405 research outputs found
Regioselective Oxidative Arylation of Indoles Bearing N-Alkyl Protecting Groups: Dual CâH Functionalization via a Concerted MetalationâDeprotonation Mechanism
The most direct method for synthesizing 2-arylindoles is oxidative coupling of an arene with an indole. We have shown that both the activity and regioselectivity of this cross-coupling reaction are correlated with the acidity of the medium. This insight has been applied to predict the best conditions for the oxidative cross-coupling of N-alkylindoles, an important class of substrates that has heretofore been incompatible with the harsh conditions required for oxidative cross-coupling. Both experimental and computational data indicate that the mechanism for CâH palladation of both the indoles and simple arenes is best described as concerted metalationâdeprotonation, regardless of the substitution on the arene
A Terbium Chlorobismuthate(III) Double Salt: Synthesis, Structure, and Photophysical Properties
We report on the structure and luminescence of a double salt trivalent rare earth ion acceptor, Tb3+, with octahedral [BiCl6]3â donor clusters. The novel TbBiCl6·14H2O (1) was prepared from aqueous BiOCl and TbCl3·6H2O. The crystal structure of compound 1 exhibits isolated [BiCl6]3â and [Tb(OH2)8]3+ clusters. Luminescence data show energy transfer from octahedral chlorobismuthate(III) clusters to rare earth metal ions. Density Functional Theory (DFT) calculations show distinctly different emission pathways at high and low excitation energies
HST Snaphot Study of Variable Stars in Globular Clusters: Inner Region of NGC 6441
[Abridged] We present the results of a Hubble Space Telescope snapshot
program to survey the inner region of the globular cluster NGC 6441 for its
variable stars. A total of 57 variable stars was found including 38 RR Lyrae
stars, 6 Population II Cepheids, and 12 long period variables. Of the RR Lyrae
stars observed in this survey, 26 are pulsating in the fundamental mode with a
mean period of 0.753d and 12 are first-overtone mode pulsators with a mean
period of 0.365d. These values match up very well with those found in
ground-based surveys. Combining all the available data for NGC 6441, we find
mean periods of 0.759d and 0.375d for the RRab and RRc stars, respectively. We
also find that the RR Lyrae in this survey are located in the same regions of a
period-amplitude diagram as those found in ground-based surveys. Although NGC
6441 is a metal-rich globular cluster, its RR Lyrae more closely resemble those
in Oosterhoff type II globular clusters. However, even compared to typical
Oosterhoff type II systems, the mean period of its RRab stars is unusually
long. We also derived I-band period-luminosity relations for the RR Lyrae
stars. Of the six Population II Cepheids, five are of W Virginis type and one
is a BL Herculis variable stars. This makes NGC 6441, along with NGC 6388, the
most metal-rich globular cluster known to contain these types of variable
stars. Another variable, V118, may also be a Population II Cepheid given its
long period and its separation in magnitude from the RR Lyrae stars. We argue
that there does not appear to be a change in the period-luminosity relation
slope between the BL Herculis and W Virginis stars, but that a change of slope
does occur when the RV Tauri stars are added to the period-luminosity relation.Comment: 28 pages, including 9 figures and 8 tables, emulateapj5/apjfonts
style. Accepted by the Astronomical Journal. Approximate publication date
September 2003. We recommend the interested reader to download the preprint
with full-resolution figures, which can be found at
http://www.astro.puc.cl/~mcatelan/Pritzl.zi
A systematic review of the use of an expertise-based randomised controlled trial design
Acknowledgements JAC held a Medical Research Council UK methodology (G1002292) fellowship, which supported this research. The Health Services Research Unit, Institute of Applied Health Sciences (University of Aberdeen), is core-funded by the Chief Scientist Office of the Scottish Government Health and Social Care Directorates. Views express are those of the authors and do not necessarily reflect the views of the funders.Peer reviewedPublisher PD
Particles at oilâair surfaces : powdered oil, liquid oil marbles, and oil foam
The type of material stabilized by four kinds of fluorinated particles (sericite and bentonite platelet clays and spherical zinc oxide) in airâoil mixtures has been investigated. It depends on the particle wettability and the degree of shear. Upon vigorous agitation, oil dispersions are formed in all the oils containing relatively large bentonite particles and in oils of relatively low surface tension (Îłla < 26 mN mâ»Âč) like dodecane, 20 cS silicone, and cyclomethicone containing the other fluorinated particles. Particle-stabilized oil foams were obtained in oils having Îłla > 26 mN mâ»Âč where the advancing airâoilâsolid contact angle Ξ lies between ca. 90° and 120°. Gentle shaking, however, gives oil-in-air liquid marbles with all the oilâparticle systems except for cases where Ξ is <60°. For oils of tension >24 mN mâ»Âč with omniphobic zinc oxide and sericite particles for which advancing Ξ â„ 90°, dry oil powders consisting of oil drops in air which do not leak oil could be made upon gentle agitation up to a critical oil:particle ratio (COPR). Above the COPR, catastrophic phase inversion of the dry oil powders to air-in-oil foams was observed. When sheared on a substrate, the dry oil powders containing at least 60 wt % of oil release the encapsulated oil, making these materials attractive formulations in the cosmetic and food industries
Nonlinear Effects in the Amplitude of Cosmological Density Fluctuations
The amplitude of cosmological density fluctuations, sigma_8, has been studied
and estimated by analysing many cosmological observations. The values of the
estimates vary considerably between the various probes. However, different
estimators probe the value of sigma_8 in different cosmological scales and do
not take into account the nonlinear evolution of the parameter at late times.
