排序方式: 共有158条查询结果,搜索用时 15 毫秒
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Lasorne B Sicilia F Bearpark MJ Robb MA Worth GA Blancafort L 《The Journal of chemical physics》2008,128(12):124307
A new practical method to generate a subspace of active coordinates for quantum dynamics calculations is presented. These reduced coordinates are obtained as the normal modes of an analytical quadratic representation of the energy difference between excited and ground states within the complete active space self-consistent field method. At the Franck-Condon point, the largest negative eigenvalues of this Hessian correspond to the photoactive modes: those that reduce the energy difference and lead to the conical intersection; eigenvalues close to 0 correspond to bath modes, while modes with large positive eigenvalues are photoinactive vibrations, which increase the energy difference. The efficacy of quantum dynamics run in the subspace of the photoactive modes is illustrated with the photochemistry of benzene, where theoretical simulations are designed to assist optimal control experiments. 相似文献
43.
Vilaseca E Isvoran A Madurga S Pastor I Garcés JL Mas F 《Physical chemistry chemical physics : PCCP》2011,13(16):7396-7407
Particle diffusion in crowded media was studied through Monte Carlo simulations in 3D obstructed lattices. Three particular aspects affecting the diffusion, not extensively treated in a three-dimensional geometry, were analysed: the relative particle-obstacle size, the relative particle-obstacle mobility and the way of having the obstacles distributed in the simulation space (randomly or uniformly). The results are interpreted in terms of the parameters that characterize the time dependence of the diffusion coefficient: the anomalous diffusion exponent (α), the crossover time from anomalous to normal diffusion regimes (τ) and the long time diffusion coefficient (D*). Simulation results indicate that there are a more anomalous diffusion (smaller α) and a lower long time diffusion coefficient (D*) when obstacle concentration increases, and that, for a given total excluded volume and immobile obstacles, the anomalous diffusion effect is less important for bigger size obstacles. However, for the case of mobile obstacles, this size effect is inverted yielding values that are in qualitatively good agreement with in vitro experiments of protein diffusion in crowded media. These results underline that the pattern of the spatial partitioning of the obstacle excluded volume is a factor to be considered together with the value of the excluded volume itself. 相似文献
44.
Isarain-Chávez E Garrido JA Rodríguez RM Centellas F Arias C Cabot PL Brillas E 《The journal of physical chemistry. A》2011,115(7):1234-1242
Solutions of about 0.25 mM of the β-blocker metoprolol tartrate (100 mg L(-1) total organic carbon) with 0.5 mM Fe(2+) in the presence and absence of 0.1 mM Cu(2+) of pH 3.0 have been comparatively degraded under electro-Fenton (EF) and photoelectro-Fenton (PEF) conditions. The electrolyses were carried out with two systems: (i) a single cell with a boron-doped diamond (BDD) anode and an air-diffusion cathode (ADE) for H(2)O(2) electrogeneration and (ii) a combined cell with a BDD/ADE pair coupled with a Pt/carbon felt (CF) cell. Overall mineralization was reached in all PEF treatments using both systems due to the efficient production of hydroxyl radical ((?)OH) from Fenton's reaction induced by UVA light and the quick photolysis of Fe(III) carboxylate complexes formed. In EF, the combined cell was much more potent than the single one by the larger (?)OH generation from the continuous Fe(2+) regeneration at the CF cathode, accelerating the oxidation of organics. However, almost total mineralization in EF was feasible using the combined cell in the presence of 0.1 mM Cu(2+), because of the parallel quick oxidation of Cu(II) carboxylate complexes by (?)OH. Metoprolol decay always followed a pseudo-first-order reaction. Aromatic products related to consecutive hydroxylation/oxidation reactions of metoprolol were detected by gas chromatography-mass spectrometry. The evolution of the aromatic 4-(2-methoxyethyl)phenol and generated carboxylic acids was followed by HPLC. The degradation rate and mineralization degree of metoprolol tartrate were limited by the removal of Fe(III) and Cu(II) complexes of ultimate carboxylic acids such as formic, oxalic, and oxamic. NH(4)(+) ion and to a lesser extent NO(3)(-) ion were released in all treatments, being quantified by ionic chromatography. 相似文献
45.
Migani A Leyva V Feixas F Schmierer T Gilch P Corral I González L Blancafort L 《Chemical communications (Cambridge, England)》2011,47(22):6383-6385
o-Nitrobenzaldehyde is photolabile because of an irreversible phototautomerization, whereas comparable aromatic compounds function as photoprotectors because the tautomerization is reversible. In this experimental and theoretical study we track down the cause of this difference to the electronic changes that occur during the tautomerization. 相似文献
46.
