Beyond two-center tight binding: Models for Mg and Zr

We describe a systematic approach to building ab initio tight-binding models and apply this to hexagonal metals Mg and Zr. Our models contain three approximations to plane-wave density functional theory (DFT): (i) we use a small basis set, (ii) we approximate self-consistency, and (iii) we approximate many-center exchange and correlation effects. We test a range of approximations for many-center exchange-correlation and self-consistency to gauge the accuracy of each in isolation. This systematic approach also allows us to combine multiple approximations in the optimal manner for our final tight-binding models. Furthermore, the breakdown of errors into those from individual approximations is expected to be a useful guide for which approximations to include in other tight-binding models. We attempt to correct any remaining errors in our models by fitting a pair potential. Our final tight-binding model for Mg shows excellent agreement with plane-wave results for a wide range of properties (e.g., errors below 10% for self-interstitial formation energies and below 3% for equilibrium volumes) and is expected to be highly transferable due to the minimal amount of fitting. Calculations with our Zr model also show good agreement with plane-wave results (e.g., errors below 2% for equilibrium volumes) except for properties where self-consistency is important, such as self-interstitial formation energies. However, for these properties we are able to generate a tight-binding model which shows excellent agreement with non-self-consistent DFT with a small basis set (i.e., many-center effects are captured accurately by our approximations). As we understand the source of remaining errors in our Zr model we are able to outline the methods required to build upon it to describe the remaining properties with greater accuracy

Teratogenic effects of five anticancer drugs on Xenopus laevis embryos

In recent years, the environmental presence of pharmaceuticals - including anticancer drugs - is an emerging issue. Because of the lack of appropriate critical studies about anticancer drug effects in frogs, the aim of the present study was to investigate lethal and teratogenic effects of five anticancer drugs widely used in large quantities, i.e. 5-flourouracil, capecitabine, cisplatin, etoposide, and imatinib, in the embryos of the South African clawed frog, Xenopus laevis, using FETAX - Frog Embryo Teratogenesis Assay in Xenopus. None of the studied anticancer drugs induced statistically significant mortality within the concentrations tested (0.01–50 mg/L, depending on the studied compound), and no growth inhibition of embryos after a 96-h exposure was observed. Except for cisplatin, the other pharmaceuticals induced an increase of developmental malformations such as abdominal edema, axial flexure, head, eyes, gut and heart malformations with statistically significant effects observed at the highest concentrations tested (50 mg/L for 5-flourouracil; 30 mg/L for etoposide and 20 mg/L for capecitabine and imatinib). The results indicate that anticancer drugs can affect embryogenesis mechanisms

Atomistic modelling of iodine-oxygen interactions in strained sub-oxides of zirconium

In water reactors, iodine stress corrosion cracking is considered the cause of pellet-cladding interaction failures, but the mechanism and chemistry are debated and the protective effect of oxygen is not understood. Density functional theory calculations were used to investigate the interaction of iodine and oxygen with bulk and surface Zr under applied hydrostatic strain (-2 % to +3 %) to simulate crack tip conditions in Zr to ZrO, using a variety of intermediate suboxides (ZrO, ZrO, ZrO and ZrO). The formation energy of an iodine octahedral interstitial in Zr was found to decrease with increasing hydrostatic strain, whilst the energy of an iodine substitutional defect was found to be relatively insensitive to strain. As the oxygen content increased, the formation energy of an iodine interstitial increased from 1.03 eV to 8.61 eV supporting the idea that oxygen has a protective effect. At the same time, a +3 % tensile hydrostatic strain caused the iodine interstitial formation energy to decrease more in structures with higher oxygen content: 4.56 eV decrease in ZrO compared to 1.47 eV decrease for pure Zr. Comparison of the substitutional and interstitial energies of iodine, to the adsorption energy of iodine, in the presence of oxygen, shows the substitutional energy of iodine onto a Zr site is more favourable for all strains and even interstitial iodine is favourable between strains of +1-5%. Although substitutional defects are preferred to octahedral interstitial defects, in the ordered suboxides, a 3 % tensile strain significantly narrows the energy gap and higher strains could cause interstitial defects to form

Passive sampling in effect-based monitoring of two European rivers - explicability of in vitro toxic potentials by detected chemicals

EU commission Water Framework Directive considers employment of passive sampling and use of effect-based tools in the monitoring of aquatic pollution. A combination of both approaches was used for monitoring of two rivers differing significantly in pollution levels. The Bosna, moderate-sized river in Bosnia-Herzegovina, which is burdened by untreated wastewaters, was sampled by semipermeable passive sampling devices (SPMD) and POCIS samplers. The Danube, the largest river in the EU with relatively low pollution level, was sampled using a mobile dynamic passive sampling device with silicone rubber (SR) and SDB-RPS Empore™ (ED) disc samplers. Both sampler sets consisted of partitioning sampler for non-polar chemicals (SPMD, SR) and adsorption sampler for the polar-ones (POCIS, ED). For the partitioning samplers, concentrations of collected chemicals in river water were derived using dissipation of performance reference compounds. For the adsorption samplers, the sampling rates were either taken from literature (POCIS) or calculated from correlated levels of chemicals that were detected both in adsorption (ED) and partitioning samplers (SR). The samples were analyzed for aryl hydrocarbon-, estrogen- and androgen receptor-mediated effects using in vitro bioassays. The effects were expressed as bioanalytical equivalents (BEQbio) of respective model compounds in water. The BEQbio levels were significantly higher in extracts from POCIS and ED samplers showing that the polar chemicals were responsible for most of the detected effects. Chemical analyses detected 103 and 209 chemicals in the Bosna and the Danube samples, respectively. The passive sampling allowed detection of chemicals at pg/L concentrations. The levels of chemicals with known biological potency for the studied endpoints were used for modeling of bioanalytical equivalents (BEQchem). The comparison of bioassay- and chemical analysis-derived equivalents showed that the detected chemicals explained mostly a low fraction of the BEQbio. Only in the case of estrogenicity in extracts of the samplers collecting polar chemicals, the BEQchem was comparable with the BEQbio levels. Both sampler combinations proved to be suitable for the detection of a large set of chemicals even at trace levels and for the complementary assessment of the biological potentials of the environmental mixtures. The SOLUTIONS Project was supported by the 7th Framework Programme EU (FP7-ENV-2013) with grant agreement no. 603437