651 research outputs found
Iodination of Alcohols over Keggin-type Heteropoly Compounds: A Simple, Selective and Expedient Method for the Synthesis of Alkyl Iodides
Different catalysts derived from Keggin-type heteropoly compounds were prepared and their catalytic activities have been compared in the iodination of benzyl alcohol with KI under mild reaction conditions. A high catalytic activity was found over tungstophosphoric acid supported on silica and titania. The effect of catalyst loading, iodine source and the nature of substituents on the aromatic ring of benzyl alcohol were investigated. Finally, several competitive reactions were studied between structurally diverse alcohols. This protocol provides a mild and expedient way for the conversion of various alcohols to their corresponding alkyl iodides with high selectivity.Keywords: Keggin-type Heteropoly Compounds, Supported Catalyst, Alcohols, Alkyl Iodides, Potassium Iodid
Solventless Synthesis of Quinoline Derivatives: Acceleration of Friedländer Reaction by Supported Heteropoly Acids
Different Keggin type heteropoly acids (HPAs) and supported ones on solids with different nature and textural properties were used in the Friedländer reaction in order to obtain quinoline derivatives. This conversion has been preceded by tungstophosphoric acid supported on silica, KSF and activated carbon as optimized catalysts in high yields and short reaction times. The general applicability of this method is demonstrated by using various substrates including ketones, β-ketoesters and β-diketones. For most substrates the reaction worked well. These catalysts were found to be reusable and considerable catalytic activity could still be achieved after the fourth run.Keywords: Friedländer reaction, quinoline derivatives, heteropoly compound, supported catalysts, solvent-free conditio
Elastic Correlations in Nucleosomal DNA Structure
The structure of DNA in the nucleosome core particle is studied using an
elastic model that incorporates anisotropy in the bending energetics and
twist-bend coupling. Using the experimentally determined structure of
nucleosomal DNA [T.J. Richmond and C.A. Davey, Nature {\bf 423}, 145 (2003)],
it is shown that elastic correlations exist between twist, roll, tilt, and
stretching of DNA, as well as the distance between phosphate groups. The
twist-bend coupling term is shown to be able to capture these correlations to a
large extent, and a fit to the experimental data yields a new estimate of G=25
nm for the value of the twist-bend coupling constant
Dodecatungstocobaltate and Sn (IV)-Substituted Polyoxometalate: Preparation, Characterization and Catalytic Performances in Solventless Synthesis of Bis(indolyl)methanes
Electrophilic substitution reaction of indole with various aldehydes and cyclohexanone were carried out in the presence of electron-transfer (K5CoW12O40.3H2O) and green Lewis acid ([(n-C4H9)4N]3 PMo2W9(Sn4+.H2O)O39) catalysts. These catalysts were characterized by N2-adsorption measurements, FT-IR, UV-Vis, 31P NMR, TGA, cyclic voltammetry and elemental analysis. Mechanisms for their catalytic activity are proposed. Both of these catalysts can be recovered and reused.Keywords: Dodecatungstocobaltate, Sn (IV)-substituted polyoxometalate, bis(indolyl)methanes, electrophilic substitution, solvent-freecondition
Acceleration and Substructure Constraints in a Quasar Outflow
We present observations of probable line-of-sight acceleration of a broad
absorption trough of C IV in the quasar SDSS J024221.87+004912.6. We also
discuss how the velocity overlap of two other outflowing systems in the same
object constrains the properties of the outflows. The Si IV doublet in each
system has one unblended transition and one transition which overlaps with
absorption from the other system. The residual flux in the overlapping trough
is well fit by the product of the residual fluxes in the unblended troughs. For
these optically thick systems to yield such a result, at least one of them must
consist of individual subunits rather than being a single structure with
velocity-dependent coverage of the source. If these subunits are identical,
opaque, spherical clouds, we estimate the cloud radius to be r = 3.9 10^15 cm.
If they are identical, opaque, linear filaments, we estimate their width to be
w = 6.5 10^14 cm. These subunits are observed to cover the Mg II broad emission
line region of the quasar, at which distance from the black hole the above
filament width is equal to the predicted scale height of the outer atmosphere
of a thin accretion disk. Insofar as that scale height is a natural size scale
for structures originating in an accretion disk, these observations are
evidence that the accretion disk can be a source of quasar absorption systems.
Based on data from ESO program 075.B-0190(A).Comment: 14 emulateapj pages, 7 figures, ApJ in pres
A discrete geometric approach for simulating the dynamics of thin viscous threads
We present a numerical model for the dynamics of thin viscous threads based
on a discrete, Lagrangian formulation of the smooth equations. The model makes
use of a condensed set of coordinates, called the centerline/spin
representation: the kinematical constraints linking the centerline's tangent to
the orientation of the material frame is used to eliminate two out of three
degrees of freedom associated with rotations. Based on a description of twist
inspired from discrete differential geometry and from variational principles,
we build a full-fledged discrete viscous thread model, which includes in
particular a discrete representation of the internal viscous stress.
Consistency of the discrete model with the classical, smooth equations is
established formally in the limit of a vanishing discretization length. The
discrete models lends itself naturally to numerical implementation. Our
numerical method is validated against reference solutions for steady coiling.
The method makes it possible to simulate the unsteady behavior of thin viscous
jets in a robust and efficient way, including the combined effects of inertia,
stretching, bending, twisting, large rotations and surface tension
- …