Balancing biofunctional and biomechanical properties using porous titanium reinforced by carbon nanotubes.

Despite the well-known advantages of the titanium-based implant systems, they still lack an optimal balance between biofunctionality and mechanical strength, especially regarding the modulation of cellular response and a desired implant osseointegration. In this work, we fabricated a nanocomposite based on porous commercially pure grade 4 titanium (c.p. Ti) reinforced with carbon nanotubes (CNT) at 5% and 10% w/w, with the aim of obtaining a nanocomposite with lower stiffness compared to traditional titanium-based implants and with the mechanical strength and bioactivity owed by the CNT. Results obtained by scanning electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy characterization showed that the CNT dispersed and incorporated into the porous c.p. Ti matrix. Interestingly, CNT were associated with a higher twining within neighbor Ti grains, which was indeed consistent with an increased in nano-hardness. Biological evaluation by MTT and Comet assay revealed that the nanocomposites did not induce genotoxicity and cytotoxicity on two different cells lines despite the presence of nickel at the surface. Accordingly, a purification step would be required before these CNT can be used for biomedical applications. Our results indicate that incorporation of CNT into porous c.p. Ti is a promising avenue to achieve an adequate balance between biofunctionality and mechanical strength in Ti-based scaffolds for tissue replacement. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 719-731, 2019.

The role of OH O and CH O hydrogen bonds and H H interactions in ethanol/methanol-water heterohexamers.

Bioethanol is one of the world's most extensively produced biofuels. However, it is difficult to purify due to the formation of the ethanol-water azeotrope. Knowledge of the azeotrope structure at the molecular level can help to improve existing purification methods. In order to achieve a better understanding of this azeotrope structure, the characterization of (ethanol)5-water heterohexamers was carried out by analyzing the results of electronic structure calculations performed at the B3LYP/6-31+G(d) level. Hexamerization energies were found to range between -36.8 and -25.8 kcal/mol. Topological analysis of the electron density confirmed the existence of primary (OH…O) hydrogen bonds (HBs), secondary (CH…O) HBs, and H…H interactions in these clusters. Comparison with three different solvated alcohol systems featuring the same types of atom-atom interactions permitted the following order of stability to be determined: (methanol)5-water > (methanol)6 > (ethanol)5-water > (ethanol)6. These findings, together with accompanying geometric and spectroscopic analyses, show that similar cooperative effects exist among the primary HBs for structures with the same arrangement of primary HBs, regardless of the nature of the molecules involved. This result provides an indication that the molecular ratio can be considered to determine the unusual behavior of the ethanol-water system. The investigation also highlights the presence of several types of weak interaction in addition to primary HBs. Graphical Abstract Water-ethanol clusters exhibit a variety of interaction types between their atoms, such as primary OH...O (blue), secondary CH...O (green) and H...H (yellow) interactions as revealed by Quantum Chemical Topology.

Intershell spacing changes in MWCNT induced by metal-CNT interactions.

The intershell spacing in different regions of a multi-walled carbon nanotube (MWCNT) was determined by analysis of high resolution transmission electron (HR-TEM) micrographs. Three general effects can be pointed out, (1) the regular intershell spacing of a CNT is bigger than that in a graphitic carbon because the curvature generates geometrical and electronic deformations which increase repulsion forces between the graphene sheets, (2) when an extra curvature appears, e.g. at the tip of a closed CNT or in a bamboo-like structure, the intershell spacing is expanded due to the extra repulsion caused by the combination of pentagonal and heptagonal rings imbibed in the hexagonal lattice, and (3) when a metal particle interacts with a CNT, the intershell spacing is compressed due to strong metal-CNT interactions.

Topological analysis of tetraphosphorus oxides (P4O 6+n (n = 0-4)).

Quantum chemical calculations were used to analyze the chemical bonding and the reactivity of phosphorus oxides (P4O6+n (n = 0-4)). The chemical bonding was studied using topological analysis such as atoms in molecules (AIM), electron localization function (ELF), and the reactivity using the Fukui function. A classification of the P-O bonds formed in all structures was done according to the coordination number in each P and O atoms. It was found that there are five P-O bond types and these are distributed among the five phosphorus oxides structures. Results showed that there is good agreement among the evaluated properties (length, bond order, density at the critical point, and disynaptic population) and each P-O bond type. It was found that regardless of the structure in which a P-O bond type is present the topological and geometric properties do not have a significant variation. The topological parameters electron density and Laplacian of electron density show excellent linear correlation with the average length of P-O bond in each bond type for each structure. From the Fukui function analysis it was possible to predict that from P4O6 until P4O8 the most reactive regions are basins over the P.

