2,253 research outputs found
Water-accelerated organic transformations
Rather than quenching all reactive intermediates and arresting the reaction, the addition of catalytic or stoichiometric (1-10 equiv.) quantities of H2O to organic and organometallic processes can lead to surprisingly beneficial effects on reaction rate, product yield, and regio-, diastereo- and enantioselectivity. A most intriguing aspect of H2O-promoted transformations is the role that this strong Lewis-base can play in providing a source for more highly Lewis-acidic species. This scenario is most likely operative when H2O is added to reaction mixtures containing alanes, but organozinc reagents or organocuprates also seem to be transformed accordingly. In addition, the oxide or hydroxide ligand on the metal presents a source for chelation interactions that change aggregation states of organometallics and can provide anchimeric assistance. In many cases, water has been found to be an effective hydrolyzing agent leading to secondary products that serve as catalysts or promoters. In some cases, it has been shown that water provides a quenching agent capable of driving chemical equilibria towards the desired products
Isolation, biology and chemistry of the disorazoles: New anti-cancer macrodiolides
The disorazoles comprise a family of 29 closely related macrocyclic polyketides isolated in 1994 from the fermentation broth of the gliding myxobacterium Sorangium cellulosum. Disorazoles A1, E and C 1 have shown exceptional biological activities toward inhibiting the proliferation of human cancer cell lines in picomolar and nanomolar concentrations through the disruption of microtubule polymerization. This review gives a brief introduction describing the biosynthesis and the significance of the disorazoles as a new class of microtubulin disruptors. Another portion of the review focuses on the biology of the disorazoles, specifically disorazole A1 and C1, and their antiproliferative efficacy against animal and human tumor cell lines, as well as the available SAR data. The majority of the discussion addresses synthetic efforts, including partial syntheses of various disorazoles and a summary of the total synthesis of disorazole C1. © 2009 The Royal Society of Chemistry
Anomalies, Hawking Radiations and Regularity in Rotating Black Holes
This is an extended version of our previous letter hep-th/0602146. In this
paper we consider rotating black holes and show that the flux of Hawking
radiation can be determined by anomaly cancellation conditions and regularity
requirement at the horizon. By using a dimensional reduction technique, each
partial wave of quantum fields in a d=4 rotating black hole background can be
interpreted as a (1+1)-dimensional charged field with a charge proportional to
the azimuthal angular momentum m. From this and the analysis gr-qc/0502074,
hep-th/0602146 on Hawking radiation from charged black holes, we show that the
total flux of Hawking radiation from rotating black holes can be universally
determined in terms of the values of anomalies at the horizon by demanding
gauge invariance and general coordinate covariance at the quantum level. We
also clarify our choice of boundary conditions and show that our results are
consistent with the effective action approach where regularity at the future
horizon and vanishing of ingoing modes at r=\infty are imposed (i.e. Unruh
vacuum).Comment: 21 pages, minor corrections, added an appendix to summarize our
notations for the Kaluza-Klein reductio
Liouville and Toda Theories as Conformally Reduced WZNW Theories
It is shown that Liouville theory can be regarded as an SL(2, R) Wess-Zumino-Novikov-Witten theory with conformal invariant constraints and that Polyakov’s SL(2, R) Kac-Moody symmetry of induced two-dimensional gravity is just one side of the WZNW current algebra. Analogously, Toda field theories can be regarded as conformal-invariantly constrained WZNW theories for appropriate (maximally noncompact) groups
Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d)
Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d) have been studied by means
of magnetization measurements in the temperature range between 1.95 K and Tc,
in an external magnetic field up to 9 T. Flux jumps were found in the
temperature range 1.95 K - 6 K, with the external magnetic field parallel to
the c axis of the investigated sample. The effect of sample history on magnetic
flux jumping was studied and it was found to be well accounted for by the
available theoretical models. The magnetic field sweep rate strongly influences
the flux jumping and this effect was interpreted in terms of the influence of
both flux creep and the thermal environment of the sample. Strong flux creep
was found in the temperature and magnetic field range where flux jumps occur
suggesting a relationship between the two. The heat exchange conditions between
the sample and the experimental environment also influence the flux jumping
behavior. Both these effects stabilize the sample against flux instabilities,
and this stabilizing effect increases with decreasing magnetic field sweep
rate. Demagnetizing effects are also shown to have a significant influence on
flux jumping.Comment: 10 pages, 6 figures, RevTeX4, submitted to Phys. Rev.
Diversity-oriented synthesis of a library of substituted tetrahydropyrones using oxidative carbon-hydrogen bond activation and click chemistry
Eighteen (2RS,6RS)-2-(4-methoxyphenyl)-6-(substituted ethyl)dihydro- 2Hpyran-4(3H)ones were synthesized via a DDQ-mediated oxidative carbon-hydrogen bond activation reaction. Fourteen of these tetrahydropyrans were substituted with triazoles readily assembled via azide-alkyne click-chemistry reactions. Examples of a linked benzotriazole and pyrazole motif were also prepared. To complement the structural diversity, the alcohol substrates were obtained from stereoselective reductions of the tetrahydropyrone. This library provides rapid access to structurally diverse non-natural compounds to be screened against a variety of biological targets. © 2011 by the authors
A new battery-charging method suggested by molecular dynamics simulations
Based on large-scale molecular dynamics simulations, we propose a new
charging method that should be capable of charging a Lithium-ion battery in a
fraction of the time needed when using traditional methods. This charging
method uses an additional applied oscillatory electric field. Our simulation
results show that this charging method offers a great reduction in the average
intercalation time for Li+ ions, which dominates the charging time. The
oscillating field not only increases the diffusion rate of Li+ ions in the
electrolyte but, more importantly, also enhances intercalation by lowering the
corresponding overall energy barrier.Comment: 11 pages, 5 figure
Optomechanical entanglement at room temperature: a simulation study with realistic conditions
Quantum entanglement is the key to many applications like quantum key
distribution, quantum teleportation, and quantum sensing. However, reliably
generating quantum entanglement in macroscopic systems has proved to be a
challenge. Here, we present a detailed analysis of ponderomotive entanglement
generation which utilizes optomechanical interactions to create quantum
correlations. We numerically calculate an entanglement measure -- the
logarithmic negativity -- for the quantitative assessment of the entanglement.
Experimental limitations, including thermal noise and optical loss, from
measurements of an existing experiment were included in the calculation, which
is intractable to solve analytically. This work will play an important role in
the development of ponderomotive entanglement devices
Optomechanical entanglement at room temperature: A simulation study with realistic conditions
Quantum entanglement is the key to many applications like quantum key distribution, quantum teleportation, and quantum sensing. However, reliably generating quantum entanglement in macroscopic systems has proven to be a challenge. Here, we present a detailed analysis of ponderomotive entanglement generation in a movable-end-mirror-type optomechanical cavity. These cavities utilize optomechanical interactions between the intracavity field and the end mirror to create quantum correlations. We numerically calculate an entanglement measure, the logarithmic negativity, for the quantitative assessment of the entanglement. Experimental limitations, including thermal noise and optical loss, from measurements of an existing experiment were included in the calculation, which is intractable to solve analytically. This analysis shows that lowering optical losses and measurement uncertainties is more important than temperature for observation of the entanglement in movable-end-mirror-type optomechanical cavity experiments. This work will play an important role in the development of ponderomotive entanglement devices
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