NMR and EPR Publications

2009

Wu S, NM Lourette, N Tolic, R Zhao, R Robinson, AV Tolmachev, RD Smith, and L Pasa-Tolic. 2009. "An integrated top-down and bottom-up strategy for broadly characterizing protein isoforms and modifications." Journal of Proteome Research 8(3):1347-1357. Abstract We present an integrated top-down and bottom-up approach facilitated by concurrent liquid chromatography-mass spectrometry (LC-MS) analysis and fraction collection for comprehensive high-throughput intact protein profiling. The approach employs high resolution reversed phase (RP) LC separations coupled on-line with a 12T Fourier transform ion cyclotron resonance (FTICR) spectrometer to profile and tentatively identify modified proteins, using detected intact protein masses in conjunction with bare protein identifications from the bottom-up analysis of the same fraction. Selected identifications are incorporated into a target ion list for subsequent offline gas phase fragmentation that uses only an aliquot of the original fraction used for bottom-up analysis.
Barry RC, Y Lin, J Wang, G Liu, and C Timchalk. 2009. "Nanotechnology-Based Electrochemical Sensors for Biomonitoring Chemical Exposures ." Journal of Exposure Science and Environmental Epidemiology 19:1-18. doi:10.1038/jes.2008.71 Abstract This manuscript highlights research focused on the development of field-deployable analytical instruments based on EC detection. Background information and a general overview of EC detection methods and integrated use of nanomaterials in the development of these sensors are provided. New developments in EC sensors using various types of screen-printed electrodes, integrated nanomaterials, and immunoassays are discussed. Recent applications of EC sensors for assessing exposure to pesticides or detecting biomarkers of disease are highlighted to demonstrate the ability to monitor chemical metabolites, enzyme activity, or protein biomarkers of disease. In addition, future considerations and opportunities for advancing the use of EC platforms for dosimetric studies are covered.
Harvey SD, GW Buchko, RB Lucke, CW Wright, AM Melville, AJ Scott, and BW Wright. 2009. "The Structure and Purity of a Reference Dye Standard used for Quantification of C.I. Solvent Red 164 in Fuels." Dyes and Pigments 82(3):307-315. doi:10.1016/j.dyepig.2009.01.015 Abstract This research describes a comprehensive analytical approach to provide structure verification and purity determination for Morton Red 26. Studies presented in this paper, based on application of numerous traditional and advanced analytical techniques, provide definitive proof that Morton Red 26 and Solvent Red 26 are not chemically equivalent and, further, that Morton Red 26 and NIST #2037 have identical chemical structures, a result that stands in contrast to common perception. Additional analytical studies, again based on the application of numerous analytical methodologies, determined that Morton Red 26 was approximately 72 percent pure, a finding that stands in contrast to the 99 percent purity value certified by the supplier (Morton International). Possible explanations and implications are briefly discussed. Several of the Morton Red 26 impurities were tentatively identified, and a host of additional impurities were partially characterized by NMR, TLC, GC/MS, and HPLC/MS studies.
