Scientific Publications 2010
2010. "Nuclear Quantum Effects in the Reorientation of Water." The Journal of Physical Chemistry Letters 1(15):2316-2321. doi:10.1021/jz100734w Abstract The molecular reorientation associated with the dynamics of the hydrogen-bond network in liquid water is investigated using quantum molecular dynamics simulations performed with the ab-initio based TTM3-F interaction potential. The reorientation dynamics calculated at different temperatures are found to be in excellent agreement with the corresponding experimental results obtained from polarization-resolved, femtosecond mid-infrared, pump-probe spectroscopic measurements. A comparison with analogous results obtained from classical molecular dynamics simulations with the same interaction potential clearly indicates that the explicit inclusion of nuclear quantum effects is critical for reproducing the measured time-dependence of the anisotropic signal. The analysis of the isotope effects indicates that the quantum effects involved in the water reorientation are mainly associated with zero-point energy differences although tunneling contributions may also be at play near the melting point.
2010. "Platinum Attachments on Iron Oxide Nanoparticle Surfaces." Journal of Applied Physics 107(9):09B311-1 through 09B311-3. doi:10.1063/1.3355899 Abstract Platinum nanoparticles supported on metal oxide surfaces have shown great potential as heterogeneous catalysts to accelerate electrochemical processes, such as the oxygen reduction reaction in fuel cells. Recently, the use of magnetic supports has become a promising research topic for easy separation and recovery of catalysts using magnets, such as Pt nanoparticles supported on iron oxide nanoparticles. The attachment of Pt on iron oxide nanoparticles is limited by the wetting ability of the Pt (metal) on ceramic surfaces. A study of Pt nanoparticle attachment on iron oxide nanoparticle surfaces in an organic solvent is reported, which addresses the factors that promote or inhibit such attachment. It was discovered that the Pt attachment strongly depends on the capping molecules of the iron oxide seeds and the reaction temperature. For example, the attachment of Pt nanoparticles on oleic acid coated iron oxide nanoparticles was very challenging, because of the strong binding between the carboxylic groups and iron oxide surfaces. In contrast, when nanoparticles are coated with oleic acid/tri-n-octylphosphine oxide or oleic acid/oleylamine, a significant increase in Pt attachment was observed. Electronic structure calculations were then applied to estimate the binding energies between the capping molecules and iron ions, and the modeling results strongly support the experimental observations.
2010. "Facile synthesized nanorod structured vanadium pentoxide for high-rate lithium batteries." Journal of Materials Chemistry 20(41):9193-9199. doi:10.1039/C0JM01306D Abstract Nano-structured vanadium oxide (V2O5) is fabricated via facile thermal-decomposition of a vanadium precursor and vanadyl oxalate produced by reacting micro-sized V2O5 with oxalic acid. The V2O5 nanorods produced by this method exhibit much better electrochemical performance than commercial micro-sized V2O5. The optimized-nanorod electrodes with a high density of (001) planar defects give the best specific discharge capacities of 270 mAh g-1 at C/2 (147 mA g-1) coupled with good cycle stability with only 0.32% fading per cycle. Even at a high rate of 4C (1176 mA g-1), the nanorod electrode still delivers 198 mAh g-1. These results suggest that the nanostructured V2O5 is a good cathode for high-rate, lithium-ion battery applications.
2010. "Nano-Structured Li3V2(PO4)3 /Carbon Composite for High Rate Lithium Ion Batteries." Electrochemistry Communications 12(12):1674-1677. doi:10.1016/j.elecom.2010.09.014 Abstract Nanostructured Li3V2(PO4)3 /carbon composite (Li3V2(PO4)3/C) is successfully prepared by incorporating precursor solution into expanded pore structure of highly mesoporous carbon. XRD, SEM and TEM are used to characterize the composite structure. The particles sizes of the samples are centered at ~ 20 nm and well dispersed in the carbon matrix. When cycled in a voltage range of 3-4.3 V, Li3V2(PO4)3/C cathode delivers a reversible capacity of 122 mAh g-1 at 1C-rate and maintains a specific discharge capacity of 83 mAh g-1 even at 32 C-rate. Therefore, nanostructured Li3V2(PO4)3 and mesoporous carbon composite has a great potential to be used as cathode material for high power lithium-ion batteries.
