Scientific Publications 2007
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2007. "Chiral Separation: Mechanism Modeling in Two-DimensionalSystems." Journal of the American Chemical Society 129(12):3545-3555. doi:10.1021/ja066422b 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. Fluid phase separations of racemates are difficult because the subtle, short-ranged differences in intermolecular interactions of like and unlike pairs of chiral molecules are typically smaller than the thermal energy. A surface restricts the configurational space available to the pair of interacting molecules, thus changing the effective interactions between them. Because of this restriction, a surface can promote chiral separation of mixtures that are racemic in bulk. In this paper, we investigate chiral symmetry breaking induced by an achiral surface in a racemate. A parallel tempering Monte Carlo algorithm with tempering over the temperature domain is used to examine the interplay between molecular geometry and energetics in promoting chiral separations. The system is restricted to evolve in two dimensions. By controlling the balance between electrostatic and steric interactions, one can direct the surface assembly of the chiral molecules toward formation of small clusters of identical molecules. When molecular shape asymmetry is complemented by dipolar alignment, chiral micellar clusters of like molecules are assembled on the surface. We examine the case of small model molecules for which the two-dimensional restriction of the pair potential is sufficient to induce chiral segregation. An increase in molecular complexity can change the balance of intermolecular interactions to the point that heterochiral pairs are energetically more favored. In this case, we find conditions in which formation of homochiral micelles is still achieved, due to a combination of multibody and entropic effects. In such systems, an examination of the pair potential alone is insufficient to predict whether the multimolecular racemate will or will not segregate.
2007. "Chirality on Surfaces: Modeling and Behaviour." Chimica Oggi 25(5):18-22. 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. Chirality has been a fascinating topic in chemistry, ever since its first observation by Biot in 1815. Its molecular basis was first understood by Pasteur in 1848. Enantiomers, identical in every way but mirror-images of each other, have similar physical properties, behave identically in chemical reactions with achiral molecules, but have very different interactions with chiral molecules. In recent decades, chirality has become an important direction in pharmaceutical research, as many drugs have stereoselective activity. This review focuses on a new aspect of chiral resolution on solid surfaces, and relationships between molecular structure, thermodynamic effects, and the result of chiral surface self-organization.
2007. "Comparing metal leaching and toxicity from high pH, low pH, and high ammonia fly ash." Fuel 86(10-11):1623-1630. doi:10.1016/j.fuel.2006.11.018 Abstract Previous work with both class F and class C fly ash indicated minimal leaching from most fly ashes tested. However, the addition of NOx removal equipment might result in higher levels of ammonia in the fly ash. We have recently been testing fly ash with a wide range of pH (3.7–12.4) originating from systems with NOx removal equipment. Leaching experiments were done using dilute CaCl2 solutions in batch and columns and a batch nitric acid method. All methods indicated that the leaching of heavy metals was different in the highest ammonia sample tested and the high pH sample. However, toxicity testing with the Microtox* system has indicated little potential toxicity in leachates except for the fly ash at the highest pH (12.4). When the leachate from the high pH fly ash was neutralized, toxicity was eliminated.
2007. "Fluctuating Two-State Light Harvesting in a Photosynthetic Membrane." Journal of Physical Chemistry C 111(25):8948-8956. doi:10.1021/jp071493y Abstract How light is converted into chemical energy in a natural photosynthetic system is of great interest in energy sciences. Using single-molecule and single-vesicle fluorescence spectroscopy and imaging, we have observed fluctuating inter-molecular protein energy transfers in the photosynthetic membranes of R. sphaeroides. Our results suggest that there are dynamic coupled and non-coupled states in the light-harvesting protein assembly.
2007. "Characterization and Hydrodesulfurization Properties of Catalysts Derivedfrom Amorphous Metal-boron Materials." Journal of Catalysis 246(2):277-292. doi:10.1016/j.jcat.2006.12.009 Abstract Unsupported and silica-supported amorphous metal-boron materials (Ni-B, Mo-O-B, and Ni-Mo-O-B) were prepared by NaBH4 reduction of aqueous or impregnated metal salts. The resulting materials were characterized by a range of techniques, including conventional and time-resolved X-ray diffraction. The latter technique was used to determine the onset of crystallization of the amorphous materials during annealing in He flow and to identify the phases formed. Annealing of unsupported Ni-B resulted in the crystallization of predominantly Ni3B, followed by Ni metal, whereas Ni-B/SiO2 formed Ni and then NiO. There was no evidence for crystallization of B-containing phases for Mo-O-B or Mo-O-B/SiO2 on annealing; instead, the predominant phase formed was MoO2. In general, the phases formed for Ni-Mo-O-B and Ni-Mo-O-B/SiO2 were consistent with those formed in the monometallic materials, but at higher annealing temperatures. Catalysts prepared by sulfiding Ni-B/SiO2 and Ni-Mo-O-B/SiO2 materials had significantly higher thiophene HDS activities than conventionally prepared sulfided Ni/SiO2 and Ni-Mo/SiO2 catalysts, whereas a sulfided Mo-O-B/SiO2 catalyst had a dramatically lower HDS activity than a sulfided Mo/SiO2 catalyst.