One of the most significant and well-known properties of entangled states is that they may lead to violations of Bell inequalities and are thus inconsistent with any local-realistic theory. However, there are entangled states that cannot violate any Bell inequality, and in general the precise relationship between entanglement and observable nonlocality is not well understood. We demonstrate that a violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality can be demonstrated in a certain kind of Bell experiment for all entangled states. Our proof of the result consists of two main steps. We first provide a simple characterization of the set of states that do not violate the CHSH inequality even after general local operations and classical communication. Second, we prove that for each entangled state sigma, there exists another state rho not violating the CHSH inequality, such that rhomultiply sign in circlesigma violates the CHSH inequality. 相似文献
47.
[reaction: see text] A readily available chiral amino alcohol has been immobilized on silica by sol-gel synthesis and grafting. The solid prepared according to the latter method led to the best enantioselectivity (77% ee) described for the asymmetric addition of diethylzinc to benzaldehyde using inorganic solids. 相似文献
48.
Touriño S Fuguet E Jáuregui O Saura-Calixto F Cascante M Torres JL 《Rapid communications in mass spectrometry : RCM》2008,22(22):3489-3500
Grape antioxidant dietary fiber (GADF) is a dietary supplement that combines the benefits of both fiber and antioxidants that help prevent cancer and cardiovascular diseases. The antioxidant polyphenolic components in GADF probably help prevent cancer in the digestive tract, where they are bioavailable. Mass spectrometry coupled to liquid chromatography is a powerful tool for the analysis of complex plant derivatives such as GADF. We use a combination of MS techniques, namely liquid chromatography/electrospray ionization time-of-flight mass spectrometry (LC/ESI-TOF-MS) and liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) on a triple quadrupole, for the identification of the polyphenolic constituents of the soluble fraction of GADF. First, we separated the mixture into four fractions which were tested for phenolic constituents using the TOF system in the full scan mode. The high sensitivity and resolution of the TOF detector over the triple quadrupole facilitate the preliminary characterization of the fractions. Then we used LC/ESI-MS/MS to identify the individual phenols through MS/MS experiments (product ion scan, neutral loss scan, precursor ion scan). Finally, most of the identities were unequivocally confirmed by accurate mass measurements on the TOF spectrometer. LC/ESI-TOF-MS combined with MS/MS correctly identifies the bioactive polyphenolic components from the soluble fraction of GADF. High-resolution TOF-MS is particularly useful for identifying the structure of compounds with the same LC/ESI-MS/MS fragmentation patterns. 相似文献
49.
Martínez-Cuenca R Durán V Arines J Ares J Jaroszewicz Z Bará S Martínez-León L Lancis J 《Optics letters》2011,36(18):3702-3704
We propose a closed-loop adaptive optical arrangement based on a single spatial light modulator that simultaneously works as a correction unit and as the key element of a wavefront sensor. This is possible by using a liquid crystal on silicon display whose active area is divided into two halves that are respectively programmed for sensing and correction. We analyze the performance of this architecture to implement an adaptive optical system. Results showing a closed-loop operation are reported, as well as a proof of concept for dealing with aberrations comparable to those typically found in human eyes. 相似文献
50.
Leyva V Corral I Schmierer T Heinz B Feixas F Migani A Blancafort L Gilch P González L 《The journal of physical chemistry. A》2008,112(23):5046-5053
The experimental UV/vis absorption spectrum of ortho-nitrobenzaldehyde (o-NBA) has been assigned by means of MS-CASPT2/CASSCF, TD-DFT, and RI-CC2 theoretical computations. Additional information on the nature of the absorbing bands was obtained by comparing the o-NBA spectrum with that of related compounds, as, e.g., nitrobenzene and benzaldehyde. For wavelengths larger than approximately 280 nm, the absorption spectrum of o-NBA is dominated by a series of weak n pi* absorptions from the NO2 and CHO groups. These weak transitions are followed in energy by a more intense band, peaking at 250 nm and arising from charge transfer pi pi* excitations involving mainly benzene and nitro orbitals. Finally, the most intense band centered at 220 nm has its origin in the overlap of two different absorptions: the first one localized in the NO2 substituent and the second one arising from a charge transfer excitation involving the NO2 and the CHO fragments, respectively. 相似文献