Scientific Publications 2008
2008. "PowerSlicing to determine fluorescence lifetimes of water-soluble organic matter derived from soils, plant biomass, and animal manures." Analytical and Bioanalytical Chemistry 390(8):2189-2194. doi:10.1007/s00216-008-1963-6 Abstract Time-resolved fluorescence spectroscopy was used to characterize water-soluble organic matter (WSOM) which plays an important role in soil ecosystem processes. WSOM was extracted from plant biomass, animal manures, and soils from controlled cropping systems studies with known histories of organic amendments. Lifetime constants were derived using the multi-way PowerSlicing method which provides a non-iterative, multi-exponential fitting of decay profiles. The lifetimes obtained by PowerSlicing were not significantly different from those obtained using the traditional discrete components analysis. The three components attributed to WSOM had lifetimes of 0.38± 0.14, 2.11±0.72, and 7.08±1.18 ns which are in agreement with previous lifetimes reported for humic substances. This study provides further support for the new paradigm for the structure of soil organic matter where the organic matter is composed of low-molecular-weight components held together by hydrogen bonding and hydrophobic interactions.
2008. "Hole-mediated Photodecomposition of Trimehtyl Acetate on a TiO2(001) Anatase Epitaxial Thin Film Surface." Journal of Physical Chemistry C 112(50):20050-20056. doi:10.1021/jp8077997 Abstract Surfaces of titanium dioxide in both rutile and anatase polymorphs have attracted significant attention in catalysis and photochemistry. The (110) orientation of rutile, and to a lesser extent other rutile orientations, have been studied on an atomic scale, yielding information on surface structure and chemical reactivity. In contrast, the thermal and photochemistry of well-defined, single-crystal anatase surfaces had not been investigated, largely because of the metastable nature of anatase , as well as the lack of availability of high-quality surfaces. Here we describe a study of the adsorption and photoreactivity of an organic adlayer, trimethyl acetate (TMA), on structurally-excellent anatase (001) epitaxial thin films grown by oxygen plasma assisted molecular beam epitaxy (OPAMBE). High-resolution scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and photodesorption spectrometry have been used to study the chemisorptions and ultraviolet (UV) light-induced photodecomposition of TMA in ultrahigh vacuum. UV light promotes hole-mediated photodecomposition of TMA, resulting in decarboxylation to yield tert-butyl radical and CO2. The photochemical rate constant is equal to that measured for OPAMBE grown rutile TiO2(110) surfaces.
2008. "Superior Cardiac Function Via Anaplerotic Pyruvate in the ImmatureSwine Heart After Cardiopulmonary Bypass and Reperfusion." American Journal of Physiology. Heart and Circulatory Physiology 295(6):H2315-H2320. doi:10.1152/ajpheart.00739.2008 Abstract Pyruvate produces inotropic responses in the adult reperfused heart. Pyruvate oxidation and anaplerotic entry into the citric acid cycle (CAC) via carboxylation are linked to stimulation of contractile function. The goals of this study were to determine if these metabolic pathways operate and are maintained in the developing myocardium after reperfusion. Immature male swine (age 10-18 days) were subjected to cardiopulmonary bypass (CPB). Intracoronary infusion of -13C-pyruvate (to achieve a final concentration of 8 mM) was given for 35 minutes starting either during weaning (Group I), after discontinuation (Group II) or without (Control) CPB. Hemodynamic data was collected. 13C NMR spectroscopy was used to determine the fraction of pyruvate entering the CAC via pyruvate carboxylation (PC) to total CAC entry (PC plus decarboxlyation via pyruvate dehydrogenase). Liquid chromatography-mass spectrometry was used to determine total glutamate enrichment.
2008. "NOx Reduction on a Transition Metal-free γ-Al2O3 Catalyst Using Dimethylether (DME)." Catalysis Today 136(1-2):46-54. Abstract NO2 and dimethylether (DME) adsorption as well as DME and NO2 coadsorption on a transition metal-free γ-alumina catalyst were investigated via in-situ transmission Fourier transform infrared spectroscopy (in-situ FTIR), residual gas analysis (RGA) and temperature programmed desorption (TPD) techniques. NO2 adsorption at room temperature leads to the formation of surface nitrates and nitrites. DME adsorption on the alumina surface at 300 K leads to molecularly adsorbed DME, molecularly adsorbed methanol and surface methoxides. Upon heating the DME-exposed alumina to 500-600 K the surface is dominated by methoxide groups. At higher temperatures methoxide groups are converted into formates. At T > 510 K formate decomposition takes place to form H2O(g) and CO(g). DME and NO2 coadsorption at 423 K do not indicate a significant reaction between DME and NO2. However, in similar experiments at 573 K, fast reaction occurs and the methoxides present at 573 K before the NO2 adsorption are converted into formates, simultaneously with the formation of isocyanates. Under these conditions, NCO can further be hydrolyzed into isocyanic acid or ammonia with the help of water which is generated during the formate formation, decomposition and/or NCO formation steps.