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Molecule Model (molecule + model)

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Chemistry50%

Selected Abstracts

Models for the adsorption and self-assembly of ethanol and 1-decanethiol on Au(111) surfaces.

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2010
A comparative study by computer simulation
Abstract Results from computer simulations, based on different models to study theadsorption and self-assembly of the ethanol and 1-decanethiol on gold surfaces, Au(111), are presented. Canonical ensemble Monte Carlo simulations were performed at 298 K using two different force fields. One from DFT calculations, where the gold electrode has an explicit structure (corrugated electrode), and the other representing an electrode, in which the structure is taken into account on an average way (flat electrode). The behavior of the ethanol adsorption on gold surfaces, with and without the 1-decanethiol presence, is analyzed. The introduction of molecular flexibility is also discussed. The relative surface density for the ethanol oxygen, adsorbed on gold, and the density profiles, in different conditions, show that the structure of the surface has a fundamental role on the way the adsorption takes place, not only on the preferential adsorption sites of the surface but also on the ethanol distribution over the electrodes. Potentials of mean force have also been calculated for the two surface models, giving the free energy barriers to the 1-decanethiol crossing of the solvent adsorption layers. The average tilt angle, obtained with a single thiol molecule in the simulation box, presents the values: ,26° for the rigid molecule model and 74° ± 18° for the flexible one. These differences are analyzed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

Infrared transient absorption spectra for excited transition of excitons and biexcitons in CuCl

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2009
Takaaki Yoshioka
Abstract Infrared transient absorption (IRTA) spectra for excitons and biexcitons in CuCl bulk crystal have been measured by pump-probe spectroscopy. The IRTA peak energy of the exciton agrees with the transition energy between Rydberg 1s to 2p states reported in one- and two-photon absorption measurement. On the other hand, the IRTA peak energy of the biexcitons locates in energy higher than that of the excitons, which is reasonable by taking hydrogen molecule model into account. In addition, our results support the enhancement of the transition energy between 1s and 2p states in quantum dots compared to the bulk case. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Association between color doppler vascularity index, angiogenesis-related molecules, and clinical outcomes in gastric cancer

JOURNAL OF SURGICAL ONCOLOGY, Issue 7 2009
Chiung-Nien Chen MD
Abstract Purpose This study was conducted to evaluate the correlation between color Doppler vascularity index (CDVI), clinical outcomes and five angiogenesis-related molecules including vascular endothelial growth factor (VEGF), placenta growth factor (PlGF), cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and calreticulin (CRT) in gastric cancer, and to develop an effective model selected from these five molecules to predict patient survival. Patients and Methods CDVI could be obtained preoperatively by transabdominal ultrasound from 30 patients. Enzyme immunoassay was adopted to determine protein level of VEGF and PlGF, and immunohistochemistry was used to detect COX-2, iNOS and CRT expression. Correlation between CDVI and five individual molecules was assessed. Multiple molecules model was developed using classification and regression tree (CART) analysis from five molecules, and was tested for patient survival in another 45 patients. Results CDVI was significantly correlated with patient survival (P,=,0.00907) and absolute number of metastatic lymph nodes (P,=,0.01). There was no significant association between CDVI and any individual molecule. The model, developed by CART consisting of VEGF and PlGF, could differentiate high and low CDVI and survival in testing group (P,=,0.00257). Conclusions CDVI was associated with lymph node metastasis, combined VEGF and PlGF expression status and patient survival in gastric cancer. J. Surg. Oncol. 2009;99:402,408. © 2009 Wiley-Liss, Inc. [source]

Electron localization functions obtained from X-ray constrained Hartree,Fock wavefunctions for mol­ecular crystals of ammonia, urea and alloxan,

ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2004
Dylan Jayatilaka
Constrained Hartree,Fock wavefunctions in the superposition of isolated molecules model have been calculated from precise X-ray diffraction data on crystals of ammonia (NH3), urea [CO(NH2)2] and alloxan [(CO)4(NH)2]. The X-ray constrained wavefunctions have been used to derive and examine `electron localization' information, quantified by the true and approximate electron localization function (ELF), and the true and approximate Fermi hole mobility function (FHMF). The plots of the Fermi hole mobility function are the first to appear in the literature. The results are compared with corresponding isolated-molecule Hartree,Fock calculations to gauge the effect of the crystal environment on the isolated molecules. An error analysis is performed to indicate the features in the plots which are well determined from the experimental data. The results from all plots are broadly consistent, but the approximate ELF shows some artifacts relative to the true ELF. [source]