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251.
Löble MW Casimiro M Thielemann DT Oña-Burgos P Fernández I Roesky PW Breher F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(17):5325-5334
2D (1)H,(89)Y heteronuclear shift correlation through scalar coupling has been applied to the chemical-shift determination of a set of yttrium complexes with various nuclearities. This method allowed the determination of (89)Y NMR data in a short period of time. Multinuclear NMR spectroscopy as function of temperature, PGSE NMR-diffusion experiments, heteronuclear NOE measurements, and X-ray crystallography were applied to determine the structures of [Y(5)(OH)(5)(L-Val)(4)(Ph(2)acac)(6)] (1) (Ph(2)acac=dibenzoylmethanide, L-Val=L-valine), [Y(2)(OTf)(3)] (3), and [Y(2)(4)(OTf)(5)] (5) (2: [(S)P{N(Me)N=C(H)Py}(3)], 4: [B{N(Me)N=C(H)Py}(4)](-)) in solution and in the solid state. The structures found in the solid state are retained in solution, where averaged structures were observed. NMR diffusion measurements helped us to understand the nuclearity of compounds 3 and 5 in solution. (1)H,(19)F HOESY and (19)F,(19)F EXSY data revealed that the anions are specifically located in particular regions of space, which nicely correlated with the geometries found in the X-ray structures. 相似文献
252.
Yannick Crémillieux Florent Goutailler Bruno Montcel Dominique Grand Gérard Vermeulen Pierre-Etienne Wolf 《Applied magnetic resonance》2012,43(1-2):167-180
The volume of polarized sample and the delay required between successive polarizations of samples represent serious constraints for dynamic nuclear polarization (DNP) applications. With these limitations in mind, a DNP polarizer, based on a super-wide bore (150-mm diameter) vertical magnet operating at 3.35?T, was designed. The working diameter for loading/unloading samples is equal to 46?mm and the microwave cavity can accommodate up to three samples. The cryostat can be cooled to 4.2?K in typically 2?h and filled with liquid helium in 1?h. Once filled with liquid helium, the cryostat hold time is on the order of 4?h and a minimum temperature of 1.19?K can be reached. In situ polarization levels at low temperature were measured between 5 and 10?% in single and multiple samples of 13C-labeled urea and glycine. 相似文献
253.
The first experimental osmotic equation of state is reported for well-defined magnetic colloids that interact via a dipolar hard-sphere potential. The osmotic pressures are determined from the sedimentation equilibrium concentration profiles in ultrathin capillaries using a low-velocity analytical centrifuge, which is the subject of the accompanying paper I. The pressures of the magnetic colloids, measured accurately to values as low as a few pascals, obey Van 't Hoff's law at low concentrations, whereas at increasing colloid densities non-ideality appears in the form of a negative second virial coefficient. This virial coefficient corresponds to a dipolar coupling constant that agrees with the coupling constant obtained via independent magnetization measurements. The coupling constant manifests an attractive potential of mean force that is significant but yet not quite strong enough to induce dipolar chain formation. Our results disprove van der Waals-like phase behavior of dipolar particles for reasons that are explained. 相似文献
254.
Dominique Brunet József Vass Edward R. Vrscay Zhou Wang 《Applied Mathematics Letters》2012,25(11):1921-1925
We construct metrics from the geodesics of the Structural Similarity index, an image quality assessment measure. An analytical solution is given for the simple case of zero stability constants, and the general solution involving the numerical solution of a nonlinear equation is also found. 相似文献
255.
Humbert A Plé K Harakat D Martinez A Haudrechy A 《Molecules (Basel, Switzerland)》2012,17(7):7709-7721
A key saggitamide intermediate corresponding to a rare sugar framework has been obtained. This approach should help to establish the overall configuration of more complex structures of the sagittamide family. 相似文献
256.
Brotin T Montserret R Bouchet A Cavagnat D Linares M Buffeteau T 《The Journal of organic chemistry》2012,77(2):1198-1201
Exceptionally high affinity for cesium cations was achieved in aqueous solution using two enantiopure cryptophanes. Complexation of cesium was evidenced by (133)Cs NMR spectroscopy and by electronic circular dichroism (ECD). Binding constants as high as 6 × 10(9) M(-1) have been measured by isothermal titration calorimetry (ITC). Very strong complexation of rubidium cations (K ~10(6) M(-1)) has also been measured. Chiral hosts allowed the detection of the two cations at low concentrations (μM) using ECD. 相似文献
257.
