Scientific Publications 2007
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2007. "Catalytic Consequences of Composition in Polyoxometalate Clusterswith Keggin Structure." Angewandte Chemie International Edition 46(41):7864-7868. doi:10.1002/anie.200701292 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. Reliable correlations among structure, composition, and function in heterogeneous catalysis require well-defined atomic connectivity within active structures and the assessment of the specific elementary steps and reaction intermediates responsible for the relevant catalytic function. The non-uniform nature of typical active structures creates significant challenges because probes of structure and function average such heterogeneity in complex ways. Polyoxometalate (POM) clusters with stable Keggin structures and well-defined atomic connectivity provide the compositional diversity required for a rigorous assessment of the consequences of composition on catalytic reactivity.
2007. "Targeted Protein Degradation by Salmonella under Phagosome-Mimicking Culture Conditions Investigated Using Comparative Peptidomics." Molecular & Cellular Proteomics. MCP 6(4):717-727. doi:10.1074/mcp.M600282-MCP200 Abstract The pathogen Salmonella enterica is known to cause both food poisoning and typhoid fever. Due to the emergence of antibiotic-resistant isolates and the threat of bioterrorism (e.g., contamination of the food supply), there is a growing need to study this bacterium. In this investigation, comparative peptidomics was used to study Salmonella enterica serovar Typhimurium cultured in either a rich medium or in an acidic, low magnesium, and minimal nutrient medium designed to roughly mimic the macrophage phagosomal compartment (within which Salmonella are known to survive). Native peptides from cleared cell lysates were enriched by using isopropanol extraction and analyzed by using both LC-MS/MS and LC-FTICR-MS. We identified 5,163 distinct peptides originating from 682 proteins and the data clearly indicated that compared to cells cultured in the rich medium, Salmonella cultured in the phagosome-mimicking medium had dramatically higher abundances of a wide variety of protein degradation products, especially from ribosomal proteins. Salmonella from the same cultures were also analyzed by using bottom-up proteomics, and when the peptidomic and proteomic data were analyzed together, two clusters of proteins targeted for proteolysis were tentatively identified. Possible roles of targeted proteolysis by phagocytosed Salmonella are discussed.
2007. "Electrospray characteristic curves: in pursuit of improved performance in the nano-flow regime." Analytical Chemistry 79(21):8030-8036. doi:10.1021/ac070800t Abstract Depending on its coordinates in the parameter space, an electrospray can manifest in one of several known regimes – stable, quasi-stable, transitional-chaotic, and non-axial – that ultimately impact measurement sensitivity and precision. An electrospray operating in cone-jet regime provides large and stable spray current, as well as smaller initial droplets that are prerequisites for higher sensitivity and quality mass spectrometric analyses. However, the dynamic conditions encountered in gradient elution-based liquid separations create difficulties for continuous operation in this regime throughout the analysis. We present a preliminary study aimed at stabilizing the electrospray in the cone-jet regime. On the basis of spray current measurements obtained using solvent conditions typically found in liquid chromatography-mass spectrometry, an improved description of the cone-jet stability island is provided by including transitions to and from the recently described astable regime. Additionally, the experimental conditions in which the astable regime marks the transition between pulsating and cone-jet regimes are further clarified.
2007. "Effect of Coal Gas Contaminants on Solid Oxide Fuel Cell Operation." ECS Transactions 11(33):63-70. Abstract The operation of solid oxide fuel cells (SOFC) was evaluated on simulated coal gas in the presence of several coal gas impurities that are expected to remain in low concentration after warm gas cleanup. Phosphorus, arsenic and sulfur were considered in this study. The presence of phosphorus and arsenic in low, 1-2 ppm, concentrations led to the slow and irreversible SOFC degradation due to the formation of the secondary phases with nickel in the upper part of the nickel-based anode close to the gas inlet. Sulfur interactions with the nickel were limited to the surface only. Cell performance losses due to sulfur exposure were reversible and independent of the presence of other impurities.
