Scientific Publications 2006
2006. "Analysis of the Salmonella typhimurium Proteome through Environmental Response toward Infectious Conditions." Molecular & Cellular Proteomics. MCP 5(8):1450-1461. doi:10.1074/mcp.M600139-MCP200 Abstract Salmonella enterica serovar Typhimurium (aka, S. typhimurium) is a facultative intracellular pathogen that causes ~40,000 reported cases of acute gastroenteritis and diarrhea a year in the United States. To develop a deeper understanding of the infectious state of S. typhimurium, liquid chromatography-mass spectrometry-based “bottom-up” proteomics was used to globally analyze the proteins present under specific growth conditions. Salmonella typhimurium LT2 strain cells were grown in contrasting culture conditions that mimicked both natural free-living conditions and an infectious state, i.e., logarithm phase, stationary phase and Mg-depleted medium growth. Initial comparisons of the LT2 strain protein abundances among cell culture conditions indicate that the majority of proteins do not change significantly. Not unexpectedly, cells grown in Mg-depleted medium conditions had a higher abundance of Mg2+ transport proteins than found in other growth conditions. A second more virulent Salmonella typhimurium strain (14028) was also studied with these growth conditions and used to directly compare to the LT2 strain. The strain comparison offers a unique opportunity to compare and contrast observations in these closely related bacteria. One particular protein family, propanediol utilization proteins, was drastically more abundant in the 14028 strain than in the LT2 strain, and may be a contributor to increased pathogenicity in the 14028 strain.
2006. "All-Boron Aromatic Clusters as Potential New Inorganic Ligands and Building Blocks in Chemistry." Coordination Chemistry Reviews 250(21-22):2811-2866. Abstract Small boron clusters as individual species in the gas phase and incorporated into solids and molecules are reviewed. While the family of known boron compounds is rich and diverse, a large body of hitherto unknown chemistry of boron has been recently identified. Free boron clusters have been recently characterized using photoelectron spectroscopy and ab initio calculations, which established the planar or quasi-planar shapes of small boron clusters for the first time. The establishment of the planar structures of small boron clusters has surprised the scientific community, as the chemistry of boron has been diversely featured by three-dimensional structures. The planarity of the small boron clusters has been further elucidated on the basis of multiple aromaticity and antiaromaticicity. Although mostly observed in the gas phase, pure boron clusters are promising molecules for coordination chemistry as potential new ligands and for materials science as new building blocks. The use of pure boron species as novel ligands has commenced, suggesting many new chemistries are ahead of us. Experimental and theoretical endeavors regarding pure boron clusters as such and incorporated into molecules and crystals are reviewed herein. The new spectroscopic results, chemical bonding, multiple aromaticity and antiaromaticity, leading to their unique structures and stability, receive our particular attention.
2006. "Surface Degradation of As2S3 Thin Films." Physics and Chemistry of Glasses 47(6):681-687. Abstract Thin films of as-deposited As2S3 glass developed a white haze under ambient conditions. To study this surface degradation, we evaluated the effects of visible light, oxygen, humidity, and temperature. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to characterize the surface of these films. Results showed that As2S3 films simultaneously exposed to light and humidity formed arsenolite (As2O3) crystals on the film surface, correlating with the observed haze. A dry and dark environment is concluded to provide the best protection for storing As2S3 thin films. Additionally, a water vapor barrier layer was shown to inhibit degradation under typically corrosive conditions.
2006. "Soft-Landing of Peptides onto Self-Assembled Monolayer Surfaces." Journal of Physical Chemistry A 110(4):1678-1687. doi:10.1021/jp0555044 Abstract Mass-selected peptide ions produced by electrospray ionization were deposited as ions by soft-landing onto fluorinated and hydrogenated self-assembled monolayer surfaces (FSAM and HSAM) surfaces using a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially designed for studying interactions of large ions with surfaces. Analysis of the modified surface was performed in situ by combining 2 keV Cs+ secondary ion mass spectrometry with FT-ICR detection of the sputtered ions (FT-ICR-SIMS). Collision energy dependent data indicated that peptide fragmentation observed in Cs+ SIMS analysis of surfaces modified by soft landing occurred in the analysis step (SIMS) rather than during ion deposition. The peptide ion deposition efficiency showed a gradual decrease with increase in collision energy which parallels the decrease in the Langevin cross section with ion velocity at impact. Peptide ion soft-landing on FSAM surfaces gave twice the sputtered ion signal seen for hydrocarbon self-assembled monolayer (HSAM) surfaces. This indicates stronger interaction of peptide ions with the FSAM surface, in good agreement with larger polarizability of fluorinated hydrocarbons. The efficiency of soft landing of different peptides on the FSAM surface increases with the charge state of the ion, consistent with an ion-polarizable molecule model for the initial stage of soft landing on SAM surfaces.
