Scientific Publications 2005
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2005. "The spectroscopic signature of the “all-surface” to “internally solvated” structural transition in water clusters in the n=17-21 size regime ." Journal of Chemical Physics 122(19):194310-1 - 194310-9. doi:10.1063/1.1899583 Abstract The existence of a transitional size regime where preferential stabilization alternates between “all-surface” (all atoms on the surface of a cluster) and “internally solvated” (one water molecule at the center of the cluster, fully solvated) configurations with the addition or the removal of a single water molecule, predicted earlier with the TTM2-F interaction potential, has been confirmed from electronic structure calculations for (H2O)n, n=17-21. The onset of the appearance of the first “interior” configuration in water clusters occurs for n=17. This trend was previously predicted by the TTM2-F interaction potential and it is confirmed from electronic structure calculations. The observed structural alternation between “interior” and “all-surface” global minima between n=17-21 is accompanied by a corresponding spectroscopic signature, namely the undulation in the position of the most red-shifted OH stretching vibrations according to the trend: “interior” configurations exhibit more red-shifted OH stretching vibrations than “all-surface” ones. These most red-shifted OH stretching vibrations form distinct groups in the intramolecular region of the spectra and correspond to localized vibrations of donor OH stretches that are connected to neighbors via “strong” (water dimer-like) hydrogen bonds and belong to a water molecule with a “free” OH stretch.
2005. "Powder XRD, SEM, and Multinuclear MAS-NMR Investigations of the Interactions Between Glass and Crystalline Phases of Li, Na, or K Ceramic Waste Forms ." Journal of the American Ceramic Society 88(8):2255-2261. Abstract Interactions between the glass and crystalline phases of ceramic waste forms were investigated via powder X-ray diffraction, scanning electron microscopy, and Si-29, Al-27, Na-23, Li-7, and Cl-35 magic angle spinning nuclear magnetic resonance spectroscopy. LiCl, NaCl, or KCl waste form samples were made with or without glass. The waste forms containing glass consist of sodalite and glass phases with minor amounts of nepheline. Samples without glass form varying amounts of sodalite and nepheline. The glass frit, intended to bind the zeolite particles together, changes in composition, showing marked increases in aluminum and alkali content.
2005. "Direct Observation of Completely Processed Calcium Carbonate Dust Particles." Faraday Discussions 130:453 - 468. doi:10.1039/b417366j Abstract This study presents, for the first time, field evidence of complete, irreversible processing of solid calcium carbonate (calcite)-containing particles and quantitative formation of liquid calcium nitrate particles apparently as a result of heterogeneous reaction of calcium carbonate-containing mineral dust particles with gaseous nitric acid. Formation of nitrates from individual calcite and sea salt particles was followed as a function of time in aerosol samples collected at Shoresh, Israel. Morphology and compositional changes of individual particles were observed using conventional scanning electron microscopy with energy dispersive analysis of X-rays (SEM/EDX) and computer controlled SEM/EDX. Environmental scanning electron microscopy (ESEM) was utilized to determine and demonstrate the hygroscopic behavior of calcium nitrate particles found in some of the samples. Calcium nitrate particles are exceptionally hygroscopic and deliquesce even at very low relative humidity (RH) of 9-11% which is lower than typical atmospheric environments. Transformation of non-hygroscopic dry mineral dust particles into hygroscopic wet aerosol may have substantial impacts on light scattering properties, the ability to modify clouds and heterogeneous chemistry.
2005. "Heterogeneous Chemistry of Individual Mineral Dust Particles with Nitric Acid. A Combined CCSEM/EDX, ESEM AND ICP-MS Study." Journal of Geophysical Research. D. (Atmospheres) 110(D10):D10208. Abstract The heterogeneous chemistry of individual dust particles from four authentic dust samples with gas-phase nitric acid was investigated in this study. Morphology and compositional changes of individual particles as they react with nitric acid were observed using conventional scanning electron microscopy with energy dispersive analysis of X-rays (SEM/EDX) and computer controlled SEM/EDX. Environmental Scanning Electron Microscopy (ESEM) was utilized to investigate the hygroscopic behavior of mineral dust particles reacted with nitric acid. Differences in the reactivity of mineral dust particles from these four different dust source regions with nitric acid were observed. Mineral dust from source regions containing high levels of calcium, namely China loess dust and Saudi coastal dust, were found to react to the greatest extent.
2005. "Activation of Large Ions in FT-ICR Mass Spectrometry." Mass Spectrometry Reviews 24(2):135-167. Abstract The advent of soft ionization techniques, notably electrospray and laser desorption ionization methods, has enabled the extension of mass spectrometric methods to large molecules and molecular complexes. This both greatly extends the applications of mass spectrometry and makes the activation and dissociation of complex ions an integral part of these applications. This review emphasizes the most promising methods for activation and dissociation of complex ions and presents this discussion in the context of general knowledge of reaction kinetics and dynamics largely established for small ions. We then introduce the characteristic differences associated with the higher number of internal degrees of freedom and high density of states associated with molecular complexity. This is reflected primarily in the kinetics of unimolecular dissociation of complex ions, particularly their slow decay and the higher energy content required to induce decomposition-the kinetic shift (KS). The longer trapping time for Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) significantly reduces the KS, which presents several advantages over other methods for the investigation of dissociation of complex molecules.
2005. "Accurate ab initio predictions of ionization energies of hydrocarbon radicals: CH₂, CH₃, C₂H, C₂H₃, C₂H₅, C₃H₃, and C₃H₅." Journal of Chemical Physics 122:Article No. 224310. doi:10.1063/1.1926274 Abstract The abstract for this journal is not available at this time.