2007. "Uranium immobilization by sulfate-reducing biofilms grown on hematite, dolomite, and calcite." Environmental Science & Technology 41(24):8349-8354. doi:10.1021/es071335k Abstract Biofilms of sulfate-reducing bacteria Desulfovibrio desulfuricans G20 wereused to reduce dissolved U(VI)and subsequently immobilize U(IV) in the presence of uranium-complexing carbonates. The biofilms were grown in three identically operated fixed bed reactors, filled with three types of minerals: one noncarbonate-bearing mineral(hematite) and two carbonate-bearing minerals (calcite and dolomite). The source of carbonates in the reactors filled with calcite and dolomite were the minerals, while in the reactor filled with hematite it was a 10 mM carbonate buffer, pH 7.2, which we added to the growth medium. Our five-month study demonstrated that the sulfate-reducing biofilms grown in all reactors were able to immobilize/reduce uranium efficiently, despite the presence of uranium-complexing carbonates.
2007. "Dipole-Dipole Interactions of High-spin Paramagnetic Centers in Disordered Systems." Applied Magnetic Resonance 30(3-4):683-702. Abstract Dipole-dipole interactions between distant paramagnetic centers (PCs) where at least one PC has spin S>1/2 are examined. The results provide a basis for the application of pulsed DEER or PELDOR methods to the measurement of distances between PC involving high-spin species. A projection operator technique based on spectral decomposition of the secular Hamiltonian is used to calculate EPR line splitting caused by the dipole coupling. This allows calculation of operators projecting arbitrary wavefunction onto high PC eigenstates when the eigenvectors of the Hamiltonian are not known. The effective spin vectors-that is, the expectation values for vector spin operators in the PC eigenstates-are calculated. The dependence of these effective spin vectors on the external magnetic field is calculated. There is a qualitative difference between pairs having at least one integer spin (non Karmers PC) and pairs of two half-integer (Kramers PC) spins. With the help of these effective spin vectors, the dipolar lineshape of EPR lines is calculated. Analytical relations are obtained for PCs with spin S=1/2 and 1. The dependence of Pake patterns on variations of zero field splitting, Zeeman energy, temperature and dipolar coupling are illustrated.
2007. "The Analysis of Combination and Overtone States of 11BF3 from 1650 to 4600 cm-1." Journal of Molecular Spectroscopy 243(1):16-31. doi:10.1016/j.jms.2007.02.019 Abstract High-resolution (0.0015-0.0035 cm-1) infrared spectra of isotopically enriched 11BF3 have been examined in detail. The analysis of the combination and overtone states within the region of study, from 1650 to 4600 cm-1, led to the assignment of over 25,000 transitions. The major perturbations were due to the Fermi resonances between states possessing one quantum of v4. With corrections through the quadratic rotational terms, the equilibrium Be and Ce values have been determined; 0.3462679 cm -1 and 0.17311506 cm-1, respectively. An improved set of equilibreium rotational constants for 10BF3, consistent with this analysis of 11BF3 are also given. The averaged equilibrium values for both isotopomers lead to a B-F bond distance of re = 130.70 ± 0.0XX pm. All of the quadratic anharmonic constants, with the exception of x33 were independently, experimentally determined. For the first time for BF3, a normal force field analysis was performed that utilized the experimentally determined, fundamental harmonic vibrational frequencies.
