Scientific Publications 2005
2005. "High-level ab-initio calculations for the four low-lying families of minima of (H2O)20: II. Spectroscopic signatures of the dodecahedron, fused cubes, face-sharing pentagonal prisms, and edge-sharing pentagonal prisms hydrogen bonding networks ." Journal of Chemical Physics 122(13):134304. Abstract We report the first harmonic vibrational spectra for each of the lowest lying isomers within the four major families of minima of (H2O)20, namely the dodecahedron, fused cubes, face-sharing pentagonal prisms and edge-sharing pentagonal prisms. These were obtained at the second-order Møller-Plesset perturbation level of theory (MP2) with the augmented correlation consistent basis set of double zeta quality (aug-cc-pVDZ) at the corresponding minimum energy geometries. The computed infrared (IR) spectra are the first ones obtained from first principles for these clusters. They were found to contain spectral features, which can be directly mapped onto the distinctive spectroscopic signatures of their constituent tetramer, pentamer and octamer fragments. The dodecahedron spectra show the richest structure in the OH stretching region and are associated with the most red-shifted OH vibrations with respect to the monomer. The lowest lying face-sharing pentagonal prism isomer displays intense IR active vibrations that are red-shifted by ~600 cm-1 with respect to the water monomer. The zero-point energy corrected MP2/CBS (complete basis set) limit binding energies (D0) for the four isomers are –163.1 kcal/mol (face-sharing pentagonal prism), -160.1 kcal/mol (edgesharing pentagonal prism), -157.5 kcal/mol (fused cubes) and –148.1 kcal/mol (dodecahedron).
2005. "Sensitivity of Ammonia Interaction with Single-Walled Carbon Nanotube Bundles to the Presence of Defect Sites and Functionalities." Journal of the American Chemical Society 127(30):10533-10538. doi:10.1021/ja042998u Abstract The abstract for this product is not available at this time.
2005. "Identifying the Potential Loss of Monitoring Wells Using an Uncertainty Analysis." Ground Water 43(6):916-925. doi:10.1111/j.1745-6584.2005.00047.x Abstract From the mid-1940s through the 1980s, large volumes of wastewater were discharged at the Hanford Site in southeastern Washington State, causing a large-scale rise (in excess of 20 m) in the water table. When wastewater discharges ceased in 1988, groundwater mounds began to dissipate. This caused a large number of wells to go dry and has made it difficult to monitor contaminant plume migration. To identify the wells that could potentially go dry, a first order uncertainty analysis was performed using a three-dimensional, finite element code (CFEST) coupled with UCODE, a nonlinear parameter estimation code. The analysis was conducted in four steps. First, key parameter values were identified by calibrating to historical hydraulic head data. Second, the model was tested for linearity, a strict requirement for representing output uncertainty. Third, results from the calibration period were used to verify model predictions by comparing monitoring wells’ wet/dry status with field data. In the final step, predictions on the number and locations of dry wells were made through the year 2048. A non-physically based model that extrapolated trends at each individual well was also tested as a predictor of a well’s wet/dry status. Results demonstrated that when uncertainty in both parameter estimates and measurement error was considered, the CFEST-based model successfully predicted the majority of dry wells, outperforming the trend model. Predictions made through the year 2048 identified approximately 50% of the wells in the monitoring well network are likely to go dry, which can aid in decisions for their replacement.
2005. "Actinide Sequestration Using Self-Assembled Monolayers on Mesoporous Supports." Environmental Science and Technology 39(5):1324-1331. Abstract Surfactant templated synthesis of mesoporous ceramics provides a versatile foundation upon which to create high efficiency environmental sorbents. These nanoporous ceramic oxides condense a huge amount of surface area into a very small volume. The ceramic oxide interface is receptive to surface functionalization through molecular self-assembly. The marriage of mesoporous ceramics with self-assembled monolayer chemistry creates a powerful new class of environmental sorbent materials called self-assembled monolayers on mesoporous supports (SAMMS). These SAMMS materials are highly efficient sorbents, whose interfacial chemistry can be fine-tuned to selectively sequester a specific target species, such as heavy metals, tetrahedral oxometallate anions and radionuclides. Details addressing the design, synthesis and characterization of SAMMS materials specifically designed to sequester actinides, of central importance to the environmental clean-up necessary after 40 years of weapons grade plutonium production, as well as evaluation of their binding affinities and kinetics are presented.
2005. "Electronic Structure and Intrinsic Redox Properties of [2Fe-2S]+ Clusters with Tri- and Tetracoordinate Iron Sites." Inorganic Chemistry 44(5):1202-1204. Abstract Using potentially bidentate ligands (-SC2H4H2), we produced [2Fe-2S]+ species of different coordination geometries by fission of [4Fe-4S]2+ complexes. Even though the ligands are monodentate in the cubane complexes, both mono- and bidentate complexes were observed in the [2Fe] fission products through self-assembly because of the high reactivity of the tricoordinate iron sites. The electronic structure of the [2Fe] species was probed using photoelectron spectroscopy and density functional calculations. It was found that tetracoordination significantly decreases the electron binding energies of the [2Fe] complexes, thus increasing the reducing capability of the [2Fe-2S]+ clusters.
2005. "Probing the Electronic Structure of [2Fe-2S] Clusters with Three Coordinate Iron Sites by use of Photoelectron Spectroscopy." Journal of Physical Chemistry A 109(9):1815-1820. Abstract Five series of [2Fe-2S] complexes, [Fe2S2Cl2-x(CN)x]-, [Fe2S2(SEt)2-xClx]-, [Fe2S2(SEt)2-x(CN)x]-, [Fe2S2Cl2-x(OAc)x]- (OAc = acetate), and [Fe2S2(SEt)2-x(OPr)x]- (OPr = Propionate) (x = 0 – 2), were produced by collision induced dissociation of the corresponding [4Fe-4S] complexes and their electronic structures were studied using photoelectron spectroscopy. All the [2Fe-2S] complexes contain a [Fe2S2]+ core similar to that in reduced [2Fe] Ferredoxins, but with different coordination geometries. For the first three series, which only involve tri-coordinated Fe sites, a linear relationship between the measured binding energies and the substitution number (x) was observed, revealing the independent ligand contributions to the total electron binding energies. The effect of the ligand increases in the order SEtClCN, conforming to their electron withdrawing ability in the same order. The carboxylate ligands in the [Fe2S2Cl2-x(OAc)x]- and [Fe2S2(SEt)2-x(OPr)x]- complexes were observed to act as bi-dentate ligands, giving rise to tetra-coordinated iron sites. This is different from their mono-dentate coordination behavior in the [4Fe-4S] cubane complexes, reflecting the high reactivity of the unsatisfied three coordinate iron site in the [2Fe-2S] complexes. The [2Fe-2S] complexes with tetra-coordinated iron sites exhibit lower electron binding energies, i.e., higher reductive activity than the all tri-coordinate planar clusters. The electronic structures of all the [2Fe-2S] complexes were shown to conform to the “inverted energy level scheme”.