Kinetics and Reactions Publications

2008

Bylaska EJ, M Dupuis, and PG Tratnyek. 2008. "One-Electron-Transfer Reactions of Polychlorinated Ethylenes: Concerted and Stepwise Cleavages." Journal of Physical Chemistry A 112(16):3712-3721. Abstract Reaction barriers were calculated by using ab initio electronic structure methods for the reductive dechlorination of the polychlorinated ethylenes: C2CL4, C2Cl4, C2HCl3, trans-1,2-C2H2Cl2, cis-1,2-C2H2Cl2, 1,1-C2H2Cl2, and C2HCl3. Concerted and stepwise cleavages of R-Cl bonds were considered. Stepwise cleavages yielded lower activation barriers than concerted cleavages for the reduction of C2Cl4, C2HCl3, and trans-1,2-C2H2Cl2 via strong reducing agents. However, for typical ranges of reducing strength concerted cleavages were found to be favored. Both gas-phase and aqueous-phase calculations predicted C2Cl4 to have the lowest reaction barrier. Additionally, the reduction of C2HCl3 was predicted to have a significant amount of selectivity of cis-1,2-C2HCl2 over the corresponding reactions leading to the trans-1,2-C2HCl2, and 1,1-C2HCl2 radicals. These results illustrate how ab initio electronic structure methods, by providing experimentally inaccessible thermodynamics properties and activation energies, are able to sort out possible reactions mechanisms of reactions that have broad relevance in environmental chemistry.
Wang P, O Hadjar, PL Gassman, and J Laskin. 2008. "Reactive Landing of Peptide Ions on Self-Assembled Monolayer Surfaces: A Alternative Approach for Covalent Immobilization of Peptides on Surfaces." Physical Chemistry Chemical Physics. PCCP 10(11):1512-1522. doi:10.1039/b717617a Abstract Soft landing of mass-selected peptide ions onto reactive self-assembled monolayer surfaces (SAMs) was performed using a newly constructed ion deposition apparatus. SAM surfaces before and after soft-landing were characterized ex situ using time of flight-secondary ion mass spectrometry (TOF-SIMS) and infrared reflection absorption spectroscopy (IRRAS). We demonstrate that reactive landing (RL) results in efficient covalent linking of lysine-containing peptides onto the SAM of N-hydroxysuccinimidyl ester terminated alkylthiol on gold (NHS-SAM). Systematic studies of the factors that affect the efficiency of RL revealed that the reaction takes place upon collision and is promoted by the kinetic energy of the ion. The efficiency of RL maximizes at ca. 40 eV collision energy. At high collision energies the RL efficiency decreases because of the competition with scattering of ions off the surface. The reaction yield is independent of the charge state of the projectile ions suggesting that peptide ions undergo efficient neutralization upon collision. Chemical and physical properties of the SAM surface are also important factors that affect the outcome of RL. The presence of chemically reactive functional groups on the SAM surface significantly improves the reaction efficiency. RL of mass- and energy-selected peptide ions on surfaces provides a highly specific approach for covalent immobilization of biological molecules onto SAM surfaces.
Wan J, TK Tokunaga, Y Kim, Z Wang, A Lanzirotti, E Saiz, and RJ Serne. 2008. "Effect of Saline Waste Solution Infiltration Rates on Uranium Retention and Spatial Distribution in Hanford Sediments." Environmental Science & Technology 42(6):1973-1978. doi:10.1021/es070684b Abstract The accidental overfilling of waste liquid from tank BX-102 at the Hanford Site 11 in 1951 put 10 metric tons of U(VI) in the vadose zone. In order to understand the dominant 12 geochemical reactions and transport processes occurred during the initial infiltration, and to 13 predict U current status and future mobility, we simulated the waste liquid spilling event in 14 laboratory sediment columns using synthesized metal waste solution. We found that, as the 15 plume propagating through sediments, dramatic pH reduction (up to 4 units) occurred at moving 16 plume fronts. Massive amounts of colloids, including U-colloids, formed at plume fronts. The 17 infiltration flow rates strongly affect U fate and transport. Slower flow rate resulted in higher 18 sediment-associated U concentrations, and higher flow rate permitted practically unretarded U 19 transport, and extensive colloid precipitation and accumulations at the plume fronts. Accelerated 20 U transport by size exclusion of U-colloids was revealed. U exceeded the source concentration of 21 U by up to 5 fold, and exceeded the source concentrations of sodium, carbonate, phosphate and 22 sulfate by much more. This first report of colloid induced accelerated U transport could be a 23 mechanism responsible for highly heterogeneous U distributions in the sediment and deep 24 migration to the groundwater.