2007. "Reliable Predictions of the Thermochemistry of Boron-Nitrogen Hydrogen Storage Compounds: BxNxHy, x=2,3 ." Journal of Physical Chemistry A 111(20):4411-4421. doi:10.1021/jp070931y Abstract Thermochemical data calculated using ab initio molecular orbital theory are reported for 16 BxNxHy compounds with x = 2, 3 and y ≥ 2x. Accurate gas phase heats of formation were obtained using coupled cluster with single and double excitations and perturbative triples (CCSD(T)) valence electron calculations extrapolated to the complete basis set (CBS) limit with additional corrections including core/valence, scalar relativistic, and spin-orbit corrections to predict the atomization energies and scaled harmonic frequencies to correct for zero point and thermal energies and estimate entropies. Computationally cheaper calculations were also performed using the G3MP2 and G3B3 variants of the Gaussian-3 method, as well as density functional theory (DFT) using the B3LYP functional. The G3MP2 heats of formation are too positive by up to ~6 kcal/mol as compared to CCSD(T)/CBS values. The more expensive G3B3 method predicts heats of formation that are too negative as compared to the CCSD(T)/CBS values by up to 3 to 4 kcal/mol. Density functional theory (DFT) using the B3LYP functional and 6-311+G** basis set predict isodesmic reaction energies to within a few kcal/mol compared to the CCSD(T)/CBS method so isodesmic reactions involving BN compounds and the analogous hydrocarbons can be used to estimate heats of formation. Heats of formation of cyclo-B3N3H12 and cyclo-B3N3H6 are, in kcal/mol at 298 K, -95.5 and -115.5, respectively using our best calculated CCSD(T)/CBS approach. The experimental value for cyclo-B3N3H6 appears to be ~7 kcal/mol too negative. Enthalpies, entropies and free energies are calculated for many dehydrocoupling and dehydrogenation reactions that convert BNH6 to alicyclic and cyclic oligomers and H2(g). Generally, the reactions are highly exothermic, and exorgonic as well, due to the release of 1 or more equivalents of H2(g). For cyclo-B3N3H12 and cyclo-B3N3H6, available experimental data for sublimation and vaporization lead to estimates of their condensed phase 298 K heats of formation: ∆Hf°[cyclo-B3N3H12(s)] = -124 kcal/mol and ∆Hf°[cyclo-B3N3H6(l)] = -123 kcal/mol. The reaction thermochemistry for dehydrocoupling of BNH6(s) to cyclo-B3N3H12(s) and the dehydrogenation of cyclo-B3N3H12(s) to cyclo-B3N3H6(l) are much less exothermic compared to the gas phase reactions due to intermolecular forces which decrease in the order BNH6 > cyclo-B3N3H12 > cyclo-B3N3H6. The condensed phase reaction free energies are less negative compared to the gas phase reactions, but still too favorable for BNH6 to be regenerated from either cyclo-B3N3H12 or cyclo-B3N3H6 by just an overpressure of H2. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
2007. "Theoretical Prediction of the Heats of Formation of C₂H₅O● Radicals Derived from Ethanoland of the Kinetics of β-C-C Scission in the Ethoxy Radical." Journal of Physical Chemistry A 111(1):113-126. doi:10.1021/jp064086f 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. Thermochemical parameters of three C₂H₅O● radicals derived from ethanol were reevaluated using coupledcluster theory CCSD(T) calculations, with the aug-cc-pVnZ (n = D, T, Q) basis sets, that allow the CC energies to be extrapolated at the CBS limit. Theoretical results obtained for methanol and two CH₃O● radicals