Theoretical analysis of uranium-doped thorium dioxide: Introduction of a thoria force field with explicit polarization

Thorium dioxide is used industrially in high temperature applications, but more insight is needed into the behavior of the material as part of a mixed-oxide (MOX) nuclear fuel, incorporating uranium. We have developed a new interatomic potential model including polarizability via a shell model, and commensurate with a prominent existing UO2 potential, to conduct configurational analyses and to investigate the thermophysical properties of uranium-doped ThO2. Using the GULP and Site Occupancy Disorder (SOD) computational codes, we have analyzed the distribution of low concentrations of uranium in the bulk material, where we have not observed the formation of uranium clusters or the dominance of a single preferred configuration. We have calculated thermophysical properties of pure thorium dioxide and Th(1−x)UxO2 which generated values in very good agreement with experimental data

Configurational analysis of uranium-doped thorium dioxide

While thorium dioxide is already used industrially in high temperature applications, more insight is needed about the behaviour of the material as part of a mixed-oxide (MOX) nuclear fuel, incorporating uranium. We have developed a new interatomic potential model, commensurate with a prominent existing UO2 potential, to conduct configurational analyses of uranium-doped ThO2 supercells. Using the GULP and Site Occupancy Disorder (SOD) computational codes, we have analysed the distribution of low concentrations of uranium in the bulk material, but have not observed the formation of uranium clusters or a single dominant configuration

The effect of water on the binding of glycosaminoglycan saccharides to hydroxyapatite surfaces: A molecular dynamics study

Classical molecular dynamics (MD) simulations have been employed to study the interaction of the saccharides glucuronic acid (GlcA) and N-acetylgalactosamine (GalNAc) with the (0001) and (011̄0) surfaces of the mineral hydroxyapatite (HAP). GlcA and GalNAc are the two constituent monosaccharides of the glycosaminoglycan chondroitin sulfate, which is commonly found in bone and cartilage and has been implicated in the modulation of the hydroxyapatite biomineralization process. MD simulations of the mineral surfaces and the saccharides in the presence of solvent water allowed the calculation of the adsorption energies of the saccharides on the HAP surfaces. The calculations show that GalNAc interacts with HAP principally through the sulfate and the carbonyl of acetyl amine groups, whereas the GlcA interacts primarily through the carboxylate functional groups. The mode and strength of the interaction depends on the orientation of the saccharide with respect to the surface and the level of disruption of the layer of water competing with the saccharide for adsorption sites on the HAP surface, suggesting that chondroitin 4-sulfate binds to the layer of solvent water rather than to HAP

Molecular dynamics simulations of bio-active phosphate-based glass surfaces

Classical molecular dynamics (MD) simulations were used to study the structural changes in the surfaces of biocompatible phosphate glasses with compositions (P2O5)0.45(CaO)x(Na2O)0.55 − x (x = 30, 35, 40) to evaluate their effect on the solubility of the material. Direct comparison of the data for the three compositions highlighted the critical role that an enhancement in Na+ concentration plays in the hydrolysis of the material, which is responsible for the release of network components into solution. The calculations also confirm that the most soluble material is (P2O5)0.45(CaO)0.30(Na2O)0.25, has the lowest calcium coordination number, thereby causing fewer cross links to phosphate chains

CaCO3 nucleation and growth at different {Ca2+}:{CO32-} ratios in aqueous environments

CaCO3 precipitation is an important process in industrial applications as well as in nature. However, its precipitation is usually impure and despite the ample amount of information available on this topic, the mechanisms playing a role during CaCO3 precipitation are still not fully unraveled. We investigated the effect of stoichiometry on the new formation (nucleation) and subsequent growth of CaCO3 over a large range of supersaturation with respect to calcite (30 > 1000), stoichiometry effects the CaCO3 formation substantially and observed trends closely match those observed with DLS. The CaCO3 precipitation kinetics are more strongly affected by the absence of Ca2+ compared to the absence of CO32-. Our results imply that, besides Ω, stoichiometry effects initial precluster size and persistence, growth mechanism and ripening time towards μm-sized crystals.m-sized crystals. Ultimately, our findings may help to improve future predictions of, or optimize the physico-chemical conditions for CaCO3 formation in industrial and geo-engineering settings

Configurational analysis of uranium-doped thorium dioxide

While thorium dioxide is already used industrially in high temperature applications, more insight is needed about the behaviour of the material as part of a mixed-oxide (MOX) nuclear fuel, incorporating uranium. We have developed a new interatomic potential model, commensurate with a prominent existing UO2 potential, to conduct configurational analyses of uranium-doped ThO2 supercells. Using the GULP and Site Occupancy Disorder (SOD) computational codes, we have analysed the distribution of low concentrations of uranium in the bulk material, but have not observed the formation of uranium clusters or a single dominant configuration

