The cohesive energy of superheavy element copernicium determined from accurate relativistic coupled-cluster theory.

The cohesive energy of bulk copernicium is accurately determined using the incremental method within a relativistic coupled-cluster approach. For the lowest energy structure of hexagonal close-packed (hcp) symmetry, we obtain a cohesive energy of -36.3 kJ mol-1 (inclusion of uncertainties leads to a lower bound of -39.6 kJ mol-1), in excellent agreement with the experimentally estimated sublimation enthalpy of -38 kJ mol-1 [R. Eichler et al., Angew. Chem. Int. Ed., 2008, 47, 3262]. At the coupled-cluster singles, doubles and perturbative triples level of theory, we find that the hcp structure is energetically quasi-degenerate with both face-centred and body-centred cubic structures. These results provide a basis for testing various density-functionals, of which the PBEsol functional yields a cohesive energy of -34.1 kJ mol-1 in good agreement with our coupled-cluster value.

Kinetics of the heterogeneous reaction of nitric acid with mineral dust particles: an aerosol flowtube study.

The heterogeneous reaction of HNO3 with mineral dust aerosol (Arizona Test Dust) was studied in an aerosol flow tube at atmospherically relevant conditions (298 K, approximately 1 atm, 6-60% RH) and using radioactively labelled HNO3. The uptake of nitric acid was found to depend on HNO3 and H2O concentrations in the gas phase. A reaction mechanism is suggested to describe the heterogeneous interaction, involving Langmuir type adsorption and surface reaction. This mechanism is incorporated in a flux based aerosol kinetic model framework that is able to reproduce the observations within the range of experimental conditions. The experiments show that the reactive surface sites of the relatively calcium poor, but silicate rich dust surface are efficiently depleted at higher HNO3 concentrations in the gas phase or longer exposure times. A set of kinetic parameters is extracted from the data, which can be used to calculate uptake coefficients as function of time, concentration and humidity for use in atmospheric chemistry models to improve especially the representation of the effects of relative humidity on dust aging and to allow following dust aging with time.

Chemical characterization of element 112.

The heaviest elements to have been chemically characterized are seaborgium (element 106), bohrium (element 107) and hassium (element 108). All three behave according to their respective positions in groups 6, 7 and 8 of the periodic table, which arranges elements according to their outermost electrons and hence their chemical properties. However, the chemical characterization results are not trivial: relativistic effects on the electronic structure of the heaviest elements can strongly influence chemical properties. The next heavy element targeted for chemical characterization is element 112; its closed-shell electronic structure with a filled outer s orbital suggests that it may be particularly susceptible to strong deviations from the chemical property trends expected within group 12. Indeed, first experiments concluded that element 112 does not behave like its lighter homologue mercury. However, the production and identification methods used cast doubt on the validity of this result. Here we report a more reliable chemical characterization of element 112, involving the production of two atoms of (283)112 through the alpha decay of the short-lived (287)114 (which itself forms in the nuclear fusion reaction of 48Ca with 242Pu) and the adsorption of the two atoms on a gold surface. By directly comparing the adsorption characteristics of (283)112 to that of mercury and the noble gas radon, we find that element 112 is very volatile and, unlike radon, reveals a metallic interaction with the gold surface. These adsorption characteristics establish element 112 as a typical element of group 12, and its successful production unambiguously establishes the approach to the island of stability of superheavy elements through 48Ca-induced nuclear fusion reactions with actinides.

Precision measurement of the 7Be(p,gamma)8B cross section with an implanted 7Be target.

The 7Be(p,gamma)8B reaction plays a central role in the evaluation of solar neutrino fluxes. We report on a new precision measurement of the cross section of this reaction, following our previous experiment with an implanted 7Be target, a raster-scanned beam, and the elimination of the backscattering loss. The new measurement incorporates a more abundant 7Be target and a number of improvements in design and procedure. The point at E(lab)=991 keV was measured several times under varying experimental conditions, yielding a value of S17(E(c.m.)=850 keV)=24.0+/-0.5 eV b. Measurements were carried out at lower energies as well. Because of the precise knowledge of the implanted 7Be density profile, it was possible to reconstitute both the off- and on-resonance parts of the cross section and to obtain from the entire set of measurements an extrapolated value of S17(0)=21.2+/-0.7 eV b.