were found to agree within ±0.5 kcal/mol with the experiment values. A set of consistent values was determined for ethanol and its radicals: (a) heats of formation (298 K) ∆Hf(C₂H₅OH) = -56.4 ±0.8 kcal/mol (exptl: -56.21 ± 0.12 kcal/mol), ∆Hf(CH₃C●HOH) = -13.1 ±0.8 kcal/mol, ∆Hf(C●H₂CH₂OH) = -6.2 ±0.8 kcal/mol, and ∆Hf(CH₃CH₂O●) = -2.7 ± 0.8 kcal/mol; (b) bond dissociation energies (BDEs) of ethanol (0 K) BDE(CH₃CHOH-H) = 93.9 ± 0.8 kcal/mol, BDE(CH₂CH₂OH-H) = 100.6 ± 0.8 kcal/mol, and BDE- (CH₃CH₂O-H) = 104.5 ± 0.8 kcal/mol. The present results support the experimental ionization energies and electron affinities of the radicals, and appearance energy of (CH₃CHOH+) cation. β-C-C bond scission in the ethoxy radical, CH₃CH₂O●, leading to the formation of C●H₃ and CH₂=O, is characterized by a C-C bond energy of 9.6 kcal/mol at 0 K, a zero-point-corrected energy barrier of E0 ‡ = 17.2 kcal/mol, an activation energy of Ea = 18.0 kcal/mol and a high-pressure thermal rate coefficient of k⍵(298 K) = 3.9 s-1, including a tunneling correction. The latter value is in excellent agreement with the value of 5.2 s-1 from the most recent experimental kinetic data. Using RRKM theory, we obtain a general rate expression of k(T,p) = 1.26 x 109p0.793 exp(-15.5/RT) s-1 in the temperature range (T) from 198 to 1998 K and pressure range (p) from 0.1 to 8360.1 Torr with N₂ as the collision partners, where k(298 K, 760 Torr) = 2.7 s-1, without tunneling and k = 3.2 s-1 with the tunneling correction. Evidence is provided that heavy atom tunneling can play a role in the rate constant for β-C-C bond scission in alkoxy radicals.
2007. "Can an Excess Electron Localise on a Purine Moiety in the Adenine-thymine Watson-Crick Base Pair? A Computational Study." International Journal of Quantum Chemistry 107(12):2224-2232. doi:10.1002/qua.21359 Abstract The electron affinity and the propensity to electron-induced proton transfer (PT) of hydrogen-bonded complexes between the Watson–Crick adenine–thymine pair (AT) and simple organic acid (HX), attached to adenine in the Hoogsteen-type configuration, were studied at the B3LYP/6-31+G** level. Although the carboxyl group is deprotonated at physiological pH, its neutral form, COOH, resembles the peptide bond or the amide fragment in the side chain of asparagine (Asn) or glutamine (Gln). Thus, these complexes mimic the interaction between the DNA environment (e.g., proteins) and nucleobase pairs incorporated in the biopolymer. Electron attachment is thermodynamically feasible and adiabatic electron affinities range from 0.41 to 1.28 eV, while the vertical detachment energies of the resulting anions span the range of 0.39 –2.88 eV. Low-energy activation barriers separate the anionic minima: aHX(AT) from the more stable single-PT anionic geometry, aHX(AT)-SPT, and aHX(AT)-SPT from the double-PT anionic geometry, aHX(AT)-DPT. Interaction between the adenine of the Watson–Crick AT base pair with an acidic proton donor probably counterbalances the larger EA of isolated thymine, as SOMO is almost evenly delocalized over both types of nucleic bases in the aHX(AT) anions. Moreover, as a result of PT the excess electron localizes entirely on adenine. Thus, in DNA interacting with its physiological environment, damage induced by low-energy electrons could begin, contrary to the current view, with the formation of purine anions, which are not formed in isolated DNA because of the greater stability of anionic pyrimidines.
