Scientific Publications 2004
A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
K
2004. "Identification and Quantification of Mineral Precipitation in Fe 0 Filings From a Column Study." Environmental Science and Technology 38(21):5757-5765. Abstract Quantifying precipitates and determining corrosion rates of zero-valent iron (Fe 0 ) during groundwater treatment were pursued in two field columns by analyzing column core samples using thermo-gravimetric analysis (TGA) combined with x-ray diffraction (XRD) and scanning electron microscopy (SEM). The core precipitates included goethite, magnetite, aragonite, and calcite as major phases with lesser amounts of Fe₂(OH)₂CO₃, and green rust, similar to other studies [1-5]. Corrosion rates derived from TGA-MS analysis of core samples ranged in 0.5 – 6.1 mmol kg -1 d -1 , higher than a previous report [6] but not unreasonable considering that the influent contained up to 13.5 mM NO₃ - . At the inlet sand-Fe 0 interface, corrosion rates were similar (4.09 and 4.86 mmol kg -1 d -1 ) for both columns. Corrosion rates derived from pore water chemistry showed a decreasing trend over time. The time-weighted average corrosion rates for both columns of different throughput fell in the range based on TGA-MS results, suggesting that the aqueous mass balance calculation could provide an alternative to estimating corrosion rates in the absence of core analyses. The porosity reduction based on water chemistry was confirmed by TGA-MS results (7–77%), where the high porosity reduction occurred at reactive regions and the low at regions near the effluent. Normalized with the treatment volume, porosity reduction values agree with other studies that used high levels of SO₄ ₂- and HCO₃ - [2,7,8]. The near 80% porosity reduction in more corroded regions, subjected to high throughput of an equivalent of 17-yr operation, is significant to be considered for long-term performance of permeable reactive barriers.
2004. "Composition-Controlled Synthesis of Bimetallic Gold-Silver Nanoparticles." Langmuir 20(25):11240-11246. Abstract This paper reports finding of an investigation of the synthesis of monolayer-capped binary gold-silver bimetallic nanoparticles that is aimed at understanding the control factors governing the formation of the bimetallic compositions. The findings have important implications to the exploration of gold-based bimetallic nanoparticles for biosensing and fuell cell catalytic nanomaterials.
2004. "Nanoparticle-Structured Ligand Framework as Electrode Interfaces." Electroanalysis 16(1-2):120-126. Abstract Nanostructured electrode based on gold nanoparticle network was developed for selective detection of metal ions.
2004. "Multicomponent Dynamical Nucleation Theory And Sensitivity Analysis ." Journal of Chemical Physics 120(19):9133-9141. Abstract Vapor to liquid multi-component nucleation is a dynamical process governed by a delicate interplay between condensation and evaporation. Since the population of the vapor phase is dominated by monomers at reasonable supersaturations, the formation of clusters is governed by monomer association and dissociation reactions. Since no potential energy barrier exists the formation of a cluster is impeded by a free energy of activation that is entropic in nature. Dynamical Nucleation Theory provides a framework in which equilibrium evaporation rate constants can be calculated and the corresponding condensation rate constants determined from detailed balance. The nucleation rate can then be obtained by solving the kinetic equations. The rate constants governing the multi-step kinetics of multi-component nucleation including sensitivity analysis and the influence of possible contaminants will be presented and discussed.
2004. "Persistent Photoconductivity in Chemically-Modified Single Wall Carbon Nanotubes ." Journal of Physical Chemistry B 108(52):19976-19981. Abstract Control of the conductivity of single wall carbon nanotubes (SWNTs) is crucial for the use of carbon nanotubes in molecular electronics. We report a new fundamental characteristic of semiconducting SWNTs – the persistent photoconductivity of chemically-modified carbon nanotube films. Covalent attachment of Ruthenium(II)-tris(2,2’-bipyridine) Ru(bpy) ²⁺/₃ to SWNT makes carbon nanotubes sensitive to light absorbed by the ruthenium complex and persistently photoconductive, thus opening opportunities for the selective light control of the conductivity. Illumination of carboxylated SWNTs with ultraviolet or visible light causes a persistent decrease in the conductivity of semiconducting films. Infrared illumination restores conductivity of SWNT films.
