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981.
Hitchcock PB Lappert MF Liu DS Sablong R 《Chemical communications (Cambridge, England)》2002,(17):1920-1921
The compounds [K((mu-N(SiMe3)C(Ph))2CH)(thf)2]infinity 1, [K(mu-N(SiMe3)C(Ph)C(H)C(Ph)NH)L]2 [L = (thf)2 2, tmen 3], [K(mu-NSi(Me)2C(Ph)C(H)C(Ph)N)(thf)3]2 4 and [K(N(H)C(Ph))2CH](thf)0.5 5 have been prepared from K[(N(SiMe3)C(Ph))2CH] and the X-ray structures of 1-4 are reported. 相似文献
982.
Greco MN Hawkins MJ Powell ET Almond HR Corcoran TW de Garavilla L Kauffman JA Recacha R Chattopadhyay D Andrade-Gordon P Maryanoff BE 《Journal of the American Chemical Society》2002,124(15):3810-3811
The serine protease cathepsin G (EC 3.4.21.20; Cat G), which is stored in the azurophilic granules of neutrophils (polymorphonuclear leukocytes) and released on degranulation, has been implicated in various pathological conditions associated with inflammation. By employing high-throughput screening, we identified beta-ketophosphonic acid 1 as a moderate inhibitor of Cat G (IC(50) = 4.1 microM). We were fortunate to obtain a cocrystal of 1 with Cat G and solve its structure by X-ray crystallography (3.5 A). Structural details from the X-ray analysis of 1.Cat G served as a platform for optimization of this lead compound by structure-based drug design. With the aid of molecular modeling, substituents were attached to the 3-position of the 2-naphthyl ring of 1, which occupies the S1 pocket of Cat G, to provide an extension into the hydrophobic S3 region. Thus, we arrived at analogue 7 with an 80-fold potency improvement over 1 (IC(50) = 53 nM). From these results, it is evident that the beta-ketophosphonic acid unit can form the basis for a novel class of serine protease inhibitors. 相似文献
983.
Amaresh RR Lakshmikantham MV Baldwin JW Cava MP Metzger RM Rogers RD 《The Journal of organic chemistry》2002,67(8):2453-2458
3,4-Cyanomethyl substituted thiophenes reacted with thionyl chloride in the presence of base to give dicyano substituted thieno(3,4-c)thiophenes. The use of selenium oxychloride furnished the corresponding cyano substituted seleno(3,4-c)thiophene. 1,2-Phenylenediacetonitriles gave the corresponding cyano substituted benzo(c)thiophenes and benzo(c)selenenophenes, respectively, upon reaction with thionyl chloride and selenium oxychloride in the presence of base. 相似文献
984.
Rashid MA Gustafson KR Crouch RC Groweiss A Pannell LK Van QN Boyd MR 《Organic letters》2002,4(19):3293-3296
Poecillastrin A (1), a new polyketide-derived macrolide lactam, was isolated from a deep-water collection of the marine sponge Poecillastra species. The structure of poecillastrin A (1) was assigned using NMR data acquired at 500 MHz with an inverse-detection cryogenic probe and at 800 MHz with a room-temperature probe. 相似文献
985.
Hayley A. Every Michael A. Hickner James E. McGrath Thomas A. Zawodzinski Jr. 《Journal of membrane science》2005,250(1-2):183-188
Methanol diffusion in two polymer electrolyte membranes, Nafion 117 and BPSH 40 (a 40% disulfonated wholly aromatic polyarylene ether sulfone), was measured using a modified pulsed field gradient NMR method. This method allowed for the diffusion coefficient of methanol within the membrane to be determined while immersed in a methanol solution of known concentration. A second set of gradient pulses suppressed the signal from the solvent in solution, thus allowing the methanol within the membrane to be monitored unambiguously. Over a methanol concentration range of 0.5–8 M, methanol diffusion coefficients in Nafion 117 were found to increase from 2.9 × 10−6 to 4.0 × 10−6 cm2 s−1. For BPSH 40, the diffusion coefficient dropped significantly over the same concentration range, from 7.7 × 10−6 to 2.5 × 10−6cm2 s−1. The difference in diffusion behavior is largely related to the amount of solvent sorbed by the membranes. Increasing the methanol concentration results in an increase in solvent uptake for Nafion 117, while BPSH 40 actually excludes the solvent at higher concentrations. In contrast, diffusion of methanol measured via permeability measurements (assuming a partition coefficient of 1) was lower (1.3 × 10−6 and 6.4 × 10−7 cm2 s−1 for Nafion 117 and BPSH 40 respectively) and showed no concentration dependence. The differences observed between the two techniques are related to the length scale over which diffusion is monitored and the partition coefficient, or solubility, of methanol in the membranes as a function of concentration. For the permeability measurements, this length is equal to the thickness of the membrane (178 and 132 μm for Nafion 117 and BPSH 40 respectively) whereas the NMR method observes diffusion over a length of approximately 4–8 μm. Regardless of the measurement technique, BPSH 40 is a greater barrier to methanol permeability at high methanol concentrations. 相似文献
986.