2007. "Valence anions in complexes of adenine and 9-methyladenine with formic acid - stabilization by intermolecular proton transfer." Journal of the American Chemical Society 129(5):1216-1224. doi:10.1021/ja066229h Abstract The photoelectron spectra of the adenine-formic acid (AFA)- and 9-methyladenine-formic acid (MAFA)- anionic complexes have been recorded with 2.540 eV photons. These spectra reveal broad features with maxima at 1.5-1.4 eV that indicate formation of stable valence anions in the gas phase. The neutral and anionic complexes of adenine/9- methyladenine and formic acid were also studied computationally at the B3LYP, second order Møller-Plesset and coupled clusters levels of theory, with the 6-31++G** and aug-cc-pVDZ basis sets. The neutral complexes form cyclic hydrogen bonds and the most stable dimers are bound by 17.7 and 16.0 kcal/mol for AFA and MAFA, respectively. The theoretical results indicate that the excess electron in both (AFA)- and (MAFA)- occupies a p* orbital localized on adenine/9-methyladenine and the adiabatic stability of the most stable anions amounts to 0.67 and 0.54 eV for AFA- and MAFA-, respectively. The excess electron attachment to the complexes induces a barrierfree proton transfer (BFPT) from the carboxylic group of formic acid to a N atom of adenine or 9-mathyladenine. As a result, the most stable structures of the anionic complexes can be characterized as neutral radicals of hydrogenated adenine(9-methyladenine) solvated by a deprotonated formic acid. The BFPT to the N atoms of adenine may be biologically relevant because some of these sites are not involved in the Watson-Crick pairing scheme and are easily accessible in the cellular environment. We suggest that valence anions of purines might be as important as those of pyrimidines in the process of DNA damage by low energy electrons. The calculations were performed at the Academic Computer Center in Gdańsk (TASK) and at the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the U.S. Department of Energy's Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory, which is operated by Battelle for the US Department of Energy. The MSCF resources were available through a Computational Grand Challenge Application grant.
2007. "Intermolecular proton transfer induced by excess electron attachmentto adenine(formic acid)n (n = 2, 3) hydrogen-bonded complexes." Chemical Physics 342(1-3):215-222. doi:10.1016/j.chemphys.2007.10.005 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 propensity of the neutral complexes between both adenine and 9-methyladenine (A/MA) with formic acid (FA) in 1:2 and 1:3 stoichiometries to bind an excess electron was studied using photoelectron spectroscopy and quantum chemistry computational methods. Although an isolated canonical adenine does not support bound valence anions, solvation by one formic acid molecule stabilizes the excess electron on adenine. The adiabatic electron affinities of the A/MA(FA)2,3 complexes span a range of 0.8–1.23 eV indicating that the anions of 1:2 and 1:3 stoichiometries are substantially more stable than the anionic A–FA dimer (EA = 0.67 eV), which we studied previously and an attachment of electron triggers double-BFPT, confirmed at the MPW1K level of theory, in all the considered systems. Hence, the simultaneous involvement of several molecules capable of forming cyclic hydrogen bonds with adenine remarkably increases its ability to bind an excess electron. The calculated vertical detachment energies for the most stable anions correspond well with those obtained using photoelectron spectroscopy. The possible biological significance of our findings is briefly discussed.
2007. "Analysis of tropical radiative heating profiles: A comparison of models and observations ." Journal of Geophysical Research. D. (Atmospheres) 112:D14218. doi:10.1029/2006JD008290 Abstract Vertical distribution of radiative heating in the atmosphere is an important driver of atmospheric circulation, especially in the tropics. Evaluation of model simulations of the Earth's radiation balance typically focus on performance at the top of the atmosphere or at the surface. This study compares the vertical distribution of clouds and radiative heating rates calculated from observations at the Department of Energy's Atmospheric Radiation Measurement (ARM) sites on the islands of Nauru and Manus to simulations performed using the Multiscale Modeling Framework (MMF) and the Community Atmosphere Model (CAM). There are significant differences between the model vertical profiles of cloud properties and radiative heating and those calculated from the ARM observations. The MMF simulation results in better representation of the observed variability in ice cloud condensed water content and resulting upper tropospheric radiative heating rates than the CAM; more realistic diurnal variability in the radiative heating profiles; and a significantly lower level of zero net radiative heating.
