Spectroscopy/Diffraction 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.
Shin Y, GA Baker, LQ Wang, and GJ Exarhos. 2008. "Investigation of the hygroscopic growth of self-assembled layers of N-alkyl-N-methylpyrrolidinium bromides at the interface between air and organic salt ." Colloids and Surfaces. A, Physicochemical and Engineering Aspects 318(1-3):254-258. doi:10.1016/j.colsurfa.2007.12.045 Abstract We report on the hygroscopic growth of self-assembled lamellae, composed of N-alkyl-N-methylpyrrolidinium bromide (CnMPB; n = 10, 12, 14, 16, 18) surfactant molecules, spontaneously formed at the interface between ambient air and the low-melting organic salt tetrabutylammonium acetate (TBAAc). The organization process to form well-defined hygroscopic bilayer patterns at the air/TBAAc interface was investigated using a combination of time-dependent X-ray diffraction (XRD) and carbon-13 cross-polarization magic angle spinning nuclear magnetic resonance (13C CP/MAS NMR) spectroscopy. CnMPB surfactants containing the highest alkyl chain lengths studied (n = 16, 18) formed highly ordered, fully-interdigitated bilayer patterns with an all-trans conformation of interior methylene carbons. In contrast, CnMPB surfactants with shorter alkane chains (n = 10, 12, 14) in this series formed less-ordered bilayer arrangements with mixed trans/gauche aliphatic character. The lamellar patterns became increasingly ordered with longer exposure to humid air at the air/salt interface.
Wu H, J Wang, Z Wang, DR Fisher, and Y Lin. 2008. "Apoferritin-Templated Yttrium Phosphate Nanoparticle Conjugates for Radioimmunotherapy of Cancers." Journal of Nanoscience and Nanotechnology 8(5):2316-2322. doi:10.1166/jnn.2008.177 Abstract We report a templated-synthetic approach based on apoferritin to prepare radionuclide nanoparticle (NP) conjugates. Non-radioactive yttrium (89Y) was used as model target and surrogate for radioyttrium (90Y) to prepare the nanoparticle conjugate. The center cavity and multiple channel structure of apoferritin offer a fast and facile method to precipitate yttrium phosphate by diffusing yttrium and phosphate ions into the cavity of apofrritin, resulting a core-shell nanocomposite. The yttrium phosphate/apoferritin nanoparticle was functionalized with biotin for further application. The synthesized nanoparticle was characterized by transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). We found that the resulting nanoparticles were uniform in size, with a diameter of around 8 nm. We tested the pre-targeting capability of the biotin-modified yttrium phosphate/apoferritin nanoparticle (yttrium phosphate/apoferritin nanoparticle) conjugate with streptavidin-modified magnetic beads and with aid of biotin-modified fluorecein isothiocyanate (FITC) tracer. This work shows that an yttrium phosphate NP conjugate provides a fast, simple and efficient method to prepare radioactive yttrium conjugate for applications in radioimmunotherapy of cancer.
Wang J, G Liu, H Wu, and Y Lin. 2008. "Sensitive electrochemical immunoassay for 2,4,6-trinitrotoluene based on functionalized silica nanoparticle labels." Analytica Chimica Acta 610(1):112-118. doi:10.1016/j.aca.2008.01.024 Abstract We present a poly(guanine)-functionalized silica nanoparticle (NP) label-based electrochemical immunoassay for sensitively detecting 2,4,6-trinitrotoluene (TNT). This immunoassay takes advantage of magnetic bead–based platform for competitive displacement immunoreactions and separation, and use electroactive nanoparticles as labels for signal amplification. For this assay, anti-TNT-coated magnetic beads interacted with TNT analog-conjugated poly(guanine)-silica NPs and formed analog-anti-TNT immunocomplexes on magnetic beads. The immunocomplexes coated magnetic beads were exposed to TNT samples, which resulted in displacing the analog conjugated poly(guanine) silica NPs into solution by TNT. In contrast, there are no guanine residues releasing into the solution in the absence of TNT. The reaction solution was then separated from the magnetic beads and transferred to the electrode surface for electrochemical measurements of guanine oxidation with Ru(bpy)32+ as mediator. The sensitivity of this TNT assay was greatly enhanced through dual signal amplifications: 1) a large amount of guanine residues on silica nanoparticles is introduced into the test solution by displacement immunoreactions and 2) a Ru(bpy)32+-induced guanine catalytic oxidation further enhances the electrochemical signal. Some experimental parameters for the nanoparticle label-based electrochemical immunoassay were studied and the performance of this assay was evaluated. The method is found to be very sensitive and the detection limit of this assay is ~ 0.1 ng mL-1 TNT. The electrochemical immunoassay based on the poly[guanine]-functionalized silica NP label offers a new approach for sensitive detection of explosives.
