Scientific Publications 2005
2005. "Effect of Crystallization on the Mechanical Properties of Zr₅₆․₇Cu₁₅․₃Ni₁₂․₅Nb₅․₀Al₁₀․₀Y₀․₅ Bulk Amorphous Alloy." Materials Science and Engineering. A. Structural Materials: Properties, Microstructure and Processing 394(1-2):302-311. Abstract Effects of crystallization behavior on the mechanical properties of Zr₅₆.₇Cu₁₅.₃Ni₁₂.₅Nb₅.₀Al₁₀.₀Y₀.₅ based bulk amorphous alloy (BAA) were studied. Differential scanning calorimetry (DSC) in Ar environment showed three-exothermic peaks at 395, 472 and 659.5°C and one-endothermic peak at 852°C. Following DSC study, as received BAA samples were heat-treated in vacuum at six different temperatures 300, 450, 600, 700, 800 and 850°C. Heat-treated samples were characterized using Vickers microhardness, X-ray diffraction (XRD), differential scanning calorimetry and field emission scanning electron microscopy (FESEM) to study crystallization behavior. It is found that samples heat-treated above the second (472°C) and third (659.5°C) exothermic peaks show high microhardness values compared to the as processed samples, and brittle cracking along the indent diagonal. As processed samples show clear evidence of shear banding. FESEM examination revealed existence of nano-scale precipitates for samples heat-treated at 600 and 700°C, while micro-scale precipitates for 850°C samples. Quasi-static compression tests showed compressive strain to failure decrease with heat-treated samples compared to as received ones. Fracture morphology of the compression test samples changes from vein pattern for as received to flat facets with multiple cracks for heat-treated samples. Indentation fracture toughness values decrease almost an order of magnitude for heat-treated samples compared to as received samples.
2005. "Adsorption and Desorption of HCI on Pt(111)." Journal of Physical Chemistry B 109(32):15506-15514. Abstract The adsorption and desorption of HCl on Pt(111) is investigated by temperature programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS), and low energy electron diffraction (LEED). Five peaks are identified in the TPD spectra prior to the onset of multilayer desorption. For (theta > 0.38 ML, theta = 1.5x1015 cm-2) HCl adsorbs molecularly at 20 K as an amorphous solid with two desorption peaks at 70 and 77 K. A third peak at 84 K is tentatively assigned to molecularly adsorbed HCl. Peaks at ~135 and 200 K are assigned to recombinative desorption of dissociated HCl, in agreement with earlier studies. Kinetic analysis is conducted and the results demonstrate a strong coverage dependent desorption energy for theta < 0.25 ML. The LEED data indicates that at low temperature the adsorbed HCl clusters into ordered islands with a (3 x 3) structure and a local coverage of 4/9 with respect to the Pt(111) substrate.
2005. "Water Adsorption, Desorption, and Clustering on FeO(111)." Journal of Physical Chemistry B 109(20):10362-10370. Abstract The adsorption of water on FeO(111) is investigated using temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). Well-ordered 2 ML thick FeO(111) films are grown epitaxially on a Pt(111) substrate. Water adsorbs molecularly on FeO(111) and desorbs with a well resolved monolayer peak. IRAS measurements as a function of coverage are performed for water deposited at 30 and 135 K. For all coverages (0.2 ML and greater) the adsorbed water exhibits significant hydrogen bonding. Differences in IRAS spectra for water adsorbed at 30 and 135 K are subtle but suggest that water adsorbed at 135 K is well ordered. Monolayer nitrogen TPD spectra from water covered FeO(111) surfaces are used to investigate the clustering of the water as a function of deposition or annealing temperature. Temperature dependent water overlayer structures result from differences in water diffusion rates on bare FeO(111) and on water adsorbed on FeO(111). Features in the nitrogen TPD spectra allow the monolayer wetting and 2-dimensional (2D) ordering of water on FeO(111) to be followed. Voids in a partially disordered first water layer exist for water deposited below 120 K and ordered 2D islands are found when depositing water above 120 K.
2005. "Complexation of the Carbonate, Nitrate, and Acetate Anions with the Uranyl Dication: Density Functional Studies with Relativistic Effective Core Potentials." Journal of Physical Chemistry A 109(50):11568-11577. doi:10.1021/jp0541462 Abstract The structures and vibrational frequencies of uranyl carbonates, [UO₂(CO₃)n](²- ²ⁿ) and [(UO₂)₃(CO₃)₆]⁶⁻, uranyl nitrates, [UO₂ (NO₃)n](²-ⁿ), and uranyl acetates, [UO₂(CH₃COO)n](²-ⁿ) (n = 1,2,3) have been calculated by using local density functional theory (LDFT). Only bidentate ligand coordination modes to the uranyl dication have been modeled. The calculated structures and frequencies are compared to available experimental data, including IR, Raman, X-ray diffraction, and EXAFS solution and crystal structure data. The energetics of ligand binding have been calculated using the B3LYP hybrid functional. In general, the structural and vibrational results at the LDFT level are in good agreement with experimental results and provide realistic pictures of solution phase and solid state behavior. For the [UO₂ (CO₃)₃]⁶⁻ anion, calculations suggest that complexity in the CO₃²⁻ stretching signature upon complexation is due to the formation of C=O and C-O domains, the latter of which can split by as much as 300 cm⁻¹. Assessment of the binding energies indicate that the [UO₂ (CO₃)₂]²⁻ anion is more stable than the [UO₂(CO₃)₃]⁴⁻ anion due to the accumulation of excess charge, whereas the tri-ligand species are the most stable in the nitrate and acetate anions.