2007. "High Resolution Infrared Study of the 2v9 and v4 Bands of 10BF2OH and 11BF2OH: Evidence of Large Amplitude Effects for the OH- Torsion and OH-Bending Modes in the 9(2) and 4(1) and Excited States." Molecular Physics 105(13-14):1833-1848. doi:10.1080/00268970701426992 Abstract High resolution (2-3x10-3cm-1) Fourier transform infrared spectra of gas phase 10B and 11B enriched and natural samples of BF2OH (difluoroboric acid) were recorded at Wuppertal and Richland. Starting from the results of previous studies [A.Perrin, M.Carvajal-Zaera, Z.Dutkiewicz, J.-M.Flaud, D.Collet, H.Bürger, J.Demaison, F.Willaert, H.Mäder, and N.W.Larsen, Mol. Phys. 102 , 1641 (2004); J. Breidung, J. Demaison, J.-F. D’Eu, L. Margulès, D. Collet, E.B. Mkadmi, A. Perrin and W. Thiel, J. Mol. Spectrosc. 228, 7, (2004)], it was possible to perform the first rovibrational analysis of the 2ν9 (first overtone of ν9, the OH torsion) and ν4 (BOH bending) bands located at about 1043.9 and 961.7 cm-1 and 1042.9 and 961.5 cm-1 for the 10BF2OH and 11BF2OH isotopic species respectively. Numerous “classic” perturbations were observed in the analysis of the 2ν9 and ν4 bands. The energy levels of the 92 bright state are indeed involved in a B- type Coriolis resonance with those of the 6191 dark state. The 41 levels are perturbed by a B-type Coriolis resonance and by an anharmonic resonance with the levels of the 7191 and the 6171 dark states respectively. In addition large amplitude effects were observed for the 2ν9 and also, more surprisingly, the ν4 bands. This results in splittings of the energy levels of about 0.005 and 0.0035 cm-1 for the 92 and 41 states respectively which are easily observable in the P and R branches for both bands. The theoretical model used to reproduce the experimental levels accounts for the classic vibration –rotation resonances. Also the large amplitude torsional (or bending) effects are accounted for within the frame of the IAM (Internal Axis Method) -like approach. The Coriolis resonances between the two torsional (or bending) substates are taken into account by {Jx,Jz} non orthorhombic terms in the v-diagonal blocks. This means that the zquantification axis deviates from the a inertial axis by an axis switching effect of ~35° for the {92,6191} system and of ~16.6° for the {41,7191,6171}) system of interacting vibrational states. The calculation of the relative line intensities for the 2ν9 and ν4 bands accounts for these axis switching effects as well as for the intensity alternation which is due to the nuclear spin statistics since the OH large amplitude torsion and/or bending motion results indeed in an exchange of the two fluorine nuclei.
2007. "High Speed Method for in Situ Multispectral Image Registration." Microscopy Research and Technique 70(4):382-389. doi:10.1002/jemt.20423 Abstract Multispectral confocal spinning disk microscopy provides a high resolution method for real-time live cell imaging. However, optical distortions and the physical misalignments introduced by the use of multiple acquisition cameras can obscure spatial information contained in the captured images. In this manuscript, we describe a multispectral method for real-time image registration whereby the image from one camera is warped onto the image from a second camera via a polynomial correction. This method provides a real-time pixel-for-pixel match between images obtained over physically distinct optical paths. Using an in situ calibration method, the polynomial is characterized by a set of coefficients using a least squares solver. Error analysis demonstrates optimal performance results from the use of cubic polynomials. High-speed evaluation of the warp is then performed through forward differencing with fixed-point data types. Image reconstruction errors are reduced through bilinear interpolation. The registration techniques described here allow for successful registration of multispectral images in real-time (exceeding 15 frame/sec) and have a broad applicability to imaging methods requiring pixel matching over multiple data channels.
2007. "Hydrogen Bonding, H-D Exchange, and Molecular Mobility in Thin Water Films on TiO2(110)." Physical Review Letters 99(19):Art.No.196103. doi:10.1103/PhysRevLett.99.196103 Abstract Hydrogen bonding, H/D exchange and diffusion in water films ( 2 monolayers) on TiO2(110) have been studied using water electron-stimulated desorption. For T < 70 K, films with one water isotope adsorbed on the Ti4+ rows and another isotope on the bridging oxygen rows can be prepared. For T > 70 K, H/D exchange and molecular diffusion between these “layers” occur with a distribution of activation energies. The results demonstrate that all the water molecules that are directly bound to TiO2(110) – i.e. water in the first and second layers – are also hydrogen bonded to each other, thus influencing the chemistry of the water/TiO2(110) interface.