Self-assembling of calcium salt of the new DNA base 5-carboxylcytosine

Supramolecular architectures involving DNA bases can have a strong impact in several fields such as nanomedicine and nanodevice manufacturing. To date, in addition to the four canonical nucleobases (adenine, thymine, guanine and cytosine), four other forms of cytosine modified at the 5 position have been identified in DNA. Among these four new cytosine derivatives, 5-carboxylcytosine has been recently discovered in mammalian stem cell DNA, and proposed as the final product of the oxidative epigenetic demethylation pathway on the 5 position of cytosine. In this work, a calcium salt of 5-carboxylcytosine has been synthesized and deposited on graphite surface, where it forms self-assembled features as long range monolayers and up to one micron long filaments. These structures have been analyzed in details combining different theoretical and experimental approaches: X-ray single-crystal diffraction data were used to simulate the molecule-graphite interaction, first using molecular dynamics and then refining the results using density functional theory (DFT); finally, data obtained with DFT were used to rationalize atomic force microscopy (AFM) results

Recalibrating the calcium trap in amino acid carboxyl groups via classical molecular dynamics simulations

In order to use classical molecular dynamics to complement experiments accurately, it is important to use robust descriptions of the system. The interactions between biomolecules, like aspartic and glutamic acid, and dissolved ions are often studied using standard biomolecular force-fields, where the interactions between biomolecules and cations are often not parameterized explicitly. In this study, we have employed metadynamics simulations to investigate different interactions of Ca with aspartic and glutamic acid and constructed the free energy profiles of Ca2+–carboxylate association. Starting from a generally accepted, AMBER-based force field, the association was substantially over and under-estimated, depending on the choice of water model (TIP3P and SPC/fw, respectively). To rectify this discrepancy, we have replaced the default calcium parameters. Additionally, we modified the σij value in the hetero-atomic Lennard-Jones interaction by 0.5% to further improve the interaction between Ca and carboxylate, based on comparison with the experimentally determined association constant for Ca with the carboxylate group of L-aspartic acid. The corrected description retrieved the structural properties of the ion pair in agreement with the original biomolecule – Ca2+ interaction in AMBER, whilst also producing an association constant comparable to experimental observations. This refined force field was then used to investigate the interactions between amino acids, calcium and carbonate ions during biogenic and biomimetic calcium carbonate mineralisation

Structures and properties of phosphate-based bioactive glasses from computer simulation: a review

Phosphate-based bioactive glasses (PBGs) dissolve harmlessly in the body with a dissolution rate which depends sensitively on composition. This makes them proposed vectors for e.g. drug delivery, or other applications where an active component needs to be delivered at a therapeutically appropriate rate. Molecular dynamics (MD) simulations provide atomic-level structural information about PBG compositions. We review recent work to show that MD is an excellent tool to unravel the connections between the PBG glass composition, its atomic structure, and its dissolution rate, which can help to optimise PBGs for specific medical applications

Neumopericardio espontáneo en el recién nacido a término

Introduction: pneumopericardium is a little frequent but potentially serious disorder, defined by the presence of air in the pericardial cavity or space. Clinical case: two cases of term newborn presented, by different birth ways, with respiratory difficulty signs, low cardiac sounds, presented but diminished pulses, radiologically proving the presence of pneumomediastinum and pneumopericardium, as well as microvoltage in the electrocardiogram. They were realized after seven days of life, with favorable evolution. Conclusions: pneumopericardium is a infrequent clinical situation. It requires a high index of clinical suspicion, since it constitutes a cause for hemodynamic instability and threat to life.RESUMENIntroducción: el neumopericardio es un trastorno poco frecuente pero potencialmente grave, definido por la presencia de aire en la cavidad pericárdica. Caso clínico: se presentan dos casos de recién nacidos a término, con vías de nacimiento diferentes, que presentaron signos de dificultad respiratoria, ruidos cardiacos apagados, pulsos presentes pero disminuidos, demostrándose radiológicamente la presencia de neumomediastino y neumopericardio, así como microvoltaje en el electrocardiograma. Se egresan a los siete días de vida con una evolución favorable. Conclusiones: el neumopericardio es una situación clínica infrecuente pero posible. Requiere un alto índice de sospecha clínica ya que es causa de inestabilidad hemodinámica y amenaza vital