30,367 research outputs found
Regioselective Intermolecular Coupling Reaction of Arylketones and Alkenes Involving C-H Bond Activation Catalyzed by an \u3cem\u3ein Situ\u3c/em\u3e Formed Cationic Ruthenium-Hydride Complex
The cationic ruthenium hydride complex, formed in situ from the treatment of the tetranuclear ruthenium hydride complex {[(PCy3)(CO)RuH]4(ÎŒ4-O)(ÎŒ3-OH)(ÎŒ2-OH)} with HBF4·OEt2, was found to be a highly effective catalyst for the intermolecular coupling reaction of arylketones and 1-alkenes to give the substituted indene and ortho-CâH insertion products. The formation of the indene products resulted from the initial alkene isomerization followed by regioselective ortho-CâH insertion of 2-alkene and dehydrative cyclization. The preliminary mechanistic studies revealed a rapid and reversible ortho-CâH bond activation followed by the rate-limiting CâC bond formation step for the coupling reaction
Efficient Dehydrogenation of Amines and Carbonyl Compounds Catalyzed by a Tetranuclear Ruthenium-Ό-oxo-Ό-hydroxo-hydride Complex
The tetranuclear ruthenium-ÎŒ-oxo-ÎŒ-hydroxo-hydride complex {[(PCy3)(CO)RuH]4(ÎŒ4-O)(ÎŒ3-OH)(ÎŒ2-OH)} (1) was found to be a highly effective catalyst for the transfer dehydrogenation of amines and carbonyl compounds. For example, the initial turnover rate of the dehydrogenation of 2-methylindoline was measured to be 1.9 sâ1 with a TON of 7950 after 1 h at 200 °C. The extensive H/D scrambling patterns observed from the dehydrogenation reaction of indoline-N-d1 and indoline-α-d2 suggest a monohydride mechanistic pathway with the CâH bond activation rate-limiting step
Chain-Selective and Regioselective Ethylene and Styrene Dimerization Reactions Catalyzed by a Well-Defined Cationic Ruthenium-Hydride Complex: New Insights on the Styrene Dimerization Mechanism
The cationic ruthenium hydride complex [(η6-C6H6)(PCy3)(CO)RuH]+BF4â was found to be a highly regioselective catalyst for the ethylene dimerization reaction to give 2-butene products (TOF = 1910 hâ1, \u3e95% selectivity for 2-butenes). The dimerization of styrene exclusively produced the head-to-tail dimer (E)-PhCH(CH3)CHâCHPh at an initial turnover rate of 2300 hâ1. A rapid and extensive H/D exchange between the vinyl hydrogens of styrene-d8 and 4-methoxystyrene was observed within 10 min without forming the dimer products at room temperature. The inverse deuterium isotope effect of kH/kD = 0.77 ± 0.10 was measured from the first-order plots on the dimerization reaction of styrene and styrene-d8 in chlorobenzene at 70 °C. The pronounced carbon isotope effect on both vinyl carbons of styrene as measured by using Singletonâs method (13C(recovered)/13C(virgin) at C1 = 1.096 and C2 = 1.042) indicates that the CâC bond formation is the rate-limiting step for the dimerization reaction. The Eyring plot of the dimerization of styrene in the temperature range of 50â90 °C led to ÎH⧧ = 3.3(6) kcal/mol and ÎS⧧ = â35.5(7) eu. An electrophilic addition mechanism has been proposed for the dimerization of styrene
Intermolecular Dehydrative Coupling Reaction of Arylketones with Cyclic Alkenes Catalyzed by a Well-Defined Cationic Ruthenium-Hydride Complex: A Novel Ketone Olefination Method via Vinyl CâH Bond Activation
The cationic rutheniumâhydride complex [(η6-C6H6)(PCy3)(CO)RuH]+BF4â was found to be a highly effective catalyst for the intermolecular olefination reaction of aryl ketones with cycloalkenes. The preliminary mechanistic analysis revealed that an electrophilic rutheniumâvinyl complex is the key species for mediating both vinyl CâH bond activation and the dehydrative olefination steps of the coupling reaction
Calibrated Langevin dynamics simulations of intrinsically disordered proteins
We perform extensive coarse-grained (CG) Langevin dynamics simulations of
intrinsically disordered proteins (IDPs), which possess fluctuating
conformational statistics between that for excluded volume random walks and
collapsed globules. Our CG model includes repulsive steric, attractive
hydrophobic, and electrostatic interactions between residues and is calibrated
to a large collection of single-molecule fluorescence resonance energy transfer
data on the inter-residue separations for 36 pairs of residues in five IDPs:
-, -, and -synuclein, the microtubule-associated protein
, and prothymosin . We find that our CG model is able to
recapitulate the average inter-residue separations regardless of the choice of
the hydrophobicity scale, which shows that our calibrated model can robustly
capture the conformational dynamics of IDPs. We then employ our model to study
the scaling of the radius of gyration with chemical distance in 11 known IDPs.