2007. "Geochemical Controls on Contaminant Uranium in Vadose Hanford Formation Sediments at the 200 Area and 300 Area, Hanford Site, Washington." Vadose Zone Journal 6(4):1004-1017. doi:10.2136/vzj2006.0184 Abstract differences in uranium contributed by contaminated vadose sediments at two locations was investigated. At the BX tank farms, alkaline waste was accidentally released to a thick vadose zone. At the 300 Area, waste of variable acidity was released by unintended infiltration through the base of settling ponds. The waste form at the BX site was devoid of dissolved silica, and reacted with fluids trapped in microfractures to precipitate uranyl silicates. These secondary deposits were isolated physically from the vadose pore space and are not readily leached into pore fluids. At the 300 Area, the aluminum-rich waste precipitated on the surfaces of sediment clasts, forming a microporous reservoir of solid-phase uranium. Interaction of this coating with water in transit through the vadose zone provides a persistent source of dissolved uranium to groundwater.
2007. "A Density Functional Theory Study of Formaldehyde Adsorption on Ceria." Surface Science 601(21):4993-5001. doi:10.1016/j.susc.2007.08.027 Abstract Molecular adsorption of formaldehyde on the stoichiometric CeO2(111) and CeO2(110) surfaces was studied using periodic density functional theory. Two adsorption modes (strong chemisorbed and weak physisorbed) were identified on both surfaces. This is consistent with recent experimental observations. On the (111) surface, formaldehyde strongly chemisorbs with an adsorption energy of 0.86 eV to form a dioxymethylene-like structure, in which a surface O lifts from the surface to bind with the C of formaldehyde. A weak physisorbed state with adsorption energy of 0.28 eV was found with the O of formaldehyde interacting with a surface Ce. On the (110) surface, dioxymethyelene formation was also observed, with an adsorption energy of 1.31 eV. The weakly adsorbed state of formaldehyde on the (110) surface was energetically comparable to the weak adsorption state on the (111) surface, but adsorption occurred through a formaldehyde C and surface O interaction. Analysis of the local density of states and charge density differences after adsorption shows that strong covalent bonding occurs between the C of formaldehyde and surface O when dioxymethylene forms. Calculated vibrational frequencies also confirm dioxymethylene formation. Our results also show that as the coverage increases, the adsorption of formaldehyde on the (111) surface becomes weak, but is nearly unaffected on the (110) surface. This work was supported by a Laboratory Directed Research and Development (LDRD) project of the Pacific Northwest National Laboratory (PNNL). The computations were performed using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory, which is a U.S. Department of Energy national scientific user facility located at PNNL in Richland, Washington. Computing time was made under a Computational Grand Challenge “Computational Catalysis”. Part of the computing time was also granted by the National Energy Research Scientific Computing Center (NERSC).
2007. "Methanol adsorption on the clean CeO₂(111) surface: A density functional theory study." Journal of Physical Chemistry C 111(28):10514-10522. doi:10.1021/jp07218y Abstract Molecular and dissociative adsorption of methanol at various sites on the stoichiometric CeO₂(111) surface have been studied using density functional theory periodic calculations. At 0.25 monolayer (ML) coverage, the dissociative adsorption with an adsorption energy of 0.55 eV is slightly favored. The most stable state is the dissociative adsorption of methanol via C-H bond breaking, forming a coadsorbed hydroxymethyl group and hydrogen adatom on two separate O₃C surface sites. The strongest molecular adsorption occurs through an O-Ce₇subC connection with an adsorption energy of 0.48 eV. At methanol coverage of 0.5 ML, the dissociative adsorption and the molecular adsorption became competitive. The adsorption energy per methanol molecule for both adsorption modes falls into a narrow range of 0.46-0.55 eV. As methanol coverage increases beyond 0.5 ML, the molecular adsorption becomes more energetically favorable than the dissociative adsorption because of the attractive hydrogen bonding between coadsorbed methanol molecules. At full monolayer, the adsorption energy of molecular adsorption is 0.40 eV per molecule while the adsorption energy for total dissociative adsorption of methanol is only 0.17 eV. The results at different methanol coverages indicate that methanol can adsorb on a defect-free CeO₂(111) surface, which are also consistent with experimental observations. This research was performed using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory, which is a U.S. Department of Energy national scientific user facility located at Pacific Northwest National Laboratory (PNNL) in Richland, Washington. Computing time was made available under a Computational Grand Challenge “Computational Catalysis”. This work also financially supported by the Laboratory Directed Research and Development project of PNNL.
