Plutonium speciation affected by environmental bacteria

Abstract

SummaryPlutonium has no known biological utility, yet it has the potential to interact with bacterial cellular and extracellular structures that contain metal-binding groups, to interfere with the uptake and utilization of essential elements, and to alter cell metabolism. These interactions can transform plutonium from its most common forms, solid, mineral-adsorbed, or colloidal Pu(IV), to a variety of biogeochemical species that have much different physico-chemical properties. Organic acids that are extruded products of cell metabolism can solubilize plutonium and then enhance its environmental mobility, or in some cases facilitate plutonium transfer into cells. Phosphate- and carboxylate-rich polymers associated with cell walls can bind plutonium to form mobile biocolloids or Pu-laden biofilm/mineral solids. Bacterial membranes, proteins or redox agents can produce strongly reducing electrochemical zones and generate molecular Pu(III/IV) species or oxide particles. Alternatively, they can oxidize plutonium to form soluble Pu(V) or Pu(VI) complexes. This paper reviews research on plutonium-bacteria interactions and closely related studies on the biotransformation of uranium and other metals.

First Hexanuclear UIV and ThIV Formate Complexes – Structure and Stability Range in Aqueous Solution

“…In the FTs of the solution samples, the Th···Th interaction was observed at R + ∆ = 3.70 Å. Although compound 3 precipitates at pH Ͼ 3.50, the intensity of the Th···Th peak is much smaller than that of the solid, suggesting that [Th 6 {µ 3 -O(H)} 8 (HCOO) 12 (H 2 O) 6 ] is not such a strong complex in solution. This is probably related to the lower hydrolysis capacity of Th IV .…”

“…A fraction of the [U 6 {µ 3 -O(H)} 8 (HCOO) 12 (H 2 O) 6 ] at different pH values was determined by fitting of the peak of the U···U interaction at R + ∆ = 3.81 Å with the same Debye-Waller factor as the solid (σ 2 = 0.0054 Å 2 ) on the assumption that the U 6 {µ 3 -O(H)} 8 core in solution has the same rigidity as in the solid. The fitting results are summarized in Table S6 and Figure S4.…”

“…The obtained species distribution curve of the hexanuclear cluster is shown in Figure 3. The formation of [U 6 {µ 3 -O(H)} 8 (HCOO) 12 (H 2 O) 6 ] starts at pH = 0.92 due to hydrolysis and coordination of HCOO -and reaches a plateau at pH Ͼ 2.31. In order to confirm the validity of this distribution curve, UV/Vis absorption spectra were measured ( Figure S2), followed by a statistical analysis [22] including two significant principal components.…”

“…The hexanuclear [M 6 {µ 3 -O(H)} 8 (HCOO) 12 (L T ) 6 ] complexes were isolated by pH adjustment of U IV and Th IV in aqueous HCOOH solution. Their structures in the solid and solution states were determined by single-crystal X-ray analysis and EXAFS spectroscopy, respectively.…”

“…[5] Polynuclear U IV species can be formed by microbial activity. [6] Despite their importance in the environment, structural data of only a very limited number of polynuclear species have been reported so far by single-crystal X-ray analysis. [7][8][9][10][11][12][13][14][15] Most of the described actinide(IV) complexes are hexanuclear, similar to the hexanuclear nanosized clusters of transition metal complexes.…”