Scientific Publications 2006
2006. "Comparison of Analytical Techniques for Analysis of Arsenic Adsorbed on Carbon." Water Quality Research Journal of Canada 41(2):185-189. Abstract Activated carbon (AC) has been extensively used to remove trace metals, particularly arsenic, from water for a number of years. To date, attempts to quantify directly the concentration of arsenic in activated carbon using non-destructive methods have been limited. High-energy ion beam based particle induced X-ray emission (PIXE) is ideally suited to investigate the issues regarding the quantification of trace metals in solids. In this study, after the adsorption of arsenic on activated carbon, arsenic concentration in granular activated carbon (GAC) and powder activated carbon (PAC) were quantified using PIXE. The PIXE results were compared with atomic absorption spectrometry (AAS) and inductively coupled plasma (ICP) measurements. Some differences are observed between these measurements. The differences are greater in the case of GAC compared to PAC. These differences are mainly due to inhomogeneous structure of GAC and PAC, which includes the variable surface properties such as surface area and pore sizes in each granule or particle. The larger differences are mainly due to the increased particle dimensions of GAC compared to PAC and the nature of the internal pore structure of GAC, which results in different amount of arsenic adsorbed on different granules of GAC or even in different regions of one granule. This inhomogenity of arsenic concentration is clearly visible in the arsenic concentration map generated for a single GAC particle using microbeam PIXE.
2006. "Fluorophore-Assisted Light Inactivation of Calmodulin Involves Singlet-Oxygen Mediated Cross-Linking and Methionine Oxidation." Biochemistry 45(15):4736-4748. doi:10.1021/bi052395a Abstract Fluorophore-assisted light inactivation (FALI) can permit the targeted inactivation of tagged proteins and, when used with cell-permeable multiuse affinity probes (MAPs), offers important advantages in identifying physiological function, because targeted protein inactivation is possible with spatial and temporal control. However, reliable applications of FALI, also known as chromophore-assisted light inactivation (CALI) with fluorescein derivatives, have been limited by lack of mechanistic information regarding sensitive proteins. To permit the rational inactivation of targeted proteins we have identified the oxidizing species and the susceptibility of specific amino acids to modification using the calcium regulatory protein calmodulin (CaM) that, like many essential proteins, regulates signal transduction through the reversible association with a large number of target proteins. Following the covalent and rigid attachment of 4’,5’-bis (1,3,2-dithoarsolan-2-yl) fluorescein (FlAsH) to helix A, we have identified light-dependent oxidative modifications of endogenous methionines to their corresponding methionine sulfoxides. Initial rates of methionine oxidation correlate with surface accessibility and are insensitive to the distance between the bound fluorophore and individual methionines, which vary between ~7 and 40 Ǻ. In addition, we observed a rapid reaction of histidines, which results in selective cross-linking with binding partners corresponding to the CaM-binding sites of smooth myosin light chain kinase and ryanodine receptor. Our results provide a rationale for proteomic screens using FALI to inhibit the function of many signaling proteins, which, like CaM, commonly present methionines at binding interfaces. Likewise, properly placed histidines will permit the capture and identification of binding partners associated with protein complexes.
2006. "Phosphoproteome Profiling of Human Skin Fibroplast Cells in Response to Low- and High-Dose Irradiation ." Journal of Proteome Research 5(5):1252-1260. Abstract The biological effect of low-dose radiation is currently not well understood. A hallmark of the response to radiation is the phosphorylation of proteins involved in DNA repair, DNA damage signaling, and cell cycle checkpoint control, which is important in prompt cellular response. The objective of the work presented here was to explore the phosphoproteome of normal human skin fibroblast (HSF) cells to reveal differences between low- and high-dose irradiation responses at the protein phosphorylation level. Several techniques —Trizol extract of proteins, methylation of the enzyme digest (peptides), enrichment of phosphopeptides with immobilized metal affinity chromatography (IMAC), nanoflow reversed-phase HPLC (nano-LC)/electrospray ionization, and tandem mass spectrometry— were combined for analysis of the HSF cell phosphoproteome following low- and high-doses of irradiation. More than 95% of the peptides identified after IMAC enrichment were phosphopeptides. Among the 493 unique phosphopeptides, 232 were singly phosphorylated, 220 were doubly phosphorylated, and 41 were triply phosphorylated, indicating the overall effectiveness of the IMAC technique to enrich both singly and multiple phosphorylated peptides. Over 700 phosphorylation sites were assigned to a total of 346 proteins, many of which are known or proposed to be highly relevant to a plethora of fundamental biological processes. The profile for proteins identified from the low-dose (2cGy) irradiated HSF cells was shown to be different from the profile obtained for proteins irradiated at the high-dose (4 Gy). This type of fundamental information regarding radiation-response to cellular events at the molecular level provides a mechanistic basis for identifying relevant molecular markers that can be used in future to better evaluate human health risks at low doses of irradiation and to develop low dose radiation counter measurements.