2004. "Comparison of Two Preparation Methods in the Redox Properties of Pd/CeO₂/Ta/Si Model Catalysts: Spin Coating versus Sputter Deposition ." Catalysis Letters 98(1):23-28. Abstract Pd/CeO2/Ta/Si model catalysts were prepared by spin coating and sputter deposition method, and characterized by means of AFM, SEM and in situ XPS, especially focusing on the redox properties of Ce and Pd elements. Compared with thin CeO₂ films (about 2.2 nm), the thicker ones (about 22 nm) maintained Ce⁴⁺ oxidation state even after treatment with H₂ up to 500 °C while the presence of Pd facilitated the reduction of ceria. The reduction of ceria brought about following that of PdO, which was explained by the spillover of hydride in Pd to CeO₂ originating from hydrogen adsorption on the Pd surface. Compared with the sputter deposition method, spin coating produced the smaller size of Pd particles, thus leading to formation of the stable PdO species against hydrogen. Based on these results, a schematic model of Pd/CeO₂/Ta/Si was suggested and it might be assumed that spin coating method provided with an environment similar to the conventional impregnation.
2004. "Synergism Between Pt/Al₂O₃ and Au/TiO₂ in the Low Temperature Oxidation of Propene." Catalysis Letters 98(1):11-15. Abstract The low temperature (<170°C) oxidation activity of supported Pt catalysts is impeded in the presence of CO. Supported Au catalysts are very effective in the removal of CO, but not propene (C₃H₆) at low temperatures (<200°C). Addition of Au/TiO₂ to Pt /Al₂O₃ either in the form of a physical mixture or as a pre-catalyst reduced the light-off temperature (T₅₀) for C₃H₆ oxidation over supported a Pt catalyst by ~54 °C in a feed of 1% CO, 400 ppm C₃H₆, 14% O₂, 2% H₂O.
2004. "Reactive Growth of Nanoscale MgO Films by Mg Atom Deposition onto O2 Multilayers." Journal of Physical Chemistry B 108(31):11666-11671. Abstract Nanometer thick layers of Mg metal vapor deposited onto a polycrystalline gold substrate at 22 K with and without O2 multilayers were examined after annealing. Auger electron spectroscopy and temperature programmed desorption of N2 were used to determine the Mg oxidation state and the surface area of the deposits immediately after deposition at 22 K, and following annealing. Deposited on 20 layers of O2, Mg oxidizes and forms an MgO film having a high surface area (~700 m2/g). The surface area decreases upon annealing, approaching that of a well-ordered MgO(100) surface by 500 K. On thinner O2 multilayers, both oxidized and metallic Mg are observed at 22 K. Mild thermal annealing (200 to 400 K) results in transport of the excess metallic Mg to, and alloy formation with, the underlying Au substrate. MgO films annealed to 1000 K display a narrow distribution of N2 binding sites, similar to well-ordered MgO(100). The film sublimes above 1000 K when heated.
2004. "Monitoring Tertiary Interactions in the Hammerhead Ribozyme Using Pulsed EPR Spectroscopy." Biophysical Journal 86(1):143A, Part 2 Suppl S. Abstract The hammerhead ribozyme is a small, self-cleaving catalytic RNA which activates a site-specific phosphodiester bond cleavage reaction. The folding pathway of the hammerhead ribozyme is critical to its catalytic activity, which has been known to depend on the metal ion concentration (DeRose, V.J., 2003, Curr. Op. Struct. Biol. 13, 317-324). Recently, it has been proposed that an extended hammerhead ribozyme that contains putative intramolecular loop-loop interactions between two helical regions has enhanced reactivity, and at lower cation concentrations (Khorvona, A., Lescoute, A., Westhof, E., Jayasena, S.D., 2003, Nat. Struc. Biol. 10, 708-712). In order to investigate potential tertiary interactions between the two loops as well as the folding pathway of the hammerhead ribozyme, site-directed spin labels have been introduced to stems I and II. Tertiary interactions can be predicted by measuring inter-spin distances (Kim, N.-K. Murali, A., DeRose, V.J., Submitted) with increasing metal concentration, and the distance distributions between two sites in the internal loops can be obtained using pulsed EPR techniques (DEER, double electron electron resonance), with which inter-spin distances can be measured up to 60Å. (Schiemann, O., Weber, A., Edwards, T.E., Prisner, T.F., Sigurdsson, S.T., J. Am. Chem. Soc. 2003, 125, 3434-3435)
2004. "Structure and DNA-Binding Sites of the SWI1 AT-rich Interaction Domain (ARID) Suggest Determinants for Sequence-Specific DNA Recognition." Journal of Biological Chemistry 279(16):16670-16676. Abstract 2 ARID is a homologous family of DNA-binding domains that occur in DNA binding proteins from a wide variety of species, ranging from yeast to nematodes, insects, mammals and plants. SWI1, a member of the SWI/SNF protein complex that is involved in chromatin remodeling during transcription, contains the ARID motif. The ARID domain of human SWI1 (also known as p270) does not select for a specific DNAsequence from a random sequence pool. The lack of sequence specificity shown by the SWI1 ARID domain stands in contrast to the other characterized ARID domains, which recognize specific AT-rich sequences. We have solved the three-dimensional structure of human SWI1 ARID using solution NMR methods. In addition, we have characterized non-specific DNA-binding by the SWI1 ARID domain. Results from this study indicate that a flexible long internal loop in ARID motif is likely to be important for sequencespecific DNA-recognition. The structure of human SWI1 ARID domain also represents a distinct structural subfamily. Studies of ARID indicate that boundary of the DNA binding structural and functional domains can extend beyond the sequence homologous region in a homologous family of proteins. Structural studies of homologous domains such as ARID family of DNA-binding domains should provide information to better predict the boundary of structural and functional domains in structural genomic studies. Key Words: ARID, SWI1, NMR, structural genomics, protein-DNA interaction.
