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PubMed2005

Thorium complexation by hydroxamate siderophores in perturbed multicomponent systems using flow injection electrospray ionization mass spectrometry.

Flow injection electrospray ionization mass spectrometry has been shown to produce simple, characteristic m/z signals for Th-hydroxamate siderophore (desferrioxamine and ferrichrome) complexes, with Th complexed as a simple 4+ ion in the environmentally relevant pH range investigated (pH 5-9). All species of interest for this study were identified optimally in the positive mode; thus, multiple species were analyzed concurrently in a single spectrum. Complexation of Th by the two siderophores was rapid in 1:1 molar aqueous solution, reaching equilibrium before the first measurement was possible at 2 min. However, a significant proportion of the equimolar siderophore remained uncomplexed. Both siderophores rapidly exchanged Th for Fe when equimolar Fe(III) was added to the Th complexes, and only a small proportion of each siderophore remained complexed with Th at equilibrium (7-30 min). The results show a difference in the affinities of the two siderophores for the metals; ferrichrome has a 5-fold higher affinity than desferrioxamine for Th and a 5-fold lower affinity than desferrioxamine for Fe. Also, siderophore-complexed Th interacted strongly with a cation-exchange resin suggesting that, even when complexed by trianionic siderophores, Th mobility will be impeded by interactions with negatively charged binding sites in subsurface environmental matrixes. These results have important implications regarding siderophore-enhanced actinide(IV) mobility in the terrestrial environment.

Calibration↗
PubMed2003

Thorium(IV) complexes of bidentate hydroxypyridinonates.

The coordination chemistry of actinide(IV) ions with hydroxypyridinone ligands has been initially explored by examining the complexation of Th(IV) ion with bidentate PR-1,2-HOPO (HL(1)()), PR-Me-3,2-HOPO (HL(2)()), and PR-3,4-HOPO-N (HL(3)()) ligands. The complexes Th(L(1)())(4), Th(L(2)())(4), and Th(L(3)())(4) were prepared in methanol solution from Th(acac)(4) and the corresponding ligand. Single-crystal X-ray diffraction analyses are reported for the free ligand PR-Me-3,2-HOPO (HL(2)()) [Ponemacr;, Z = 8, a = 8.1492(7) A, b = 11.1260(9) A, c = 23.402(2) A, alpha = 87.569(1) degrees, beta = 86.592(1) degrees, gamma = 87.480(1) degrees ], and the complex Th(L(2)())(4).H(2)O [Pna2(1) (No. 33), Z = 4, a = 17.1250(5) A, b = 12.3036(7) A, c = 23.880 (1) A]. A comparison of the structure of the metal complex Th-PR-Me-3,2-HOPO with that of free ligand PR-Me-3,2-HOPO reveals that the ligand geometry is the same in the free ligand and in the metal complex. Amide hydrogen bonds enhance the rigidity and stability of the complex and demonstrate that the Me-3,2-HOPO ligands are predisposed for metal chelation. Solution thermodynamic studies determined overall formation constants (log beta(140)) for Th(L(1)())(4), Th(L(2)())(4), and Th(L(3)())(4) of 36.0(3), 38.3(3), and 41.8(5), respectively. Species distribution calculations show that the 4:1 metal complex Th(L)(4) is the dominant species in the acidic range (pH < 6) for PR-1,2-HOPO, in weakly acidic to physiological pH range for PR-Me-3,2-HOPO and in the high-pH range (>8) for PR-3,4-HOPO-N. This finding parallels the relative acidity of these structurally related ligands. In the crystal of [Th(L(2)())(4)].H(2)O, the chiral complex forms an unusual linear coordination polymer composed of linked, alternating enantiomers.

Algorithms↗
PubMed2004

Natural and anthropogenic enrichments of molybdenum, thorium, and uranium in a complete peat bog profile, Jura Mountains, Switzerland.

A core from an ombrotrophic Swiss bog representing 12 370 (14)C years of peat accumulation was evaluated as a possible archive of atmospheric deposition of Mo, Th and U. Calcium, Sr, and Ba were also determined to quantify weathering inputs, Mn to follow possible redox transformations, and Rb to identify plant uptake. Each of these elements was determined using ICP-MS, following digestion in a microwave heated autoclave using 3 ml HNO(3) and 0.1 ml HBF(4). Calcium and Sr clearly identify the thickness of the ombrotrophic zone because they are enriched in the minerogenic zone relative to the concentration of mineral matter. The concentration of Ba, however, is proportional to the concentration of mineral matter in all samples, and is not added to peat column by weathering reactions at the peat-sediment interface. The lowest element concentrations are found during the Holocene climate optimum (5320 to 8030 (14)C year BP) with the following natural background values (n= 18): Mo 0.08 +/- 0.02 microg g(-1), U 0.029 +/- 0.008 microg g(-1), Ba 5.2 +/- 2.6 microg g(-1), Th 0.070 +/- 0.022 microg g(-1) and Rb 0.63 +/- 0.09 microg g(-1). By far the highest concentrations of Ba, Mn, Rb and Th were found during the Younger Dryas cold climate event (10 590 (14)C year BP) when the flux of atmospheric soil dust was at its post-glacial maximum. Molybdenum and U are elevated in concentration throughout the minerogenic zone because of sediment weathering and this masks the atmospheric signal in samples older than ca. 8000 (14)C year BP (ca. 9000 calendar years). Enrichment factors (EF) calculated using Sc as a conservative, lithogenic element shows that minerogenic peats are enriched in Mo up to 18x and U 26x, relative to the natural "background" values. During the two millennia prior to industrialisation, the accumulation rate of atmospheric Mo averaged 0.23 +/- 0.13 microg m(-2) year(-1). With the onset of the Industrial Revolution, Mo accumulation rates rapidly and continuously increased to approximately 10 microg m(-2) year(-1) in the late 1980s. These data suggest that Mo in atmospheric aerosols today is derived predominately from anthropogenic emissions. Uranium does not show the same enrichment pattern which suggests that steel-making rather than coal combustion is the primary source of atmospheric Mo contamination at this site.

Calcium↗