2006. "Design and operating characteristics of a transient kinetic analysis catalysis reactor system employing in situ transmission Fourier transform infrared." Review of Scientific Instruments 77(9):Art. No. 094104. Abstract A novel apparatus for gas-phase heterogeneous catalysis kinetics is described. The apparatus enables fast isotopic transient kinetic analysis (ITKA) to be performed in which both the gaseous and adsorbed species inside the catalytic reactor are monitored simultaneously with rapid-scan transmission FTIR, and its gaseous effluent can be monitored by mass spectroscopy during rapidly switching of reagent gas streams. This enables a more powerful version of the well-known steady-state isotopic kinetic analysis (SSITKA) technique in which the vibrational spectra of the gas phase and adsorbed species are also probed: FTIR-SSITKA. Unique reactor characteristics include tungsten construction, liquid nitrogen cooling or heating (~200-700 K), fast reactor disassembly and reassembly, and catalyst loading in a common volume. The FTIR data acquisition rate of this apparatus (3 Hz) is 10-fold faster than previously reported instruments. A 95% signal decay time of ~3 seconds for gas switching was measured. Very good temperature reproducibility and uniformity (< ±3K) was observed by in-situ rotational temperature analysis, which allows accurate calibration of the reactor thermocouple to the reactor gas temperature. Finally, FTIR-SSITKA capabilities are demonstrated for CO2 isotope switching over a -alumina sample at 75 C, which reveal an adsorbed carbonate species with an average surface residence time of =148±5 seconds and a coverage of ~2.5x1015 molecules cm-2.
2006. "Defect Distribution and Dissolution Morphologies on Low-Index Surfaces of alpha-Quartz ." Geochimica et Cosmochimica Acta 70(5):1113-1127. doi:10.1016/j.gca.2005.11.019 Abstract The dissolution of prismatic and rhombohedral quartz surfaces by KOH/H2O solutions was investigated by atomic force microscopy. Rates of dissolution of different classes of surface features (e.g., steps, voids, dislocation etch pits) were measured. The prismatic surface etched almost two orders of magnitude faster than the rhombohedral surface, mostly due to the difference in the number and the rate of dissolution of extended defects, such as dislocations. Because of the presence of imperfect twin boundaries, defect densities on the prismatic surface were estimated at 50 – 100 µm2, whereas the rhombohedral surface possessed only ~0.5 – 1.0 µm2, mostly in the form of crystal voids. Crystal voids etched almost one order of magnitude faster on the prismatic surface than on the rhombohedral surface due to differences in the number and the density of steps formed by voids on the different surfaces. In the absence of extended defects, both surfaces underwent step-wise dissolution at similar rates. Average rates of step retreat were comparable on both surfaces (~3 – 5 nm/h on the prismatic surface and ~5 – 10 nm/h on the rhombohedral surface). Prolonged dissolution left the prismatic surface reshaped to a hill-and-valley morphology, whereas the rhombohedral surface dissolved to form coalescing arrays of oval-shaped etch pits.
2006. "Voltammetric Analysis of Europium at Screen-Printed Electrodes Modified with Salicylamide Self-Assembled on Mesoporous Silica." Analyst 131(12):1342-1346. doi:10.1039/b609211j Abstract Mercury-free sensors for europium (Eu3+) assay, based on chemical modification of screen-printed carbon electrodes (SPCEs), with self-assembled salicylamide ligands on mesoporous silica (Sal-SAMMS) have been developed. The preconcentration of Eu3+ at SAMMS-based sensors utilize the binding affinity between the salicylamide ligand and Eu3+, which can be accomplished at open circuit potential without electrolyte and solution degassing. This was followed by the anodic stripping voltammetric Eu detection in a new medium. Due to the strong covalent bonding of the functional groups on mesoporous silica, the SAMMS based sensors with a built-in 3-electrode system can be reused for tens of measurements with minimal degradation, enabling the establishment of the calibration curve and lowering the costs. Linear response was found in the range of 75 to at least 500 ppb Eu3+ after a 5 minute preconcentration period. The detection limit was 10 ppb after a 10 minute preconcentration, and this limit can be improved with increased preconcentration time. Reproducibility (%R.S.D) of 100 ppb Eu2+ was 10% for a single sensor (5 measurements) and 10% for 5 sensors. The reproducibility can be improved through the precision of manufacturing of the sensors, in which SAMMS modification can be done in situ, increasing the user-friendliness of the sensors.
2006. "Room Temperature Solvent-free Synthesis of Monodisperse Magnetite Nanocrystals." Journal of Nanoscience and Nanotechnology 6(3):852-856. doi:10.1166/jnn.2006.135 Abstract We have successfully demonstrated a facile, solvent-free synthesis of highly crystalline and monodisperse Fe3O4 nanocrystallites at ambient temperature avoiding any heating. Solid state reaction of inorganic Fe(II) and Fe(III) salts with NaOH was found to produce highly crystalline Fe3O4 nanoparticles. The reaction, if carried out in the presence of surfactant such as oleic acid-oleylamine adduct, generated monodisperse Fe3O4 nanocrystals extractable directly from the reaction mixture. The extracted nanoparticles were capable of forming self-assembled, two-dimensional and uniform periodic array. The new process utilizes inexpensive and nontoxic starting materials, and does not require a use of high boiling point and toxic solvents, thus is amenable to an environmentally desirable, large-scale synthesis of nanocrystals.
2006. "Reproducible Tip Fabrication and Cleaning for UHV STM ." Ultramicroscopy 108(9):873-877. doi:10.1016/j.ultramic.2008.02.010 Abstract Several technical modifications related to the fabrication and ultra-high vacuum (UHV) treatment of the tips have been implemented to improve a reliability of the tip preparation for high-resolution scanning tunneling microscopy. The widely used drop-off technique for the tip electrochemical etching has been further refined to enable a reproducible fabrication of the tungsten tips with a radius 3 nm. Simple and flexible setup for the tip UHV annealing has been developed and employed. The Ar ion sputtering with subsequent annealing has been adopted for a final tip treatment. The proper tip preparation has been demonstrated by imaging an atomic structure of the rutile TiO2(110) surface.