Synthese et application de nouveaux sulfures a chaine perfluoree

Metallation of thiols R_FC₂H₄SH followed by alkylation with iodides R′_FC₂H₄I leads either to symmetrical or to unsymmetrical sulphides R_FC₂H₄SC₂H₄R′_F (with R_F=R′_F or R_F ≠ R′_F). All compounds obtained are good solvents of gases (particularly O₂, CO, CO₂, N₂).This property allows their application as biological carriers of dissolved gases.     

Saddle‐Shaped Cyclic Indole Tetramers: 3D Electroactive Molecules

We present a joint theoretical and experimental study of a series of cyclic indole tetramers aimed at understanding the fundamental electronic properties of this 3D platform and evaluating its potential in the construction of new semiconductors. To this end, we combined absorption and Raman spectroscopy, cyclic voltammetry, and spectroelectrochemistry with DFT calculations. Our results suggest that this platform can be easily and reversibly oxidized. Additionally, it has a HOMO that matches very well with the workfunction of gold, therefore charge injection from a gold electrode is expected to occur without significant barriers. Interestingly, the cyclic tetraindoles allow for good electron delocalization in spite of their saddle‐shaped structures. The steric constraints introduced by N‐substitution significantly inhibits ring inversion of the central cyclooctatetraene unit, whereas it only barely affects the optical and electrochemical properties (a slightly higher oxidation potential and a blueshifted absorption upon alkylation are observed).     

Semidefinite programming hierarchies for constrained bilinear optimization

Mathematical Programming - We give asymptotically converging semidefinite programming hierarchies of outer bounds on bilinear programs of the form $${\mathrm {Tr}}\big [H(D\otimes E)\big ]$$ ,...     

Bioinspired Scaffolding by Supramolecular Amines Allows the Formation of One- and Two-Dimensional Silica Superstructures

Silica materials attract an increasing amount of interest in (fundamental) research, and find applications in, for example, sensing, catalysis, and drug delivery. As the properties of these (nano)materials not only depend on their chemistry but also their size, shape, and surface area, the controllable synthesis of silica is essential for tailoring the materials to specific applications. Advantageously, bioinspired routes for silica production are environmentally friendly and straightforward since the formation process is spontaneous and proceeds under mild conditions. These strategies mostly employ amine-bearing phosphorylated (bio)polymers. In this work, we expand this principle to supramolecular polymers based on the water-soluble cationic cyanine dye Pinacyanol acetate. Upon assembly in water, these dye molecules form large, polyaminated, supramolecular fibers. The surfaces of these fibers can be used as a scaffold for the condensation of silicic acid. Control over the ionic strength, dye concentration, and silicic acid saturation yielded silica fibers with a diameter of 25 nm and a single, 4 nm pore. Unexpectedly, other unusual superstructures, namely, nummulites and spherulites, are also observed depending on the ionic strength and dye concentration. Transmission and scanning electron microscopy (TEM and SEM) showed that these superstructures are formed by aligned silica fibers. Close examination of the dye scaffold prior silicification using small-angle X-ray scattering (SAXS), and UV/Vis spectroscopy revealed minor influence of the ionic strength and dye concentration on the morphology of the supramolecular scaffold. Total internal reflection fluorescence (TIRF) during silicification unraveled that if the reaction is kept under static conditions, only silica fibers are obtained. Experiments performed on the dye scaffold and silica superstructures evidenced that the marked structural diversity originates from the arrangement of silica/dye fibers. Under these mild conditions, external force fields can profoundly influence the morphology of the produced silica.     

Transition metal complexes with pyrazole-based ligands. Part 28. Synthesis,structural, DFT and thermal studies of cadmium(II) halides and zinc(II) chloride complexes with 3,5-dimethylpyrazole-1-carboxamidine

The complex formation of 3,5-dimethylpyrazole-1-carboxamidinium nitrate, HL·HNO₃ with ammine complexes of cadmium(II) halides (Cl, Br, I) and zinc(II) chloride has been investigated under self-controlled reaction conditions. The complexes have been characterized by X-ray diffraction, FT-IR spectroscopy, thermal analysis and quantum chemical calculations. In the case of cadmium bromide and iodide salts, isostructural complexes with composition of [CdX₂(HL)₂] were formed. With CdCl₂ a binuclear octahedral [Cd₂(HL)₄(μ-Cl)₂](NO₃)₂ complex is obtained. Zinc(II) chloride with HL·HNO₃ gives [Zn(HL)₂Cl]NO₃, the zinc center exhibiting severely distorted five-coordinate stereochemistry, intermediate between an ideal trigonal bipyramid and a square pyramid. The course of complex formation as well as the thermal properties of the compounds has been explained using the HSAB principle. The assignment of the FT-IR spectra was supported by DFT computations.     

