1,720,994 research outputs found
Stability and potential degradation of the α′,β′-epoxyketone pharmacophore on ZnO nanocarriers: insights from reactive molecular dynamics and density functional theory calculations
No full textWe investigate the structure and dynamics of a zinc oxide nanocarrier loaded with Carfilzomib, an epoxyketone proteasome inhibitor developed for treating multiple myeloma. We demonstrate that, even though both bare and functionalized zinc oxide supports have been used for drug delivery, their interactions with the reactive functional groups of the ligands could be detrimental. This is because pharmacophores like α′,β′-epoxyketones should preserve the groups required for the drug activity and be capable of leaving the vehicle at the target site. Earlier studies showed that even when ZnO is functionalized with oleic acid surfactants, the drug could reach parts of the surface and remain stably adsorbed. Herein, we have used reactive molecular dynamics simulations and quantum chemistry calculations to explore the potential interactions of the Carfilzomib functional groups with the typical surfaces of ZnO supports. We have found that Carfilzomib can adsorb on the (0001)Zn-terminated polar surface through the carbonyl oxygens and the epoxyketone moiety. These strong connections could prevent the drug release and induce the epoxy ring opening with its consequential inactivation. Therefore, regulating the dosage to maintain the desired level of drug bioavailability is paramount. These findings emphasize the need for appropriate carrier functionalizations to efficiently entrap, transport, and release the cargo at the target sites and the crucial role played by predictive/descriptive computational techniques to complement and drive experiments to the most appropriate selections of the materials to optimize drug delivery
Metal adsorption on oxide polar ultrathin films
No full textThe adsorption of Au and Pd atoms on two nanostructured titania monolayers grown on the Pt(111) surface is investigated via a computational approach. These phases present compact regions (zig-zag-like stripes) with titanium atoms at the oxide–metal interface and oxygen in the top-most overlayer, sometimes intercalated by point defects, i.e. holes exposing the bare metal support, and give rise to very regular patterns extending for large distances. A Pd atom experiences a rather flat energy landscape on the compact regions whereas it is strongly bound to the defects which act as nucleation centers, whence the interest of these substrates as nanotemplates for the growth of metal clusters. The interaction of a Au atom with these phases is peculiarly different: a charge transfer from the underlying Pt(111) support occurs so that Au gets negatively charged and strongly interacts with a titanium atom extracted from the interface in the compact regions, whereas it penetrates less easily than Pd into the defective holes due to its larger size. These results are discussed as paradigmatic examples of the interaction of metals with polar ultrathin films of oxides grown on metal supports, a novel and promising field in materials science
Disclosing gate-opening/closing events inside a flexible metal-organic framework loaded with CO2 by reactive and essential dynamics
No full textWe have combined reactive molecular dynamics simulations with principal component analysis to provide a clearer view of the interactions and motion of the CO2 molecules inside a metal-organic framework and the movements of the MOF components that regulate storage, adsorption, and diffusion of the guest species. The tens-of-nanometer size of the simulated model, the capability of the reactive force field tuned to reproduce the inorganic-organic material confidently, and the unconventional use of essential dynamics have effectively disclosed the gate-opening/closing phenomenon, possible coordinations of CO2 at the metal centers, all the diffusion steps inside the MOF channels, the primary motions of the linkers, and the effects of their concerted rearrangements on local CO2 relocations
Structure of a TiOx zigzag-like monolayer on pt(111)
No full textThe structure of a monolayer phase of TiOx on Pt(111) has been investigated by low-energy electron diffraction (LEED), atomic resolved scanning tunneling microscopy (STM), and density functional (DF) calculations. According to LEED, the rectangular unit cell (6.8 × 8.6 Å2) is incommensurate with respect to the Pt(111) substrate unit cell. The STM data show a clear zigzag-like motif and dimensions in perfect agreement with the LEED data. A structural model, which is in tune with the whole set of experimental data, has been obtained by a DF geometry optimization starting from a guessed structure proposed on the basis of chemical considerations and the comparison with literature data. The stoichiometry of the monolayer is Ti6O8 and the Ti atoms are formally in the +2.7 oxidation state, in agreement with previously reported photoemission data. However, two different types of Ti atoms have been found, that is, Ti atoms coordinated by four oxygen atoms, which give rise to the brighter bumps in the zigzag-like STM motif, and Ti atoms coordinated by only three oxygen atoms, which appear darker in the STM images. Analogously, two different types of oxygen atoms can be distinguished, with those lying in the throughs of the STM images (“bridge” oxygens) being less coordinated and in a lower oxidation state. The energetics of the interaction of the oxide monolayer with the Pt substrate has been computationally evaluated. Even if the oxide/metal interaction is important in determining the high stability and the structure of the oxide film, it conveys that this interaction is only weakly directional, thus, justifying the incommensurate nature of the film
Designing ligand-enhanced optical absorption of thiolated gold nanoclusters
No full textThe optical spectra of thiolated Au25(SR)18/Au23(SR)16 clusters with
different R residues are investigated via TDDFT simulations. Significant
enhancements in the optical region and effective electron delocalization
are simultaneously achieved by tuning the ligands’ steric hindrance and
electronic conjugating features, producing a resonance phenomenon
between the Au–S core motif and the ligand fragment
Cooperative Phase Transformation in Self-Assembled Metal-on-Oxide Arrays
No full textThe thermal behavior of a composite system formed by gold nanoclusters self-organized on a TiOx/Pt(111) ultrathin film is investigated via first-principles simulations. A cooperative phase transformation from a rectangular to an hexagonal phase occurs at high temperature, by which Au clusters do not coalesce, but rearrange their shape and positions together with the more mobile regions of the oxide. A model describing the atomistic processes behind this transformation is proposed that is in full agreement with available experimental data
Defect evolution in oxide nanophases: The case of a zigzag-like TiOx phase on Pt(111)
No full textThe structure of a monolayer phase of TiOx on Pt(111) showing a zigzag-like contrast is investigated by scanning tunneling microscopy (STM) and density-functional calculations. Because of its peculiar defectivity, strongly dependent on the postdeposition thermal treatments, this system is an ideal model to study the structure and the evolution of defects in oxide nanophases. Atomistic models for each of the detected defects are obtained, which accurately reproduce the STM images showing that the experimentally observed defects essentially consist of Ti vacancies or irregular atomic distributions within the troughs exposing the bare substrate surface and that their formation energy is quite small, so that the system is under kinetic control in the given conditions of T and pO2
Alloying effects on the optical properties of Ag-Au nanoclusters from TDDFT calculations
No full textThe optical properties of alloyed AgAu 147-atom cuboctahedral nanoclusters are theoretically investigated as a function of composition and chemical ordering via a time-dependent density functional theory (TDDFT) approach. Compositions 3763%, 4654%, and 6337%, in AgAu, and three types of chemical ordering, coreshell, multishell and maximum mixing, are considered. Additionally, the optical spectra of pure Ag clusters with several structural motifs are also studied. It is found that (a) pure Ag clusters exhibit a neater dependence of the absorption peak on the shape of the cluster than Au clusters, (b) the absorption spectrum of alloyed clusters is not strongly affected by changes in chemical ordering, possibly because of their limited size, and (c) the optical absorption peak smoothly shifts to higher energies, gets narrower, and substantially gains in intensity by increasing Ag concentration, in excellent agreement with available experimental data. An analysis of the character of the electronic transitions mostly contributing to the absorption peak allows us to rationalize the notable difference between Ag and Au in terms of optical properties and the effect of alloying
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
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