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31.
Caravan P Parigi G Chasse JM Cloutier NJ Ellison JJ Lauffer RB Luchinat C McDermid SA Spiller M McMurry TJ 《Inorganic chemistry》2007,46(16):6632-6639
The amphiphilic gadolinium complex MS-325 ((trisodium-{(2-(R)-[(4,4-diphenylcyclohexyl) phosphonooxymethyl] diethylenetriaminepentaacetato) (aquo)gadolinium(III)}) is a contrast agent for magnetic resonance angiography (MRA). MS-325 consists of two slowly interconverting diastereoisomers, A and B (65:35 ratio), which can be isolated at pH > 8.5 (TyeklAr, Z.; Dunham, S. U.; Midelfort, K.; Scott, D. M.; Sajiki, H.; Ong, K.; Lauffer, R. B.; Caravan, P.; McMurry, T. J. Inorg. Chem. 2007, 46, 6621-6631). MS-325 binds to human serum albumin (HSA) in plasma resulting in an extended plasma half-life, retention of the agent within the blood compartment, and an increased relaxation rate of water protons in plasma. Under physiological conditions (37 degrees C, pH 7.4, phosphate buffered saline (PBS), 4.5% HSA, 0.05 mM complex), there is no statistical difference in HSA affinity or relaxivity between the two isomers (A 88.6 +/- 0.6% bound, r1 = 42.0 +/- 1.0 mM(-1) s(-1) at 20 MHz; B 90.2 +/- 0.6% bound, r1 = 38.3 +/- 1.0 mM(-1) s(-1) at 20 MHz; errors represent 1 standard deviation). At lower temperatures, isomer A has a higher relaxivity than isomer B. The water exchange rates in the absence of HSA at 298 K, kA298 = 5.9 +/- 2.8 x 10(6) s(-1), kB298 = 3.2 +/- 1.8 x 10(6) s(-1), and heats of activation, DeltaHA = 56 +/- 8 kJ/mol, DeltaHB = 59 +/- 11 kJ/mol, were determined by variable-temperature 17O NMR at 7.05 T. Proton nuclear magnetic relaxation dispersion (NMRD) profiles were recorded over the frequency range of 0.01-50 MHz at 5, 15, 25, and 35 degrees C in a 4.5% HSA in PBS solution for each isomer (0.1 mM). Differences in the relaxivity in HSA between the two isomers could be attributed to the differing water exchange rates. 相似文献
32.
Dufour A Girods P Masson E Normand S Rogaume Y Zoulalian A 《Journal of chromatography. A》2007,1164(1-2):240-247
Two methods for the sampling and analysis of tar produced from wood pyrolysis were compared. The first method used a conventional cold-trapping technique in solvent-filled impingers followed by liquid injection. The second one is a new application of multibed solid-phase adsorbent (SPA) tubes followed by thermal desorption (TD). Both methods are based on gas chromatography (GC) coupled with mass spectrometry (MS). Quantification was performed with a well reproducible GC-MS method with three internal deuterated standards. The SPA/TD method offers several advantages. No solvent is required, the detection levels are improved, and gas chromatography separation is easier. Moreover, sampling time is reduced from about 1h (for the conventional cold-trapping technique in impingers) to a few seconds. No discrimination was observed between the two sampling methods for the 10 quantified compounds (aromatic compounds from benzene to phenanthrene and phenols) except for benzene. 相似文献
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35.
Dr. Adrien T. Normand Dr. Quentin Bonnin Dr. Stéphane Brandès Dr. Philippe Richard Prof. Paul Fleurat-Lessard Dr. Charles H. Devillers Cédric Balan Prof. Pierre Le Gendre Dr. Gerald Kehr Prof. Gerhard Erker 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(11):2803-2815
Tame d0 phosphidotitanocene cations stabilized with a pendant tertiary phosphane arm are reported. These compounds were obtained by one-electron oxidation of d1 precursors with [Cp2Fe][BPh4]. The electronic structure of these compounds was studied experimentally (EPR, UV/Vis, and NMR spectroscopy, X-ray diffraction analysis) and through DFT calculations. The theoretical analysis of the bonding situation by using the electron localization function (ELF) shows the presence of π-interactions between the phosphido ligand and Ti in the d0 complexes, whereas dπ–pπ repulsion prevents such interactions in the d1 complexes. In addition, CH–π interactions were observed in several complexes, both in solution and in the solid state, between the phosphido ligand and the phosphane arm. The d0 complexes were found to be light sensitive, and decompose through Ti−P bond homolysis to give TiIII species. A naked d0 phosphidotitanocene cation has been trapped by reaction with diphenylacetylene, yielding a Ti/P frustrated Lewis pair (FLP), which was found to be less reactive than a previously reported Zr analog. 相似文献
36.
