2009. "Probing the Dynamics of a Protein Hydrophobic Core by Deutron Solid-State Nuclear Magnetic Resonance Spectroscopy ." Journal of the American Chemical Society 131(38):13651-13658. doi:10.1021/ja902977u Abstract With the goal of investigating dynamical features of hydrophobic cores of proteins over a wide range of temperatures, the villin headpiece subdomain protein (HP36) was labeled at a "single" site corresponding to any one of the two -C5D3 groups of Leucine-69, which is located in a key position of the core. The main techniques employed are deuteron NMR quadrupolar echo line shape analysis, and T1Z (Zeeman) and T1Q (Quadrupolar order) relaxation experiments performed at 11.7 and 17.6T over the temperature range of 112 to 298K. The experimental data are compared with computer simulations. The deuteron line shapes give an excellent fit to a three-mode motional model that consists of a) fast 3-site rotational jumps about the pseudo C3 methyl spinning axis, b) slower reorientation of the spinning axis, described by diffusion along a restricted arc and c) large angle jumps between traces of rotameric conformers. Relaxation behavior is described by a phenomenological distribution of activation energies for 3-site hops at high temperatures that collapses to a single, distinctly smaller value for lower temperatures.
2009. "Absolute integrated intensities of vapor-phase hydrogen peroxide (H202) in the mid-infrared at atmospheric pressure." Analytical and Bioanalytical Chemistry 395(2):377-386. doi:doi:10.1007/s00216-009-2805-x Abstract We report quantitative broadband infrared spectra of vapor-phase hydrogen peroxide (H2O2) with all spectra pressure broadened to atmospheric pressure. The spectra were generated by flowing a concentrated solution (83 weight%) of H2O2 into a gently heated disseminator and diluting with a flow of pure nitrogen carrier gas. The water vapor lines were subtracted from the resulting spectra to yield the spectrum of pure H2O2. Comparison with previous results for the ν6 band strength (including hot bands) compares favorably with the results of Klee et al. [(1999) J. Mol. Spectr. 195, 154] as well as HITRAN. The present results are 433 and 467 cm-2 atm-1 (±8% and ±3% at 298 and 323 K, respectively) for the band strength, matching well the Klee value (S = 467 cm-2 atm-1 at 296 K) for the integrated band. Other bands in the 520-7500 cm-1 interval and their potential for atmospheric monitoring are discussed.
2008. "Stability of black carbon in soils across a climatic gradient." Journal of Geophysical Research. Biogeosciences 113(G2):Art. No. G02027. Abstract The recalcitrant properties of black carbon (BC) grant it to be a significant pool of stable C in soils. Up to now, however, the longevity of BC under different climates is still unclear. In this study, we used BC samples from historical charcoal blast furnace sites to examine the stability of BC across a climatic gradient of mean annual temperatures (MAT) from 3.9 to 17.2ºC. The results showed that C concentration and C storage in the BC-containing soils at a soil depth of 0 - 0.2 m were 9.0 and 4.7 times higher than those in adjacent soils, respectively. Carbon in the BC-containing soils was more stable, with a significantly lower amount of labile C fraction (4.4 mg g C-1 vs. 27.5 mg g C-1) and longer half-life of the recalcitrant C fraction (59 years vs. 9 years) than the adjacent soils determined from incubation experiments. The stability of BC was primarily due to its inherently recalcitrant chemical composition as suggested by short-term incubation and solid state 13C nuclear magnetic resonance spectra of isolated BC particles. A significant negative relationship between C storage and MAT (-0.62; P<0.01) further indicated that C storage was decreased with warmer climate. However, the lack of a relationship between MAT and BC mineralization (P>0.05) suggested that the stability of the remaining BC was similar between sites with very different MAT. Despite the fact that warming or cooling result in immediate consequences for BC stocks, it may have little impact on the stability of the remaining BC over the period studied.