Kwak JH, D Mei, CWW Yi, DH Kim, CHF Peden, L Allard, and J Szanyi. 2009. "Understanding the nature of surface nitrates in BaO/gamma-Al2O3 NOx storage materials: A combined experimental and theoretical study ." Journal of Catalysis 261(1):17-22. Abstract The special role of the interface between the active catalytic phase (metal or metal oxide) and the oxide support in determining the properties of practical catalysts has long been recognized; however, it is still very poorly understood in most systems
Johnson BR, BJ Riley, SK Sundaram, JV Crum, CH Henager, Jr, Y Zhang, V Shutthanandan, CE Seifert, RM Van Ginhoven, CE Chamberlin, A Rockett, D Hebert, and A Aquino. 2009. "Synthesis and Characterization of Bulk Vitreous Cadmium Germanium Arsenide." Journal of the American Ceramic Society 92(6):1236-1243. doi:10.1111/j.1551-2916.2009.03001.x Abstract Abstract Cadmium-germanium-diarsenide (“CGA”) glasses were synthesized in bulk form (~2.4 cm3) using the procedures adapted from the literature. Several issues involved in the fabrication and quenching of amorphous CdGexAs2 (x = 0.45, 0.65, 0.85, 1.00) are described. An innovative processing route is presented to enable quenching of vitreous, crack-free ingots with sizes up to 10 mm diameter, and 30 – 40 mm long. Specimens from selected ingots were characterized using thermal analysis, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, particle-induced X-ray emission, Rutherford backscattering, secondary ion mass spectrometry, X-ray diffraction, density, and optical spectroscopy. Variations in properties as a function of processing conditions and composition are described. Results show that the density of defect states in the middle of the band gap and near the band edges can be decreased three ways: through suitable control of the processing conditions, by doping the material with hydrogen, and by increasing the concentration of Ge in the glass.
Fernandez CA, JG Roberts, EM Hoppes, RJ Wiacek, GE Fryxell, JT Bays, MG Warner, CM Wang, JE Hutchinson, and RS Addleman. 2009. "Advancements Toward the Greener Processing of Engineered Nanomaterials -- Effect of Core Size on the Dispersibility and Transport of Gold Nanocrystals in Near-Critical Solvents." Small 5(8):961-969. doi:10.1002/smll.200801207 Abstract In this work, we explore the dispersibility of octanethiol-stabilized gold nanocrystals of different core sizes in compressed ethane and propane over a wide range of fluid conditions. The dispersibility of the nanocrystals was obtained through the Surface Plasmon Resonance (SPR) absorption spectra of solutions. Three models, the total interaction theory, the sedimentation coefficient equation, and the Chrastil method, are briefly discussed as tools to interpret the experimental results. Nanoparticle dispersibility-versus-density plots are strongly dependent on nanoparticle size and solvent conditions, with the dispersion of larger nanocrystals more dependant on changes of pressure or density at a given temperature. These results showed a notable correlation with the calculated sedimentation coefficients of the nanocrystals in both solvents. The Chrastil equation was successfully applied to predict and describe the dispersibility of the gold nanocrystals as a function of density, showing that the high stabilities of the nanocrystals dispersions are a result of the very strong solvent-nanocrystal interactions. For the range of nanoparticle sizes studied, compressed ethane at 25 ºC led to a greater tunability of nanoparticle dispersion when compared with compressed propane at 65 ºC. On the other hand, for equivalent pressures compressed propane was found to provide better solubility than ethane due to its higher density. The results of this study quantitatively demonstrate that compressed fluids can offer pressure tunable, size selective control of nanoparticle solvation and transport. This ability has clear advantages over conventional solvents and direct application to various nanomaterials processes, such as separation, transport and purification of nanocrystals.
Ferguson MR, KR Minard, and KM Krishnan. 2009. "Optimization of nanoparticle core size for magnetic particle imaging." Journal of Magnetism and Magnetic Materials 321(10):1548-1551. Abstract Magnetic Particle Imaging (MPI) is a powerful new diagnostic visualization platform designed for measuring the amount and location of superparamagnetic nanoscale molecular probes (NMPs) in biological tissues. Promising initial results indicate that MPI can be extremely sensitive and fast, with good spatial resolution for imaging human patients or live animals. Here, we present modeling results that show how MPI sensitivity and spatial resolution both depend on NMP-core physical properties, and how MPI performance can be effectively optimized through rational core design. Monodisperse magnetite cores are attractive since they are readily produced with a biocompatible coating and controllable size that facilitates quantitative imaging.
