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41.
γ-alkylation of α,β-unsaturated ketones: α'-phenylsulfonyl groups as regioselective control elements
Peter T. Lansbury Gregory E. Bebernitz Susan C. Maynard Ciro J. Spagnuolo 《Tetrahedron letters》1985,26(2):169-172
The α'-phenylsulfonyl derivative of E-3-penten-2-one () undergoes predominant γ-alkylation with a variety of alkyl iodides when first converted into a trilithiated intermediate with excess lithium diisopropylamide in tetrahydrofuran-hexane. 相似文献
42.
The synthesis and characterization of the 5- and 7-monosubstituted 2-methyl-8-quinolinols where the substituents are fluorine, chlorine, bromine, iodine, nitro, amino, and sulfonic acid groups were carried out. The bischelates with copper(II) of those ligands containing hydrogen, fluorine, chlorine, bromine, iodine, and nitro are also reported. 相似文献
43.
Russell WK Russell DH Busby MB Kolberg A Li S Maynard DK Sanchez-Vindas S Zhu W Vigh G 《Journal of chromatography. A》2001,914(1-2):325-330
Artifact-free, high-resolution matrix-assisted laser desorption ionization (MALDI) time-of-flight mass spectra have been obtained for the labile, single-isomer, tert.-butyldimethylsilyl ether derivatives of alpha-, beta- and gamma-cyclodextrins by optimizing the MALDI sample preparation method. 2,5-Dihydroxybenzoic acid, a 3:1 mixture of 2,5-dihydroxybenzoic acid and 1-hydroxyisoquinoline, and 2,4,6-trihydroxyacetophenone were investigated as MALDI matrices with methanol and acetonitrile as matrix solvents. Partial-to-complete loss of the tert.-butyldimethylsilyl groups was observed when the commonly used 2,5-dihydroxybenzoic acid was the MALDI matrix and/or methanol was the solvent, both with and without trifluoroacetic acid as additive. Loss of the labile tert.-butyldimethylsilyl groups was avoided with 2,4,6-trihydroxyacetophenone as MALDI matrix and acetonitrile as matrix solvent. Good ion intensities were achieved for the (M+Na)+ and (M+K)+ quasimolecular ions in the positive-ion mode. Minor byproducts were observed in some of the samples and the information was used to aid the optimization of the synthetic work. 相似文献
44.
B. Josephson G. Jungner J. G. Reinhold D. W. Wilson L. Cuny Y. Abe S. Kawaguchi A. v. Christiani V. Anger O. Rosenheim R. Ehrström K. Täufel H. Thaler G. Widmann E. Kirk W. R. Bloor H. H. Williams B. N. Erickson I. Avrin S. S. Bernstein I. G. Macy G. Ellis L. A. Maynard R. N. Chopra A. C. Roy R. Feulgen H. Grünberg K. Imhäuser C. A. Grau V. Oliva E. Epstein und H. Lieb 《Fresenius' Journal of Analytical Chemistry》1941,122(3-4):149-160
Ohne Zusammenfassung 相似文献
45.
Milind Kandlikar Gurumurthy Ramachandran Andrew Maynard Barbara Murdock William A. Toscano 《Journal of nanoparticle research》2007,9(1):137-156
Uncertainties in conventional quantitative risk assessment typically relate to values of parameters in risk models. For many
environmental contaminants, there is a lack of sufficient information about multiple components of the risk assessment framework.
In such cases, the use of default assumptions and extrapolations to fill in the data gaps is a common practice. Nanoparticle
risks, however, pose a new form of risk assessment challenge. Besides a lack of data, there is deep scientific uncertainty
regarding every aspect of the risk assessment framework: (a) particle characteristics that may affect toxicity; (b) their
fate and transport through the environment; (c) the routes of exposure and the metrics by which exposure ought to be measured;
(d) the mechanisms of translocation to different parts of the body; and (e) the mechanisms of toxicity and disease. In each
of these areas, there are multiple and competing models and hypotheses. These are not merely parametric uncertainties but
uncertainties about the choice of the causal mechanisms themselves and the proper model variables to be used, i.e., structural
uncertainties. While these uncertainties exist for PM2.5 as well, risk assessment for PM2.5 has avoided dealing with these
issues because of a plethora of epidemiological studies. However, such studies don’t exist for the case of nanoparticles.