2010. "Effects of Hydration and Oxygen Vacancy on CO2 Adsorption and Activation on β-Ga2O3(100)." Langmuir 26(8):5551-5558. doi:10.1021/la903836v Abstract The effects of hydration and oxygen vacancy on CO2 adsorption on the β-Ga2O3(100) surface have been studied using density functional theory slab calculations. Adsorbed CO2 is activated on the dry perfect β-Ga2O3(100) surface, resulting in a carbonate species. This adsorption is slightly endothermic, with an adsorption energy of 0.07 eV. Water is preferably adsorbed molecularly on the dry perfect β-Ga2O3(100) surface with an adsorption energy of -0.56 eV, producing a hydrated perfect β-Ga2O3(100) surface. Adsorption of CO2 on the hydrated surface as a carbonate species is also endothermic, with an adsorption energy of 0.14 eV, indicating a slight repulsive interaction when H2O and CO2 are coadsorbed. The carbonate species on the hydrated perfect surface can be protonated by the co-adsorbed H2O to a bicarbonate species, making the overall process exothermic with an adsorption energy of -0.13 eV. The effect of defects on CO2 adsorption and activation has been examined by creating an oxygen vacancy on the dry β-Ga2O3(100) surface. The formation of an oxygen vacancy is endothermic, by 0.34 eV, with respect to a free O2 molecule in the gas phase. Presence of the oxygen vacancy promoted the adsorption and activation of CO2. In the most stable CO2 adsorption configuration on the dry defective β-Ga2O3(100) surface with an oxygen vacancy, one of the oxygen atoms of the adsorbed CO2 occupies the oxygen vacancy site and the CO2 adsorption energy is -0.31 eV. Water favors dissociative adsorption at the oxygen vacancy site on the defective surface. This process is instantaneous with an adsorption energy of -0.62 eV. These results indicate that, when water and CO2 are both present in the adsorption system simultaneously, the water molecule will compete with CO2 for the oxygen vacancy sites and impact CO2 adsorption and conversion negatively. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. A portion of the computing time was granted by the scientific user projects using the Molecular Science Computing Facility in the William R. Wiley Environmental Molecular Sciences Laboratory (EMSL). The EMSL is a DOE national scientific user facility located at PNNL, and supported by the DOE’s Office of Science, Biological and Environmental Research.
2010. "Reactivity of Fe0 Atoms with mixed CCI4 and D2O films over FeO (111)." Journal of Physical Chemistry C 114(40):17136-17141. doi:10.1021/jp103896k Abstract The interaction of Fe0 with chlorinated hydrocarbons in an aqueous environment is important for the utilization of Fe0 nanoparticles in groundwater remediation technologies. This article builds upon prior work that utilized an "atom dropping" technique to show that Fe0 atoms react readily with pure CCl4 and D2O upon contact at 30 K to form the ClFeCCl3 and DFeOD insertion complexes, respectively. Here we deposit Fe atoms into films containing both D2O and CCl4 as separate layers. Temperature programmed desorption (TPD) is used to show that the ClFeCCl3 and DFeOD insertion complexes are unreactive with each other and both molecular D2O and CCl4 up to the desorption temperature of each species on an FeO(111) substrate. These results suggest that the Fe insertion complexes are energetically favorable and are thus relatively stable with respect to subsequent reactions.
2010. "Protein Solvation from Theory and Simulation: Exact Treatment of Coulomb Interactions in Three-Dimensional Theories." Journal of Chemical Physics 132(6):064106. doi:10.1063/1.3299277 Abstract Solvation forces dominate protein structure and dynamics. Integral equation theories allow a rapid and accurate evaluation of the effect of solvent around a complex solute, without the sampling issues associated with simulations of explicit solvent molecules. Advances in integral equation theories make it possible to calculate the angle dependent average solvent structure around an irregular molecular solution. We consider two methodological problems here: the treatment of long-ranged forces without the use of artificial periodicity or truncations and the effect of closures. We derive a method for calculating the long-ranged Coulomb interaction contributions to three-dimensional distribution functions involving only a rewriting of the system of integral equations and introducing no new formal approximations. We show the comparison of the exact forms with those implied by the supercell method. The supercell method is shown to be a good approximation for neutral solutes whereas the new method does not exhibit the known problems of the supercell method for charged solutes. Our method appears more numerically stable with respect to thermodynamic starting state. We also compare closures including the Kovalenko–Hirata closure, the hypernetted-chain _HNC_ and an approximate three-dimensional bridge fu nction combined with the HNC closure. Comparisons to molecular dynamics results are made for water as well as for the protein solute bovine pancreatic trypsin inhibitor. The proposed equations have less severe approximations and often provide results which compare favorably to molecular dynamics simulation where other methods fail.