2004. "[SiAu4]: Aurosilane." Angewandte Chemie International Edition 43(16):2125-2129. Abstract Because of the strong relativistic effects, the chemistry of gold differs substantially from the rest of the coinage metals. [1-6] The relativistic stabilization of the 6s orbital in gold gives rise to an anomalously high electron affinity of Au, which has been compared to the halogens, [5,7,8] such as in the recently predicted tetraaurides [MAu4] (M=Ti, Zr, Th).[9] The most remarkable chemistry of gold is the isolobal analogy between a gold phospane unit {AuPR3} and a hydrogen atom, [10-12] which has been exploited to bring out tetra- and hyper-coordination in compounds, such as [C(AuPR3)4] and [C(AuPR3)5]+[13-17]. Herein we show that a single gold atom can also exhibit chemistry analogous to the hydrogen atom. We report experimental and theoretical evidence that a serious of Si-Au clusters, [SiAun] (n=2-4), are structurally and electronically similar to SiHn. Photoelectron spectroscopy (PES) of corresponding [SiAun]- anions reveals that [SiAu4] has a large energy gap of 2.4eV, thus indicating extremely chemically stable molecule.
2004. "The Role of Strain and Ligand Effects in the Modification of the Electronic and Chemical Properties of Bimetallic Surfaces." Physical Review Letters 93(15):Art. No. 156801. doi:10.1103/PhysRevLett.93.156801 Abstract The abstract for this product is not available at this time.
2004. "Heterogeneous Chemistry of Individual Mineral Dust Particles from Different Dust Source Regions: The Importance of Particle Mineralogy." Atmospheric Environment 38(36):6253-6261. Abstract The heterogeneous chemistry of individual dust particles from four different dust source regions is investigated on a particle-by-particle basis using state-of-the-art scanning electron microscopy techniques including computer-controlled scanning electron microscopy/computer-controlled X-ray analysis (CCSEM/EDX). Morphology and compositional changes of individual particles as they react with nitric acid are observed. Clear differences in the reactivity of mineral dusts from these four different dust regions with nitric acid could be observed. Mineral dust from source regions containing high levels of calcium, such as those found in parts of China and Saudi Arabia, are found to react to the greatest extent. Calcium containing minerals, such as calcite (CaCO3) and dolomite (CaMg(CO3)2), react to form nitrate salt whereas other calcium containing minerals such as gypsum (CaSO4·2H2O) do not react. The importance of particle chemical composition and mineralogy in the heterogeneous chemistry of mineral dust aerosols is definitively borne out in this study of individual dust particles.