We identify a strong correlation between the distance to the dividing line
between folded proteins and IDPs in the mean charge and hydrophobicity space
and the scaling exponent of the radius of gyration with chemical distance along
the protein.Comment: 16 pages, 10 figure
Aqueous Phase C-H Bond Oxidation Reaction of Arylalkanes Catalyzed by a Water-Soluble Cationic Ru(III) Complex [(pymox-Me\u3csub\u3e2\u3c/sub\u3e)\u3csub\u3e2\u3c/sub\u3eRuCl\u3csub\u3e2\u3c/sub\u3e]\u3csup\u3e+\u3c/sup\u3eBF\u3csub\u3e4\u3c/sub\u3e\u3csup\u3e-\u3c/sup\u3e
The cationic complex [(pymox-Me2)RuCl2]+BF4â was found to be a highly effective catalyst for the CâH bond oxidation reaction of arylalkanes in water. For example, the treatment of ethylbenzene (1.0 mmol) with t-BuOOH (3.0 mmol) and 1.0 mol % of the Ru catalyst in water (3 mL) cleanly produced PhCOCH3 at room temperature. Both a large kinetic isotope effect (kH/kD = 14) and a relatively large Hammett value (Ï = â1.1) suggest a solvent-caged oxygen rebounding mechanism via a Ru(IV)-oxo intermediate species
Dipolar effect in coherent spin mixing of two atoms in a single optical lattice site
We show that atomic dipolar effects are detectable in the system that
recently demonstrated two-atom coherent spin dynamics within individual lattice
sites of a Mott state. Based on a two-state approximation for the two-atom
internal states and relying on a variational approach, we have estimated the
spin dipolar effect. Despite the absolute weakness of the dipole-dipole
interaction, it is shown that it leads to experimentally observable effects in
the spin mixing dynamics.Comment: 4 pages, 3 color eps figures, to appear in Phys. Rev. Let
Vanishing Hawking Radiation from a Uniformly Accelerated Black Hole
We consider quantum fields around uniformly accelerated black holes. At a
particular value of the acceleration, the Bogolubov transformation which would
be responsible for the late-time Hawking radiation, is found to be trivial.
When this happens, Hawking's thermal radiation, Doppler-shifted or not, is
absent to the asymptotic inertial observers despite the nonzero Hawking
temperature, while the co-moving observers find the black hole radiance exactly
balanced by the acceleration heat bath. After a brief comparison to the
classical system of a uniformly accelerated charge, we close with two important
comments. (Phys. Rev. Lett. 75 (1995) 382)Comment: LaTeX, 10pages, 2 figures (a typo in Eq.(3) corrected; minor
revisions to accomodate the length limitation of the journal
The Schwinger Mechanism, the Unruh Effect and the Production of Accelerated Black Holes
We compute the corrections to the transition amplitudes of an accelerated
Unruh ``box'' that arise when the accelerated box is replaced by a ``two level
ion'' immersed in a constant electric field and treated in second quantization.
There are two kinds of corrections, those due to recoil effects induced by the
momentum transfers and those due to pair creation. Taken together, these
corrections show that there is a direct relationship between pair creation
amplitudes described by the Heisenberg-Euler-Schwinger mechanism and the Unruh
effect, i.e. the thermalisation of accelerated systems at temperature where is the acceleration. In particular, there is a thermodynamical
consistency between both effects whose origin is that the euclidean action
governing pair creation rates acts as an entropy in delivering the Unruh
temperature. Upon considering pair creation of charged black holes in an
electric field, these relationships explain why black holes are created from
vacuum in thermal equilibrium, i.e. with their Hawking temperature equal to
their Unruh temperature.Comment: Revised version: expanded introduction and discussion of pair
creation of black holes, 2figures added, 22 pages, Late
Flavor and CP Violation with Fourth Generations Revisited
The Standard Model predicts a very small CP violation phase %= \arg M_{12} \simeq \arg\,(V^*_{ts}V_{tb})^2B_s\bar B_s\lambda^2\eta\Phi_{B_s}\sin2\Phi_{B_s}t'\Delta m_{B_s}{\cal B}(B \to X_s\ell^+\ell^-)f_{B_s}\sin2\Phi^{\rm
SM4}_{B_s} \sim -0.33m_{b'} = 4800.06 < |V_{t'b}| < 0.13\Gamma(Z\to b\bar b)\Delta m_{D}{\cal
B}(K^+\to\pi^+\nu\bar\nu){\cal
B}(K_L\to\pi^0\nu\bar\nu)V_{t'd}$.Comment: 8 pages, 11 figure
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