2010. "Ultrafast Interfacial Proton-Coupled Electron Transfer." Chemical Reviews 110(12):7082-7099. doi:10.1021/cr1001595 Abstract Interfaces between metallic or semiconducting solids and protic solvent adsorbates or liquids represent one of the most important, and yet hardly explored material environments for proton coupled electron transfer (PCET) processes. PCET mediated dynamical phenomena driven by light, electron, and chemical potentials are central in energy transduction processes of vast economic and environmental importance including the photocatalytic splitting of H₂O, the photo and electrochemical reduction of CO₂, and the conversion of chemical to electrical energy in fuel cells. Experimental and theoretical investigations of the dynamical aspects of PCET at solid surfaces are particularly challenging because relatively localized charges within a solvent couple in the presence of strong interfacial potentials to delocalized states of electronic continua of semiconductor or metal electrodes. Moreover, the localized charges are never the bare protons and electrons that balance chemical equations, but rather are dressed particles with associated polarization clouds inhomogeneously distributed and comprised variously of free electrons, lattice ions, and solvent molecules. The polarization clouds screen the Coulomb potential on the medium specific time scales and impose energetic costs associated with transport through the inhomogeneous region of interfaces between the solid and molecular environments. We introduce some recent theoretical studies aimed at providing an atomistic description on metal-protic solvent interface and modeling of simple processes such as the discharge of H⁺ at a metal interface. Because of the paucity of experimental research and embryonic stage of theory, our goal is to present some key theoretical concepts and early experimental efforts based primarily on a surface science approach to ultrafast electron induced dynamics. In order to introduce some key features of interfacial PCET in the strong and intermediate coupling regimes, we discuss specific examples of photoinduced dissociation of alkanes on metals and photoinduced PCET dynamics of methanol covered TiO₂ surfaces.
2010. "Framework Stability of Nanocrystalline NaY in Aqueous Solution at Varying pH." Langmuir 26(9):6695-6701. doi:10.1021/la9040198 Abstract Nanocrystalline zeolites (with crystal sizes of less than 50 nm) are versatile, porous nanomaterials with potential applications in a broad range of areas including bifunctional catalysis, drug delivery, environmental protection, and sensing, to name a few. The characterization of the properties of nanocrystalline zeolites on a fundamental level is critical to the realization of these innovative applications. Nanocrystalline zeolites have unique surface chemistry that is distinct from conventional microcrystalline zeolite materials and that will result in novel applications. In the proposed work, magnetic resonance techniques (solid state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR)) will be used to elucidate the structure and reactivity of nanocrystalline zeolites and to motivate bifunctional applications. Density functional theory (DFT) calculations will enhance data interpretation through chemical shift, quadrupole coupling constant, g-value and hyperfine calculations.
2010. "Mapping protein abundance patterns in the brain using voxelation combined with liquid chromatography and mass spectrometry." Methods 50(2):77-84. Abstract Voxelation creates expression atlases by high-throughput analysis of spatially registered cubes or voxels harvested from the brain. The modality independence of voxelation allows a variety of bioanalytical techniques to be used to map abundance. Protein expression patterns in the brain can be obtained using liquid chromatography (LC) combined with mass spectrometry (MS). Here we describe the methodology of voxelation as it pertains particularly to LC-MS proteomic analysis: sample preparation, instrumental set up and analysis, peptide identification and protein relative abundance quantitation. We also briefly describe some of the advantages, limitations and insights into the brain that can be obtained using combined proteomic and transcriptomic maps
