Scientific Publications 2004
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2004. "Solvation of the Azide Anion (N3-)in Water Clusters and Aqueous Interfaces: A Combined Investigation by Photoelectron Spectroscopy, Density Functional Calculations, and Molecular Dynamics Simulations." Journal of Physical Chemistry A 108(39):7820-7826. Abstract We report a photoelectron spectroscopy and computational study of hydrated N3- anion clusters, N3-(H2O)n (n=0-16), in the gas phase. Photoelectron spectra of the solvated azide anions were observed to consist of a single peak, similar to that of the bare N3-, but the spectral width was observed to broaden as a function of cluster size due to solvent relaxation upon electron detachment. The adiabatic and vertical electron detachment energies were measured as a function of solvent number. The measured electron binding energies indicate that the first four solvent molecules have much stronger interactions with the solute anion, forming the first solvation shell.
2004. "Direct Experimental Observation of the Low Ionization Potentials of Guanine in Free Oligonucleotides by Using Photoelectron Spectroscopy." Proceedings of the National Academy of Sciences of the United States of America 101(51):17588-17592. Abstract Photodetachment photoelectron spectroscopy is used to probe the electronic structure of mono-, di-, and trinucleotide anions in the gas phase. A weak and well defined threshold band was observed in the photoelectron spectrum of 2' -deoxyguanosine 5' -mono-phosphate at a much lower ionizztion energy than the other three mononucleotides. Density function theory calculations revealed that this unique spectral feature is caused by electron-detachment from a п orbital of the guanine base on 2’ –deoxyguanosine 5’ –monop0hosphate, whereas the lowest ionization channel for the other three mononucleotides takes place from the phosphate group. This low-energy feature was shown to be a “fingerprint” in all the spectra of dinucleotides and trinucleotides that contain the guanine base. The current experiment provides direct spectroscopic evidence that the guanine base is the site with the lowest ionization potential in oligonucleotides and DNA and is consistent with the fact that guanine is most susceptible to oxidation to give the guanine cation in DNA damage.
2004. "Solvent-Mediated Folding of a Doubly Charged Anion." Journal of the American Chemical Society 126(3):876-883. Abstract The microsolvation of suberate dianion, -O2C(CH2)6CO2-, with two separate charge centers was studied by photoelectron spectroscopy and molecular dynamics simulation one solvent molecule at a time for up to 20 waters.
2004. "Carbon Paste Electrode Modified with Carbamoylphosphonic Acid Functionalized Mesoporous Silica: A New Mercury-Free Sensor for Uranium Detection." Electroanalysis 16(10):870-873. Abstract This study reports a new approach for developing a uranium (U(VI)) electrochemical sensor that is mercury-free, solid-state, and has less chance for ligand depletion than existing sensors. A carbon-paste electrode modified with carbamoylphosphonic acid self-assembled monolayer on mesoporous silica was developed for uranium detection based on an adsorptive square-wave stripping votammetry technique. Voltammetric responses for U(VI) detection are reported as a function of pH, preconcentration time, and aqueous phase U(VI) concentration. The uranium detection limit is 25 ppb after 5 minutes preconcentration and improved to 1 ppb after 20 minutes preconcentration. The relative standard deviations are normally less than 5%.
2004. "Electrophilic Aromatic Substitutions of Amine and Sulfonate onto Fine-Grained Activated Carbon for Aqueous-Phase Metal Ion Removal ." Separation Science and Technology 39(14):3263-3279. Abstract This paper describes the synthesis and characterization of functionalized activated carbon. Evaluation of the activated carbon materials for metal removal from aqueous solution is also discussed.
2004. "Modification of SiO2 Nanowires with Metallic Nanocrystals from Supercritical CO2." Journal of Nanoscience and Nanotechnology 4(1/2):82-85. Abstract Through hydrogen reduction of metal precursors in supercritical CO2, Cu and Pd nanocrystals were deposited onto SiO2 nanowires (NWs) to form different types of nanostructured materials, including nanocrystal-NW, spherical aggregation-NW, shell-NW composites and “mesoporous” metals supported by the framework of NWs. This supercritical fluid deposition technique represents an attractive approach for modifying NWs because of its generality and simplicity and the modified NWs could be potentially useful as catalysts and for further fabrication of multifunctional composites.
2004. "Supercritical Fluid Synthesis and Characterization of Catalytic Metal Nanoparticles on Carbon Nanotubes." Journal of Materials Chemistry 14(5):908-913. Abstract A rapid, convenient and environmentally benign method has been developed for the fabrication of metal nanoparticlemultiwall carbon nanotube (MWCNT) composites. Nanoparticles of palladium, rhodium and ruthenium are deposited onto functionalized MWCNTs through a simple hydrogen reduction of metal--diketone precursors in supercritical carbon dioxide, and are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses. These highly dispersed nanoparticles, with a narrow range of size distribution and good adhesion on MWCNT surfaces, are expected to exhibit promising catalytic properties for a variety of chemical reactions. Preliminary experiments demonstrate that Pd nanoparticles supported on MWCNTs are effective catalysts for hydrogenation of olefins in carbon dioxide. The Pd nanoparticleMWCNT composite also shows a high electrocatalytic activity in oxygen reduction for potential fuel cell application.