Lucrèce Matheron Séverine Clavier Oumar Diebate Philippe Karoyan Gérard Bolbach Dominique Guianvarc’h Emmanuelle Sachon 《Journal of the American Society for Mass Spectrometry》2012,23(11):1981-1990
This study aims at improving the MALDI-TOF detection of a phosphorylated peptide containing a cysteine residue by ??-elimination of H3PO4 hardly enriched by classical methods. The experimental conditions were optimized on this phosphopeptide (biot-pAdd) and its nonphosphorylated counterpart (biot-Add). The major side-reactions were H2S elimination on the cysteine residues and H2O elimination on the non phosphorylated serine residue of biot-Add. The former dilutes the MALDI-TOF signal for the desired species. The latter gives a product similar to what is obtained by H3PO4 elimination and should prompt to caution when working with a mixture between phosphorylated and non phosphorylated peptides. Modifications on the solvent, the reaction temperature and time, the nature, and concentration of the base were made. Major improvement of the selectivity of the reaction was observed in 30?% ACN, at room temperature for 4?h. However, these optimizations are specific to these sequences and should be performed anew for different peptides. The selectivity of the reaction towards H3PO4 elimination is improved, but the persistence of side-reactions renders a previous sample fractionation necessary. In these optimized conditions, the ionization enhancement is 3-fold and the detection limits for biot-pAdd are similar to biot-Add (100?fmol). 相似文献
258.
Gérard Kerkyacharian Oleg Lepski Dominique Picard 《Probability Theory and Related Fields》2001,121(2):137-170
In the framework of denoising a function depending of a multidimensional variable (for instance an image), we provide a nonparametric
procedure which constructs a pointwise kernel estimation with a local selection of the multidimensional bandwidth parameter.
Our method is a generalization of the Lepski's method of adaptation, and roughly consists in choosing the “coarsest” bandwidth
such that the estimated bias is negligible. However, this notion becomes more delicate in a multidimensional setting. We will
particularly focus on functions with inhomogeneous smoothness properties and especially providing a possible disparity of
the inhomogeneous aspect in the different directions. We show, in particular that our method is able to exactly attain the
minimax rate or to adapt to unknown degree of anisotropic smoothness up to a logarithmic factor, for a large scale of anisotropic
Besov spaces.
Received: 11 November 1999 / Revised version: 14 November 2000 / Published online: 24 July 2001 相似文献
259.
Alain ValtzChien-Bin Soo Christophe Coquelet Dominique RichonDaniel Amoros Hubert Gayet 《Fluid Phase Equilibria》2011,309(1):15-19
To simulate cyclohexane to cyclohexanol oxidation reactors, the acquisition and modeling of vapor-liquid equilibria of the key components, under the process conditions, are essential. n-Hexanoic acid is a co-product of the reaction. Vapor-liquid equilibrium data are reported for the cyclohexane + n-hexanoic acid binary system at four temperatures: 413, 423, 464 and 484 K. All measurements have been carried out using an apparatus based on the “static-analytic” method, with two ROLSI™ pneumatic capillary samplers. The generated data are successfully correlated using two equations of state, the Peng-Robinson (PR) and the Perturbed Chain Statistical Association Fluid Theory (PC-SAFT). Both models are capable of representing the experimental data, but the PC-SAFT EoS uses less binary interaction parameters. 相似文献
260.
Jacques Gilbert Dominique Rousselle Charles Gansser Claude Viel 《Journal of heterocyclic chemistry》1979,16(1):7-11
A new snythesis of 6H-pyrido[4,3-b]carbazoles is described starting from substituted cyclohexanones involving the combination of Borsche's carbazole preparation and Cranwell and Saxton's ellipticine synthesis where the starting materials are easily available. The dehydrogenation step is accomplished at an early stage. In some cases (11-desmethyl ellipticines derivatives), 7H-pyrido[3,4-c]carbazoles were also obtained. 相似文献