Scientific Publications 2007
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2007. "The Nucleation and growth of Calcium Phosphate by Amelogenin." Journal of Crystal Growth 304(2):407-415. Abstract The nucleation processes involved in calcium phosphate formation in tooth enamel are not well understood but are believed to involve proteins in the extracellular matrix. The ability of one enamel protein, amelogenin, to promote the nucleation and growth of calcium phosphate was studied in an in vitro system involving metastable supersaturated solutions. It was found that recombinant amelogenin (rM179 and rp(H)M180) promoted the nucleation of calcium phosphate compared to solutions without protein. The amount of calcium phosphate increased with increasing supersaturation of the solutions and increasing protein concentrations up to 6.5 µg/ml. At higher protein concentrations, the amount of calcium phosphate decreased. The kinetics of nucleation were studied in situ and in real time using a quartz crystal microbalance (QCM) and showed that the protein reduced the induction time for nucleation compared to solutions without protein. This work shows a nucleation role for amelogenin in vitro which may be promoted by the association of amelogenin into nanosphere templates, exposing charged functionality at the surface. This research was performed at Pacific Northwest National Laboratory, operated by Battelle for the US-DOE. A portion of the research was performed in the EMSL, a national scientific user facility sponsored by the DOE-OBER at PNNL.
2007. " A smoothed particle hydrodynamics model for reactive transport and mineral precipitation in porous and fractured porous media." Water Resources Research 43(5):Art. No. W05437. doi:10.1029/2005WR004770 Abstract A numerical model based on smoothed particle hydrodynamics (SPH) was used to simulate reactive transport and mineral precipitation in porous and fractured porous media. The model was used to study effects of the Damkohler and Peclet numbers and pore-scale heterogeneity on reactive transport and the character of mineral precipitation, and to estimate effective reaction coefficients and mass transfer coefficients. The changes in porosity, fluid and solute fluxes and transport parameters resulting from mineral precipitation were also investigated. The simulation results show that the SPH, Lagrangian particle method, is an effective tool for studying pore scale flow and transport. The particle nature of SPH allows complex physical processes such as diffusion, reaction and mineral precipitation to be modeled with relative ease.
2007. "Ab initio simulations of the electrochemical activation of water." Molecular Simulation 33(4&5):429-436. doi:10.1080/08927020601154207 Abstract First principles periodic density functional theory (DFT) has been applied to simulate the electrochemical interface between water and various (111) metal surfaces. The chemistry of water at these electrified interfaces is simulated and the parameters relevant to the macroscopic behavior of the interface, such as the capacitance and the potential of zero charge (PZC) are examined. In addition, we examine the influence of co-adsorbed CO upon the equilibrium potential for the activation of water over Pt(111). We find that for copper and platinum there is a potential window over which water is inert, but on Ni(111) water is always found in some dissociated form (as adsorbed OH* or H*, depending on the applied potential). Furthermore, the relaxation of water molecules via the flip/flop rotation is an important contribution to the interfacial capacitance. Our calculations for the coadsorbed H₂O/CO system indicate that the adsorption of CO affects the binding energy of OH, such that water activation occurs at a higher equilibrium potential.
2007. "First-Principles Prediction of Equilibrium Potentials for WaterActivation by a Series of Metals." Journal of the Electrochemical Society 154(12):F217-221. doi:10.1149/1.2783780 Abstract The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. In this paper, we describe and apply an ab initio quantum-mechanical model to examine the electrochemical dissociation of water over a number of close-packed and near-close-packed metal surfaces. We have examined a series of metals important for electrochemical energy generation and corrosion-resistant alloy development including Ni, Cu, Ru, Au, Mo, Pd, and Pt. Advances in electrochemical theory depend on a detailed understanding of the interplay between surface chemistry and electrochemical phenomena. Herein, we have used ab initio quantum-mechanical methods to examine the double-layer regions for H₂O over these metals and compare the equilibrium potentials for the initial steps of water reduction and oxidation at the surface with known experimental quantities. We find that in its current form, the model developed herein is semiquantitative: it allows for the correct prediction of trends and the size of the double-layer regions, but in some cases it results in significant deviation with known absolute equilibrium potentials. Additional discussion is provided that outlines steps that may be taken to improve the quantitative accuracy of this model.