2007. "The future of liquid chromatography-mass spectrometry in metabolic profiling and metabolomic studies for biomarker discovery." Biomarkers in Medicine 1(1):159-185. doi:doi: 10.2217/17520363.1.1.159 Abstract The future utility of liquid chromatography-mass spectrometry (LC-MS) in metabolic profiling and metabolomic studies for biomarker discover will be discussed, beginning with a brief description of the evolution of metabolomics and the utilization of the three most popular analytical platforms in such studies: NMR, GC-MS, and LC-MS. Emphasis is placed on recent developments in high-efficiency LC separations and sensitive electrospray ionization approaches and the benefits to incorporating both in LC-MS-based approaches. The advantages and disadvantages of various quantitative approaches are reviewed, followed by the current LC-MS-based tools available for candidate biomarker characterization and identification. Finally, a brief prediction on the future path of LC-MS-based methods in metabolic profiling and metabolomic studies is given.
2007. "Low Energy Chemical Sputtering of ATJ Graphite by Atomic and Molecular Deuterium Ions." Physica Scripta T128:50-54. doi:10.1088/0031-8949/2007/T128/010 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. We present experimental chemical sputtering results for D+, D+2 and D+3 ions incident on ATJ graphite in the energy range 5–60 eVD−1, and compare them with simulations for deuterated amorphous carbon impacted by neutral D, D2 and D3. The measured methane yields/D for the different species compared at the same energy/D diverge below about 60 eVD−1, the incident triatomic molecular ions leading to the largest yields/D, and the atomic ions to the smallest, reaching a factor of two difference at 10 eV/D. The measured yields/D are in reasonable agreement with molecular dynamics simulations over the entire calculated energy range. The model surfaces were prepared by D, D2 and D3 impacts in a way that mimics the experiment. For D2 incident at energies below 15 eV/D, the simulations show a strong dependence of the sputtering yields on the vibrational state of the incident projectile.
2007. "Manipulation and Patterning of the Surface Hydrogen Concentrationon Pd(111) by Electric Fields." Angewandte Chemie International Edition 46(30):5757-5761. doi:10.1002/anie.200604498 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. Modification of the structure of materials at the nanoscale level is one goal of current nanoscience research. For example, by purposefully modifying the spatial distribution of adsorbates, the rate of chemical reactions could be controlled on a local scale. Herein, we show how this goal can be accomplished in the case of hydrogen on Pd(111) through the application of local electric fields. Hydrogen adsorption on the Group 10 metals is particularly interesting, because these metals are used as catalysts in a variety of industrial processes, including hydrogenation and dehydrogenation reactions.[1, 2] Electric fields on surfaces are also of primary interest in electrochemistry,[3, 4] and despite the considerable amount of experimental and theoretical work done to date,[5–12] there still remains more work to be done before a clear understanding of electric-field-induced phenomena at the atomic scale can be gained.
2007. "Non-Targeted Bystander Effects Induced by Ionizing Radiation." Mutation Research 616(1-2):159-164. Abstract Radiation induced bystander effects refer to those responses occurring in cells that were not subject to energy deposition events following ionizing radiation. These bystander cells may have been neighbors of irradiated cells, or physically separated, but subject to soluble secreted signals from irradiated cells. Bystander effects have been observed in vitro and in vivo and for various radiation qualities. In tribute to an old friend and colleague, Anthony V. Carrano who would have said "well what are the critical questions that should be addressed, and so what?": in this manuscript we review the evidence for non-targeted radiation induced bystander effects with emphasis on prevailing questions in this rapidly developing research field, and the potential significance of bystander effects in evaluating the detrimental health effects of radiation exposure.