2007. "Water-induced Bulk Ba(NO3)2 Formation From NO2 Exposed Thermally Aged BaO/Al2O3." Applied Catalysis. B, Environmental 72(3-4):233-239. Abstract Phase changes in high temperature treated (> 900 °C) 8 or 20 wt% BaO supported on Al2O3 model lean NOx trap (LNT) catalysts, induced by NO2 and/or H2O adsorption, were investigated with powder X-ray Diffraction (XRD), solid state 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy, and NO2 Temperature Programmed Desorption (TPD) experiments. After calcination in dry air at 1000 °C, the XRD and solid state 27Al MAS NMR results confirm that stable surface BaO and bulk BaAl2O4 phases are formed for 8 and 20 wt% BaO/Al2O3, respectively. Following NO2 adsorption over these thermally treated samples, no additional phase changes are observed based on XRD results. However, when water was added to the thermally aged samples after NO2 exposure, the formation of crystalline Ba(NO3)2 particles was observed in both samples. Solid state 27Al MAS NMR is shown to be a good technique for identifying the various Al species present in the materials during the processes studied here. NO2 TPD results demonstrate a significant loss of uptake for the 20 wt% model catalysts upon thermal treatment. However, the described phase transformations upon subsequent water treatment gave rise to the partial recovery of NOx uptake, demonstrating that such a water treatment of thermally aged catalysts can provide a potential method to regenerate LNT materials.
2006. "Characterization of NOx Species in Dehydrated and Hydrated Na- and Ba-Y, FAU Zeolites Formed in NO₂ Adsorption." Journal of Electron Spectroscopy and Related Phenomena 150(2-3):164-170. doi:10.1016/j.elspec.2005.05.007 Abstract Adsorbed ionic NOx species formed upon the interaction of NO₂ with dehydrated or hydrated Na-, and Ba-Y, FAU zeolites were characterized using FTIR/TPD, solid state NMR, and XANES techniques. NO₂ disproportionates on both dehydrated catalyst materials forming NO⁺ and NO₃⁻ species. These ionic species are stabilized by their interactions with the negatively charged zeolite framework and the charge compensating cations (Na⁺ and Ba²⁺), respectively. Although the nature of the adsorbed NOx species formed on the two catalysts is similar, their thermal stabilities are strongly dependent on the charge compensating cations. In the presence of water in the channels of these zeolite materials new paths open for reactions between NO⁺ and H₂O, and NO₂ and H₂O, resulting in significant changes in the adsorbed ionic species observed. These combined spectroscopic investigations afforded the understanding of the interactions between water and the NO₂ on these zeolite catalysts.
2006. "Structural Investigations of Silica Polyamine Composites: Surface Coverage, Metal Ion Coordination, and Ligand Modification." Industrial and Engineering Chemistry Research 45(19):6538-6547. doi:10.1021/ie0601448 Abstract Silanization of the silica gel surface in the synthesis of silica gel polyamine composites uses (chloropropyl)-trichlorosilane (CPTCS). It is possible to substitute a molar fraction of reagent CPTCS with methyltrichlorosilane (MTCS), creating a mixed silane surface layer. Two types of silica gels were modified with a seriesof MTCS:CPTCS molar ratios. Solid-state CP/MAS 29Si and 13C NMR spectroscopies were used to evaluate the surface silane composition. Surface silane coverage was markedly improved for the resulting gels. When polyamines were grafted to the resultant MTCS:CPTCS silane layers, it was shown that the decrease in the number of propyl attachments to the polyamine resulted in increased quantities of “free amines”. Optimum MTCS:CPTCS ratios were determined for three polyamines grafted onto one silica gel. A substantial free amine increase was observed for poly(allylamine) (PAA). Metal uptake studies show increases in Cu(II) capacity and/or an improvement in Cu(II) mass-transfer kinetics. The effect of polymer molecular weight upon Cu(II) capacity was investigated for each polyamine. Substantial differences in Cu(II) capacity between 50 000 MW poly(vinylamine) (PVA) and >1000 MW PVA were evident. Similar differences between 25 000 MW poly(ethyleneimine) (PEI) and 1200 MW PEI were found. The mass-transfer kinetics was shown to be improved for composites prepared using a large fraction of MTCS in the reagent silane mixture. This resulted in substantial improvements in the 10% breakthrough Cu(II) capacity for PVA (50 000 MW). PEI composites were further modified to form an amino-acetate ligand. The impact of the MTCS:CPTCS silane ratio on the acetate ligand loading and ultimately on the Cu(II) capacity at pH ) 2 was investigated. A ratio of 12.5:1 was shown to result in an acetate modified PEI composite with a Cu(II) capacity 140% of the Cu(II) capacity of the same composite prepared with “CPTCS only”.