Even if such studies are done in the future, they will be very specific to a particular type of engineered nanoparticle and
not generalizable to other nanoparticles. Therefore, risk assessment for nanoparticles will have to deal with the various
uncertainties that were avoided in the case of PM2.5. Consequently, uncertainties in estimating risks due to nanoparticle
exposures may be characterized as ‘extreme’. This paper proposes a methodology by which risk analysts can cope with such extreme
uncertainty. One way to make these problems analytically tractable is to use expert judgment approaches to study the degree
of consensus and/or disagreement between experts on different parts of the exposure–response paradigm. This can be done by
eliciting judgments from a wide range of experts on different parts of the risk causal chain. We also use examples to illustrate
how studying expert consensus/disagreement helps in research prioritization and budget allocation exercises. The expert elicitation
can be repeated over the course of several years, over which time, the state of scientific knowledge will also improve and
uncertainties may possibly reduce. Results from expert the elicitation exercise can be used by risk managers or managers of
funding agencies as a tool for research prioritization. 相似文献
46.
47.
Polynorbornenes substituted with two different peptide sequences from the RGD-containing integrin cell-binding domain of fibronectin are potent inhibitors of human foreskin fibroblast cell adhesion to fibronectin-coated surfaces. Ring-opening metathesis polymerization (ROMP) using Ru==CHPh(Cl)(2)(PCy(3))(DHIMes) (1) as an initiator produced polymers substituted with GRGDS and PHSRN peptide sequences. The inhibitory activity was quantified for these polymers and compared to the free peptides and GRGES-containing controls. A homopolymer substituted with GRGDS peptides was significantly more active than the free GRGDS peptide (IC(50) of 0.18 +/- 0.03 and 1.33 +/- 0.20 mM respectively), and the copolymer containing both GRGDS and PHSRN is the most potent inhibitor (IC(50) of 0.04 +/- 0.01 mM). These results demonstrate that significant enhancements of observed biological activity can be obtained from polymeric materials containing more than one type of multivalent ligand and that ROMP is a useful method to synthesize such well-defined copolymers. 相似文献
48.
Burke W.J. Maynard N.C. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》2000,28(6):1903-1911
During geomagnetic disturbances, momentum and energy are transferred in significant quantities from interplanetary space to the magnetosphere-ionosphere system through the mediation of charged particles and electric fields. The most dramatic manifestations occur in the plasma sheet and the conjugate auroral ionosphere. However, electric fields observed during magnetic storms also penetrate the inner magnetosphere that maps to subauroral latitudes in the ionosphere. For example, a sudden commencement shock wave initiating the March 1991 magnetic storm created a new radiation belt within minutes. Particle and field measurements by Combined Release and Radiation Effects Satellite (CRRES) near the equatorial plane of the magnetosphere and by Defense Meteorological Satellite Program (DMSP) satellites in the topside ionosphere during the magnetic storm of June 1991 indicate that penetration electric fields energized the stormtime ring current and rapidly transported plasma within subauroral ion drift (SAID) structures at midlatitudes and in upward drafting plasma bubbles at low latitudes. Through enhanced transport or chemical reactions, the SAIDs dug deep plasma troughs at topside altitudes. Equatorial plasma bubbles developed while the ring current was unable to shield the electric field from the innermost magnetosphere 相似文献
49.
50.
From the standard interaction between electrons and two level systems a superconductive pairing is envisaged. The solutions of the Eliashberg equations for the critical temperature as well as the zero temperature gap lead to expressions as exp (?1/√λ0) instead of exp (?1/λ0) in the BCS case, which enhances considerably the superconducting properties in the weak coupling case. 相似文献