A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

Effect of Temperature

Gaussian (14s13p10d8f6g)/[6s6p5d4f3g] atomic natural orbital valence basis sets have been derived for relativistic energy-consistent small-core lanthanide pseudopotentials of the Stuttgart–Bonn variety. The existing set of lanthanide pseudopotentials has been supplemented by corresponding potentials for lanthanum and lutetium in order to arrive at a set analogous to the one available for the actinides. Multiconfiguration self-consistent field and subsequent multireference averaged coupled-pair functional calculations are presented for the first to fourth ionization potentials of all lanthanide elements. Molecular calibration studies using the coupled-cluster singles, doubles, and perturbative triples approach are reported for the monohydrides, monoxides, and monofluorides of lanthanum and lutetium.

Valence basis sets for relativistic energy-consistent small-core actinide pseudopotentials

Gaussian (14s13p10d8f6g)/[10s8p5d4f3g] valence basis sets using a segmented contraction scheme have been derived for relativistic energy-consistent small-core lanthanide pseudopotentials of the Stuttgart-Bonn variety. The present basis sets are only slightly larger than previously published (14s13p10d8f6g)/[6s6p5d4f3g] atomic natural orbital basis sets, which use a generalized contraction scheme, and achieve a similar accuracy in atomic and molecular calculations. For calibration purposes multi-configuration self-consistent field and subsequent multi-reference averaged coupled-pair functional calculations are presented for the first to fourth ionization potentials of all lanthanide elements. In addition, results of molecular calibration studies using the coupled-cluster singles, doubles and perturbative triples approach as well as gradient-corrected density functional theory are reported for the monohydrides, monoxides and monofluorides of lanthanum and lutetium.

Segmented contraction scheme for small-core lanthanide pseudopotential basis sets

Reference LCIB-ARTICLE-2007-010doi:10.1021/cr030726oView record in Web of Science Record created on 2007-02-14, modified on 2017-05-12

Inorganic and bioinorganic solvent exchange mechanisms.

Summary

Siderophores are chelators with extremely strong affinity for ferric iron and are best known for their capacity to feed microorganisms with this metal. Despite their preference for iron, they can also chelate numerous other metals with variable affinities. There is also increasing evidence that metals other than iron can activate the production of siderophores by bacteria, thereby implicating siderophores in the homeostasis of metals other than iron and especially heavy metal tolerance. This article considers this new concept that siderophores play a role in protecting bacteria against metal toxicity and discusses the possible contribution of these chelators to the transport of biological relevant metals in addition to iron.

New roles for bacterial siderophores in metal transport and tolerance

The structures of the complexes UO2Fn(H2O)5-n2-n, n = 3−5, have been studied by EXAFS. All have pentagonal bipyramid geometry with U−F of and U−H2O distances equal to 2.26 and 2.48 A, respectively. On the other hand the complex UO2(OH)42- has a square bipyramid geometry both in the solid state and in solution. The structures of hydroxide and fluoride complexes have also been investigated with wave function based and DFT methods in order to explore the possible reasons for the observed structural differences. These studies include models that describe the solvent by using a discrete second coordination sphere, a model with a spherical, or shape-adapted cavity in a conductor-like polarizable continuum medium (CPCM), or a combination of the two. Solvent effects were shown to give the main contribution to the observed structure variations between the uranium(VI) tetrahydroxide and the tetrafluoride complexes. Without a solvent model both UO2(OH)4(H2O)2- and UO2F4(H2O)2- have the same square bipyramid geometry...

Solvent effects on uranium(VI) fluoride and hydroxide complexes studied by EXAFS and quantum chemistry.

The local structure of U(VI), U(IV), and Th(IV) sulfato complexes in aqueous solution was investigated by U-L3 and Th-L3 EXAFS spectroscopy for total sulfate concentrations 0.05 ≤ [SO42-] ≤ 3 M and 1.0 ≤ pH ≤ 2.6. The sulfate coordination was derived from U−S and Th−S distances and coordination numbers. The spectroscopic results were combined with thermodynamic speciation and density functional theory (DFT) calculations. In equimolar [SO42-]/[UO22+] solution, a U−S distance of 3.57 ± 0.02 A suggests monodentate coordination, in line with UO2SO4(aq) as the dominant species. With increasing [SO42-]/[UO22+] ratio, an additional U−S distance of 3.11 ± 0.02 A appears, suggesting bidentate coordination in line with the predominance of the UO2(SO4)22- species. The sulfate coordination of Th(IV) and U(IV) was investigated at [SO42-]/[M(IV)] ratios ≥8. The Th(IV) sulfato complex comprises both, monodentate and bidentate coordination, with Th−S distances of 3.81 ± 0.02 and 3.14 ± 0.02 A, respectively. A similar coo...

EXAFS investigation of U(VI), U(IV), and Th(IV) sulfato complexes in aqueous solution.

The structures of aqueous M4+(aq) and MF3+(aq), where M is uranium(IV) or thorium(IV), have been determined by LIII edge EXAFS using data from solutions of 1.5 M HClO4 in which the M(IV) concentrations ranged from 0.03 to 0.3 M. A least-squares refinement of the data for the aqua ions indicated 10.8 ± 0.5 water molecules in the first hydration sphere of both ions and M−O bond distances for U(IV) and Th(IV) of 2.42 ± 0.01 and 2.45 ± 0.01 A, respectively. By considering both previous structure information and the EXAFS data, we selected N = 10 ± 1 as the most likely coordination number of both M(IV) aqua ions. EXAFS measurements from acidic aqueous uranium(IV) and thorium(IV) solutions containing fluoride show that large changes in the first coordination sphere occur. The experimental data indicates an asymmetrical distribution of the distances, probably as a result of differing M−F and M−O bond lengths. These can be described by a model that contains two different bond distances, one M−F distance at 2.10 A...

Structure of the Aqua Ions and Fluoride Complexes of Uranium(IV) and Thorium(IV) in Aqueous Solution an EXAFS Study.

The colloid chemistry of acid rock drainage solution from an abandoned Zn–Pb–Ag mine

Bacteria have a great influence on the migration behaviour of heavy metals in the environment. Lipopolysaccharides form the main part of the outer membrane of Gram-negative bacteria. We investigated the interaction of the uranyl cation (UO22+) with lipopolysaccharide (LPS) from Pseudomonas aeruginosa by using potentiometric titration and time-resolved laser-induced fluorescence spectroscopy (TRLFS) over a wide pH and concentration range. Generally, LPS consists of a high density of different functionalities for metal binding such as carboxyl, phosphoryl, amino and hydroxyl groups. The dissociation constants and corresponding site densities of these functional groups were determined using potentiometric titration. The combination of both methods, potentiometry and TRLFS, show that at an excess of LPS uranyl phosphoryl coordination dominates, whereas at a slight deficit on LPS compared to uranyl, carboxyl groups also become important for uranyl coordination. The stability constants of one uranyl carboxyl complex and three different uranyl phosphoryl complexes and the luminescence properties of the phosphoryl complexes are reported.

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Henry Moll

Papers

Solvent effects on uranium(VI) fluoride and hydroxide complexes studied by EXAFS and quantum chemistry.

EXAFS investigation of U(VI), U(IV), and Th(IV) sulfato complexes in aqueous solution.

Structure of the Aqua Ions and Fluoride Complexes of Uranium(IV) and Thorium(IV) in Aqueous Solution an EXAFS Study.

The colloid chemistry of acid rock drainage solution from an abandoned Zn–Pb–Ag mine

Interaction of uranium(VI) with lipopolysaccharide.