1,721,012 research outputs found
Role of coverage on the electron properties of sulfur chemisorbed on Cu(100): ab initio calculations
No full textWe present an ab initio study of the electronic properties of the S∕Cu(100) surface, with sulfur chemisorbed in the c(2×2) geometry, and compare it with the p(2×2) phase. We find that the two geometries, observed, respectively, at 0.5 ML and 0.25 ML of sulfur coverage, affect both the density of states and the dispersion and charge distribution of the hybrid S-Cu electronic states. The same superstructures occur under suitable experimental conditions also when organic molecules containing a sulfur atom as a headgroup, like MBO and CH3S, are chemisorbed on Cu(100). We show that the electronic properties of the S-Cu hybrid in simple S∕Cu(100) may be used to interpret succesfully the experimental results of these two complex molecular systems
Optical Response of Copper Surface to Carbon Monoxide Deposition
No full textThe optical response of the Cu surface upon CO deposition is investigated from the clean Cu(110) to the reconstructed CO/Cu(110)-p(2×1) geometry through ab initio electronic structure calculations. We ascribe the relevant structures in the calculated reflectance anisotropy spectrum of the reconstructed phase to the persistence of surface states transitions. These are excited by light polarized along the direction perpendicular to the one found at the clean surface. We devise a simple model for the evolution of the optical response in the adsorption process, identifying three different regimes. The impurity regime, at very low coverages, is characterized by a critical coverage that enhances the actual one by a factor of ≃ 30, close to the value estimated experimentally
Thermodynamics and kinetics of ion translocation in the human wild-type and E-1' A α7 nicotinic receptor
No full textWe use an all-atom model of the human nicotinic acetylcholine receptor α7 in a conductive conformation, to provide the first available mapping of the potential of mean force for the ion translocation across the channel. The modeling is based on MD simulations combined with the milestoning method with Voronoi tessellation. The quality of the protein model and description is confirmed by the agreement with experimental data for proteins of the same family. The specific mutation E-1' A at the cytoplasmatic filter is here shown to strongly affect both sodium and chloride permeation, leading to a complete inversion of selectivit
Ab initio characterization of surface states at the S/Cu(100) interface
No full textS headgroups are present in many organic molecules and realize their adsorption on metallic surfaces. We calculate ab initio the electronic structure of S/Cu(100) adopting the same geometry as that of the S atom in the C7H5NOS molecule on the same surface. The interface, represented by the S overlayer and by the Cu subsurface layer, is characterized quantitatively by the surface state dispersion of the S-Cu hybrids (bonding and antibonding). The role of the S atom as “hook” for the whole molecule is strongly supported by our calculations. Our results are in quantitative agreement with the photoemission results of C7H5NOS on Cu and also in qualitative agreement with more complicated biological adsorbates on different metallic surface
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A possible desensitized state conformation of the human alpha7 nicotinic receptor: A molecular dynamics study
No full textThe determination of the conformational states corresponding to diverse functional roles of ligand gated ion channels is subject of intense investigation with various techniques, from X-rays structure determination to electrophysiology and computational modeling. Even with a certain number of structures becoming recently available, only few major structural features distinguishing conductive open channel from the non conductive resting protein have been highlighted, while high-resolution details are still missing. The characterization of the desensitized conformation(s) is even more complex, and only few specific characteristics have been identified. Furthermore, experimental data provide conflicting information for different ion channels, adding further complexity to the topic. Desensitization is defined as the transition of the agonist-bound open channel into an ion channel configuration inactive even in the presence of agonists. In this work, we analyze a conformation corresponding to a non conductive state obtained via molecular dynamics simulations of a homology model of the human α7 nicotinic receptor complexed with agonists. We highlight some characteristics that could associate it to a desensitized state. The obtained structure is assessed against experimental data for other ligand gated ion channels that have been putatively associated to active, inactive and desensitized conditions
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