2005. "Atomic and Electronic Structure of the Fe₃O₄ (111)/MgO(111) Model Polar Oxide Interface." Physical Review. B, Condensed Matter 72(19):195401. doi:10.1103/PhysRevB.72.195401 Abstract High resolution transmission electron microscopy (HRTEM) and density functional calculations are used to study the effect of interface polarity on the atomic and electronic structure of the prototype Fe₃O₄(111)/MgO(111) polar oxide interface. We show that atomically abrupt interfaces exist between the MgO(111)-substrate and magnetite(111) film in regions separated by Fe nanocrystals, and propose a solution for this oxide-oxide interface structure. Comparisons of through-focus/through-thickness experimental HRTEM images with calculated images for model interface structures suggest metal-oxygen-metal (i.e., Mg-O-Fe) interface bonding with octahedral (B) coordination of the first Fe monolayer, rather than the combination of tetrahedral-octahedral-tetrahedral (ABA) stacking also found in Fe₃O₄. First-principles calculations for all the different models find metal-induced gap states in the interface oxygen layer. Consistent with the HRTEM results, the MgO-Fe₃O₄ interface stacking ...Mg/O/Mg/O/3FeB/O/FeAFeBFeA… is calculated to be the energetically most favorable, and effectively screening the MgO(111) substrate surface polarity. The data and calculations exclude mixing of Mg and Fe across the interface, in contrast to the commonly invoked mechanism of cation mixing at compound semiconductor polar interfaces.
2005. "Structural and Catalytic Properties of the Alkali Metal Ion-Exchanged Y-Zeolites by 29Si and 27Al Solid-State NMR and FT-IR Spectroscopy." Key Engineering Materials 277-279:708-719. Abstract A series of cation exchanged Y-zeolites were prepared by exchanging cations with various alkali (M+, M=Li, Na, K, Cs) metals. The structural and catalytic properties of the alkali metal exchanged Y-zeolites have been investigated by a number of analytical techniques. Comparative elemental analyses were determined by an Energy Dispersive Spectroscopy X-ray (EDS), X-ray Photoelectron Spectroscopy (XPS), Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) and X-ray Fluorescence (XRF) before and after cation substitution. The framework and non-framework Al coordination and the Si/Al ratios of the Y-zeolites were investigated by MAS Solid-State Nuclear Magnetic Resonance (NMR) spectroscopy. The Al NMR spectra were characterized by two 27Al resonance signals at 12 and 59 ppm, indicating the presence of the non-framework and framework Al respectively. The intensities of these resonances were used to monitor the amount of the framework and non-framework of Al species in the series of exchanged zeolites.
2005. "Physical and Catalytic Properties of the Na-exchanged Y-Zeolites with Different Si/Al Ratios." Key Engineering Materials 277-279:720-731. Abstract A series of sodium-exchanged Y-zeolites with different Si/Al ratios have been prepared from the proton and ammonium ion forms of Y-zeolite(faujasite) by means of a solution ion exchange. The prepared catalysts have been characterized by the various analytical techniques and the NOx conversion rates of the catalysts were measured with non-thermal plasma assisted catalytic system. Specific surface areas measured by the BET increased in the order of the NaY series 708, 712, 100, 720, 760. The results of the elemental analyses showed that the Si/Al ratio of the catalysts increased gradually in the order of NaY 100, NaY 712, NaY 720, NaY 760, NaY 780.
2005. "Simple Fabrication of a Highly Sensitive and Fast Glucose Biosensor using Enzyme Immobilized in Mesocellular Carbon Foam." Advanced Materials 17(23):2828-2833. Abstract We fabricated a highly sensitive and fast glucose biosensor by simply immobilizing glucose oxidase in mesocellular carbon foam. Due to its unique structure, the MSU-F-C enabled high enzyme loading without serious mass transfer limitation, resulting in high catalytic efficiency. As a result, the glucose biosensor fabricated with MSU-F-C/GOx showed a high sensitivity and fast response. Given these results and the inherent electrical conductivity, we anticipate that MSU-F-C will make a useful matrix for enzyme immobilization in various biocatalytic and electrobiocatalytic applications.
2005. "Surface SN2 Reaction by H₂O on Chlorinated Si(100)-2 x 1 Surface." Journal of Physical Chemistry B 109:10909-10914. doi:10.1021/jp0505983 Abstract No abstract available for this article at this time.
2005. "Preparation of a Magnetically Switchable Bioelectrocatalytic System Employing Cross-Linked Enzyme Aggregates in Magnetic Mesocellular Carbon Foam." Angewandte Chemie International Edition 44(45):7427-7432. doi:10.1002/anie.200502995 Abstract Nanostructured magnetic materials (NMMs)[1] have attracted much attention recently because of their broad biotechnological applications including support matrices for enzyme immobilization,[2] immunoassays,[3] drug delivery,[4] and biosensors.[ 5] Specifically, the easy separation and controlled placement of NMMs by means of an external magnetic field enables their application in the development of immobilized enzyme processes[2] and the construction of magnetically controllable bio-electrocatalytic systems.[5, 6] Herein, we demonstrate the use of immobilized enzymes in NMMs for magnetically switchable bio-electrocatalysis.
2005. "Simple Synthesis of Hierarchically Ordered Mesocellular Mesoporous Silica Materials Hosting Crosslinked Enzyme Aggregates." Small 1(7):744-753. Abstract : Hierarchically ordered mesocellular mesoporous silica materials (MMS) were synthesized using a single structure directing agent under neutral conditions for the first time. The mesocellular pores are synthesized without adding any pore expander, and the walls of cellular pores in MMS are composed of SBA-15 type mesopores. The small-angle X-ray scattering (SAXS) pattern of MMS revealed the presence of ordered pore structures with two different length scales. The current MMS possesses four different pore systems; complementary micro/mesopores, main 13 nm mesopores, 40 nm mesocellular spherical pores, and textural inter-particle macropores. Nanometer-scale enzyme reactors (NER) were developed in mesocellular mesoporous silica (MMS) via a ship-in-a-bottle approach, which employs adsorption of enzymes followed by cross-linking using glutaraldehyde (GA) treatment. The resulting NER show an impressive stability and activity with an extremely high loading of enzymes. For example, NER containing α-chymotrypsin (NER-CT) could hold 0.5 g CT in 1 g of silica, but the specific activity of NER-CT was 10.4 times higher than that of the adsorbed CT with a lower loading (0.07 g CT per 1 g of silica), which was further decreased by a continuous leaching of adsorbed CT. NER-CT showed excellent stability without any leaching, i.e. no activity decrease at all in a rigorously-shaking condition for two weeks (a half-life with 3.8 years), while the conventional adsorption method resulted in a half-life of 3.6 days in the same condition.