A fast, simple, and reliable hydrophilic interaction liquid chromatography method for the determination of ascorbic and isoascorbic acids

A reliable method for the determination of total vitamin C must be able to resolve ascorbic acid (AA) and the epimeric isoascorbic acid (IAA) and determine the sum of AA and its oxidized form dehydroascorbic acid. AA and IAA are polar molecules with a low retention time in conventional reversed phase systems, and hence of difficult resolution. Hydrophilic interaction chromatography using a TSKgel Amide-80 stationary phase with isocratic elution was successful in resolving the two epimers. The column was compatible with injections of high concentrations of metaphosphoric acid, tris(2-carboxyethyl)-phosphine, and EDTA without drift of baseline and retention time. Total AA and IAA were extracted, stabilized, and reduced in one step at 40 °C, using 5% m-phosphoric acid, 2 mM of EDTA, and 2 mM of tris(2-carboxyethyl)-phosphine as reducing agent. This simple, fast, and robust hydrophilic interaction chromatography-DAD method was applied for the analysis of food products namely fruit juices, chestnut, and ham and also in pharmaceutical and multivitamin tablets. Method validation was performed on the food products, including parameters of precision, accuracy, linearity, limit of detection, and quantification (LOQ). The absence of matrix interferences was assessed by the standard addition method and Youden calibration. The method was fast, accurate, and precise with a LOQ_AA of 1.5 mg/L and LOQ_IAA of 3.7 mg/L. The simple experimental procedure, completed in 1 h, the possibility of using IAA as an internal standard, and low probability of artifacts are the major advantages of the proposed method for the routine determination of these compounds in a large number of samples.     

Hydrothermal Synthesis,Crystal Structures and Effect of Non Bonding Interactions in Crystal Packing of Two Mixed‐Ligand Metal Complexes with Glycolato and 2,2′‐Dipiridylamine and with Benzilato and Imidazole

Two new mixed‐ligand complexes [Fe(HG)₂(dipyam)] ( 1 ) (HG = glycolato and dipyam = 2,2′‐dipyridylamine) and [Cu(HB)₂(im)₂]·2H₂O ( 2 ) (HB = benzilato and im = imidazole) have been hydrothermally synthesized and structurally characterised by X‐ray diffraction. In both cases the metallic centre is in an octahedral environment, strongly distorted in 2 (4+2 coordination). The α‐hydroxycarboxylato ligands (glycolato or benzilato) present different coordinative behaviour, bidentade chelate through the hydroxyl oxygen and one carboxy oxygen in 1 and through the two oxygen atoms of the carboxylate group in 2 . The complexes are extended into 2D frameworks through hydrogen bonding and π···π or C‐H···π interactions. The complexes were also characterized by elemental analysis, FT‐IR and UV‐vis spectroscopy and room temperature magnetic measurements.     

Crystallographic report: Bis(2‐diphenylglycolato‐O)bis(1,10‐phenanthroline‐N,N′)zinc(II), [Zn(C14H11O3)2(C12H8N2)2]

The structure of [Zn(HB)₂(1,10‐phen)₂] (HB = diphenylglycolato) comprises mononuclear molecules with the zinc(II) cation situated on a two fold axis and octahedrally coordinated by an N₄O₂ donor set. Copyright © 2004 John Wiley & Sons, Ltd.     

Structure of partially premixed n-heptane–air counterflow flames

To avoid the complexities associated with the droplet/vapor transport and nonuniform evaporation processes, a fundamental investigation of liquid fuel combustion in idealized configurations is very useful. An experimental–computational investigation of prevaporized n-heptane nonpremixed and partially premixed flames established in a counterflow burner is described. There is a general agreement between various facets of our nonpremixed flame measurements and the literature data. The partially premixed flames are characterized by a double flame structure. This becomes more distinct as the strain rate decreases and partial premixing increases, which also increases the separation distance between the two reaction zones. The peak partially premixed flame temperature increases with increasing premixing of the fuel stream. The peak CO₂ and H₂O concentrations are relatively insensitive to partial premixing. The CO and H₂ peak concentrations on the premixed side increase as the fuel-side equivalence ratio decreases. These species are transported to the nonpremixed reaction zone where they oxidize. The C₂ species have peaks in the premixed reaction zone. The concentrations of olefins are ten times larger than those of the corresponding paraffins. The oxidizer is present in partially premixed flames throughout the combustion system and there are no regions characterized by simultaneous high temperature and high fuel concentration. As a result, pyrolysis reactions leading to soot formation are greatly diminished.