1,720,990 research outputs found
Modeling (100) hydrogen-induced platelets in silicon: a multiscale molecular dynamics approach
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Piezo-spectroscopic determination of residual stresses in an Al2O3/NiAl FGM
No full textFGM composites have been prepared using Al2O3 and NiAl powders. Pure Al2O3 and NiAl layers have been joined trough a mixed layer (70% vol Al2O3 and 30% vol NiAl). The residual stress in Al2O3 has been experimentally determined by monitoring the stress-induced frequency shift of a fluorescence band due to chromium impurities naturally present in the Al2O3 powder. The stress in Al2O3 is compressive increasing in absolute value when moving from pure alumina to pure NiAl. In the mixed Al2O3/NiAl the stress present large fluctuations from site to site due to local microstructural inhomogeneities
Tracking the Chiral Recognition of Adsorbed Dipeptides at theSingle-Molecule Level
No full textHerein we report on the direct observation of chiral recognition events of adsorbed diphenylalanine by scanning tunneling microscopy (STM). The interaction among individual di-d-phenylalanine (d-Phe-d- Phe) molecules and the discrimination of d-Phe-d-Phe from its enantiomer l-Phe-l-Phe on Cu(110) is followed by STM and rationalized by using first principles and classical
molecular dynamics techniques. We find that the stereoselective
assembly of adsorbed di-phenylalanine enantiomers into
molecule pairs and chains takes place through mutually
induced conformational changes, thereby illustrating at the
single-molecule level the more than half a century old
prediction of Pauling
Molecular Dynamics Simulations of the Silica–Cell Membrane Interaction: Insights on Biomineralization and Nanotoxicity
No full textThe interaction of
silica (SiO2) with biological systems
is complex and contradictory. On the one hand, silica is at the basis
of several biomineralization processes (e.g., in sponges). On the
other hand, silica nanoparticles and dust may lead to silicosis and,
at the cellular level, hemolysis. These toxic responses are strongly
dependent on the silica polymorph and their root causes are still
under debate. Both silica biomineralization and silica-induced nanotoxicity
could be related to similar mechanisms of molecular recognition between
the cellular membranes and the surface of the SiO2 particles.
On the basis of this hypothesis, we employed classical molecular dynamics
simulations, coupled to advanced sampling techniques, to achieve an
atomistic picture of the interactions between different types of silica
nanoparticles and the membrane of erythrocytes. Our predicted free-energy
profiles associated with membrane crossing give no evidence for segregation
of nanoparticles at the membrane/water interface, irrespective of
their Si nuclearity, structure, and charge. The associated molecular
trajectories, however, are suggestive of a possible direct translocation
mechanism, in which silica nanoclusters elicit both local and large-scale
effects on the membrane dynamics and stability. This gives hints on
possible pathways for silica nanotoxicity based on nanoparticle-induced
membrane perforation
Deposition of calcium ion on rutile (110): a first principle investigation
No full textThe deposition of calcium ions is the first and most crucial step of apatite nucleation on ceramic supports from ionic solution. This process is believed to initiate the growth of bone-like material on the surface of biocompatible implants. We have investigated the adsorption of Ca/sup 2+/ from water solution on the rutile TiO/sub 2/ (110) surface by means of first principles techniques. The preferential binding site of the calcium ion on the hydrated oxide surface was determined through a series of static calculations. Molecular dynamics simulations were then performed to elucidate the deposition pathway. The driving force for adsorption is identified in the electrostatic interaction between the Ca/sup 2+/ complexes and negatively charged deprotonated sites present on the hydrated TiO/sub 2/ (110) surface. (35 References)
Impact of the Conformational Variability of Oligopeptides on the Computational Prediction of Their CD Spectra
No full textAlthough successful in the structural determination of ordered biomolecules, the spectroscopic investigation of oligopeptides in solution is hindered by their complex and rapidly changing conformational ensemble. The measured circular dichroism (CD) spectrum of an oligopeptide is an ensemble average over all microstates, severely limiting its interpretation, in contrast to ordered biomolecules. Spectral deconvolution methods to estimate the secondary structure contributions in the ensemble are still mostly based on databases of larger ordered proteins. Here, we establish how the interpretation of CD spectra of oligopeptides can be enhanced by the ability to compute the same observable from a set of atomic coordinates. Focusing on two representative oligopeptides featuring a known propensity toward an α-helical and β-hairpin motif, respectively, we compare and cross-validate the structural information coming from deconvolution of the experimental CD spectra, sequence-based de novo structure prediction, and molecular dynamics simulations based on enhanced sampling methods. We find that small conformational variations can give rise to significant changes in the CD signals. While for the simpler conformational landscape of the α-helical peptide de novo structure prediction can already give reasonable agreement with the experiment, an extended ensemble of conformers needs to be considered for the β-hairpin sequence
Structural and Computational Assessment of the Influence of Wet-Chemical Post-Processing of the Al-Substituted Cubic Li7La3Zr2O12
No full textLi7La3Zr2O12 (LLZO) and related compounds are considered as promising candidates for future all-solid-state Li-ion battery applications. Still, the processing of those materials into thin membranes with the right stoichiometry and crystal structure is difficult and laborious. The sensitivity of the Li-ion conductive garnets against moisture and the associated Li+/H+ cation exchange makes their processing even more difficult. Formulation of suitable polymer/ceramic hybrid solid state electrolytes could be a prosperous way to reach the future large scale production of solid state Li-ion batteries. In fact, solvent mediated and/or slurry based wet-processing of the LLZO, e.g., tape-casting, could result in irreversible Li-ion loss of the pristine material due to Li+/H+ cation exchange. The concomitant structural changes and loss in functionality in terms of Li-ion conductivity are the results of the above process. Therefore, in the present work a systematic study on the chemical stability and structural retention of Al-substituted LLZO in different solvents is reported. It was found that Li+/H+ exchange in LLZO occurs upon solvent immersion, and its magnitude is dependent on the availability of -OH functional groups of the solvent molecules. As a result, a larger degree of Li+/H+ exchange causes higher increase of the lattice parameter of the LLZO, determined by synchrotron diffraction analyses. The expansion of the cubic unit cell was ascertained, when Li+ was replaced by H+ in the host lattice, by ab initio computational studies. The application of the most common solvent as dispersion medium, i.e., high purity water, causes the most significant Li+/H+ exchange and, therefore, structural change, while acetonitrile was proven to be the best suitable solvent for wet postprocessing of LLZO. Finally, computational calculations suggested that the Li+/H+ exchange could result in diminished ionic, i.e., mixed Li+-H+, conductivity due to the insertion of protons with lower mobility than that of Li-ions
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