2005. "157 nm Pellicles (Thin Films) for Photolithography: Mechanistic Investigation of the VUV and UV-C Photolysis of Fluorocarbons." Journal of the American Chemical Society 127(23):8320-8337. doi:10.1021/ja0440654 Abstract The use of 157 nm as the next lower wavelength for photolithography for the production of semiconductors has created a need for transparent and radiation-durable polymers for use in soft pellicles, the polymer films which protect the chip from particle deposition. The most promising materials for pellicles are fluorinated polymers, but currently available fluorinated polymers undergo photodegradation and/or photodarkening upon long term exposure to 157 nm irradiation. To understand the mechanism of the photodegradation and photodarkening of fluorinated polymers, mechanistic studies on the photolysis of liquid model fluorocarbons, including perfluorobutylethyl ether and perfluoro-2 H-3-oxa-heptane, were performed employing UV, NMR, FTIR, GC, and GC/MS analyses. All hydrogen-containing compounds showed decreased photostability compared to the fully perfluorinated compounds. Irradiation in the presence of atmospheric oxygen showed reduced photostability compared to deoxygenated samples. Photolysis of the samples was performed at 157, 172, 185, and 254 nm and showed only minor wavelength dependence. Mechanisms for photodegradation of the fluorocarbons are proposed, which involve Rydberg excited states. Time-dependent density functional theory has been used to predict the excitation spectra of model compounds.
2005. "Synthesis and Characterization of Silver Hollandite and its Application in Emission Control." Chemistry of Materials 17(17):4335-4343. doi:10.1021/cm0506508 Abstract Silver hollandite, Ag1.8Mn8O16, has been synthesized by ion exchange of cryptomelane in AgNO3 melt. Compared to the previously described synthesis process, thermal decomposition of AgMnO4 at 970oC under 5 kbar oxygen for 7 days, this newly developed synthesis process is easily carried out, enabling synthesis of significant quantities for evaluation, testing, and scale up. Silver hollandite prepared by this new method has much smaller crystal size and thus much higher surface area compared with the previously available material. Application of silver hollandite for emission control has been examined. This material is an excellent low temperature SO2 absorbent as well as a highly active catalyst for CO and NO oxidation. Silver-hollandite maintains its catalytic oxidation activity even while it is simultaneously aging by adsorption of SO2.
2005. "Probing the Electronic Structure of Mono-Nitrogen Doped Aluminum Clusters Using Anion Photoelectron Spectroscopy." European Physical Journal. D, Atomic, molecular and optical physics. 34(1-3):9-14. Abstract We report a photoelectron spectroscopic investigation of mono-nitrogen doped aluminum cluster anions AlnN− (n = 2−22). Well-resolved spectra were obtained at three photon energies (355, 266, and 193 nm), revealing the structural and electronic evolution as the number of aluminum atoms increases in the doped clusters. For small AlnN (n < 9) clusters, the Al atoms may be viewed to be monovalent, similar to pure aluminum clusters. Even-odd alternation of the electron affinities was observed for AlnN clusters, suggesting that neutral clusters with odd n are closed shell and those with even n are open shell. The most interesting observation is the similarity between the spectra of AlnN− and Al−( n−1) for n > 12. This observation suggests that these clusters can be described as (AlN)Al−(n−1), i.e., an AlN unit weakly interacting with Al−(n−1) clusters. The electronic and atomic structural implications of this observation are discussed.
2005. "Magnetic Properties in Transition-Metal-Doped Gold Clusters: M@Au6 (M=Ti, V, Cr)." Physical Review Letters 95(25):253401-1 - 253401-4. doi:10.1103/PhysRevLett.95.253401 Abstract The electronic structure and magnetic properties in a series of transition-metal-doped Au clusters, MAu6_ (M _ Ti;V; Cr), are investigated experimentally using photoelectron spectroscopy (PES) and density functional calculations. PES features due to the impurity atoms and the Au6 host are clearly observed. It is found that all the MAu6_ and MAu6 clusters possess a planar structure, in which the transition metal atom is located in the center of an Au6 ring and carries large magnetic moments (2, 3, and 4 _B for MAu6, M _ Ti, V, and Cr, respectively).
2005. "Gold as Hydrogen, An Experimental and Theoretical Study of the Structures and Bonding in Disilicon Gold Clusters Si2Aun- and Si2Aun (n=2 and 4) and Comparisons to Si2H2 and Si2H4." Journal of Physical Chemistry A 109(19):4366-4374. Abstract In a previous communication, we showed that a single Au atom behaves like H in its bonding to Si in a series of Si-Au clusters, SiAun (n=2-4) (Kiran et al. Angew. Chem., Int. Ed. 2004, 43, 2125). In this article, we show that the H analogy of Au is more general. We find that the chemical bonding and potential energy surfaces of two disilicon Au clusters, Si2Au2 and Si2Au4, are analogous to Si2Au2 and Si2Au4, respectively. Photoelectron spectroscopy and ab initio calculations are used to investigate the geometrical and electronic structures of Si2Au-2, Si2Au-4, and their neutral species. The most stable structures for both Si2Au2 and Si2Au-2 are found to be C2v, in which each Au bridges the two Si atoms. For Si2Au-4, two nearly degenerate dibridged structures in a cis (C2h) and a trans (C2v) configuration are found to be the most stable isomers. However, in the neural potential energy surface of Si2Au4, a monobridged isomer is the global minimum. The ground-state structures of Si2Au-2, Si2Au-4 are confirmed by comparing the computed vertical detachment energies with the experimental data. The various stable isomers found for Si2Au2 and Si2Au4 are similar to those known for Si2H2 and Si2H4, respectively. Geometrical and electronic structure comparisons with the corresponding silicon hydrides are made to further establish the isolobal analogy between a gold atom and a hydrogen atom.
