Absolute rate constants for some intermolecular reactions of alpha-aminoalkylperoxyl radicals. Comparison with alkylperoxyls

Seven alpha-aminoalkylperoxyl radicals have been generated by 355 nm laser flash photolysis (LFP) of oxygen-saturated di-tert-butyl peroxide containing mono-, di-, and trialkylamines and a dialkylarylamine. All these peroxyls possess absorptions in the near-UV (strongest for the trialkylamine-derived peroxyls) which permits direct monitoring of the kinetics of their reactions with many substrates. The measured rate constants for hydrogen atom abstraction from some phenols and oxygen atom transfer to triphenylphosphine demonstrated that all seven alpha-aminoalkylperoxyls have similar reactivities toward each specific substrate. More importantly, a comparison with literature data for alkylperoxyls shows that alpha-aminoalkylperoxyls and these alkylperoxyls have essentially the same reactivities. The combination of LFP and alkylamines provides a quick, reliable method for determining absolute rate constants for alkylperoxyl radical reactions, an otherwise laborious task.     

Super-resolution and Raman chemical imaging: from multiple low resolution images to a high resolution image

Imaging in Raman spectroscopy is a valuable tool for analytical chemistry. Although molecular characterization at micron level is achieved for many applications, it usually fails producing chemical images of micron size samples as expected in chemical, environmental and biological analysis. The aim of the work is to introduce the potential of super-resolution in vibrational spectroscopic imaging. This original chemometrics approach uses several low resolution images of the same sample in order to retrieve a higher resolution chemical image. It is thus possible to overcome in a certain way some physical and instrumentals limitations. To illustrate the methodology, sub-micronic details of a Si/Au sample are retrieved from low resolution images with different super-resolution algorithms. The better results are obtained with Iterative L2/Bilateral Total Variation regularization method. The use of a regularization procedure gives also better results since its first property is to preserve edges during the reconstruction of the super-resolved image. This concept of chemical image data processing should open new analytical opportunities.     

Nanostructured poly(urethane)s and poly(urethane-urea)s from reactive solutions of poly[styrene-b-butadiene-b-(methyl methacrylate)]-triblock copolymers

Poly[Styrene-b-Butadiene-b-(Methyl Methacrylate)], SBM triblock copolymers have been incorporated in different polyurethane, PU formulations in order to prepare nanostructured materials. Macrodiols used for PU synthesis were based on a central bis-phenol A, BPA unit with two hydroxyl-terminated oligo(oxypropylene), BPA-PO_x or oligo(oxyethylene), BPA-EO chains with varying lengths. The initial solubility of the three blocks and the rheological behavior of the solutions in macrodiols and also in two diisocyanates, isophorone diisocyanate, IPDI, and 1,3-xylylene diisocyanate, XDI have been first characterized. The PMMA block is the most soluble and its role during the reaction is to stabilize the initial nanostructure or to control the reaction-induced microphase separation.Block copolymers can be dissolved first in the macrodiol, or preferably in the diisocyanate. With BPA-PO_x and low SBM content (<10 wt%), transparent linear or crosslinked PU with well dispersed triblock nanoparticles have been prepared, depending on the molar mass of the macrodiol and on the concentration of diblock SB impurities present in the triblock. For high SBM concentrations (>50 wt%), a twin screw extruder had to be used for the blending. Under well-defined conditions, transparent linear PUs and linear segmented polyurethane-ureas have been prepared.This study confirms that for designing a nanostructured material from a reactive mixture with a triblock additive, one block, called “the nanostructuring block” has to remain soluble up to the end of the reaction.     

Reversible core-interconversion of an iron(III) dihydroxo bridged complex

Complexes [Fe(Hhbi)(2)(NO(3))].2EtOH (1.2EtOH) and [Fe(2)(mu-OH)(2)(Hhbi)(4)].2H(2)O.8EtOH (2.2H(2)O.8EtOH) crystallize in the orthorhombic Fdd2 and P4(2)2(1)2 space groups, respectively (Hhbi(-) = the monoanion of 2-(2'-hydroxyphenyl benzimidazole). Complex 1 exhibits paramagnetic relaxation as evidenced by Mossbauer spectroscopy, and significant axial zero-field splitting (1.5 cm(1) 相似文献   

Reaction of iminopropadienones with amines--formation of zwitterionic intermediates, ketenes, and ketenimines

Five aryliminopropadienones 4a- d have been synthesized by flash vacuum thermolysis (FVT) by using two different precursors in each case. These compounds were deposited at 50 K at a pressure of ca. 10(-6) mbar together with three different nucleophiles, namely, trimethylamine (TMA), dimethylamine (DMA), and diethylamine (DEA), in order to study their reactions as neat solids during warm-up by FTIR spectroscopy. The reaction with TMA showed that a zwitterionic species (5 and/or 6) was formed in all the cases. With DMA and DEA, an alpha-oxoketenimine and/or an imidoylketene (7 and 8 or 9 and 10) was formed as the final product. In addition, several bands were observed, which can be assigned to zwitterionic intermediates (11 or 12). Optimized structures and vibrational spectra for all products were calculated at the B3LYP/6-31G(d) level of theory by using the polarizable continuum model (epsilon = 5).     

Experimental and theoretical investigation of HC5N adsorption on amorphous ice surface: simulation of the interstellar chemistry

HC 5N adsorbed on amorphous water ice at 10 K presents an interaction with the ice surface and induces the restructuring of the ice amorphous bulk. Warming up the sample induces the HC 5N desorption from the H 2O ice film, between 120 and 160 K, and the associated desorption energy is 90 kJ/mol. This value is in good agreement with that calculated E d (80 kJ/mol) and gives evidence that the amorphous ice surface is essentially dynamic. From theoretical calculations, it is shown that the HC 5N moiety presents a curvature and is no more linear and stabilized by two strong N...H bonds (2.09 and 2.29 A) and one H...O bond (1.84 A).     

Breaking of ketene bonds during HCl addition to trimethylsilylketene

IR spectroscopy is coupled with the matrix isolation technique to study the reaction of trimethylsilylketene with HCl. From 50 K trimethylsilylketene reacts with hydrogen chloride, leading to the cleavage of the Si-C bond and the formation of trimethylsilyl chloride and acetyl chloride, through intermediate trimethylsilylacetyl chloride which was identified. A reaction profile for this result is proposed based on a theoretical study carried out at the DFT level.     

The first example of a hetero-tetranuclear [(VO)Gd](2) complex: synthesis, crystal structure and magnetic properties of [VOLGd(hfa)(2)CH(3)OH](2).2CH(3)OH.2(CH(3))(2)CO

A cyclic tetranuclear [V(IV)O-Gd(III)](2) complex with VO and Gd ions alternately arrayed, behaves, from the magnetic point of view, as two independent dinuclear entities each having a S= 4 ground state, as a consequence of an active and ferromagnetic VO-Gd interaction through the double phenoxo bridge and a magnetically inactive VO-Gd interaction through the amide bridge.     

Sur l'équation fonctionnelle ∫T(ψ(t+s)−ψ(s))3ds=sint

Clearly the equation given in the title has no solution in $C^{\alpha }$, $\alpha >\frac{1}{3}$. We give an explicit solution in $C^{1/3}$. The motivation for this question, and other questions of the same type, comes from the forthcoming article by H. Brezis. To cite this article: J.-P. Kahane, C. R. Acad. Sci. Paris, Ser. I 341 (2005).