Search results for "waves"
showing 10 items of 1766 documents
Microwave-Assisted Organocatalytic Enantioselective Intramolecular aza-Michael Reaction with α,β-Unsaturated Ketones
2011
An organocatalytic enantioselective intramolecular aza-Michael reaction of carbamates bearing conjugated ketones as Michael acceptors is described. By using 9-amino-9-deoxy-epi-hydroquinine as the catalyst and pentafluoropropionic acid as a co-catalyst, a series of piperidines, pyrrolidines, and the corresponding benzo-fused derivatives (indolines, isoindolines, tetrahydroquinolines, and tetrahydroisoquinolines) can be obtained in excellent yields and enantioselectivities. In addition, the use of microwave irradiation at 60 °C improves the efficiency of the process giving rise to the final products with comparable yields and enantiomeric excesses. Some mechanistic insights are also consider…
A combined experimental and theoretical study of the thermal cycloaddition of aryl azides with activated alkenes.
2011
International audience; Reactions were performed from aryl azides on the one hand, and activated alkenes coming from β-dicarbonyl compounds or malonodinitrile on the other hand, either with recourse to conventional heating or to microwave activation, to afford 1-aryl-1H-1,2,3-triazoles. The mechanism and the regioselectivity of the reactions involving β-dicarbonyl compounds have been theoretically studied using DFT methods at the B3LYP/6-31G* level: they are domino processes comprising a tautomeric equilibrium of the β-dicarbonyl compounds with their enol forms, a 1,3-dipolar cycloaddition of the enol forms with the aryl azides (high activation energy), and a dehydration process (lower acti…
Amphiphilic Polysaccharide Block Copolymers for pH-Responsive Micellar Nanoparticles
2017
A full polysaccharide amphiphilic block copolymer was prepared from end group-functionalized dextrans using copper-mediated azide-alkyne click chemistry. Sufficient modification of the reducing end in both blocks was achieved by microwave-enhanced reductive amination in a borate-buffer/methanol solvent system. The combination of a hydrophilic dextran block with a hydrophobic acetalated dextran block results in an amphiphilic structure that turns water-soluble upon acid treatment. The material has a low critical micelle concentration and self-assembles in water to spherical micellar nanoparticles. The formed nanoparticles have a narrow size distribution below 70 nm in diameter and disassembl…
Microwave-Assisted Synthesis of New Selenazole Derivatives with Antiproliferative Activity
2013
New aryl-hydrazinyl-1,3-selenazole and aroyl-hydrazonyl-1,3-selenazoles were synthesized via Hantzsch type condensation reactions of selenosemicarbazides with α-halogenocarbonyl derivatives, under classical versus microwave heating conditions. Excellent yields and shorter reaction times were obtained under irradiation conditions. The structures of the synthesized compounds were assigned based on spectroscopic data (FT-IR, 1 H-NMR), MS and elemental analysis. Selenazole derivatives were screened for their anti-proliferative effects against two leukemia cell lines (CCRF-CEM and HL60) and three carcinoma cell lines (MDA-MB231, HCT116 and U87MG).
Measurement of polarization amplitudes and CP asymmetries in B 0 → Φk *(892)0
2014
An angular analysis of the decay $B^0 \to \phi K^*(892)^0$ is reported based on a $pp$ collision data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected at a centre-of-mass energy of $\sqrt{s} = 7$ TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave $K^+ \pi^-$ and $K^+K^-$ contributions are taken into account and found to be significant. A comparison of the $B^0 \to \phi K^*(892)^0$ and $\bar{B}^0 \to \phi \bar{K}^*(892)^0$ results shows no evidence for direct CP violation in the rate asymmetry, in th…
Totally dressed SDCI calculations: An application to HF and F2
1995
A previously proposed procedure including the linked and unlinked contributions due to Triple and Quadruple excitations into a size-consistent SDCI-like model has been applied to HF and F2 single-bond systems. The procedure is a non-iterative approximation to the more general total dressing model, which is based on the intermediate Hamiltonians theory. Three basis sets have been employed: the correlation consistent cc-pVTZ basis, a similar one including 3d1f polarization functions, and another including one set of g polarization functions. Excellent agreement with experiment and high-quality calculations is obtained for both equilibrium distances and spectroscopic constants. The possibiliti…
A theoretical study of the electronic spectrum of biphenyl
1995
Abstract The electronic spectrum of biphenyl in the energy range up to 6.0 eV has been studied using multiconfigurational second-order perturbation theory (CASPT2) and a basis set of ANO type, including polarization functions on all carbon atoms. The calculated spectrum gives conclusive assignments to all valence excited singlet states and the low-lying triplet states. The change of the torsional angle between the two benzene rings in the different excited states is shown to be of considerable importance and explains the different excitation energies observed in the gas phase as compared to solution or crystalline biphenyl at low temperatures. The intense transition to the 1 1B1u state is m…
Azobenzene Containing Low-Molecular Weight Organic Glasses for Optical Recording
2013
Abstract In this work photoinduced processes and holographic surface relief formation in azobenzene containing low- molecular weight organic glasses were studied. The molecular glasses due to trans-cis isomerisation and photo- orientation of molecules possess high sensitivity to the light irradiation and therefore they are promising media for holographic recording. Electric field of linearly polarized light causes an alignment of molecule dipoles perpendicularly to the electric field vector and this process is accompanied by an appearance of photoinduced optical anisotropy in organic glasses. The photoinduced birefringence and dichroism induced by 532 nm light was studied. Holographic recor…
Experimental and theoretical study of the nonlinear birefringence in the formation process of vector solitons in a total polarization control ring ca…
2022
Abstract In this work, we present the numerical and experimental investigation of the polarization dynamics in a free birefringence mode-locked fiber laser. The laser includes a double-pass Erbium-doped fiber amplifier and 20-m long bi-twisted fiber at a twist rate of ± 6 turns m−1 to mitigate both, linear and circular birefringence effects. We found ellipticity changes due to nonlinear birefringence in the 20-m long fiber during pulse formation and propagation. In contrast with previously reported works, the inclusion of bi-twisted fiber allows investigate the nonlinear effects independently from the linear ones. The experimental behavior was confirmed by numerical simulations based on spl…
Nonlinear mode coupling in a birefringent microstructured fiber tuned by externally applied hydrostatic pressure
2015
We studied the effect of power coupling between two linearly polarized modes, which occurs during nonlinear propagation in an externally tuned birefringent microstructured fiber. We investigated both experimentally and numerically the possibility of measuring hydrostatic pressure by tracking the nonlinear power coupling between the fiber polarization modes. We analyzed the impact of the fiber length exposed to pressure and the input polarization state on the coupling efficiency. We also revealed that the observation of nonlinear power coupling between the polarization modes is limited by linear coupling occurring in the leadthroughs to the pressure chamber. Moreover, we demonstrated that th…