Interplay between the Reorientational Dynamics of the B3H8- Anion and the Structure in KB3H8

The structure and reorientational dynamics of KB3H8 were studied by using quasielastic and inelastic neutron scattering, Raman spectroscopy, first-principles calculations, differential scanning calorimetry, and in situ synchrotron radiation powder X-ray diffraction. The results reveal the existence of a previously unknown polymorph in between the alpha\u27- and beta-polymorphs. Furthermore, it was found that the [B3H8](-) anion undergoes different reorientational motions in the three polymorphs alpha, alpha\u27, and beta. In alpha-KB3H8, the [B3H8](-) anion performs 3-fold rotations in the plane created by the three boron atoms, which changes to a 2-fold rotation around the C-2 symmetry axis of the [B3H8](-) anion upon transitioning to alpha\u27-KB3H8. After transitioning to beta-KB3H8, the [B3H8](-) anion performs 4-fold rotations in the plane created by the three boron atoms, which indicates that the local structure of beta-KB3H8 deviates from the global cubic NaCl-type structure. The results also indicate that the high reorientational mobility of the [B3H8](-) anion facilitates the K+ cation conductivity, since the 2-orders-of-magnitude increase in the anion reorientational mobility observed between 297 and 311 K coincides with a large increase in K+ conductivity

Brachiopod-based oxygen-isotope thermometer: Update and review

In the early 1950\u2019s, McCrea and Epstein and co-workers laid the foundation for the oxygen isotope-based thermometers. Many variations of the thermometer have been since formulated based on synthetic and biogenic carbonates. Overall, the use and application of oxygen isotope thermometers must consider and be specific as to the mineralogy, and whether it is synthetic, abiogenic or biogenic carbonate. Here, we propose an updated and refined oxygen-isotope thermometer based on a large database of articulated brachiopods from high to low latitudes, cold to warm and shallow to deep-water regimes. In general, brachiopod-based oxygen isotopes are offset from abiogenic calcite precipitated in thermodynamic equilibrium by about -1 . They maintain this offset and that allows for the determination of robust ambient water temperatures over the full marine spectrum. Thus, the specific brachiopod-based oxygen-isotope thermometer applies, with few exceptions, to most modern articulated brachiopods, and potentially their ancient counterparts, and it is as follows: T\ub0C =17.3750 \u2013 4.2535 (\u3b4c-\u3b4w) + 0.1473 (\u3b4c-\u3b4w)2 (N=578, r2 = 0.980) Furthermore, it is imperative that mineralogy and taxa be considered for their appropriateness in the application of oxygen isotope thermometers on synthetic, abiogenic and biogenic marine carbonates. Articulated brachiopods are ideal recorders of oceanographic parameters due to their sessile nature, widespread distribution, high abundance in the Paleozoic and Mesozoic, high resilience to most environmental stresses (e.g., climate change - global warming, ocean acidification), and the resistance of the calcite shell \u2013 the archive \u2013 to post-depositional diagenetic alteration

The high-pressure phase of boron, {\gamma}-B28: disputes and conclusions of 5 years after discovery

{\gamma}-B28 is a recently established high-pressure phase of boron. Its structure consists of icosahedral B12 clusters and B2 dumbbells in a NaCl-type arrangement (B2){\delta}+(B12){\delta}- and displays a significant charge transfer {\delta}~0.5- 0.6. The discovery of this phase proved essential for the understanding and construction of the phase diagram of boron. {\gamma}-B28 was first experimentally obtained as a pure boron allotrope in early 2004 and its structure was discovered in 2006. This paper reviews recent results and in particular deals with the contentious issues related to the equation of state, hardness, putative isostructural phase transformation at ~40 GPa, and debates on the nature of chemical bonding in this phase. Our analysis confirms that (a) calculations based on density functional theory give an accurate description of its equation of state, (b) the reported isostructural phase transformation in {\gamma}-B28 is an artifact rather than a fact, (c) the best estimate of hardness of this phase is 50 GPa, (d) chemical bonding in this phase has a significant degree of ionicity. Apart from presenting an overview of previous results within a consistent view grounded in experiment, thermodynamics and quantum mechanics, we present new results on Bader charges in {\gamma}-B28 using different levels of quantum-mechanical theory (GGA, exact exchange, and HSE06 hybrid functional), and show that the earlier conclusion about significant degree of partial ionicity in this phase is very robust

Elastic and vibrational properties of alpha and beta-PbO

The structure, electronic and dynamic properties of the two layered alpha (litharge) and beta (massicot) phases of PbO have been studied by density functional methods. The role of London dispersion interactions as leading component of the total interaction energy between layers has been addressed by using the Grimme's approach, in which new parameters for Pb and O atoms have been developed. Both gradient corrected and hybrid functionals have been adopted using Gaussian-type basis sets of polarized triple zeta quality for O atoms and small core pseudo-potential for the Pb atoms. Basis set superposition error (BSSE) has been accounted for by the Boys-Bernardi correction to compute the interlayer separation. Cross check with calculations adopting plane waves that are BSSE free have also been performed for both structures and vibrational frequencies. With the new set of proposed Grimme's type parameters structures and dynamical parameters for both PbO phases are in good agreement with experimental data.Comment: 8 pages, 5 figure