Bruce C. Garrett Donald G. Truhlar A. J. C. Varandas Normand C. Blais 《国际化学动力学杂志》1986,18(9):1065-1077
We present calculations of the rate constants for the title reactions on a new accurate potential energy surface with a 9.65 kcal mol?1 barrier and a carefully fitted long-range attraction. The low-temperature thermal rate constant decreases from the previously calculated value, corresponding to a surface with a barrier of 9.80 kcal mol?1, which is opposite to the direction of change expectedbecause of the change in barrier height. This demonstrates the sensitivity of tunneling contributions to more global characteristics of the surface. The excited-state (n = 1) rate constants alsochange slightly, but not nearly enough to settle the controversial disagreement of theory with experiment for these rate constants. 相似文献
37.
A novel solid-phase strategy allows the efficient preparation of "traceless" sulfahydantoins. A total of 28 derivatives, with crude purity generally higher than 85%, were prepared by parallel synthesis. Through reductive alkylations, Mitsunobu reactions, and sulfamoylation reactions on oxime resin, the synthetic strategy affords sulfahydantoin derivatives selectively substituted at N(2), N(5) and N(2), N(5) positions, although yields of disubstituted compounds are lower. The mild reaction conditions involved lead to sulfahydantoins without racemization. 相似文献
38.
Pd/Al2O3 catalysts modified by cerium or lanthanum promoters are tested for hydrocarbon conversion: methylcyclopentane (MCP) hydrogenolysis, 2-methylpentane (2MP) isomerization and 3-methylhexane (3MH) hydrocracking, deshydrocyclization and aromatization. The following parameters are reviewed: (i) precursor salt of palladium (chloride or nitrate), (ii) rare earth nature (La or Ce), (iii) rare earth content within the range 0–100% and (iv) impregnation mode (coimpregnation or successive impregnations). The influence of chloride coming from the precursor salt of palladium on the catalytic behaviour is strongly underlined. Chlorine anions are trapped by rare earth cations at the interface, as evidenced in a subsequent paper dealing with characterization studies of these same catalysts (K. Kili, L. Hilaire, F. Le Normand, submitted). Although the reactions readily occur on metallic sites, as evidenced by 13C labelled experiments, the addition of rare earth increases the activity and modifies the selectivity, especially for 2MP isomerization. These changes are rationalized in terms of significant modification of the kinetic surface parameters (competitive hydrogen and hydrocarbon coverages). This is explained by (i) lowering of the hydrogen coverage of the palladium sites accompanying surface diffusion on the interface with the support and (ii) creation of new selective sites at the transition metal–rare earth interface. The other parameters investigated yield only minor changes of the catalytic behaviour. 相似文献
39.
Pierre-Alexandre Paquet-Côté Kellie L. Tuck Jean-Philippe Paradis Bim Graham Normand Voyer 《Tetrahedron letters》2017,58(50):4672-4676
Seeking to increase the selectivity of antimicrobial peptides for prokaryotic cells, we incorporated a bis-dipicolyl amine (bis-DPA) ligand at the N-terminus of de novo designed model peptides. The Zn2·bisDPA complex increases the interaction of peptides with anionic model membranes, while decreasing interactions with zwitterionic model membranes. Further, it improves the peptides’ antimicrobial activity and decreases their hemolytic activity without substantial changes to their secondary structure. Therefore, incorporating a Zn2·bisDPA complex is a useful strategy to enhance the selectivity of antimicrobial peptides. 相似文献
40.
The evaporation kinetics of pure Romascone® (methyl 2,2‐dimethyl‐6‐methylene‐1‐cyclohexanecarboxylate) and Romascone® when mixed with vinyl acetate (VAc) nanoparticles have been determined by using thermogravimetric analysis. For pure Romascone®, the evaporation rate follows an Arrhenius dependence with temperature. When Romascone® is mixed with VAc nanoparticles, two evaporation mechanisms are identified depending on the presence of comonomer and crosslinking degree. (a) Evaporation limited by the presence of non‐interactive nanoparticles. The evaporation rate is governed by the evolution of the equilibrium vapor pressure that depends on the volume fraction of volatile molecules. (b) Evaporation limited by the diffusion of volatile molecules through a polymeric particle wall. Since the diffusion depends on the physical state or structure of the polymeric nanoparticle phase, the volume fraction of volatile molecules is a determinant parameter. Furthermore, a sudden modification in the evolution of the diffusion coefficient with volatile volume fraction gives rise to discussion on phase transition. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献