2010. "Experimental Determination of the Effect of the Ratio of B/Al on Glass Dissolution along the Nepheline (NaAlSiO4) – Malinkoite (NaBSiO4) Join." Geochimica et Cosmochimica Acta 74:2634-2654. doi:10.1016/j.gca.2009.09.006 Abstract The dissolution kinetics of five glasses along the NaAlSiO4-NaBSiO4 join were used to evaluate how the structural variations associated with boron-aluminum substitution affect the rate of dissolution. The composition of each glass varied inversely in mol% of Al2O3 (5 to 25 mol%) and B2O3 (20 to 0 mol%) with Na2O (25 mol%) and SiO2 (50 mol%) making up the remaining amount, in every case Na/(Al+B) = 1.0. Single-pass flow-through experiments (SPFT) were conducted under dilute conditions as a function of solution pH (from 7.0 to 12.0) and temperature (from 23° to 90°C). Analysis by 27Al and 29Si MAS-NMR suggests Al (~98% Al) and Si atoms (~100% Si) occupy a tetrahedral coordination whereas, B atoms occupy both tetrahedral (B) and trigonal (B) coordination. The distribution of B fractionated between B(ring) and B(non-ring) moieties, with the B(ring)/B(non-ring) ratio increases with the B/Al ratio. The MAS-NMR results also indicated an increase in the fraction of B with an increase in the B/Al ratio. But despite the changes in the B/Al ratio and B coordination, the 29Si spectra maintain a chemical shift between -88 to -84 ppm for each glass. Unlike the 29Si spectra, the 27Al resonances shift to more positive values with an increase in the B/Al ratio which suggests mixing between the Al and B sites, assuming avoidance between tetrahedral trivalent cations (Al-O-B avoidance). Raman spectroscopy was use to augment the results collected from MAS-NMR and demonstrated that NeB4 (glass sample with the highest B content) was glass-glass phase separated (e.g., heterogeneous glass). Results from SPFT experiments suggest a forward rate of reaction and pH power law coefficients, , that are independent of B/Al under these neutral to alkaline test conditions for all homogeneous glasses. The temperature dependence shows an order of magnitude increase in the dissolution rate with a 67°C increase in temperature and suggests dissolution is controlled by a surface-mediated reaction, evident by the activation energy, Ea, being between 44 ±8 and 48 ±7 kJ/mol. Forward dissolution rates, based on Na and Si release, for homogeneous glasses are independent of the B/Al ratio, whereas dissolution rates based on Al and B release are not. Dissolution rates based on B release increase with an increase in the fraction of B(ring). Finally in accord with previous studies, the data discussed in this manuscript suggest rupture of the Al-O and Si-O bond as the rate-limiting step controlling the dissolution of these glasses.
2010. "CdSe/ZnS quantum dots based electrochemical immunoassay for the detection of phosphorylated bovine serum albumin." Biosensors and Bioelectronics 26(3):1109-1113 . doi:10.1016/j.bios.2010.08.021 Abstract A CdSe/ZnS quantum dot (QD) based electrochemical immunoassay of phosphorylated bovine serum albumin as a protein biomarker is presented. The QDs were used as labels and were conjugated with the secondary anti-phosphoserine antibody in a heterogeneous sandwich immunoassay. First, the primary BSA antibody was immobilized on polystyrene microwells, followed by the addition of BSA-OP. After that, the QD-labeled anti-phosphoserine antibody was added into microwells for immunorecognition. Finally, the bound QD was dissolved in an acid-dissolution step and was detected by electrochemical stripping analysis. The measured current responses were proportional to the concentration of BSA-OP. Under optimal conditions, the voltammetric response was linear over the range of 0.5 - 500 ng mL-1 of BSA-OP, with a detection limit of 0.5 ng mL-1 at a deposition potential of -1.2 V for 120 s. It also shows good reproducibility with a relative standard deviation of 8.6% of six times determination of 25 ng mL-1 of BSA-OP. This QD-based electrochemical immunoassay offers great promise for simple and cost-effective analysis of protein biomarkers.