Theoretical design of stable small aluminium-magnesium binary clusters.

We explore in detail the potential energy surfaces of the Al(x)Mg(y) (x, y = 1-4) systems as case studies to test the utility and limitations of simple rules based on electron counts and the phenomenological shell model (PSM) for bimetallic clusters. We find that it is feasible to design stable structures that are members of this set of small Al-Mg binary clusters, using simple electron count rules, including the classical 4n + 2 Hückel model, and the most recently proposed PSM. The thermodynamic stability of the title compounds has been evaluated using several different descriptors, including the fragmentation energies and the electronic structure of the systems. Three stable systems emerge from the analysis: the Al(4)Mg, Al(2)Mg(2) and Al(4)Mg(4) clusters. The relative stability of Al(4)Mg is explained by the stability of the Al(4)(2-) subunit to which the Mg atom donates its electrons. Here the Mg(2+) sits above the aromatic 10 π-electron Al(4)(2-) planar ring. The Al(2)Mg(2) and Al(4)Mg(4) clusters present more complicated 3D structures, and their stabilities are rationalized as a consequence of their closed shell nature in the PSM, with 10 and 20 itinerant electrons, respectively.

An orbital and electron density analysis of weak interactions in ethanol-water, methanol-water, ethanol and methanol small clusters.

A computational study of (ethanol)(n)-water, n = 1 to 5 heteroclusters was carried out employing the B3LYP∕6-31+G(d) approach. The molecular (MO) and atomic (AO) orbital analysis and the topological study of the electron density provided results that were successfully correlated. Results were compared with those obtained for (ethanol)(n), (methanol)(n), n = 1 to 6 clusters and (methanol)(n)-water, n = 1 to 5 heteroclusters. These systems showed the same trends observed in the (ethanol)(n)-water, n = 1 to 5 heteroclusters such as an O---O distance of 5 Å to which the O-H---O hydrogen bonds (HBs) can have significant influence on the constituent monomers. The HOMO of the hetero(clusters) is less stable than the HOMO of the isolated alcohol monomer as the hetero(cluster) size increases, that destabilization is higher for linear geometries than for cyclic geometries. Changes of the occupancy and energy of the AO are correlated with the strength of O-H---O and C-H---O HBs as well as with the proton donor and/or acceptor character of the involved molecules. In summary, the current MO and AO analysis provides alternative ways to characterize HBs. However, this analysis cannot be applied to the study of H---H interactions observed in the molecular graphs.

The dynamic behavior of a liquid ethanol-water mixture: a perspective from quantum chemical topology.

Quantum Chemical Topology (QCT) is used to reveal the dynamics of atom-atom interactions in a liquid. A molecular dynamics simulation was carried out on an ethanol-water liquid mixture at its azeotropic concentration (X(ethanol)=0.899), using high-rank multipolar electrostatics. A thousand (ethanol)(9)-water heterodecamers, respecting the water-ethanol ratio of the azeotropic mixture, were extracted from the simulation. Ab initio electron densities were computed at the B3LYP/6-31+G(d) level for these molecular clusters. A video shows the dynamical behavior of a pattern of bond critical points and atomic interaction lines, fluctuating over 1 ns. A bond critical point distribution revealed the fluctuating behavior of water and ethanol molecules in terms of O-H···O, C-H···O and H···H interactions. Interestingly, the water molecule formed one to six C-H···O and one to four O-H···O interactions as a proton acceptor. We found that the more localized a dynamical bond critical point distribution, the higher the average electron density at its bond critical points. The formation of multiple C-H···O interactions affected the shape of the oxygen basin of the water molecule, which is shown in three dimensions. The hydrogen atoms of water strongly preferred to form H···H interactions with ethanol's alkyl hydrogen atoms over its hydroxyl hydrogen.

Average structural analysis of tar obtained from pyrolysis of wood.