Proper epidemiological, risk assessment and exposure analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and related halogenated aromatic hydrocarbons (HAHs) requires accurate measurements of these chemicals both in the species of interest and in various exposure matrices (i.e. biological, environmental, food and feed). High-resolution instrumental analysis techniques are established for these chemicals, however, these procedures are very costly and time-consuming and as such, they are impractical for large scale sampling studies (i.e. for epidemiological studies and assessment of areas with widespread contamination). Accordingly, numerous bioanalytical methods have been developed for the detection of these chemicals in extracts from a variety of matrices, the majority of which take advantage of the ability of these chemicals to activate the aromatic hydrocarbon receptor (AhR) and the AhR signal transduction pathway. Here we review the currently available in vitro AhR-based cell bioassay systems with a focus on recent recombinant reporter gene cell lines that have been developed for detection and relative quantitation of TCDD and related HAHs. Comparison of the relative sensitivities of the various cell bioassays and examples of their use in screening and analysis of environmental, biological, and food and feed samples are presented. Currently available experimental results and validation studies demonstrate the utility of these cell bioassay systems to provide a relatively rapid, accurate, and cost effective screening approach for the detection of TCDD and related HAHs in a variety of environmental, biological, food and feed samples. The availability of these cell bioassay systems will not only facilitate the large scale sampling studies needed for accurate assessment of contamination and exposure to these environmental chemicals, but they provide avenues for the identification of novel classes of TCDD-like chemicals. 相似文献
987.
Acetonitrile and [D3]acetonitrile in the vicinal region of a planar AgX fiber contain linear dipole–dipole linked oligomers as shown by 1) comparison of infrared band intensity ratios in the gaseous and condensed phases and 2) remarkable plots of absorbance (C? N stretch) versus time during evaporation from an AgX planar fiber element. The plots (CH3CN 2252 cm?1, CD3CN 2262 cm?1) reveal the presence of octamers, hexamers, tetramers, and dimers along with some heptamer, trimer, and monomer structures. A novel isotope effect arises from the somewhat smaller size of the CD3CN resulting in an increase in the CN band intensity. The organized oligomers may be termed pseudocrystals and are the main components responsible for absorption intensity in the infrared spectrum of acetonitrile, on the AgX planar fiber or in an IR cell. 相似文献
988.
Density functional theory (BPW91/TZ2P) is used to explore the nature of cation-cation interactions (CCIs) that exist between two actinyl cations in solution. Solvation, which is modeled using COSMO, favors the complexes (ONpO-ONpO)2+ and (ONpO-OUO)3+ over separated NpO2+(aq) and UO2(2+)(aq) cations because of the quadratic dependence of solvation on charge. For (OUO-OUO)4+, solvation effects, even though very large, are unable to overcome intrinsic electrostatic repulsion between the units. The actinyl-actinyl complexes are T-shaped, with the oxygen of one unit coordinated to the actinide metal of the other unit. The association free energies of (ONpO-ONpO)2+ and (ONpO-OUO)3+ are calculated as -42.1 and -29.2 kcal/mol. Explicit consideration of the first solvation shell at the B3LYP/LANL2DZ level suggests that the free energies of binding may be overestimated. The Hg2(2+) dication, though not considered a "traditional" CCI, is very similar to the actinyl-actinyl interaction. The binding free energy of Hg2(2+) in solution is calculated as -16.0 kcal/mol. 相似文献
989.
Frank Gahlmann Michael Sch fer Sylvia Magull 《Journal of organometallic chemistry》1992,440(3):263-275
The reaction of iPr2InCl (1) with KF and 15-crown-5 in acetonitrile at room temperature leads to the toluene-soluble crown ether salt [K(15-crown-5)2][iPr2InCl2] (2) and to the MeCN-soluble diorganoindium fluoride iPr2InF (3). Pure 3 can be isolated, when the reaction is carried out with KF but without crown ether at −15°C. Crystals of 1 und 2, suitable for X-ray structure determinations, were obtained when 1 and 2 were recrystallized from toluene. 1 exists as infinite chains of the monomeric unit iPr2InCl, while the unit cell of 2 contains separate ions. 相似文献
990.
Roland Boese Dieter Bläser Michael Nussbaumer Tadeusz Marek Krygowski 《Structural chemistry》1992,3(5):363-368
The crystal and molecular structure of nitrobenzene was determined at 103 K by X-ray diffraction, yieldingR=0.034 and a highly precise geometry of the molecule (esds of bond lengths 0.001 Å and bond angles 0.1°). The bond angles in the ring agree very well with additive scheme based on angular substituent parameters. X-X electron density maps support the view that the C-N bond does not exhibit-character, and, hence, the nitro group interacts with the ring mostly by inductive effects. 相似文献