2010. "Soft X-Ray Spectroscopic Study of Dense Strontium-Doped Lanthanum Manganite Cathodes for Solid Oxide Fuel Cell Applications." Journal of the Electrochemical Society 158(2):B99-B105. doi:10.1149/1.3519075 Abstract The modification of the Mn charge-state, chemical composition and electronic structure of La0.8Sr0.2MnO3 (LSMO) cathodes for solid oxide fuel cell (SOFC) applications remains an area of interest, due to the poorly understood enhanced catalytic activity (often referred to as the "burn-in" phenomenon) observed after many hours of operation. Using a combination of core-level X-ray photoemission spectroscopy (XPS), X-ray emission/absorption spectroscopy (XES/XAS), resonant inelastic X-ray scattering (RIXS) and resonant photoemission spectroscopy (RPES), we have monitored the evolution of these properties in LSMO at various stages of fabrication and operation. By rapidly quenching and sealing in vacuum, we were able to directly compare the pristine (as-fabricated) LSMO with both "heat-treated" (800°C in air, and no bias) and "burnt-in" (800°C in air, -1 V bias) LSMO cathodes i.e. before and after the activation observed in our electrochemical impendence spectroscopy measurements. Comparison between the O K-edge XAS/XES and Mn L3,2-edge XAS of pristine and “burnt-in” LSMO cathodes revealed a severe change in the oxygen environment along with a reduced Mn2+ presence near the surface following activation. The change in the oxygen environment is attributed to SrxMnyOz formation, along with possible passive SrO and Mn3O4 species. We present evidence from our “heat-treated” samples that SrxMnyOz regions form at elevated temperatures in air before the application of a cathodic bias. Our core-level XPS, Mn L3,2-edge RIXS and Mn L3 RPES studies of “heat-treated” and pristine LSMO determined that SOFC environments result in La-deficiency (severest near the surface) and stronger Mn4+ contribution, leading to the increased insulating character of the cathode prior to activation. The passive Mn2+ species near the surface and increased hole-doping (>0.6) of the LSMO upon exposure to the operating environment are considered responsible for the initially poor performance of the SOFC. Meanwhile, the improved oxygen reduction following the application of a cathodic bias is considered to be due to enhanced bulk oxygen-ion diffusion resulting from the migration of Mn2+ ions towards the LSMO/electrolyte interface and the SrxMnyOz regions facilitating enhanced bulk oxygen reduction reaction kinetics.
2010. "Emission Zone Control in Blue Organic Electrophosphorescent Devices Through Chemical Modification of Host Materials ." Applied Physics Letters 96(5):Art. No. 053306. doi:10.1063/1.3298556 Abstract We report blue organic light-emitting devices with iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2’]picolinate (FIrpic) as an emitter doped into a series of phosphine oxide-based host materials that have significantly different charge transport properties: 4-(diphenylphosphoryl)-N,N-diphenylaniline (HM-A1), N-(4-diphenylphosphoryl phenyl) carbazole (PO12), 9-(6-(diphenylphosphoryl)pyridin-3-yl)-9H-carbazole (HM-A5), and 6-(diphenylphosphoryl)-N,N-diphenylpyridin-3-amine (HM-A6). Depending on the nature of the host material, the location of the emission zone can be moved within the emissive layer from the hole transport layer interface to the electron-transport layer interface. The charge transport properties of the materials were evaluated using single carrier devices.
2010. "Thermochemistry of Lewis Adducts of BH3 and Nucleophilic Substitution of Triethylamine on NH3BH3 in Tetrahydrofuran." Inorganic Chemistry 49(22):10512-10521. doi:10.1021/ic101481c Abstract The thermochemistry of the formation of Lewis adducts of BH3 in tetrahydrofuran (THF) solution and the gas phase and the kinetics of substitution on ammonia borane (AB) by triethylamine are reported. The dative bond energy of Lewis adducts were predicted using density functional theory at the B3LYP/DZVP2 and B3LYP/6-311+G** levels and correlated ab initio molecular orbital theories, including MP2, G3(MP2), and G3(MP2)B3LYP, and compared with available experimental data and CCSD(T)/CBS theory results. The analysis showed that the G3 methods using either the MP2 or B3LYP geometries reproduce the benchmark results usually to within ~1 kcal/mol. Energies calculated at the MP2/aug-cc-pVTZ level for geometries optimized at the B3LYP/DZVP2 or B3LYP/6-311+G** levels give dative bond energies 2-4 kcal/mol larger than benchmark values. The enthalpies for forming adducts in THF were determined by calorimetry and compared with the calculated energies for the gas phase reaction: THF:BH3 + L L:BH3 + THF. The formation of AB in THF was observed to yield significantly more heat than the reaction in gas phase, consistent with strong solvation of AB. Substitution of NEt3 on AB is an equilibrium process in THF solution (K 0.2 at 25 °C). The reaction obeys a reversible bimolecular kinetic rate law with the Arrhenius parameters: log A = 14.7 ± 1.1 and Ea = 28.1 ± 1.5 kcal/mol. Simulation of the mechanism using the SM8 continuum solvation model shows the reaction most likely proceeds primarily by a classical SN2 mechanism. Pacific Northwest National Laboratory is operated by Battelle for the USDOE.