Conventional analytical methods such as (1)H NMR, vapor pressure osmometry (VPO) and elemental analysis were used to characterize the tar obtained from pyrolysis of pine. The major fraction of tar obtained during pyrolysis of pine at different temperatures was the insoluble fraction in n-heptane which corresponds to asphaltenes; this fraction was characterized and analyzed using average structural parameters. The structural unit of the tar is composed of one aromatic ring substituted by aliphatic chains, olefinic groups and the presence of oxygenated groups. Two of such average structures determined with this methodology corresponds to 4-formyl-2,6-dimethoxy-3-[(1E)-prop-1-en-1-yl]-5-propylbenzoic acid and 2,3,5-trimethoxy-6-[(1E)-prop-1-en-1-yl]-4-propylbenzaldehyde.

Heterogeneous CO(2) evolution from oxidation of aromatic carbon-based materials.

Carbon dioxide is one of the main gaseous products in oxidation of carbonaceous materials via both homogeneous and heterogeneous reactions. However, the mechanisms of heterogeneous CO(2) evolution during oxidation of aromatic carbon-based materials are not known in detail. Using density functional theory, a new oxidation mechanism of aromatic hydrocarbons with atomic oxygen was suggested to consist of four main steps, namely, (1) adsorption of oxygen atom, (2) insertion of O atom into the ring, (3) rearrangement to form a five-membered ring and four-membered ring lactone group, and (4) desorption of CO(2). Using naphthoxy radical as a model system, the proposed reaction pathway can explain how some of the experimentally observed CO(2) is formed.

Efectos cooperaiivos en heterotetrámeros (etanol)3-auua / Cooperatve effeccts in (ethanol)3-water heterotetramers / Efeitos cooperativos em heterotetrámeros (etanol)3-água

La teoría de funcionales de la densidad (DFT: B3LYP/6-31+G(d)) fue empleada para la optimización de agregados estables sobre la superficie de energía potencial de los heterotetrámeros (etanol)3-agua. Las energías de tetramerización pueden llegar a valores hasta de -21,00 kcal/mol. Esta energía no se puede obtener considerando solo contribuciones de interacciones entre dos moléculas del agregado, lo cual sugiere la presencia de efectos cooperativos globales (positivos). Tales efectos son reflejados en distancias menores de los puentes de hidrógeno y distancias menores oxígeno-oxígeno, lo mismo que en elongaciones mayores del enlace O-Hen la molécula dadora de protón con un corrimiento hacia el rojo mayor en los heterotetrámeros, comparado con los heterodímeros de etanol-agua y el dímero de etanol. La mayor cooperatividad fue observada en los cuatro puentes de hidrógeno dispuestos en el patrón geométrico cíclico más grande posible, actuando todas las moléculas como aceptoras y dadoras de protón simultáneamente. Un análisis similar al de la caracterización de heterotetrámeros de (etanol)3-agua se llevó a cabo para los heterotetrámeros (metanol)3-agua y tetrámeros de etanol y metanol. La comparación de estos valores mostró que existe una gran similitud entre todos los parámetros analizados para agregados con el mismo patrón geométrico.

Density Functional Theory (DFT: B3LYP/6-31 + G(d)) was used for the optimization of clusters on the potential energy surface of (ethanol)3-water heterotetramers. The tetramerization energies can reach values up to -21.00 kcal/ mol. This energy can not be obtained by just considering the contributions from interactions between two cluster molecules, which suggests of the presence of global cooperative effects (positive). These effects are reflected in smaller hydrogen bond distances and smaller oxygen-oxygen distances, as well as in greater elongations of the O-H proton donor bond with a stronger "red-shift" in the heterotetramers compared to the ethanol-water heterodimers and the ethanol dimer. The largest cooperativity effect was observed in the four hydrogen bonds arranged in the largest possible cyclic geometric pattern, where all the molecules act as proton acceptor and donor simultaneously. A similar analysis to the characterization of (ethanol)3-water heterotetramers was carried out on (methanol)3-water heterotetramers, and ethanol and methanol tetramers, whose comparison showed a great similarity between all evaluated parameters for the clusters with equal geometric pattern.