2004. "Biotransformation of Two-Line Silica-Ferrihydrite by a Dissimilatory Fe(III)-Reducing Bacterium: Formation of Carbonate Green Rust in the Presence of Phosphate." Geochimica et Cosmochimica Acta 68(13):2799-2814. Abstract The reductive biotransformation of two Si-ferrihydrite (0.01 and 0.05 mole% Si) coprecipiates by Shewanella putrefaciens, strain CN32, was investigated in 1,4-piperazinediethanesulfonic acid-buffered media (pH ~7) with lactate as the electron donor. Anthraquinone-2,6-disulfonate (electron shuttle) that stimulates respiration was present in the media. Experiments were performed without and with PO43- (ranging from 1 to 20 mmol/L in media containing 50 mmol/L Fe). Our objectives were to define the combined effects of SiO44- and PO43- on the bioreducibility and biomineralization of ferrihydrites under anoxic conditions. Iron reduction was measured as a function of time, solids were characterized by powder X-ray diffraction (XRD) and Mossbauer spectroscopy, and aqueous solutions were analyzed for Si, P, Cl- and inorganic carbon. Both of the ferrihydrites were rapidly reduced regardless of the Si content. Si concentration had no effect on the reduction rate or mineralization products. Magnetite was formed in the absence of PO43- whereas carbonate green rust GR(CO32-) ([FeII(6-x)FeIIIx(OH)12]x+(CO32-)0.5x.yH2O) and vivianite [Fe3(PO4)2.8H2O], were formed when PO43- was present. GR(CO32-) dominated as a mineral product in samples with < 4 mmol/L PO43-. The Fe(II)/Fe(III) ratio of GR(CO32-) varied with PO43- concentration; it was 2 in the 1 mmol/L PO43- and approached 1 in the 4- and 10-mmol/L PO43- samples. GR appeared to form by solid-state transformation of ferrihydrite. Medium PO43- concentration dictated the mechanism of transformation. In 1 mmol/L PO43- media, an intermediate Fe(II)/Fe(III) phase with structural Fe(II), which we tentatively assigned to a protomagnetite phase, slowly transformed to GR with time. In contrast, in medium with >4 mmol/L PO43-, a residual ferrihydrite with sorbed Fe2+ phase transformed to GR. Despite similar chemistries, PO43- was shown to have a profound effect on ferrihydrite biotransformations while that of SiO44- was minimal.
2004. "Intercomparison of Volatile Organic Carbon Measurement Techniques and Data at La Porte During the TexAQS2000 Air Quality Study." Environmental Science and Technology 38(1):221-228. Abstract The Texas Air Quality Study 2000 (TexAQS2000) investigated the photochemical production of ozone and the chemistry of related precursors and reaction products in the vicinity of Houston, Texas. The co-location of four instruments for the measurement of volatile organic carbon compounds (VOCs) allowed a unique opportunity for the intercomparison of the different in-situ measuring techniques. The instruments included three gas chromatographs, each with a different type of detector, and a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) with each system designed to measure a different suite of VOCs. Correlation plots and correlation statistics are presented for species measured by more than one of these instruments. The GC instruments were all in agreement to within 10-20% (slope) with coefficients of variation (r2) of ≥0.85. The PTR-MS agreement with other instruments was more dependent on species with some very good agreements (r2 values of ~0.95 for some aromatics) but isoprene, acetaldehyde and propene were substantially less highly correlated (0.55‹r2‹0.80). At least part of these differences were undoubtedly due to the timing of sample acquisition in an environment in which VOC levels changed very rapidly on both quantitative and temporal scales.
2004. "Non-Thermal Plasma-assisted NOx Reduction over Alkali and Alkaline Earth Ion Exchanged Y, FAU Zeolites." Catalysis Today 89(1-2):135-141. Abstract The catalytic activities of a series of alkali and alkaline earth cation exchanged Y,FAU zeolites were investigated in the non-thermal plasma-assisted NOx reduction reaction using a simulated diesel engine exhaust gas mixture. The catalytic activity of the Y,FAU zeolite showed significant variations with both the nature of the charge compensating cation, and the method of catalyst preparation. Our results show that conventional multiple solution ion exchange is insufficient to prepare the most active catalyst for the given cationic form. The highest NOx conversion level was achieved over a Ba-Y,FAU which was prepared by a multiple ion exchange method, in which each solution ion exchange step was followed by a high temperature calcination. A systematic change in the catalytic activity was observed as a function of the charge density around the charge compensating cation. For both catalyst series (alkali and alkaline earth ion exchanged Y,FAU), the specific activity decreased with increasing electrostatic field around the charge compensating cation. The large difference in the NOx reduction activity at a given e/r ratio, however, may suggest different reaction mechanisms for the two sets of catalysts. Indeed, there is a noticeable difference in the product distribution (selectivity) for the alkali and alkaline earth series of catalysts. Our results also reveal that extreme care must be taken when catalytic activities are compared for seemingly similar materials. We found that two base zeolite materials with identical Si/Al ratios, obtained from the same manufacturer but from different synthesis batches show significantly different catalytic behavior.