We show that estimates of the amplitude of cosmological density fluctuations
derived from cosmic flows are systematically higher than those inferred at
early epochs from the CMB because of nonlinear evolution at later times. We
discuss the past and future evolution of linear and nonlinear perturbations,
derive corrections to the value of sigma_8 and compare amplitudes after
accounting for these differences.Comment: 9 pages, 4 figures, 1 table. Accepted for publication in JCA
The Orphan G Protein-coupled Receptors GPR41 and GPR43 Are Activated by Propionate and Other Short Chain Carboxylic Acids
n/
Alkali Metal Bismuth(III) Chloride Double Salts
Evaporative co-crystallization of MCl (M = Na, K, Rb, Cs) with BiOCl in aqueous HCl produces double salts: MxBiyCl(x+3y)·zH2O. The sodium salt, Na2BiCl5·5H2O (monoclinic P21/c, a = 8.6983(7) Ă
, b = 21.7779(17) Ă
, c = 7.1831(6) Ă
, ÎČ = 103.0540(10)°, V = 1325.54(19) Ă
3, Z = 4) is composed of zigzag chains of ÎŒ2-Cl-cis-linked (BiCl5)n2nâ chains. Edge-sharing chains of NaCln(OH2)6ân octahedra (n = 0, 2, 3) are linked through ÎŒ3-Cl to Bi. The potassium salt, K7Bi3Cl16 (trigonal Râ3c, a = 12.7053(9) Ă
, b = 12.7053(9) Ă
, c = 99.794(7) Ă
, V = 13,951(2) Ă
3, Z = 18) contains (Bi2Cl10)4â edge-sharing dimers of octahedra and simple (BiCl6)3â octahedra. The K+ ions are 5- to 8-coordinate and the chlorides are 3-, 4-, or 5-coordinate. The rubidium salt, Rb3BiCl6·0.5H2O (orthorhombic Pnma, a = 12.6778(10) Ă
, b = 25.326(2) Ă
, c = 8.1498(7) Ă
, V = 2616.8(4) Ă
3, Z = 8) contains (BiCl6)3â octahedra. The Rb+ ions are 6-, 8-, and 9-coordinate, and the chlorides are 4- or 5-coordinate. Two cesium salts were formed: Cs3BiCl6 (orthorhombic Pbcm, a = 8.2463(9) Ă
, b = 12.9980(15) Ă
, c = 26.481(3) Ă
, V = 2838.4(6) Ă
3, Z = 8) being comprised of (BiCl6)3â octahedra, 8-coordinate Cs+, and 3-, 4-, and 5-coordinate Clâ. In Cs3Bi2Cl9 (orthorhombic Pnma, a = 18.4615(15) Ă
, b = 7.5752(6) Ă
, c = 13.0807(11) Ă
, V = 1818.87(11) Ă
3, Z = 4) Bi octahedra are linked by ÎŒ2-bridged Cl into edge-sharing Bi4 squares which form zigzag (Bi2Cl9)n3nâ ladders. The 12-coordinate Cs+ ions bridge the ladders, and the Clâ ions are 5- and 6-coordinate. Four of the double salts are weakly photoluminescent at 78 K, each showing a series of three excitation peaks near 295, 340, and 380 nm and a broad emission near 440 nm
EGFR oligomerization organizes kinase-active dimers into competent signalling platforms
Epidermal growth factor receptor (EGFR) signalling is activated by ligand-induced receptor dimerization. Notably, ligand binding also induces EGFR oligomerization, but the structures and functions of the oligomers are poorly understood. Here, we use fluorophore localization imaging with photobleaching to probe the structure of EGFR oligomers. We find that at physiological epidermal growth factor (EGF) concentrations, EGFR assembles into oligomers, as indicated by pairwise distances of receptor-bound fluorophore-conjugated EGF ligands. The pairwise ligand distances correspond well with the predictions of our structural model of the oligomers constructed from molecular dynamics simulations. The model suggests that oligomerization is mediated extracellularly by unoccupied ligand-binding sites and that oligomerization organizes kinase-active dimers in ways optimal for auto-phosphorylation in trans between neighbouring dimers. We argue that ligand-induced oligomerization is essential to the regulation of EGFR signalling
Spillway-Induced Salmon Head Injury Triggers the Generation of Brain αII-Spectrin Breakdown Product Biomarkers Similar to Mammalian Traumatic Brain Injury
Recent advances in biomedical research have resulted in the development of specific biomarkers for diagnostic testing of disease condition or physiological risk. Of specific interest are αII-spectrin breakdown products (SBDPs), which are produced by proteolytic events in traumatic brain injury and have been used as biomarkers to predict the severity of injury in humans and other mammalian brain injury models. This study describes and demonstrates the successful use of antibody-based mammalian SBDP biomarkers to detect head injury in migrating juvenile Chinook salmon (Oncorhynchus tshawytscha) that have been injured during passage through high-energy hydraulic environments present in spillways under different operational configurations. Mortality and injury assessment techniques currently measure only near-term direct mortality and easily observable acute injury. Injury-based biomarkers may serve as a quantitative indicator of subacute physical injury and recovery, and aid hydropower operators in evaluation of safest passage configuration and operation actions for migrating juvenile salmonids. We describe a novel application of SBDP biomarkers for head injury for migrating salmon. To our knowledge, this is the first documented cross-over use of a human molecular biomarker in a wildlife and operational risk management scenario
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