2005. "Reactions of Laser-Ablated Uranium Atoms with H₂O in Excess Argon: A Matrix Infrared and Relativistic DFT Investigation of Uranium Oxyhydrides ." Inorganic Chemistry 44(7):2159-2168. doi:10.1021/ic0483951 Abstract Laser-ablated U atoms react with H₂O during condensation in excess argon. Infrared absorptions at 1416.3, 1377.1, and 859.4 cm⁻¹ are assigned to symmetric H-U-H, antisymmtric H-U-H, and U=O stretching vibrations of the primary reaction product H₂UO. Uranium monoxide, UO, also formed in the reaction, inserts into H₂O to produce HUO(OH), which absorbs at 1370.5, 834.3, and 575.7 cm⁻¹. The HUO(OH) uranium(IV) product undergoes ultraviolet photoisomerization to a more stable H₂UO₂ uranium(VI) molecule, which absorbs at 1406.4 and 885.9 cm⁻¹. The addition of another water molecule to either HUO(OH) or H₂UO₂ produces H₂UO(OH)₂. Several of these species, particularly H₂UO₂, appear to form Ar coordinated complexes. The predicted vibrational frequencies, relative absorption intensities, and isotopic shifts from relativistic DFT calculations are in good agreement with observed spectra, which further support the identification of novel uranium oxyhydrides from matrix infrared spectra.
2005. "Catalytic Adsorptive Stripping Determination of Trace Chromium (VI) at Bismuth Film Electrodes." Talanta 65(1):144-148. Abstract A sensitive adsorptive stripping voltammetric protocol at a bismuth film electrode for trace measurements of chromium (VI) in the presence of diethylenetriammine pentaacetic acid (DTPA) is described. The new protocol is based on accumulation of the Cr-DTPA complex at a preplated bismuth film electrode held at –0.80V, followed a negatively-going square-wave voltammetric waveform. Factors influencing the stripping performance including the film preparation, solution pH, DTPA concentration, deposition potential and deposition time, have been optimized. The resulting performance compares well with that observed for analogous measurements at mercury film electrodes. A preconcentration time of 2 min results in a detection limit of 0.3 nM Cr(VI) and a relative standard deviation at 20 nM of 5.1% (n=25). Applicability to river water samples is demonstrated. The attractive behavior of the new “mercury-free” chromium sensor holds great promise for on-site environmental and industrial monitoring of chromium (VI).
2005. "Adsorptive Stripping Voltammetric Measurements of Trace Uranium at the Bismuth Film Electrode." Analytica Chimica Acta 535(1-2):9-13. Abstract Bismuth-coated carbon-fiber electrodes have been successfully applied for adsorptive-stripping voltammetric measurements of trace uranium in the presence of cupferron. The new protocol is based on the accumulation of the uranium-cupferron complex at a preplated bismuth film electrode held at –0.30 V (vs. Ag/AgCl), followed by a negatively-sweeping square-wave voltammetric waveform. Factors influencing the stripping performance, including the film preparation, solution pH, cupferron concentration, adsorption potential and time have been optimized. The resulting performance compares well with that observed for analogous measurements at mercury film electrodes. A detection limit of 0.3 g/L is obtained in connection to a 10 min adsorption time. The response is linear up to 50 g/L and the relative standard deviation at 50 g/L uranium is 3.8% (n=10; 2 min adsorption). Potential interferences are examined. Applicability to sea water samples is demonstrated. The attractive behavior of the new “mercury-free” uranium sensor holds great promise for on-site environmental and industrial monitoring of uranium.
2005. "Novel Hybrid Materials with High Stability for Electrically Switched Ion Exchange: Carbon Nanotubes/Polyaniline/Nickel Hexacyanoferrate Nanocomposites." Chemical Communications (17):2226-2228. doi:10.1039/b500417a Abstract A novel and stable carbon nanotubes /polyaniline /nickel hexacyanoferrates composite film has been synthesized with electrodeposition method, and the possibility for removing cesium through an electrically switched ion exchange has been evaluated in a mixture containing NaNO3 and CsNO3.
2005. "Incorporation of Hydroxypyridinone (HOPO) Ligands into Self-Assembled Monolayers on Mesoporous Supports for Selective Actinide Sequestration." Environmental Science and Technology 39(5):1332-1337. doi:10.1021/es049169t Abstract In this study, three isomers of hydroxypyridinones, 1,2-HOPO, 3,2-HOPO, and 3,4-HOPO, were attached to self-assembled monolayers on mesoporous silica. (SAMMS). The HOPO-SAMMS materials have superior solid adsorbents properties: they do not suffer from solvent swelling, their rigid, open pore structure allow rapid sorption kinetics, their extremely high surface area enables the installation of high functional density, and being silica-based they are compatible with vitrification into a final glasseous waste form. Kinetics, equilibrium, and selectivity of the adsorptions of actinide on the HOPO-SAMMS at various pHs, and in the presences of other metal cations, anions and competing ligands are reported. Rapid sequestration of U (VI), Np (V) and Pu (IV) was observed. Very little competition from transition metal cations and common species was observed.