Chemical investigation of hassium (element 108).

The periodic table provides a classification of the chemical properties of the elements. But for the heaviest elements, the transactinides, this role of the periodic table reaches its limits because increasingly strong relativistic effects on the valence electron shells can induce deviations from known trends in chemical properties. In the case of the first two transactinides, elements 104 and 105, relativistic effects do indeed influence their chemical properties, whereas elements 106 and 107 both behave as expected from their position within the periodic table. Here we report the chemical separation and characterization of only seven detected atoms of element 108 (hassium, Hs), which were generated as isotopes (269)Hs (refs 8, 9) and (270)Hs (ref. 10) in the fusion reaction between (26)Mg and (248)Cm. The hassium atoms are immediately oxidized to a highly volatile oxide, presumably HsO(4), for which we determine an enthalpy of adsorption on our detector surface that is comparable to the adsorption enthalpy determined under identical conditions for the osmium oxide OsO(4). These results provide evidence that the chemical properties of hassium and its lighter homologue osmium are similar, thus confirming that hassium exhibits properties as expected from its position in group 8 of the periodic table.

Heterogeneous reaction of NO2 on diesel soot particles.

Soot particles were collected from a diesel engine using a procedure that realistically mimics exhaust gas conditions in tailpipes and during dilution at room temperature. After being sampled, the particles were exposed to NO2 concentrations and relative humidity in ranges relevant for the troposphere using 13N as tracer. Gas-phase nitrous acid(HONO) and irreversibly bound (i.e., chemisorbed) species were the main reaction products with initial yields of 80-90% and about 10%, respectively. Neither NO nor HNO3 were detectable. The HONO formation increased with increasing engine load (i.e., with a decreasing air to fuel ratio, lambda). The reaction rates of HONO and chemisorbed NO2 increased with increasing NO2 concentration and did not depend on relative humidity. At the beginning of reaction, the uptake coefficient averaged over 3 min ranged from 5 x 10(-6) to 10(-5) for NO2 concentrations between 2 and 40 ppb. The HONO formation rates decreased with time, indicating consumption of reactive surface species, while the chemisorption rates remained almost constant. The total HONO formation potential of the particles was estimated to about 1.3 x 10(17) molecules/mg of diesel soot or to about 4.7 mg/kg of diesel fuel, indicating that the reaction between NO2 and diesel soot particles does not provide a significant secondary HONO source in the atmosphere. A Langmuir-Hinshelwood type reaction mechanism was proposed that adequately describes the observed results and also allows discussing important general features of reactions on soot.

Analysis of size-classified ice crystals by capillary electrophoresis.

In order to analyse the main inorganic cations (NH4+, K+, Na+, Ca2+, Mg2+) and anions (Cl-, NO3-, SO4(2-)) as well as carboxylic and dicarboxylic acids in ice crystals by capillary electrophoresis, electrolyte systems were developed and optimised with respect to limits of detection, resolution, reproducibility and analysis time. We applied indirect UV detection, which enables the simultaneous detection of multiple components. Salicylic acid and 4-methylaminophenolsulfate were used as UV-active co-ions for analysis of anions and cations, respectively. The special features of these systems were low limits of detection in the range 0.3-0.9 micromol L(-1), i.e. absolute limits of detection were in the fmol range, and short analyses times. Separations of cations as well as anions including carboxylic and dicarboxylic acids were completed within 4 min allowing a high sample throughput. Furthermore, the applicability of the newly developed electrolyte systems was demonstrated by comparative analyses with ion chromatography and by first field experimental studies.

Thyroid hormone antagonizes an aldosterone-induced protein: a candidate mediator for the late mineralocorticoid response.

In the urinary bladder of the toad Bufo marinus, the basal rate of synthesis of a number of proteins was modulated in a bidirectional way (i.e., induced or repressed) by aldosterone and by triiodothyronine (T3). Each hormone was therefore characterized by a distinct domain of response. When both hormones were added simultaneously, the two domains consistently overlapped at least for one protein, termed AIP-1, or aldosterone-induced protein 1 (Mr approximately 65 kilodaltons, pi = 6.7, as analyzed by two-dimension gel electrophoresis). The physiological role of AIP-1 is unknown, but could be related to the late mineralocorticoid response. In five experiments, T3 (60 nM, 18-hr incubation) consistently repressed AIP-1, while aldosterone-dependent sodium transport (late response) was significantly inhibited, as previously described. The repression of AIP-1 was also observed as early as 6 hr after aldosterone addition. In addition, sodium butyrate (3 mM), which was previously shown to also selectively inhibit the late mineralocorticoid response, was also able to repress AIP-1. Our results suggest that AIP-1 is one of the proteins involved in the mediation of the late mineralocorticoid response.