Liu Y, W Chen, S Wang, AG Joly, SL Westcott, and BK Woo. 2008. "X-Ray Luminescence of LaF3:Tb3+ and LaF3:Ce3+, Tb3+ Water Soluble Nanoparticles." Journal of Applied Physics 103(6):Art. No. 063105. doi:10.1063/1.2890148 Abstract Utilizing scintillation nanoparticles as agents for photodynamic therapy for cancer treatment necessitates the use of biocompatible and water soluble nanoparticles. In this article, we report the synthesis and X-ray luminescence of water soluble Ce and Tb doped LaF3 nanoparticles. The nanoparticles are conjugated with folic acid and meso-tetra (o-carboxyphenyl) porphyrin. X-ray luminescence is observed from the nanoparticles in both powder and solution samples. More importantly, singlet oxygen has been detected from the conjugated system following X-ray excitation. These preliminary observations indicate that water-soluble scintillation nanoparticles can be potentially used in photodynamic therapy for deep-tissue cancer treatment.
Laskin J, P Wang, and O Hadjar. 2008. "Soft-Landing of Peptide IOns Onto Self-Assembled Monolayer Surfaces: an Overview." Physical Chemistry Chemical Physics. PCCP 10(8):1079-1090. doi:10.1039/b712710c Abstract This review is focused on what has been learned in recent research studies concerned with fundamental aspects of soft-landing and reactive landing of peptide ions on self-assembled monolayer surfaces (SAMs). Peptide ions are particularly attractive model systems that provide important insights on the behavior of soft landed proteins, while SAMs provide a convenient and flexible platform for tailoring the interfacial properties of metals and semiconductor surfaces. Deposition of mass-selected ions on surfaces is accompanied by a number of processes including charge reduction, neutralization, covalent and non-covalent binding, and thermal desorption of ions and molecules from the substrate. Factors that affect the competition between these processes are discussed.
Baer DR, JE Amonette, MH Engelhard, DJ Gaspar, AS Karakoti, SVNT Kuchibhatla, P Nachimuthu, J Nurmi, Y Qiang, V Sarathy, S Seal, A Sharma, PG Tratnyek, and CM Wang. 2008. "Characterization Challenges for Nanomaterials." Surface and Interface Analysis 40(3-4):529-537. doi:10.1002/sia.2726 Abstract Nanostructured materials are increasingly subject to nearly every type of chemical and physical analysis possible. Because of their small feature size there is a significant focus on tools with high spatial resolution. Because of their high surface area, it is also natural to characterize nanomaterials using tools designed to analyze surfaces. Regardless of the approach, nanostructured materials present a variety of obstacles to adequate, useful and needed analysis. This paper provides short overviews to some of the issues and complications including: particle stability, environmental effects, specimen handling, surface coating, contamination and time. Some specific examples are provided from a our work focused on ceria nanoparticles and iron metal-core/oxide-shell nanoparticles in which we use a combination of tools for routine analysis including XPS, TEM, and XRD and apply other methods as needed to obtain essential information.
Hayes JA, DM Schubert, JE Amonette, P Nachimuthu, and RS Disselkamp. 2008. "Ultraviolet stimulation of hydrogen peroxide production using aminoindazole, diaminopyridine, and phenylenediamine solid polymer complexes of Zn(II)." Journal of Photochemistry and Photobiology. A, Chemistry 197(2-3):245-252. doi:10.1016/j.jphotochem.2007.12.031 Abstract Hydrogen peroxide is a valuable chemical commodity whose production relies on expensive methods. If an efficient, sustainable, and inexpensive solar-mediated production method could be developed from the reaction between dioxygen and water then its use as a fuel may be possible and gain acceptance. Hydrogen peroxide at greater than 10 M possesses a high specific energy, is environmentally clean, and is easily stored. However, the current method of manufacturing H2O2 via the anthraquinone process is environmentally unfriendly making the unexplored nature of its photochemical production from solar irradiation of interest. Here the concentration and quantum yield of hydrogen peroxide produced in an ultraviolet (UV-B) irradiated environment using aromatic and nitrogen-heterocyclic ring complexes of zinc(II) as solid substrates was studied. The amino-substituted isomers of the substrates indazole, pyridine, and phenylenediamine solid polymer complexes are examined. Samples exposed to the ambient atmosphere (e.g., aerated) were irradiated with a low power lamp with emission from 280-360 nm. Irradiation of various zinc complexes revealed Zn-5-aminoindazole to have the greatest first-day production of 63 mM/day with a 37% quantum yield. Para-phenylenediamine (PPAM) showed the greatest long-term stability and thus suggests H2O2 is produced photocatalytically. Isomeric forms of the catalyst’s organic components (e.g., amino groups) did have an effect on the production. Irradiation of diaminopyridine isomers indicated 2,3-diamino and 3,4-diamino structures were the most productive, each generating 32 mM/day hydrogen peroxide. However, the 2,5-diamino isomer showed no peroxide production. A significant decrease in hydrogen peroxide production in all but PPAM was noticed in the samples, suggesting the possibility of a catalyst poisoning mechanism. The samples ability to produce H2O2 is rationalized by proposing a reaction mechanism and examining the stability of the resonance structures of the different isomers.