2005. "Carbon Nanotubes (CNTs) for the Development of Electrochemical Biosensors ." Frontiers in Bioscience 10(1):492-505. Abstract Carbon nanotube (CNT) is a very attractive material for the development of biosensors because of its capability to provide strong electrocatalytic activity and minimize surface fouling of the sensors. This article reviews our recent developments of oxidase- and dehydrogenase-amperometric biosensors based on the immobilization of CNTs, the co-immobilization of enzymes on the CNTs/Nafion or the CNT/Teflon composite materials, or the attachment of enzymes on the controlled-density aligned CNT-nanoelectrode arrays. The excellent electrocatalytic activities of the CNTs on the redox reactions of hydrogen peroxide, nicotinamide adenine dinucleotide (NADH), and homocysteine have been demonstrated. Successful applications of the CNT-based biosensors reviewed herein include the low-potential detections of glucose, organophosphorus compounds, and alcohol.
2005. "Low–potential Amperometric Determination of Hydrogen Peroxide with a Carbon Paste Electrode Modified with Nanostructured Cryptomelane-type Manganese Oxides." Electrochemistry Communications 7(2):166-172. Abstract Nanostructured cryptomelane-type manganese oxides were synthesized, characterized, and evaluated for chemical sensing. Cryptomelane -type manganese oxides are nanofibrous crystals with sub-nanometer open tunnels that provide a unique property for sensing applications. Carbon paste electrodes (CPEs), modified with the nanostructured cryptomelane-type manganese oxides, were investigated for amperometric detection of hydrogen peroxide. With an operating potential of +0.3 V versus Ag/AgCl, H2O2 produces catalytic oxidation currents at the modified CPE, which can be exploited for quantitative determinations. The amperometric signals are linearly proportional to H2O2 concentration in the range 1.0×10-4 ~ 6.9×10-4 M with a correlation coefficient of 0.995 (n = 7). At a signal-to-noise ratio of 3, a detection limit of 2 M can be observed for the carbon paste electrode modified with 5.5 wt% cryptomelane-type manganese oxides. In addition, the sensor has a good stability and reproducibility. The construction and renewal are simple and inexpensive. A possible response mechanism was proposed and discussed. The significant electrocatalytic activity of the modified CPE may result from the nanostructure of cryptomelane-type manganese oxides.
2005. "Electrocatalytic Reactivity for Oxygen Reduction of Palladium-Modified Carbon Nanotubes Synthesized in Supercritical Fluid." Electrochemistry Communications 7(3):267-274. Abstract The electrocatalytic reactivity of palladium-modified carbon nanotubes (Pd-CNTs) for the oxygen reduction reaction (ORR) was investigated at the glassy carbon electrode surface in 1 M H2SO4 saturated by oxygen. Carbon nanotubes modified by palladium nanoparticles were synthesized in supercritical carbon dioxide and characterized by transmission electron micrograph. The electrocatalytic activity of the CNTs film and Pd–CNTs film toward oxygen reduction was studied using cyclic voltammetry and linear sweep voltammetry methods. The molecular oxygen reduction at the Pd-CNTs electrode started at a more positive potential than that at the CNTs electrode. A possible reaction mechanism was proposed in which the ORR may proceed through two-step two-electron processes for the Pd-CNTs modified electrode. Experimental results revealed that Pd-CNTs possess a remarkable activity and high stability for oxygen reduction in acid medium, which implies the potential applications of the Pd–CNTs for constructing electrodes of fuel cells.
2005. "Platinum/Carbon Nanotube Nanocomposite Synthesized in Supercritical Fluid as Electrocatalysts for Low-Temperature Fuel Cells." Journal of Physical Chemistry B 109(30):14410-14415. Abstract Carbon nanotube (CNT)-supported Pt nanoparticles catalysts have been synthesized in supercritical carbon dioxide (scCO2) using platinum (II) acetylacetonate as metal precursor. The structure of the catalysts has been characterized with transmission electron micrograph (TEM) and X-ray photoelectron spectroscopy (XPS). TEM images show that platinum particles size is in the range of 5-10nm. XPS analysis indicates the presence of zero-valence platinum. The Pt-CNT exhibited high catalytic activity both for methanol oxidation and oxygen reduction reaction. The higher catalytic activity has been attributed to the large surface area of carbon nanotubes and the decrease in the overpotential for methanol oxidation and oxygen reduction reaction. Cyclic voltammetric measurements at different scan rates showed that the oxygen reduction reaction at the Pt-CNT electrode is a diffusion-controlled process. Analysis of the electrode kinetics using Tafel plot suggests that Pt-CNT from scCO2 provides a strong electrocatalytic activity for oxygen reduction reaction. For the methanol oxidation reaction, a high ratio of forward anodic peak current to reverse anodic peak current was observed at room temperature, which implies good oxidation of methanol to carbon dioxide on the Pt-CNT electrode. This work demonstrates that Pt-CNT nanocomposites synthesized in supercritical carbon dioxide are effective electrocatalysts for low-temperature fuel cells.
2005. "PtRu/Carbon Nanotube Nanocomposite Synthesized in Supercritical Fluid: A Novel Electrocatalyst for Direct Methanol Fuel Cell." Langmuir 21(24):11474-11479. Abstract This manuscript describes a novel approach for synthesis of Pt-Ru/CNTs nanocomposites in supercritical fluid and demonstrated that Pt-Ru/CNTs nanocomposites synthesized in supercritical fluid are effective electrocatalysts for direct methanol fuel cells.
2005. "Nernatic Solvation of Segmented Polymer Chains." Nano Letters 5(9):1757-1760. doi:10.1021/nl051108l Abstract We examine the effect of polymer chain segmentation on the recently discovered ability of nematic solvents to elongate and align polymer chain solutes. Coordinated single molecule spectroscopy and beads-on-a-chain simulations are used to study the orientational and conformational order of a series of segmented conjugated polymers, dissolved in the nematic liquid crystal, 5CB. The order parameters for alignment and elongation are both observed to decrease with increasing segmentation, reflecting an interplay among conformational entropy, solvation anisotropy, and bending energy of the polymer chain.