2007. "Fluorine doping in dilute magnetic semiconductor Sn1–xFexO2." Journal of Materials Science 18(11):1151-1155. doi:10.1007/s10854-007-9145-4 Abstract Recent studies have reported room-temperature ferromagnetism (FM) in Fe doped SnO2. The FM in semiconductors due to transition metal doping has been argued to be carrier mediated. Fluorine (F) doping in sure SnO2 has been reported to significantly increase the carrier concentration. In this work, we investigated the role of F doping in the range from 0% to 0.79% on the FM of chemically synthesized single phase Sn1xFexO2 using X-ray diffraction, UV-Vis spectrophotometry, particle-induced X-ray emission, particle-induced gamma ray emission and magnetometry. The saturation magnetization Ms (0.03 emu/g) increased by a factor of 2.5 and the lattice volume and band gap energy decreased by 0.35 A3 and 0.2eV, respectively, with 0.67% F doping (F/Sn atom %) compared to the sample without any fluorine.
2007. "Ferromagnetism in chemically synthesized CeO2 nanoparticles by Ni doping." Physical Review. B, Condensed Matter 76(16):165206-1 - 165206-8. doi:10.1103/PhysRevB.76.165206 Abstract This work reports the discovery of room-temperature ferromagnetism in 5 - 9 nm sized Ce1-xNixO2 nanoparticles (0.01 ≤ x ≤ 0.10) prepared using a sol-gel based chemical method at room temperature and under ambient conditions. Particle induced x-ray emission studies were used to determine the dopant concentrations. Magnetic measurements of the chemically synthesized Ce1-xNixO2 samples at room temperature showed coercivity in the 40 - 120 Oe range, and the saturation magnetization showed a maximum of 1.21 memu/g (8.59×10-4 μB/Ni ion) for x = 0.04. Average crystallite sizes and lattice parameters estimated from x-ray diffraction and transmission electron microscopy studies showed a gradual decrease with x in the entire doping range while the lattice strain showed a minimum for x = 0.04. Optical studies revealed direct band gap energies ranging from 3.23 to 3.99 eV with a minimum for x = 0.04. A high Curie temperature of TC = 550 K was obtained for x = 0.04.
2007. "Development of a Non-Invasive Biomonitoring Approach to Determine Exposure to the Organophosphorus Insecticide Chlorpyrifos in Rat Saliva." Toxicology and Applied Pharmacology 219(2-3):217-225. doi:10.1016/j.taap.2006.10.002 Abstract Abstract Non-invasive biomonitoring approaches are being developed using reliable portable analytical systems to quantify dosimetry utilizing readily obtainable body fluids, such as saliva. In the current study, rats were given single oral gavage doses (1, 10 or 50 mg/kg) of the insecticide chlorpyrifos (CPF), saliva and blood were collected from groups of animals (4/time-point) at 3, 6, and 12 hr post-dosing, and the samples were analyzed for the CPF metabolite trichlorpyridinol (TCP). Trichlorpyridinol was detected in both blood and saliva at all doses and the TCP concentration in blood exceeded saliva, although the kinetics in blood and saliva were comparable. A physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) model for CPF incorporated a compartment model to describe the time-course of TCP in blood and saliva. The model adequately simulated the experimental results over the dose ranges evaluated. A rapid and sensitive sequential injection (SI) electrochemical immunoassay was developed to monitor TCP, and the reported detection limit for TCP in water was 6 ng/L. Computer model simulation in the range of the Allowable Daily Intake (ADI) or Reference Dose (RfD) for CPF (0.01-0.003 mg/kg/day) suggest that the electrochemical immunoassay had adequate sensitivity to detect and quantify TCP in saliva at these low exposure levels. To validate this approach further studies are needed to more fully understand the pharmacokinetics of CPF and TCP excretion in saliva. The utilization of saliva as a biomonitoring matrix, coupled to real-time quantitation and PBPK/PD modeling represents a novel approach with broad application for evaluating both occupational and environmental exposures to insecticides.
2007. "Spin resolved photoelectron spectroscopy of Fe3O4: the case against half-metallicity." Journal of Physics. Condensed matter 19(31):Art. No. 315218. Abstract Many materials have been theoretically predicted to be half-metallic, and hence suitable for use as pure spin sources in spintronic devices. Yet to date, remarkably few of these predictions have been experimentally verified. We have used spin polarized photoelectron spectroscopy to study one candidate half-metallic system, Fe3O4. Such experiments are normally hampered by difficulties in producing clean stoichiometric surfaces with a polarization that is truly representative of that of the bulk. However, by utilizing higher photon energies than have traditionally been used for such experiments, we can study polarization in ‘as received’ samples, essentially ‘looking through’ the disrupted surface. High quality, strain relieved, ex situ prepared Fe3O4 films have been thoroughly characterized by diffraction, transport and magnetometry studies of their crystallographic, electronic and magnetic properties. The spectroscopic results are found to agree fairly closely with previously published experimental data on in situ grown thin films and cleaved single crystals. However, despite the higher photoelectron kinetic energies of the experiment, it has not been possible to observe 100% polarization at the Fermi level. Hence, our data do not support the claim of true half-metallicity for Fe3O4.