Cwiertny DM, J Baltrusaitis, GJ Hunter, A Laskin, M Scherer, and VH Grassian. 2008. "Characterization and Acid-Mobilization Study of Iron-Containing Mineral Dust Source Materials." Journal of Geophysical Research. D. (Atmospheres) 113(D5):Art. No. D05202. doi:10.1029/2007JD009332 Abstract Processes that solubilize the iron in mineral dust aerosols may increase the amount of iron supplied to ocean surface waters, and thereby stimulate phytoplankton productivity. It was recently proposed that mixing of mineral dusts with SO2 and HNO3 produces extremely acidic environments that favor the formation of bioavailable Fe(II). Here, four authentic mineral dust source materials (Saudi Beach sand (SB), Inland Saudi sand (IS), Saharan Sand (SS) and China Loess (CL)) and one commercial reference material (Arizona Test Dust (AZTD)) were spectroscopically characterized, and their dissolution at pH 1 was examined in aqueous batch systems. Spectroscopic analyses indicated that the bulk and near-surface region of all samples possessed similar elemental compositions and that iron was unevenly distributed among dust 10 particles. Mössbauer spectroscopy revealed Fe(III) in all samples, although SB, CL and AZTD also contained appreciable Fe(II). Both Fe(II) and Fe(III) were primarily substituted into aluminosilicates, although CL, AZTD and IS also contained Fe(III) oxides. Total iron solubility (defined as the summed concentration of dissolved Fe(II) and Fe(III) measured after 24 h) ranged 14 between 4-12% of the source materials’ iron content, but did not scale with either the surface area or the iron content of the samples. This suggests that other factors such as iron speciation and mineralogy may play a key role in iron solubility. Also, the elevated nitrate concentrations encountered from nitric acid at pH 1 suppressed dissolution of Fe(II) from AZTD, CL and SB particles, which we propose results from the surface-mediated, non-photochemical reduction of nitrate by Fe(II).
Grate JW, OB Egorov, MJ O'Hara, and TA Devol. 2008. "Radionuclide Sensors for Environmental Monitoring: From Flow Injection Solid-Phase Absorptiometry to Equilibration-Based Preconcentrating Minicolumn Sensors with Radiometric Detection." Chemical Reviews 108(2):543-562. doi:10.1021/cr068115u Abstract The development of in situ sensors for ultratrace detection applications in process control and environmental monitoring remains a significant challenge. Such sensors must meet difficult detection limit requirements while selectively detecting the analyte of interest in complex or otherwise challenging sample matrixes. Nowhere are these requirements more daunting than in the field of radionuclide sensing. The detection limit requirements can be extremely low. Nevertheless, a promising approach to radionuclide sensing based on preconcentrating minicolumn sensors has been developed. In addition, a method of operating such sensors, which we call equilibration-based sensing, has been developed that provides substantial preconcentration and a signal that is proportional to analyte concentration, while eliminating the need for reagents to regenerate the sorbent medium following each measurement. While this equilibration-based sensing method was developed for radionuclide sensing, it can be applied to nonradioactive species as well, given a suitable on-column detection system. By replacing costly sampling and laboratory analysis procedures, in situ sensors could have a significant impact on monitoring and long term stewardship applications. The aim of this review is to cover radionuclide sensors that combine some form of selective sorption with a radiometric detection method, andas a primary aimto comprehensively review preconcentrating minicolumn sensors for radionuclide detection. As a secondary aim, we will cover radionuclide sensors that combine sorption and scintillation in formats other than minicolumn sensors. We are particularly concerned with the detection of alpha- and beta-emitting radionuclides, which present particular challenges for measurements in liquid media.
