Towards data management for PX structure determination with CCP4

Importance of a nanoscience approach in the understanding of major aqueous contamination scenarios: case study from a recent coal ash spill

A coal ash spill that occurred from an ash impoundment pond into the Dan River, North Carolina, provided a unique opportunity to study the significance and role of naturally occurring and incidental nanomaterials associated with contaminant distribution from a large-scale, acute aquatic contamination event. Besides traditional measurements of bulk watercolumn and sediment metal concentrations, the nanoparticle (NP) analyses are based on cross-flow ultrafiltration (CFUF) and advanced transmission electron microscopy (TEM) techniques. A drain pipe fed by coal ash impoundment seepage showed a high level of arsenic, with concentrations many times over the EPA limit. The majority of the arsenic was found sorbed to large aggregates dominated by incidental iron oxyhydroxide (ferrihydrite) NPs, while the remainder of the arsenic was truly dissolved. These ferrihydrites were probably formed in situ where Fe(II) was leached through subsurface flowpaths into an aerobic environment, and further act as a significant contributor to the elevated As concentrations in downstream sediments after the spill. In addition, we discovered and describe a photocatalytic nano-TiO2 phase (anatase) present in the coal ash impacted river water that was also carrying/transporting transition metals (Cu, Fe), which may also have environmental consequences.

Pairwise assembly of organopalladium(II) units with cyanurato(3-) and trithiocyanurato(3-) ligands: formation of chiral Pd12, Pd10, and Pd9 cage-molecules

The o-palladated, chloro-bridged dimers [Pd{2-phenylpyridine(-H)}-μ-Cl]₂ and [Pd{N,N-dimethylbenzylamine(-H)}-μ-Cl]₂ react with cyanuric acid in the presence of base to afford closed, chiral cage-molecules in which 12 organo-Pd(II) centers, located in pairs at the vertices of an octahedron, are linked by four tetrahedrally arranged cyanurato(3−) ligands. Incomplete (Pd₁₀) cages, having structures derived from the corresponding Pd₁₂ cages by replacing one pair of organopalladium centers with two protons, have also been isolated. Reaction of [Pd{2-phenylpyridine(-H)}-μ-Cl]₂ with trithiocyanuric acid gives an entirely different and more open type of cage-complex, comprising only nine organopalladium centers and three thiocyanurato(3−) ligands: cage-closure in this latter system appears to be inhibited by steric crowding of the thiocarbonyl groups.

The o-palladated, chloro-bridged dimers [Pd{2-phenylpyridine(-H)}-μ-Cl]₂ and [Pd{N,N-dimethylbenzylamine(-H)}-μ-Cl]₂ react with cyanuric acid in the presence of base to afford closed, chiral cage-molecules (point group T) in which 12 organo-Pd(II) centers located about the vertices of an octahedron are linked by four tetrahedrally arranged cyanurato(3−) ligands. Incomplete (Pd₁₀) cages have also been isolated. Reaction of [Pd{2-phenylpyridine(-H)}-μ-Cl]₂ with trithiocyanuric acid gives a cage-complex comprising only nine organopalladium centers and three thiocyanurato(3−) ligands.

Immobilization of 99-technetium (VII) by Fe(II)-goethite and limited reoxidation

During the nuclear waste vitrification process volatilized (99)Tc will be trapped by melter off-gas scrubbers and then washed out into caustic solutions, and plans are currently being contemplated for the disposal of such secondary waste. Solutions containing pertechnetate [(99)Tc(VII)O(4)(-)] were mixed with precipitating goethite and dissolved Fe(II) to determine if an iron (oxy)hydroxide-based waste form can reduce Tc(VII) and isolate Tc(IV) from oxygen. The results of these experiments demonstrate that Fe(II) with goethite efficiently catalyzes the reduction of technetium in deionized water and complex solutions that mimic the chemical composition of caustic waste scrubber media. Identification of the phases, goethite + magnetite, was performed using XRD, SEM and TEM methods. Analyses of the Tc-bearing solid products by XAFS indicate that all of the Tc(VII) was reduced to Tc(IV) and that the latter is incorporated into goethite or magnetite as octahedral Tc(IV). Batch dissolution experiments, conducted under ambient oxidizing conditions for more than 180 days, demonstrated a very limited release of Tc to solution (2-7 μg Tc/g solid). Incorporation of Tc(IV) into the goethite lattice thus provides significant advantages for limiting reoxidation and curtailing release of Tc disposed in nuclear waste repositories.