2006. "Silica Polyamine Composites: New Supramolecular Materials for Cation and Anion Recovery and Remediation." Macromolecular Symposia 235(1):161-178. doi:10.1002/masy.200650320 Abstract The surface coverage of amorphous silica gels used in the synthesis of silica polyamine composites has been investigated by 29Si NMR. By diluting the polyamine anchor silane, chloropropyl trichlorosilane, with methyl trichlorosilane it was found that surface coverage could be markedly improved for a range of amine polymers after grafting to the silica surface. The commensurate decrease in the number of anchor points and increase in the number of free amines results in an increase in metal capacity and/or an improvement in capture kinetics. Solid state CPMAS-13C NMR has been employed to investigate the structure and metal ion binding of a series of these composite materials. It is reported that the highly branched polymer, poly(ethyleneimine) (PEI) exhibits much broader 13C NMR resonances than the linear polymers poly(allylamine) (PAA) and poly(vinylamine) (PVA). These results are understood in terms of the low energy conformations calculated from molecular modeling studies. Three new applications of the technology are also presented: 1) separation of lanthanides as a group from ferric ion and all other divalent ions; 2) a multi step process for recovering and concentrating the valuable metals in acid mine drainage; 3) a process for removing low level arsenic and selenium in the presence of sulfate using immobilized cations on the composite materials.
2006. "Oxidation of Black Carbon by Biotic and Abiotic Processes." Organic Geochemistry 37(11):1477-1488. doi:10.1016/j.orggeochem.2006.06.022 Abstract The objectives of this study were to quantify the relative importance of either biotic or abiotic oxidation of biomass-derived black carbon (BC) and to characterize the surface properties and charge characteristics of oxidized particulate BC. We incubated BC and BC-soil mixtures at two different temperatures (30ºC and 70ºC) with and without microbial inoculation, nutrient additions, or manure amendments for four months. Abiotic processes were more important for oxidation of BC than biotic processes during this short-term incubation, as inoculation with microorganisms did not change any of the measured parameters. Black C incubated at both 30ºC and 70ºC without microbial activity showed dramatic decreases in pH (in water) from 5.4 to 5.2 and 3.4, as well as increases in cation exchange capacity (CEC at pH 7) by 53% and 538% and in oxygen (O) contents by 4% and 38%, respectively. Boehm titration and Fourier transform infrared (FTIR) spectroscopy suggested that the formation of carboxylic functional groups was the reason for the enhanced CEC during oxidation. The analyses of BC surface properties by X-ray photoelectron spectroscopy (XPS) indicated that the oxidation of BC particles initiated on the surface. Incubation at 30ºC only enhanced oxidation on particle surfaces, while oxidation during incubation at 70ºC penetrated into the interior of particles. Such short-term oxidation of BC has great significance for the stability of BC in soils as well as for its effects on soil fertility and biogeochemistry.
2005. "Oxidation of Polymer-derived SiAICN Ceramics." Journal of the American Ceramic Society 88(11):3075-3080. doi:10.1111/j.1551-2916.2005.00542.x Abstract The oxidation behavior of polymer-derived amorphous SiAlCNs was studied in the temperature range of 900°–1200°C. The results revealed that while at 900°C the oxidation of the SiAlCNs follows typical parabolic kinetics, at higher temperatures the oxidation rates of the materials decrease with annealing time. Long-term oxidation rate of the SiAlCNs is much lower than the lowest values reported for chemical vapor deposition of SiC and Si3N4. Structures of the oxide scales were studied using solid-state nuclear magnetic resonance. We proposed that oxide scales formed for the SiAlCNs possess a unique network structure of the oxide scale in which aluminum atoms block the path of oxygen diffusion, thus lowering the oxidation rates. Such a unique structure was likely formed gradually with annealing time, leading to a continuous decrease in oxidation rate.
2005. "NO2 Adsorption on BaO/Al2O3: The Nature of Nitrate Species." Journal of Physical Chemistry B 109(1):27-29. doi:10.1021/jp045082i Abstract The nature of nitrate species formed in the Al₂O₃, 8wt%, and 20wt% BaO/Al₂O₃ catalysts was investigated in a combined TPD, FTIR and 15N solid state NMR study. The results strongly suggest the formation of a monolayer bidentate nitrate on the alumina support that forms upon NO₂ exposure. This monolayer nitrate decomposes at lower temperature than bulk Ba(NO₃)₂ and its only decomposition product is NO₂. A bulk-like Ba(NO₃)₂ phase also forms with its characteristic set of TPD, IR and NMR features. The amount of NOx stored in the monolayer nitrate is proportional to the surface area of the catalyst, while that in the bulk nitrate increases with BaO coverage.