Binding and antimineralocorticoid activities of spirolactones in toad bladder.

The role of the soluble pool (cytoplasmic or cytosolic) of [3H]-aldosterone binding sites in the toad bladder was assessed by the use of two spirolactones, prorenone and spironolactone as a reference drug. Prorenone fulfills all the criteria for a specific competitive antagonist of aldosterone for its effect on Na+ transport. Compared with spironolactone (Ki approximately equal to 1 microM), prorenone was about eightfold less potent (Ki approximately equal to 8 microM). Competition for [3H]aldosterone binding sites by spironolactone and prorenone revealed an order of potency (spironolactone greater than prorenone) that corresponded to their antagonist activities in the Na+ transport assay. There was a linear correlation between the effects of the two spirolactones on the aldosterone-stimulated Na+ transport and their ability to displace [3H]aldosterone from its binding sites in the soluble pool. Finally [3H]prorenone binding sites were detected in the soluble pool but an insignificant number of antagonist-receptor complexes were found associated with the nuclear pool. Our study indicates that the aldosterone binding sites of the soluble pool are indeed mineralocorticoid receptors, which are probably the first intracellular mediators leading to an increased Na+ reabsorption.

Testosterone: a specific competitive antagonist of aldosterone in the toad bladder.

Testosterone (100 nM to 40 microM) antagonized the effect of aldosterone (10 nM) on Na+ transport in the toad bladder measured in vitro as short-circuit current (SCC). Half-maximal inhibition occurred at an antagonist-agonist molar ratio of 150:1. The antagonist action of testosterone was reversed by addition of more aldosterone. The antagonism was specific in the sense that testosterone (20 microM) did not inhibit the response of the SCC to oxytocin (50 mU/ml). By itself, testosterone (up to 20 microM) had no agonist activity on base-line SCC. Finally, testosterone (500 nM to 20 microM) specifically displaced [3H]aldosterone (5 nm) from its cytoplasmic and nuclear binding sites in bladders incubated in vitro at 25 or 0 degrees C and labeled at steady state. There was a significant linear correlation between the effect of testosterone on the aldosterone-dependent SCC and its effect on [3H]aldosterone binding sites in the cytoplasm and in the nucleus. We conclude that 1) testosterone is a specific competitive antagonist of aldosterone, and 2) [3H]aldosterone nuclear and cytoplasmic binding sites could be mineralocorticoid receptors, mediating the action of aldosterone on Na+ transport.

Thyroid hormone-aldosterone interaction on Na+ transport in toad bladder.

Repeated administration of thyroxine (T4) in vivo (2 microgram/100 g body wt for 6 days) lowered by 2.3 times (P less than 0.025, df = 18) the basal rate of Na+ transport measured by the short-circuit current (SCC) in vitro in the urinary bladder of the toad (Bufo marinus). This difference was not accounted for by a change in the plasma aldosterone concentration. Moreover the response of the SCC to aldosterone in vitro was markedly inhibited in bladders from T4-treated animals (P less than 0.001, df = 18). These findings raised the possibility of a direct interaction between thyroid hormone and aldosterone in the target cell. The effects of L-triiodothyronine (T3) and aldosterone were examined in vitro. T3 alone (60 nM) had no significant effect on the base-line SCC (deltamuA = -14 +/- 11 (SE) muA per hemibladder; P greater than 0.3, n = 10). By contrast, T3 (60 nM) inhibited the response of the SCC to aldosterone from 6 to 8 h after its addition (deltamuA = -98 +/- 19 muA per hemibladder; P less than 0.001, n = 10). The inhibition by T3 was present at 6 nM (P less than 0.01, n = 10) and became not significant at 0.6 nM. T3 had no significant effect on base-line or aldosterone-stimulated H+ transport. Thyroid hormone might therefore regulate the late response of the SCC to aldosterone at the level of its target cell.