DNA damage by lipid peroxidation products: implications in cancer, inflammation and autoimmunity

Oxidative stress and lipid peroxidation (LPO) induced by inflammation, excess metal storage and excess caloric intake cause generalized DNA damage, producing genotoxic and mutagenic effects. The consequent deregulation of cell homeostasis is implicated in the pathogenesis of a number of malignancies and degenerative diseases. Reactive aldehydes produced by LPO, such as malondialdehyde, acrolein, crotonaldehyde and 4-hydroxy-2-nonenal, react with DNA bases, generating promutagenic exocyclic DNA adducts, which likely contribute to the mutagenic and carcinogenic effects associated with oxidative stress-induced LPO. However, reactive aldehydes, when added to tumor cells, can exert an anticancerous effect. They act, analogously to other chemotherapeutic drugs, by forming DNA adducts and, in this way, they drive the tumor cells toward apoptosis. The aldehyde-DNA adducts, which can be observed during inflammation, play an important role by inducing epigenetic changes which, in turn, can modulate the inflammatory process. The pathogenic role of the adducts formed by the products of LPO with biological macromolecules in the breaking of immunological tolerance to self antigens and in the development of autoimmunity has been supported by a wealth of evidence. The instrumental role of the adducts of reactive LPO products with self protein antigens in the sensitization of autoreactive cells to the respective unmodified proteins and in the intermolecular spreading of the autoimmune responses to aldehyde-modified and native DNA is well documented. In contrast, further investigation is required in order to establish whether the formation of adducts of LPO products with DNA might incite substantial immune responsivity and might be instrumental for the spreading of the immunological responses from aldehyde-modified DNA to native DNA and similarly modified, unmodified and/or structurally analogous self protein antigens, thus leading to autoimmunity

Variations of the FeGa3 structure type in the systems CoIn3-xZnx and CoGa3-xZnx

We present an investigation of the quasibinary systems CoIn3-xZnx and CoGa3-xZnx which were structurally characterized by X-ray diffraction experiments and, in the case of CoGa3-xZnx, additionally by neutron powder diffraction experiments. The limiting compositions were found to be x=0.81(2) and x=0.73(2) for COIn3-xZnx and CoGa3-xZnx, respectively. The isotypic binary compounds CoIn3 and CoGa3 crystallize with the FeGa3 structure type (tetragonal, space group P42/mnm, Z=4) in which the p-block atoms form an array of columns of centered cubes defined by two different crystallographic sites. The substitution of In or Ga by Zn takes place in an ordered fashion and produces "colored" variants of the FeGa3 parent structure: In both systems Zn enters exclusively the position corresponding to the cube centers. Additionally, in CoIn3-xZnx this position is substituted in such a way that for a composition CoIn2.5Zn0.5, columns of Zn- and In- filled ln(8) cubes along the c axis alternate. The latter substitution pattern is accompanied by a symmetry lowering of the parent FeGa3 structure: The structure of CoIn3-xZnx is described by the space group P4(2)/m in which the cube center position is split into two separate sites. By performing first-principles electronic structure calculations we investigated the general bonding situation of the compounds CoIn3 and CoGa3 and the particular electronic effect when incorporating Zn. With respect to the density of states of the binary compounds the exchange of Ga or In by Zn virtually affects only the electronic states just below the Fermi level. On increasing Zn concentration a dip is created in the density of states which approximately coincides with the location of the Fermi level for an electron count corresponding to limiting composition of the two systems. (C) 2002 Elsevier Science (USA)

FeGa3 and RuGa3: Semiconducting intermetallic compounds

The intermetallic compounds FeGa3 and RuGa3 were prepared from the elements using a Ga flux and their structures were refined from single-crystal X-ray data. Both compounds crystallize with the FeGa3 structure type (tetragonal, space group P4(2)/mnm, Z=4). Electrical resistivity measurements revealed a semiconducting behavior for FeGa3 and RuGa3, which is in contrast to the good metallic conductivity observed for the isotypic compound CoGa3. The origin of the different electronic properties of these materials was investigated by first-principle calculations. It was found that in compounds adopting the FeGa3 structure type the transition metal atoms and Ga atoms interact strongly. This opens a d-p hybridization bandgap with a size of about 0.31 eV in the density of states at the Fermi level for 17-electron compounds (i.e., FeGa3 and RuGa3). The electronic structure of CoGa3 (an 18-electron compound) displays rigid band behavior with respect to FeGa3. As a consequence, the Fermi level in CoGa3 becomes located above the d-p hybridization gap which explains its metaltic conductivity. (C) 2002 Elsevier Science (USA)

The Hume-Rothery compound Mn₈Ga_27.4Zn_13.6: separated Zn₁₃-clusters interspersed in a primitive cubic host lattice

Acentric three-dimensional coordination polymers bis(isonicotinato)zinc (1) and bis(4-pyridylacrylato)cadmium · H₂O (2) were synthesized under hydro(solvo)thermal conditions; they exhibit a threefold (see picture) and fivefold diamondoid structure, respectively. Both 1 and 2 are active for second harmonic generation and exhibit remarkable thermal stability