2005. "A Renewable Electrochemical Magnetic Immunosensor Based on Gold Nanoparticle Labels." Journal of Nanoscience and Nanotechnology 5(7):1060-1065. Abstract A particle-based renewable electrochemical magnetic immunosensor was developed by using magnetic beads and a gold nanoparticle label. Anti-IgG antibody-modified magnetic beads were attached to a renewable carbon paste transducer surface by magnets that were fixed inside the sensor. A gold nanoparticle label was capsulated to the surface of magnetic beads by sandwich immunoassay. Highly sensitive electrochemical stripping analysis offers a simple and fast method to quantify the capatured gold nanoparticle tracer and avoid the use of an enzyme label and substrate. The stripping signal of gold nanoparticle is related to the concentration of target IgG in the sample solution. A transmission electron microscopy image shows that the gold nanoparticles were successfully capsulated to the surface of magnetic beads through sandwich immunoreaction events. The parameters of immunoassay, including the loading of magnetic beads, the amount of gold nanoparticle conjugate, and the immunoreaction time, were optimized. The detection limit of 0.02 μg ml-1of IgG was obtained under optimum experimental conditions. Such particle-based electrochemical magnetic immunosensors could be readily used for simultaneous parallel detection of multiple proteins by using multiple inorganic metal nanoparticle tracers and are expected to open new opportunities for disease diagnostics and biosecurity.
2005. "Electrochemical Sensor for Organophosphate Pesticides and Nerve Agents Using Zirconia Nanoparticles as Selective Sorbents ." Analytical Chemistry 77(18):5894-5901. Abstract Electrochemical sensor for detection of organophosphate (OP) pesticides and nerve agents using zirconia (ZrO2) nanoparticles as selective sorbents is presented. Zirconia nanoparticles were electrodynamically deposited onto the polycrystalline gold electrode by cyclic voltammetry. Because of a strong affinity of zirconia to the phosphoric group, nitroaromatic OPs strongly bind to the ZrO2 nanoparticle surface. The electrochemical characterization and anodic stripping voltammetric performance of bound OPs were evaluated using cyclic voltammetric and square-wave voltammetric (SWV) analysis. SWV was used to monitor the amount of bound OPs and provide simple, fast, and facile quantitative methods for nitroaromatic OP compounds. The sensor surface can be regenerated by successively running SWV scanning. Operational parameters, including the amount of nanoparticles, adsorption time, and the pH of the reaction medium have been optimized. The stripping voltammetric response is highly linear over the 5–200ng/mL (ppb) methyl parathion range examined (2-min adsorption), with a detection limit of 1 ng/mL (10 min accumulation), and good precision (RSD=5.3 %, n = 10). The promising stripping voltammetric performances open new opportunities for fast, simple, and sensitive analyzing of OPs in environmental and biological samples. These findings can lead to a widespread use of electrochemical sensors to detect OP contaminates.
2005. "Electrochemical Stripping Analysis of Organophosphate Pesticides and Nerve Agents." Electrochemistry Communications 7(4):339-343. Abstract A sensitive electrochemical stripping voltammetric method for analyzing organophosphate (OP) compounds was developed using a carbon paste electrochemical (CPE) transducer. OPs strongly adsorb on a CPE surface and provide facile electrochemical quantitative methods for electroactive OP compounds. Operational parameters have been optimized, and the stripping voltammetric performance has been studied using square wave voltammetry. The adsorptive stripping voltammetric response is highly linear over the 1-60 mol/L methyl parathion range examined (2-min adsorption), with a detection limit of 0.05 u mol/L (10 min accumulation) and good precision (RSD=3.2%, n =10). These findings can lead to a widespread use of electrochemical sensors to detect OP contaminates.
2005. "Sequential Injection/Electrochemical Immunoassay for Quantifying the Pesticide Metabolite 3, 5, 6-Trichloro-2-Pyridinol." Electrochemistry Communications 7(12):1463-1470. Abstract An automated and sensitive sequential injection electrochemical immunoassay was developed to monitor a potential insecticide biomarker, 3, 5, 6-trichloro-2-pyridinol. The current method involved a sequential injection analysis (SIA) system equipped with a thin-layer electrochemical flow cell and permanent magnet, which was used to fix 3,5,6-trichloro-2-pyridinol (TCP) antibody coated magnetic beads (TCP-Ab-MBs) in the reaction zone. After competitive immunoreactions among TCP-Ab-MBs, TCP analyte, and horseradish peroxidase (HRP) labeled TCP, a 3, 3’, 5, 5’-tetramethylbenzidine dihydrochloride and hydrogen peroxide (TMB-H2O2) substrate solution was injected to produce an electroactive enzymatic product. The activity of HRP tracers was monitored by a square wave voltammetric scanning electroactive enzymatic product in the thin-layer flow cell. The voltammetric characteristics of the substrate and the enzymatic product were investigated under batch conditions, and the parameters of the immunoassay were optimized in the SIA system. Under the optimal conditions, the system was used to measure as low as 6 ng L-1 (ppt) TCP, which is around 50-fold lower than the value indicated by the manufacturer of the TCP RaPID Assay® kit (0.25 ug/L, colorimetric detection). The performance of the developed immunoassay system was successfully evaluated on tap water and river water samples spiked with TCP. This technique could be readily used for detecting other environmental contaminants by developing specific antibodies against contaminants and is expected to open new opportunities for environmental and biological monitoring.