Du Y, NA Deskins, Z Zhang, Z Dohnalek, M Dupuis, and I Lyubinetsky. 2009. "Imaging Consecutive Steps of O2 Reaction with Hydroxylated TiO₂(110): Identification of HO₂ and Terminal OH Intermediates." Journal of Physical Chemistry C 113(2):666-671. Abstract We report results of the combined experimental and theoretical investigation of the molecular oxygen reaction with a partially hydroxylated TiO₂(110) surface. The consecutive steps of both primary and secondary site-specific reactions have been tracked with high-resolution scanning tunneling microscopy (STM). For the first time, we have directly imaged stable, adsorbed hydroperoxyl (HO₂) species, which is believed to be a key intermediate in many heterogeneous photochemical processes but generally metastable and “elusive” until now. We also found terminal hydroxyl groups, another critical but never directly observed intermediates. A conclusive evidence that O₂ reacts spontaneously with a single bridging OH group as an initial reaction step is provided. The experimental results are supported by density functional theory (DFT) calculations that have determined species energies and configurations. Reported observations provide a basis for a consistent description of the elementary reaction steps and offer molecular-level insight into the underlying reaction mechanisms. In a broader perspective, the results are expected to have far reaching implications for various catalytic systems involving the interconversion of O₂ and H₂O.
Hlaing Oo WM, LV Saraf, MH Engelhard, V Shutthanandan, L Bergman, J Huso, and MD Mccluskey. 2009. "Suppression of conductivity in Mn-Doped ZnO Thin Films." Journal of Applied Physics 105(1):013715. doi:10.1063/1.3063730 Abstract We studied the dopant concentration distribution and conductivity in ZnO:Mn films grown by metalorganic chemical vapor deposition (MOCVD). The ion beam, surface and microstructural properties of undoped ZnO films were compared with Mn-doped ZnO films. Suppression of ZnO conductivity was noticed up to ~ 4.5 atom% Mn doping. The presence of Mn2+, confirmed by X-ray photoelectron spectroscopy (XPS), is correlated with the reduction in conductivity. No major change in the activation energy (~40 meV) and a reduction in the Zn/O ratio as a function of Mn concentration in highly sensitive proton induced X-ray emission (PIXE) technique also support this hypothesis. We discuss our results from a view point of homogeneous Mn distribution, elemental XPS ratio offsets and secondary phase formations in ZnO films.
Wang H, J Wang, D Choi, Z Tang, H Wu, and Y Lin. 2009. "EQCM Immunoassay for Phosphorylated Acetylcholinesterase as a Biomarker for Organophosphate Exposures Based on Selective Zirconia Adsorption and Enzyme-Catalytic Precipitation ." Biosensors and Bioelectronics 24(8):2377-2383. Abstract A zirconia (ZrO2) adsorption-based immunoassay by electrochemical quartz crystal microbalance (EQCM) has been initially developed, aiming at the detection of phosphorylated acetylcholinesterase (AChE) as a potential biomarker for bio-monitoring exposures to organophosphate (OP) pesticides and chemical warfare agents. Hydroxyl-derivatized monolayer was preferably chosen to modify the crystal serving as the template for directing the electro-deposition of ZrO2 film with uniform nanostructures. The resulting ZrO2 film was utilized to selectively capture phosphorylated AChE from the sample media. Horseradish peroxidase (HRP)-labeled anti-AChE antibodies were further employed to recognize the captured phosphorylated protein. Enzyme-catalytic oxidation of the benzidine substrate resulted in the accumulation of insoluble product on the functionalized crystal. Ultrasensitive EQCM quantification by mass-amplified frequency responses as well as rapid qualification by visual color changes of product could be thus achieved. Moreover, 4-chloro-1-naphthol (CN) was comparably studied as an ideal chromogenic substrate for the enzyme-catalytic precipitation. Experimental results show that the developed EQCM technique can allow for the detection of phosphorylated AChE in human plasma. Such an EQCM immunosensing format opens a new door towards the development of simple, sensitive, and field-applicable biosensor for biologically monitoring low-level OP exposures.

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