Ozensoy E, DR Herling, and J Szanyi. 2008. "NOx Reduction on a Transition Metal-free ?-Al2O3 Catalyst Using Dimethylether (DME)." Catalysis Today 136(1-2):46-54. Abstract NO2 and dimethylether (DME) adsorption as well as DME and NO2 coadsorption on a transition metal-free γ-alumina catalyst were investigated via in-situ transmission Fourier transform infrared spectroscopy (in-situ FTIR), residual gas analysis (RGA) and temperature programmed desorption (TPD) techniques. NO2 adsorption at room temperature leads to the formation of surface nitrates and nitrites. DME adsorption on the alumina surface at 300 K leads to molecularly adsorbed DME, molecularly adsorbed methanol and surface methoxides. Upon heating the DME-exposed alumina to 500-600 K the surface is dominated by methoxide groups. At higher temperatures methoxide groups are converted into formates. At T > 510 K formate decomposition takes place to form H2O(g) and CO(g). DME and NO2 coadsorption at 423 K do not indicate a significant reaction between DME and NO2. However, in similar experiments at 573 K, fast reaction occurs and the methoxides present at 573 K before the NO2 adsorption are converted into formates, simultaneously with the formation of isocyanates. Under these conditions, NCO can further be hydrolyzed into isocyanic acid or ammonia with the help of water which is generated during the formate formation, decomposition and/or NCO formation steps.
Verrier CLM, JH Kwak, DH Kim, CHF Peden, and J Szanyi. 2008. "NOx uptake on alkaline earth oxides (BaO, MgO, CaO and SrO) supported on ?-Al2O3." Catalysis Today 136(1-2):121-127. doi:doi:10.1016/j.cattod.2007.12.138 Abstract NOx uptake experiments were performed on a series of alkaline earth oxide (AEO) (MgO, CaO, SrO, BaO) on γ-alumina materials. Temperature Programmed Desorption (TPD) conducted on He flow revealed the presence of two kinds of nitrate species: i.e. bulk and surface nitrates. The ratio of these two types of nitrate species strongly depends on the nature of the alkaline earth oxide. The amount of bulk nitrate species increases with the basicity of the alkaline earth oxide. This conclusion was supported by the results of infrared and 15N solid state NMR studies of NO2 adsorption. Due to the low melting point of the precursor used for the preparation of MgO/Al2O3 material (Mg(NO3)2), a significant amount of Mg was lost during sample activation (high temperature annealing) resulting in a material with properties were very similar to that of the γ-Al2O3 support. The effect of water on the NOx species formed in the exposure of the AEO-s to NO2 was also investigated. In agreement with our previous findings for the BaO/γ-Al2O3 system, an increase of the bulk nitrate species and the simultaneous decrease of the surface nitrate phase were observed for all of these materials.
Ilton ES, and PS Bagus. 2008. "Ligand field effects on the multiplet structure of the U4f XPS of UO2." Surface Science 602(5):1114-1121. doi:10.1016/j.susc.2008.01.010 Abstract Ab initio, fully relativistic four component theory was used to determine atomic and interatomic many-body effects for the 4f X-ray photoelectron spectrum of an embedded UO8-12 cluster representing UO2. Many-body effects were included through the use of configuration interaction wavefunctions that allow the mixing of XPS allowed and XPS forbidden configurations. Charge transfer configurations were not included. This work extends our earlier studies on simulations of the U 4f XPS for the free U4+ cation. While the main XPS features are similar in both cases, ligand field effects changed the multiplet structure in important ways that better simulated experimental data for UO2. Neither initial nor final state covalency significantly reduced the 4f-5f exchange integrals, and the differences between the atom and cluster model was due to ligand field splitting of the 5f band and increased distributions of intensity from XPS allowed to XPS forbidden peaks. The prominent 7 eV satellites associated with UO2 were absent in the simulations, and provides further evidence that these satellites are due to charge transfer and not other interatomic effects.

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