2005. "Sensitive Electrochemical Detection of Enzymatically-generated Thiocholine at Carbon Nanotube Modified Glassy Carbon Electrode." Electrochemistry Communications 7(11):1163-1169. Abstract A carbon nanotube modified glassy-carbon (CNT/GC) electrode was used for enhancing the sensitivity of electrochemical measurements of enzymatically-generated thiocholine. Cyclic voltammetric and amperometric characteristics of thiocholine at CNT/GC, glassy carbon, carbon paste, and gold electrodes were compared. The CNT layer leads to a greatly improved anodic detection of enzymatically generated thiocholine product including lower oxidation overpotential (0.15 V) and higher sensitivity because of its electrocatalytic activity, fast electron transfer and large surface area. The sensor performance was optimized with respect to the operating conditions. Under the optimal batch conditions, a detection limit of 5 ×10 -6 mol/L was obtained with good precision (RSD = 5.2%, n=10). Furthermore, the attractive response of thiocholine on a CNT/GC electrode has allowed it to be used for constant-potential flow injection analysis. The detection limit was greatly improved to 0.3 ×10-6 mol/L. The high sensitivity electrochemical detection of enzymatically generated thiocholine with a CNT sensing platform holds great promise to prepare an acetylcholinesterase biosensor for monitoring organophosphate pesticides and nerve agents.
2005. "Enzyme Nanoparticles-Based Electronic Biosensor." Chemical Communications 2005(27):3481-3483. doi:10.1039/b504943a Abstract A novel method for fabricating electronic biosensors based on coupling enzyme nanoparticles and self assembly technology is illustrated. Redox horseradish peroxidase nanoparticles were prepared by desolvation with ethanol and subsequent crosslinking with glutaraldehyde. The cross-linked enzyme nanoparticles were functionalized by cysteine to introduce thiol groups on the nanoparticle surface. Immobilized enzyme nanoparticle on the gold electrode by self-assembly kept redox and electrocatalytic activities, and was used to develop reagentless biosensors for H2O2 detection without promoters and mediators. The new approach is simple, low cost and circumvents complications associated with solution systems. It is a universal immobilization method for biosensor, biomedical devices, biofuel cells and enzymatic bioreactors fabrication and expected to open new opportunities for biosensor, clinical diagnostics, and for bioanalysis, in general.
2005. "Ultrasensitive Voltammetric Detection of Trace Heavy Metal Ions Using Carbon Nanotube Nanoelectrode Array." Analyst 130(7):1098-1101. doi:10.1039/b419447k Abstract We describe an ultrasensitive voltammetric detection of trace heavy metal ions using nanoelectrode arrays (NEAs) that are based on low-site density carbon nanotubes (CNTs). The NEAs were prepared by sealing the side-walls of CNTs with an epoxy passive layer that reduces the current leakage and eliminates the electrode capacitance, leading to a low background current. This provides a high signal-to-noise ratio. The CNTs-NEAs coated with a bismuth film were used successfully for voltammetric detection of trace cadmium and lead (II) at the sub-ppb level. The detection limit of 0.04 g/L was obtained under optimum experimental conditions. The attractive behavior of the new carbon NEA sensing platform holds great promise for onsite environmental monitoring and biomonitoring of toxic metals.
2005. "A New Mechanism for the Production of Highly Vibrationally Excited OH in the Mesosphere: An AB Initio Study of the Reactions of O-2(A (3)Sigma(+)(u) and A ' (3)Delta(u))+H ." Journal of Chemical Physics 122(10):104315. doi:10.1063/1.1862233g Abstract In an attempt to explain the observed nightglow emission from OH(v=10) in the mesosphere that has the energy greater than the exothermicity of the H+O₃ reaction, potential energy surfaces were calculated for reactions of high lying electronic states of O₂(A ³ Σu+ and A' ³Δu) with atomic hydrogen H(²S) to produce the ground state products OH(²II)+O(³P). From collinear two-dimensional scans, several adiabatic and nonadiabatic pathways have been identified. Multiconfigurational single and double excitation configuration interaction calculations show that the adiabatic pathways on a ⁴Δ potential surface from O₂(A ' ³Δ)+H and a ⁴Σ⁺ potential surface from O₂(A ³Σ⁺u)+H are the most favorable, with the zero-point corrected barrier heights of as low as 0.191 and 0.182 eV, respectively, and the reactions are fast. The transition states for these pathways are collinear and early, and the reaction coordinate suggests that the potential energy release of ca. 3.8 eV (larger than the energy required to excite OH to v=10) is likely to favor high vibrational excitation.
2005. "Human Plasma N-Glycoproteome Analysis by Immunoaffinity Subtraction, Hydrazide Chemistry, and Mass Spectrometry." Journal of Proteome Research 4(6):2070-2080. Abstract The enormous complexity, wide dynamic range of relative protein abundance of interest (over 10 orders of magnitude), and tremendous heterogeneity (due to post-translational modifications, such as glycosylation) of the human blood plasma proteome severely challenges the capabilities of existing analytical methodologies. We describe here the comprehensive analysis of human plasma N-glycoproteins using the combination of immunoaffinity subtraction and glycoprotein capture to reduce both the protein concentration range and the overall sample complexity. Six high-abundance plasma proteins were simultaneously removed using a pre-packed, immobilized antibody column. N-linked glycoproteins were then captured from the depleted plasma using hydrazide resin, enzymatically digested, and the bound, N-linked glycopeptides were released using peptide-N-glycosidase F. Following strong cation exchange (SCX) fractionation, the deglycosylated peptides were analyzed by reversed-phase capillary liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). A total of 2140 different N-glycopeptides were confidently identified using stringent criteria, covering 371 non-redundant N-glycoproteins with the majority of them being extracellular or membrane proteins. The strategy significantly improved the detection, enabling the identification of a number of low-abundance proteins, exemplified by interleukin-1 receptor antagonist protein (~200 pg/mL), cathepsin L (~1 ng/mL), and transforming growth factor beta 1 (~2 ng/mL). A total of 712 N-glycosylation sites were identified and the confidence of these site identifications was further validated by accurate mass measurements using high resolution liquid chromatography coupled to Fourier transform ion cyclotron resonance mass spectrometry (LC-FTICR). This study provides the basis for future high-throughput measurements using the accurate mass and time tag approach.