2007. "Fabrication of Polymer Electrolyte Membrane Fuel Cell MEAs Utilizing Inkjet Print Technology." Journal of Power Sources 171 (2):575-584. doi:10.1016/j.jpowsour.2007.07.017 Abstract Utilizing drop-on-demand technology, we have successfully developed hydrogen-air polymer electrolyte membrane fuel cells (PEMFC) and have demonstrated their performance to be similar to conventionally fabricated systems. Prototype membrane electrode assemblies (MEAs) were fabricated utilizing commercial desktop inkjet printers by depositing the active catalyst electrode layer directly from print cartridges onto a Nafion® polymer membrane. Preliminary results indicate open circuit voltages up to 0.84 V and power densities of 31 mW/cm2 as compared to 0.9 V and 42 mW/cm2 for commercial MEAs tested on our experimental test apparatus. The objective of this work is to demonstrate that drop-on-demand technology can be used to produce MEAs comparable in structure and performance to commercially available MEAs and to demonstrate that this approach provides highly controlled and repeatable automated processing that can result in improved precious metal catalyst efficiency, improved structural integrity and ultimately reduced PEMFC MEA materials and fabrication costs.
2007. "Signature OH Absorption Spectrum from cluster Models of Solvation: a solvent-to-solute charge transfer state." Journal of Physical Chemistry A 111(42):10478-10482. doi:10.1021/jp074617f Abstract ab initio electronic structure theories applied to cluster models support the characterization of the signature of the OH absorption spectrum to be a solvent-to-solute charge transfer state affected by the hydrogen bonding environment in the region of 250 nm (calculated). The vertical excited states were calculated at the TDDFT level of theory with using OH(H2O)n clusters (n = 0-7, 16) with companion calculations at the EOM-CCSD level of theory for n ≤ 7. An intense solvent-to-solute charge transfer transition was calculated for n = 16 cluster where the donor and acceptor molecular orbitals are in favorable alignment. In the other smaller clusters the transitions in this region were found to be weak. The present findings are consistent with the experimental absorption at 230 nm suggested to be a solvent-to-solute charge transfer and provide insight into the electronic states and orbitals that give rise to the intensity of the band. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program, and was performed in part using the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a DOE national scientific user facility located at the Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for DOE.
2007. "Cooperative Hydrogen Bonding in Amyloid Formation." Protein Science 16(4):761-764. doi:10.1110/ps.062609607 Abstract The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Amyloid diseases, including Alzheimer's and prion diseases, are each associated with unbranched protein fibrils. Each fibril is made of a particular protein, yet they share common properties. One such property is nucleation-dependent fibril growth. Monomers of amyloid-forming proteins can remain in dissolved form for long periods, before rapidly assembly into fibrils. The lag before growth has been attributed to slow kinetics of formation of a nucleus, on which other molecules can deposit to form the fibril. We have explored the energetics of fibril formation, based on the known molecular structure of a fibril-forming peptide from the yeast prion, Sup35, using both classical and quantum (density functional theory) methods. We find that the energetics of fibril formation for the first three layers are cooperative using both methods. This cooperativity is consistent with the observation that formation of amyloid fibrils involves slow nucleation and faster growth.
2007. "Structure and Electronic Spectra of DNA Mini-hairpins with Gn:Cn Stems." Journal of Physical Chemistry B 111(45):13101-13106. doi:10.1021/jp072303m Abstract The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The solution structure of a synthetic DNA mini-hairpin possessing a stilbenediether linker and three G:C base pairs has been obtained using 1H NMR spectral data and constrained torsion angle molecular dynamics. Notable features of this structure include a compact hairpin loop having a short stilbene-guanine plane-toplane distance and approximate B-DNA geometry for the three base pairs. Comparison of the electronic spectra of mini-hairpins having one-to-four G:C base pairs and stilbenediether or hexamethyleneglycol linkers reveals the presence of features in the UV and CD spectra of the stilbene-linked hairpins that are not observed for the ethyleneglycol-linked hairpins. Investigation of the electronic structure of a stilbene-linked hairpin having a single G:C base pair by means of time-dependent density functional theory shows that the highest occupied molecular orbital, but not the lowest unoccupied molecular orbital, is delocalized over the stilbene and adjacent guanine. The calculated UV and CD spectra are highly dependent upon hairpin conformation, but reproduce the major features of the experimental spectra. These results illustrate the utility of an integrated experimental and theoretical approach to understanding the complex electronic spectra of л-stacked chromophores.