Bank TL, RK Kukkadapu, AS Madden, ME Baldwin, and PM Jardine. 2008. "Effects of gamma-sterilization on the physico-chemical properties of naturalsediments." Chemical Geology 251(1-4):1-7. doi:10.1016/j.chemgeo.2008.01.003 Abstract A series of experiments were completed to determine the effects of soil sterilization on various soil chemical properties including U(VI) sorption, soil pH, natural organic matter (NOM), cation exchange capacity (CEC), and iron oxidation state. Soils under investigation were a saprolitic sequence of interbedded weathered shale and limestone collected from the Oak Ridge Reservation (ORR). Sediments were sterilized by either steam sterilization at 121oC or by γ-irradiation using a cobalt-60 source. Subsamples of sediments were pretreated with dithionate-citrate-bicarbonate (DCB) and/or H2O2 to remove reducible Fe(III) oxides and NOM. Results from aerobic U(VI) sorption experiments indicated that γ-sterilized sediments sorbed more U(VI) compared to non-sterile sediments. Results from sorption experiments completed using DCB and H2O2-treated samples indicated that the iron oxide and NOM fractions of the sediment accounted for the majority of U(VI) sorption and that γ-irradiation of these phases resulted in increased sorption of U(VI). Mössbauer spectra of γ-sterilized sedimentsdisplayed a decrease in the amount of ferric iron associated with goethite and a small increase in the amount of reduced iron in silicate minerals compared to spectra from non-sterile samples. Our results suggest that sterilization by γ-irradiation induced iron reduction that may have increased sorption of U(VI) on these sediments.
Li XS, GE Fryxell, CM Wang, and MH Engelhard. 2008. "The Synthesis of Ag-Doped Mesoporous TiO2 ." Microporous and Mesoporous Materials 111(1-3):639-642. doi:10.1016/j.micromeso.2007.07.042 Abstract Ag-doped mesoporous titanium oxide was prepared using non-ionic surfactants and easily handled titanium precursors, under mild reaction conditions. In contrast to the stabilizing effect of Cd-doping on mesoporous TiO2, Ag-doping was found to significantly destabilize the mesoporous structure.
Gaan S, G Sun, K Hutches, and MH Engelhard. 2008. "Effect of Nitrogen Additives on Flame Retardant Action of Tributyl Phosphate: Phosphorus ? Nitrogen Synergism." Polymer Degradation and Stability 93(1):99-108. doi:10.1016/j.polymdegradstab.2007.10.013 Abstract The effect of nitrogen additives like urea, guanidine carbonate and melamine formaldehyde on the flame retardant efficacy of tributyl phosphate (TBP) has been investigated. From the LOI tests on treated cotton it is clear that the nitrogen additives have synergistic action. Estimation of activation energy of decomposition of treated cotton indicated that nitrogen additives enhance the thermal stability during the burning process. SEM pictures of chars formed after LOI test showed the formation of protective polymeric coating on the surface. The surface of chars formed were evaluated using FTIR-ATR and XPS analysis which showed that the coating was composed of Phosphorus-Nitrogen-Oxygen containing species. Formation of this coating during the burning process could lead to the synergistic interaction of phosphorus and nitrogen. Based on the experimental data we have further proposed several reaction mechanisms which could contribute to synergistic action and formation of protective coating on the surface of char.
Hopkins RJ, Y Desyaterik, AV Tivanski, RA Zaveri, CM Berkowitz, T Tyliszczak, MK Gilles, and A Laskin. 2008. "Chemical Speciation of Sulfur in Marine Cloud Droplets and Particles: Analysis of Individual Particles from the Marine Boundary Layer Over the California Current." Journal of Geophysical Research. D. (Atmospheres) 113(D4):D04209. doi:10.1029/2007/JD008954 Abstract Detailed chemical speciation of the dry residue particles from individual cloud droplets and interstitial aerosol collected during the Marine Stratus Experiment (MASE) was performed using a complementary combination of microanalysis techniques. Techniques include computer controlled scanning electron microscopy with energy dispersed analysis of X-rays (CCSEM/EDX), time-of-flight secondary ionization mass spectrometry (TOFSIMS), and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). Samples were collected at the ground site located in Point Reyes National Seashore, approximately 1 km from the coast. This manuscript focuses on the analysis of individual particles sampled from an air mass that originated over the open ocean and then passed through the area of the California current located along the northern California coast. Based on composition, morphology, and chemical bonding information, two externally mixed, distinct classes of sulfur containing particles were identified: chemically modified (aged) sea salt particles and secondary formed sulfate particles. The results indicate substantial heterogeneous replacement of chloride by methanesulfonate (CH3SO3 -) and non-sea salt sulfate (nss-SO4 2-) in sea-salt particles with the characteristic ratios of CH3SO3 −/nss-SO4 2−> 0.6. Although this value seems too high for a mid-latitude site, our model calculations suggest that high CH3SO3 -/nss-SO4 2- ratios are expected during the early stages of dimethyl sulfide (DMS) oxidation when CH3SO3H forms more rapidly than H2SO4.

Next Displaying results 1 - 10 of 663