2005. "Improved Proteome Coverage by Using High Efficiency Cysteinyl-peptide Enrichment: The Human Mammary Epithelial Cell Proteome." Proteomics 5(5):1263-1273. Abstract Automated multidimensional capillary liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been increasingly applied in various large scale proteome profiling efforts. However, comprehensive global proteome analysis remains technically challenging due to issues associated with sample complexity and dynamic range of protein abundances, which is particularly apparent in mammalian biological systems. We report here the application of a high efficiency cysteinyl-peptide enrichment (CPE) approach to the global proteome analysis of human mammary epithelial cells (HMECs) which significantly improved both sequence coverage of protein identifications and the overall proteome coverage. The cysteinyl-peptides were specifically enriched by using a thiol-specific covalent resin, fractionated by strong cation exchange chromatography, and subsequently analyzed by reversed-phase capillary LC-MS/MS. An HMEC tryptic digest without CPE was also fractionated and analyzed under the same conditions for comparison. The combined analyses of HMEC tryptic digests with and without CPE resulted in a total of 14,416 confidently identified peptides covering 4,294 different proteims with an estimated 10% gene coverage of the human geome. By using the high efficiency CPE, an additional 1,096 relatively low abundance proteins were identified, resulting in 34.3% increase in proteome coverage; 1,390 protems were observed with increased sequence coverage. Comparative protein distribution analyses revealed that the CPE method is not biased by protein molecular weight, pI, gene location, cellular location, or bioloical functions. These results demonstrate that the use of the CPE approach provides improved efficiency in comprehensive proteome-wide analyses of highly complex mammalian biological systems.
2005. "Probing Single-Molecule Protein Conformational Dynamics." Accounts of Chemical Research 38(7):557-565. Abstract Protein conformational fluctuations and dynamics, often associated with static and dynamic inhomogeneities, play a crucial role in biomolecular functions. It is extremely difficult to characterize such spatially and temporally inhomogeneous dynamics in an ensemble-averaged measurement, especially when the proteins involve in a multiple-step and multiple-conformation complex chemical interactions and transformations, such as in enzymatic reactions, protein-protein interactions, protein-DNA interactions, and ion-channel membrane protein activities. Single-molecule spectroscopy is a powerful approach to analyze protein conformational dynamics under physiological conditions, providing dynamic perspectives on a molecular-level understanding of protein structure-function mechanisms.
2005. "Site-Specific Raman Spectroscopy and Chemical Dynamics of Nanoscale Interstitial Systems." Journal of Physics. Condensed matter 17(7):R333-R355. doi:10.1088/0953-8984/17/7/R02 Abstract Site-specific spectroscopy is critical for a molecular-level understanding of the mechanisms and dynamics of the inhomogeneous chemical processes crucial for catalysis, surface and interfacial chemistry, and membrane protein dynamics in living cells. Surface enhanced Raman scattering (SERS) spectroscopy and microscopy combined with atomic force microscopy (AFM) using metal-coated AFM tips have proven to be powerful in spectroscopic analysis of inhomogeneous processes, providing correlated topographic and spectroscopic information from nanoscale-specific sites under highly heterogeneous environments. It has been recently observed that SERS spectral fluctuations are pertinent to the site-specific spectroscopy and microscopy.
2005. "Monte Carlo Simulation of the Spatial Distribution of Energy Deposition for an Electron Microbeam." Radiation Research 163(4):468-472. Abstract Dosimetry calcutions characterizing the spatial variation of the energy deposited by the slowing and stopping of energetic are reported and compared with experimental measurements from an electron microbeam facility. The computations involve event-by-event, detailed-histories Monte Carlo simulations of low-energy electrons interacting in water vapor. Simulations of electron tracks with starting energies from 30 to 80 keV are used to determine energy deposition distributions in thin cylindrical rings as a function of penetration and radial distance from a beam source. Experimental measurements of the spatial distribution of an electron microbeam in air show general agreement with the density-scaled simulation results for water vapor at these energies, yielding increased confidence in the predictions of Monte Carlo track-structure simulations for applications of the microbeam as a single-cell irradiator.
2005. "Formation and Characterization of Thorium Methylidene CH₂=ThHXComplexes." Inorganic Chemistry 44(23):8610-8616. doi:10.1021/ic051153w Abstract The abstract for this journal article is not available at this time.
2005. "Formation of Epitaxial Oxide Nanodots on Oxide Substrate: Cu₂O on SrTiO₃(100)." Surface Science 589(1-3):120-128. Abstract X-ray photoelectron spectroscopy analysis during the oxygen plasma assisted molecular beam epitaxy, combined with atomic force microscopy, scanning Auger microscopy, and theoretical simulation studies have been used to evaluate the mechanism of single-phase Cu₂O nanodot formation on the SrTiO₃(100) surface. Formation of pure crystalline Cu₂O nanodots occurs rather in a narrow growth parameter window, outside which a coexistence of the multiple phases has been observed. Cuprous oxide nanodots on the SrTiO₃(100) substrate follow a growth mechanism which differs significantly from the growth modes observed for the majority of semiconductor quantum dots. Growth starts without wetting layer formation with appearance of well-ordered truncated square-based nanodots at submonolayer coverages. At the initial stages of growth, the nanodot size is only weakly changes with coverage and exponentially scales with temperature. After reaching a critical, temperature dependent dot density (~ 10¹³ cm-² for 760 K growth temperature), growth of mid-sized nanoclusters starts through coalescence, which is eventually followed by large dome-shaped cluster formation at higher coverages. The coexistence of the different types of the clusters at high coverages results in a multi-modal distribution of sizes and shapes.
