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721.
Recently, an analytic two-particle density matrix (2DM) has been derived for the quintet state of four electrons interacting via two-body harmonic forces. Here we use this 2DM to extract the exact pair density $\Gamma (\mathbf{r}_1,\mathbf{r}_2)$ . This is then employed in the known two-particle partial differential equation for the pair density amplitude to extract the Pauli potential $v_P(\mathbf{r}_1,\mathbf{r}_2)$ for this quintet state. 相似文献
722.
Dr. Laura Rubio‐Pérez Dipl.‐Chem. Ramón Azpíroz Dr. Andrea Di Giuseppe Dr. Victor Polo Dr. Ricardo Castarlenas Prof. Jesús J. Pérez‐Torrente Prof. Luis A. Oro 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(45):15304-15314
A general regioselective rhodium‐catalyzed head‐to‐tail dimerization of terminal alkynes is presented. The presence of a pyridine ligand (py) in a Rh–N‐heterocyclic‐carbene (NHC) catalytic system not only dramatically switches the chemoselectivity from alkyne cyclotrimerization to dimerization but also enhances the catalytic activity. Several intermediates have been detected in the catalytic process, including the π‐alkyne‐coordinated RhI species [RhCl(NHC)(η2‐HC?CCH2Ph)(py)] ( 3 ) and [RhCl(NHC){η2‐C(tBu)?C(E)CH?CHtBu}(py)] ( 4 ) and the RhIII–hydride–alkynyl species [RhClH{? C?CSi(Me)3}(IPr)(py)2] ( 5 ). Computational DFT studies reveal an operational mechanism consisting of sequential alkyne C? H oxidative addition, alkyne insertion, and reductive elimination. A 2,1‐hydrometalation of the alkyne is the more favorable pathway in accordance with a head‐to‐tail selectivity. 相似文献
723.
Enrique Poulain Alberto Rubio‐Ponce Victor Hugo Uc Virineya Bertin Oscar Olvera‐Neria 《International journal of quantum chemistry》2013,113(13):1794-1802
Nitrous oxide (N2O) is an intermediate compound formed during catalysis occurring in automobile exhaust pipes. In this work, the N2O capture and activation by Pt and Pd atoms in the ground and excited states of many multiplicities are studied. Pt and Pd + N2O reactions are studied at multireference second‐order perturbation level of theory using Cs symmetry. The PtN2O (1A′, 5A′, and 5A″) species are spontaneously created from excited states. Only the 5A′ and 5A″ states exhibit N2O activation reaction paths when N2O approaches Pt end‐on by the N or O atoms side or side‐on yielding NO or N2 as products, respectively. Pt+ cations ground and excited states, capture N2O, although only Pt+ (6A′ and 6A″) states show N2O activation yielding O and N2 as products. In the Pd atom case, PdN2O (1A′ and 5A″) species are also spontaneously created from excited states. The 5A″ state exhibits N2O activation yielding N2 + O as products. Pd+ cations in both ground and excited states capture N2O; however, only the [PdN2O]+ (4A′, 4A″, 6A′, and 6A″) states in side‐on approaches and (6A′) in end‐on approach activate the N2O and yield the N2 bounded to the metal and O as product. The results obtained in this work are discussed and compared with previous calculations of Rh and Au atoms. The reaction paths show a metal–gas dative covalent bonding character. Löwdin charge population analyses for Pt and Pd active states show a binding done through charge donation and retrodonation between the metals and N2O. © 2013 Wiley Periodicals, Inc. 相似文献
724.
Rodríguez G Barbosa-Barros L Rubio L Cócera M López-Iglesias C de la Maza A López O 《Colloids and surfaces. B, Biointerfaces》2011,84(2):108-394
The characterization of different bicellar aggregates and the effects of these systems on the stratum corneum (SC) microstructure have been studied. Dynamic light scattering (DLS) and freeze fracture electron microscopy (FFEM) techniques showed that both of the systems studied, dimyristoyl-phosphatidylcholine/dihexanoyl-phosphocholine (DMPC/DHPC) and dipalmitoyl-phosphocholine (DPPC)/DHPC, were formed by small discoidal aggregates at room temperature (20°C). Treating skin with DMPC/DHPC bicelles does not affect the SC lipid microstructure, whereas bicellar systems formed by DPPC and DHPC can promote the formation of new structures in the SC lipid domains. This indicates the passage of lipids from bicelles through the SC layers and also a possible interaction of these lipids with the SC lipids. Given the absence of surfactant in the bicellar composition and the small size of these structures, the use of these smart nano-systems offers great advantages over other lipid systems for dermatological purposes. Bicelles could be promising applications as drug carriers through the skin. This contribution, based on the new biological use of bicelles, may be useful to scientists engaged in colloid science and offers a new tool for different applications in skin and cosmetic research. 相似文献
725.
Campo J Nierop KG Cammeraat E Andreu V Rubio JL 《Journal of chromatography. A》2011,1218(30):4817-4827
The heating effect on the soil organic matter (SOM) of a Mediterranean soil was studied in two fractions (macro- and microaggregates) and in two environments (soil under canopy of Quercus coccifera and bare soil between plants). Samples were heated under laboratory conditions at different temperatures (220, 380 and 500°C) to establish their effects on the SOM quality and quantity by comparison with unheated control samples (25°C). The SOM content in the soil under canopy was higher than in the bare one and in the microaggregate fractions than in the macroaggregate ones. Increasing temperatures caused, in general, the decrease of SOM content in both soils as well as in both aggregate classes. The quality of SOM was determined after extraction with 0.1 M NaOH and analysed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Obtained pyrolysates were characterized by the presence of polyphenols and other aromatic pyrolysis products (lipids, polysaccharides, proteins and lignin derivatives). Some of the products in these control samples, and furthermore the presence of black carbon (BC) markers (e.g. benzene, pyridine and toluene), confirmed the occurrence of past wildfires in the study zone. The composition of the SOM extracted from the soils heated at 220°C, was quite similar to that obtained from unheated soils. The products derived from polysaccharides and lignin, and some coming from polyphenols, were not detected in the pyrolysates of the soil heated at 380 and 500°C. 相似文献
726.
E. Chigo Anota H. Hernández Cocoletzi E. Rubio Rosas 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,63(2):271-273
Based on the density functional theory whitin the local density aproximation, we
investigated the adsorption of the ozone molecule by the boron nitride sheet. To model the
sheet we used a planar C
n
H
m
cluster; four high symmetry sites in the mesh were considered. A total energy calculation
indicates that the boron nitride sheet remains planar and the ozone is adsorbed with an
energy of 0.41 eV; the ozone reacts with the sheet forming an epoxy group and an oxygen
molecule in an unstable configuration. 相似文献
727.
Norah M. Hoffmann Heiko Appel Angel Rubio Neepa T. Maitra 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(8):180
The exact factorization approach, originally developed for electron-nuclear dynamics, is extended to light-matter interactions within the dipole approximation. This allows for a Schrödinger equation for the photonic wavefunction, in which the potential contains exactly the effects on the photon field of its coupling to matter. We illustrate the formalism and potential for a two-level system representing the matter, coupled to an infinite number of photon modes in the Wigner-Weisskopf approximation, as well as to a single mode with various coupling strengths. Significant differences are found with the potential used in conventional approaches, especially for strong couplings. We discuss how our exact factorization approach for light-matter interactions can be used as a guideline to develop semiclassical trajectory methods for efficient simulations of light-matter dynamics. 相似文献