinear wave equation which describes attenuation and dispersion laws that match observations. This wave equation is a generalization of the Westervelt equation, and also leads to a fractional version of the Khokhlov-Zabolotskaya-Kuznetsov and Burgers' equations.     

Accurate measurements of peak variances: importance of this accuracy in the determination of the true corrected plate heights of chromatographic columns

The true efficiency of a column is derived from the differences between the variances of the peak profiles of the same compound recorded in the presence and the absence of the chromatographic column. These variances are usually derived using one of three methods: (1) the retention time of the peak apex and its half-height width; (2) the moments of the best fit between the experimental data and a hybrid response function, e.g., an exponentially convoluted Gaussian; or (3) the exact moments of the experimental band profiles. Comparisons of the results of these methods show that the first method is always inaccurate because all the band profiles recorded are strongly tailing. The peak fit method is accurate only for 4.6mm I.D. columns operated with instruments having low extra-column volume but fails for short narrow-bore columns due to the severe tailing of peaks passing through the complex channels of the extra-column volumes and to the inaccuracies in the fit of experimental data to the selected function. Although far better, the moment method may be inaccurate when the zero dead volume union used to measure the extra-column peak variances has a higher permeability than the column, causing the upstream part of the instrument to operate under comparatively low pressures.     

Self-templating polythiophene derivatives: electronic decoupling of conjugated strands through staggered packing

Whereas molecular electronics needs well-controlled 3D geometries for decoupling or interconnecting individual molecules, conjugated polymers form disordered structures when deposited on a substrate. We show that this trend can be overcome in polythiophene derivatives designed so as to exploit weak sulfur-bromine interactions. A self-template effect follows, leading to staggered organizations of well-aligned electronically decoupled conjugated strands, as observed in situ by scanning tunneling microscopy and spectroscopy on graphite.