2005. "Polymer-Ceramic Conversion of Liquid Polyaluminasilazanes for SiAlCN Ceramics." Journal of the American Ceramic Society 88(9):2415-2419. Abstract Liquid-phased polyaluminasilazanes were synthesized by simply reacting a liquid polyureasilazane with aluminum isopropoxide. The reaction was studied by FTIR and MS. The resultant polyaluminasilazanes were then pyrolysized to form amorphous SiAlCN ceramics at 1000 oC in flowing N2. The structural evolution during pyrolysis was studied using solid-sate NMR and FTIR. Spectral analysis revealed that the amorphous structures of the ceramics consisted of SiC2N2 and SiCN3 as major building units, small amounts of SiC3N and SiN4 units, and penta or hexa coordinated aluminum with nitrogen. Such units were connected with each other through C-C/C=C bonds or by shearing N to form network structures. The results also revealed that relative amount of these units strongly depended on Al-content.
2004. "Expanding Your Laboratory by Accessing Collaboratory Resources." Analytical and Bioanalytical Chemistry 378(6):1408-1410. Abstract The Environmental Molecular Sciences Laboratory (EMSL) in Richland, Washington, is the home of a research facility setup by the United States Department of Energy (DOE). The facility is atypical because it houses over 100 cutting-edge research systems for the use of researchers all over the United States and the world. Access to the lab is requested through a peer-review proposal process and the scientists who use the facility are generally referred to as ‘users’. There are six main research facilities housed in EMSL, all of which host visiting researchers. Several of these facilities also participate in the EMSL Collaboratory, a remote access capability supported by EMSL operations funds. Of these, the High-Field Magnetic Resonance Facility (HFMRF) and Molecular Science Computing Facility (MSCF) have a significant number of their users performing remote work. The HFMRF in EMSL currently houses 12 NMR spectrometers that range in magnet field strength from 7.05T to 21.1T. Staff associated with the NMR facility offers scientific expertise in the areas of structural biology, solid-state materials/catalyst characterization, and magnetic resonance imaging (MRI) techniques. The way in which the HFMRF operates, with a high level of dedication to remote operation across the full suite of High-Field NMR spectrometers, has earned it the name “Virtual NMR Facility”. This review will focus on the operational aspects of remote research done in the High-Field Magnetic Resonance Facility and the computer tools that make remote experiments possible.
2003. "Porous Alumina Prepared from Diethylaluminum Amide, Acetone, and Water." Chemistry of Materials 15(1):51-56. Abstract Mesoporous aluminas are valued catalysts because they exhibit a combination of properties that allow both long life and activity. The surface area, acidity, stability, and pore size of the alumina directly influence lifetime and activity. Increased surface area and acidity, along with decreased pore size, lead to increased activity. However, these same characteristics also decrease lifetime. The properties of alumina are mutually dependent, and can be mutually opposed. Aluminas with better activity and longer life will result from a better understanding of these trends given the preparative method and thermal history.
2001. "Examination of Cadmium(II) Complexation by the Suwannee River Fulvic Acid Using 113Cd NMR Relaxation Measurements." Environmental Science and Technology 35(24):4900-4904 . Abstract Aquatic and terrestrial fulvic acids are environmentally important because they affect the bioavailability and transport of metal ions. Prior studies demonstrated that Cd(lI) binds to the oxygen containing functional groups of fulvic acids. The complexation of Cd(lI) is further investigated in this study using 113Cd NMR relaxation measurements. Spin-lattice (T1), and spin- spin (Tz) relaxation times are measured over a range of Cd(II):FA ratios. The results clearly indicate two types of Cd(lI) binding sites for the Suwannee River FA (SRFA). A series of model ligands were also examined to gain further understanding of the two types of binding motifs present in the fulvic acid. The results for a model compound containing four carboxylate functionalities in near proximity, correspond very closely to the results obtained for the strong binding sites of the Cd(II)-SRF A complexes.