2007. "Spatial Mapping of Protein Abundances in the Mouse Brain by Voxelation Integrated with High-Throughput Liquid Chromatography ─ Mass Spectrometry." Genome Research 17(3):328-336. doi:doi:10.1101/gr.5799207 Abstract Temporally and spatially resolved mapping of protein abundance patterns within the mammalian brain is of significant interest for understanding brain function and molecular etiologies of neurodegenerative diseases; however, such imaging efforts have been greatly challenged by complexity of the proteome, throughput and sensitivity of applied analytical methodologies, and accurate quantitation of protein abundances across the brain. Here, we describe a methodology for comprehensive spatial proteome mapping that addresses these challenges by employing voxelation integrated with automated microscale sample processing, high-throughput LC system coupled with high resolution Fourier transform ion cyclotron mass spectrometer and a “universal” stable isotope labeled reference sample approach for robust quantitation. We applied this methodology as a proof-of-concept trial for the analysis of protein distribution within a single coronal slice of a C57BL/6J mouse brain. For relative quantitation of the protein abundances across the slice, an 18O-isotopically labeled reference sample, derived from a whole control coronal slice from another mouse, was spiked into each voxel sample and stable isotopic intensity ratios were used to obtain measures of relative protein abundances. In total, we generated maps of protein abundance patterns for 1,028 proteins. The significant agreement of the protein distributions with previously reported data supports the validity of this methodology, which opens new opportunities for studying the spatial brain proteome and its dynamics during the course of disease progression and other important biological and associated health aspects in a discovery-driven fashion.
2007. "Accelerated Weathering of High-Level and Plutonium-bearing Lanthanide Borosilicate Waste Glasses under Hydraulically Unsaturated Conditions." Applied Geochemistry 22(9):1841-1859. doi:10.1016/j.apgeochem.2007.03.056 Abstract A can-in-canister waste package design has been proposed for disposal of excess weapons plutonium at the proposed mined geologic repository at Yucca Mountain, NV. by the U. S. Department of Energy Office of Fissile Material Disposition. This configuration consists of a high-level waste (HLW) canister fitted with a rack that holds mini-canisters containing a Pu-bearing lanthanide borosilicate (LaBS) waste glass and/or ceramic (~15% of the total canister volume). The larger canister is then filled with HLW glass, SRL-202, (~85% of the total canister volume). A 6-year pressurized unsaturated flow (PUF) test was conducted to investigate waste form/waste form interactions that may occur when water penetrates the canisters and contacts the waste forms. Volumetric water content was observed to increase steadily during PUF testing from accumulation of water mass as waters of hydration associated with alteration phases formed on the glass surface. Periodic excursions in effluent pH, electrical conductivity, and solution chemistry were monitored and correlated with the formation of a clay phase(s) during the test. Thermodynamic modeling of select effluent solution samples suggests the dominant secondary reaction product for the SRL-202 glass is a smectite di-octahedral clay phase(s), possibly nontronite [Na0.33Fe2(AlSi)4O10(OH)2•n(H2O)] or beidellite [Na0.33Al2.33Si3.67O10(OH)2]. This phase was identified in SEM images as discrete spherical particles found growing out of a gel-layer on reacted SRL-202 glass. Plutonium analyses of filtered and unfiltered solutions indicate that >80% of the Pu exiting the PUF system is as filterable particulates. In this advection-dominated system, Pu is migrating principally as colloids after being released from the LaBS glass. Analysis of reacted LaBS glass using SEM-EDS illustrates that Pu has segregated into a discrete disk-like phase, possibly PuO2. Alteration products that contain the neutron absorber Gd have not been positively identified. Separation of the Pu and its neutron absorbers during glass dissolution and transport is a potential criticality concern in the proposed repository. However, the translation and interpretation of these long-term PUF test results to actual disposed waste packages requires further analysis.
2007. "Novel Magnetic Hydrogen Sensing: A Case Study Using Antiferromagnetic Hematite Nanoparticles." Nanotechnology 18(16):Art. No. 165502. doi:10.1088/0957-4484/18/16/165502 Abstract Hydrogen sensing is a critical component of safety to address wide spread public perceptions of the hazards of production, storage, transportation and use of hydrogen in proposed future automobiles and in various other applications. A nanoscale magnetic hydrogen sensor is proposed based on the experimental observation of systematically varying the saturation magnetization and remanence of nanoscale antiferromagnetic hematite with hydrogen flow. The saturation magnetization and remanence of the nanoscale hematite sample showed an increase of one to two orders of magnitude in the presence of flowing hydrogen gas at concentrations in the 1 to 10% range and at 575 K, suggesting that a practical magnetic hydrogen sensor could be developed using this material and the novel magnetic sensing method. Thermogravimetric analysis of the hematite sample shows significant mass loss when hydrogen gas is introduced. Xray diffraction and x-ray photoelectron spectroscopy studies ruled out any impurity phase formation as a result of gas-sample interaction. This work thus facilitates the use of the magnetic properties of an antiferromagnetic material as gas sensing parameters, thus exploring the concept of ‘magnetic gas sensing’.