A teoria de funcionais de densidade (DFT: B3LYP/6-31+G(d)) foi empregada para a otimização de agregados sobre a superfície de energia potencial dos heterotetrâmeros (etanol)3-água. As energias de tetramerização podem alcançar valores de até -21.00 kcal/mol. Esta energia não pode ser obtida por apenas considerando as contribuições das interações entre agregados de duas moléculas, o que sugere a presença global dos cooperativos efeitos (positivos). Tais efeitos são refletidos em menores comprimentos das pontes de hidrogênio e distâncias oxigênio-oxigênio, e também em maiores alongamentos da ligação O-H na molécula doadora de prótons, com um maior "red-shift" associado nos heterotetrâmeros do que nos heterodímeros de etanol-água e no dímero de etanol. A mais alta cooperatividade foi observada com as quatro pontes de hidrogênio dispostas no maior padrão geométrico cíclico possível, atuando simultaneamente todas as moléculas como aceptoras e doadoras de prótons. Uma análise similar ao da caracterização de heterotetrâmeros de (eta-nol)3-água se levou a cabo sobre heterotetrâmeros de (metanol)3-água e metanol, cuja comparação mostrou uma grande similaridade entre todos os parâmetros analisados para agregados com igual padrão geométrico.

A linear energy relationship between activation energy and absolute hardness: a case study with the O(3P) atom-addition reactions to polyaromatic hydrocarbons.

A new linear relationship between absolute hardness and global activation energy of O-addition reaction to a series of aromatic hydrocarbons (benzene, naphthalene, phenanthrene, and pyrene) is presented. A total of seventeen O((3)P)-addition reactions were evaluated. Thermal rate constants were calculated for each elementary reaction and used to estimate the total rate constants. This information was employed to obtain the global activation energy. A new linear relationship is shown and is estimated that it can be used within the RC-TST framework to predict relative rate constants for any reaction within an O-addition to PAH class from just absolute hardness values.

Low-temperature catalytic adsorption of NO on activated carbon materials.

The catalytic adsorption of NO on activated carbon materials provides an appropriated alternative for the control of low-concentration emissions of this air pollutant. The surface complexes formed upon NO adsorption at 30 degrees C were studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). The effects of the addition of O2 and the presence of copper as a catalyst were studied. Copper assisted the oxygen transfer to the carbon matrix. For the Cu-impregnated carbon sample, the presence of O2 favored NO adsorption by increasing the breakthrough time, the adsorption capacity, and the formation of nitrogen and oxygen complexes of higher thermal stabilities, which mainly desorbed as NO and CO2.

Molecular interaction of (ethanol)2-water heterotrimers.

The potential energy surface of the (ethanol)2-water heterotrimers for the trans and gauche conformers of ethanol was studied using density functional theory. The same approximation was used for characterizing representative clusters of (ethanol)3, (methanol)3, and (methanol)2-water. Trimerization energies and enthalpies as well as the analysis of geometric parameters suggest that the structures with a cyclic pattern in the three hydrogen bonds of the type O-H---O (primary hydrogen bonds), where all molecules are proton donor-acceptor at the same time, are more stable than those with just two primary hydrogen bonds. Additionally, we propose the formation of "secondary hydrogen bonds" between hydrogen atoms of the methyl group of ethanol and the oxygen atom of water or other ethanol molecule (C-H---O), which were found to be weaker than the primary hydrogen bonds.

Effect of Ni and Pd on the geometry, electronic properties, and active sites of copper clusters.

The geometry, electronic properties, and active sites of copper clusters doped with Ni or Pd atoms, Cu(n)()(-)(1)M (n = 2-6; M = Ni, Pd) have been investigated using first-principles methods. Planar structures are energetically favorable in Cu(n)()(-)(1)Ni (n = 2-6). However, for Pd-doped clusters, three-dimensional structures are competitive in energy, and for n = 6, the most stable structure is not planar. Several properties of doped copper clusters present odd-even oscillations as the number of copper atoms grow. The different atomic ground-state configuration of Ni and Pd determines the bonding and electronic properties of doped copper clusters. The interaction between impurities and copper atoms can modify the chemical hardness and active sites of doped copper clusters markedly inducing directionality in the reactivity. This effect is relevant to the behavior of catalysts as well as in the growth of metallic films.

Theoretical study of the interaction of molecular oxygen with copper clusters.

A new method based on frontier orbital theory has been used to investigate the binding site of molecular oxygen to neutral and anion copper clusters. It has been shown that one can make useful predictions of the binding sites based on the knowledge of the donor local reactivity of the cluster using the condensed Fukui function, f(-)(Ff). In this way, it was found that Cu(3), Cu(5), and Cu(5)(-) have the highest reactivity toward molecular oxygen.