2006. "Ferromagnetism in Ti-Doped ZnO Nanoclusters above Room Temperature." IEEE Transactions on Magnetics 42(10):2697-2699. doi:10.1109/TMAG.2006.879723 Abstract Ferromagnetism is observed at room temperature, when a small percentage (5%) of non-magnetic titanium is added to zinc atoms to form Ti-doped ZnO nanoclusters in the oxygen atmosphere. The nanocluster films are prepared at room temperature by a technique that is a combination of high pressure sputtering along with aggregation. A Super-conducting Quantum Interference Device (SQUID) measures the magnetic properties of this cluster films at various temperatures. Ti dopant exhibits +4 oxidation state through out the cluster film. Coercivity of the samples decreased exponentially with the increase of temperature.
2006. "Size dependent specific surface area of nanoporous film assembled by core-shell iron nanoclusters." Journal of Nanomaterials 2006(Special Issue 2):Art. No. 54961. doi:10.1155/JNM/2006/54961 Abstract Nanoporous films of core-shell iron nanoclusters have improved possibilities for remediation, chemical reactivity rate and environmentally favorable reaction pathways. Conventional methods often have difficulties to yield stable monodispersed core-shell nanoclusters. We produced core-shell clusters by a cluster source that utilizes combination of Fe target sputtering along with gas aggregations in an inert atmosphere at 7ºC. Sizes of core-shell iron-iron oxide nanoclusters are observed with transmission electron microscopy (TEM). The specific surface areas of the porous films obtained from Brunauer-Emmett-Teller (BET) process is size dependent and compared with the calculated data.
2006. "Synthesis and Characterization of Stable Iron–Iron Oxide Core–Shell Nanoclusters for Environmental Applications." Journal of Nanoscience and Nanotechnology 6(2):568-572. doi:10.1166/jnn.2006.074 Abstract Iron–iron oxide core–shell nanoclusters are of great interest due to their potential applications as a remedy for environmental contamination. We report the room-temperature synthesis of core–shell iron–iron oxide nanoclusters using our novel cluster deposition system. Various types of measurements such as Transmission Electron Microscopy, X-ray Diffraction, X-ray Photon Spectroscopy, and Electron Energy Loss Spectroscopy are conducted in characterizing nanoclusters. Stable, monodispersive iron–iron oxide core–shell nanocrystals are identified.
2006. "Magnesium inhibition of calcite dissolution kinetics." Geochimica et Cosmochimica Acta 70(3):583-594. Abstract We present evidence of inhibition of calcite dissolution by dissolved magnesium through direct observations of the (104) surface using atomic force microscopy (AFM) and vertical scanning interferometry (VSI). Far from equilibrium, the pattern of magnesium inhibition is dependent on solution composition and specific to surface step geometry. In CO2-free solutions (pH 8.8), dissolved magnesium brings about little inhibition even at concentrations of 0.8 x 10-3 molal. At the same pH, magnesium concentrations of less than 0.05 x 10-3 molal in carbonate-buffered solutions generate significant inhibition, although no changes in surface and etch pit morphology are observed. As concentrations exceed magnesite saturation, the dissolution rate shows little additional decrease; however, selective pinning of step edges results in unique etch-pit profiles, seen in both AFM and VSI datasets. Despite the decreases in step velocity, magnesium addition in carbonated solutions also appears to activate the surface by increasing the nucleation rate of new defects. These relationships suggest that the modest depression of the bulk rate measured by VSI reflects a balance between competing reaction mechanisms that simultaneously depress the rate through selective inhibition of step movement, but also enhance reactivity on terraces by lowering the energy barrier to new etch-pit formation.