2005. "Luminescence from the trans-Dioxotechnetium(V) Chromophore." Journal of the American Chemical Society 127(43):14978-14979. Abstract Photophysical properties of the trans-dioxotechnetium(V) chromophore are reported for the first time. The complexes [TcO₂(L)₄] ⁺ (L=pyridine or 4-picoline) and [TcO₂(CN)₄]³ ⁻ are luminescent from a ³Eg excited state in the near IR with emission maxima ranging from 715-750 nm. DFT calculations predicted the observed red-shift in emission energy relative to trans-dioxorhenium(V) congeners. Distinct vibronic progressions are observed in the symmetric O=Tc=O and Tc-L stretching frequencies in the 8 K emission spectra and excited state lifetimes mirrored trends of the analogous Re(V) complexes.
2005. "Determination of Organophosphate Pesticides at a Carbon Nanotube/Organophosphorus Hydrolase Electrochemical Biosensor." Analytica Chimica Acta 530(2):185-189. Abstract An amperometric biosensor for oganophosphorus (OP) pesticides based on a carbon-nanotube (CNT) modified transducer and an organophosphorus hydrolase (OPH) biocatalyst is described. A bilayer approach with the OPH layer atop of the CNT film was used for preparing the CNT/OPH biosensor. The CNT layer leads to a greatly improved anodic detection of the enzymatically-generated p-nitrophenol product, including higher sensitivity and stability. The sensor performance was optimized with respect to the surface modification and operating conditions. Under the optimal conditions the biosensor was used to measure as low as 0.15 M paraoxon and 0.8 M methyl parathion with sensitivities of 25 and 6 nA/µM, respectively.
2005. "Insights into the Radiation Response of Pyrochlores from Calculations of Threshold Displacement Events." Journal of Applied Physics 98(8):086110. Abstract We have used molecular dynamics simulations to examine the displacement threshold energy (Ed) surface for cations and anions in Gd2Ti2O7 and Gd2Zr2O7 pyrochlores. In both pyrochlores, the Ed surface is highly anisotropic and it requires less energy to displace anions than cations. Both anion and cation Ed values are higher in the titanate compared to the zirconate. Titanium displacement energies are in excess of 170 eV for all directions examined, because cation exchange is less energetically favorable in Gd2Ti2O7 compared to Gd2Zr2O7. These high energy Ti displacements result in the formation of defect clusters that may prevent efficient defect recovery. This provides an explanation for the difference in susceptibility to amorphization between titanate and zirconate pyrochlores.
2005. "Molecular Dynamics Simulation of Defect Production in Collision Cascades in Zircon." Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms 228(1-4):299-303. Abstract Defect production in collision cascades in zircon has been examined by molecular dynamics simulations using a partial charge model combined with the Ziegler-Biersack-Littmark potential. U, Zr, Si and O recoils with energies ranging from 250 eV to 5 keV were simulated in the NVE ensemble. To obtain good statistics, 5-10 cascades in randomly chosen directions were simulated for each ion and energy. The damage consists of mainly Si and O Frenkel pairs, a smaller number of Zr Frenkel pairs, and Zr on Si antisite defects. Defect production, interstitial clustering, ion beam mixing and Si-O-Si polymerization increase with PKA mass and energy.
2005. "Experimental and Computational Study of Steric andElectronic Effects on the Coordination of Bulky,Water-Soluble Alkylphosphines to Palladium underReducing Conditions: Correlation to Catalytic Activity." Organometallics 24(5):962-971. doi:10.1021/om049241w Abstract The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Sterically demanding, water-soluble alkylphosphine ligands 2-(di-tert-butylphosphino)- ethyltrimethylammonium chloride (t-Bu-Amphos) and 4-(di-tert-butylphosphino)-N,N-dimethylpiperidinium chloride (t-Bu-Pip-phos) in combination with palladium salts provided active catalysts for the cross-coupling of aryl halides under mild conditions in aqueous solvents, whereas 4-(dicyclohexylphosphino)-N,N-dimethylpiperidinium chloride (Cy-Pipphos) gave a less active catalyst. Catalyst activity increased with increasing cone angle of the ligands, but the ø electronic parameter determined from the symmetric C-O stretching frequency of LNi(CO)₃ did not correlate with catalyst activity. Catalyst activity correlated with other calculated electronic parameters, such as the HOMO-LUMO energy gap of the ligand and the HOMO energy level of the LPd(0) species. Multinuclear NMR spectroscopic studies showed that t-Bu-Amphos and t-Bu-Pip-phos rapidly form L₂Pd(0) (L= t-Bu-Amphos or t-Bu-Pip-phos) complexes when reacted with Pd(OAc)₂ under reducing conditions over a range of L:Pd ratios. In contrast, the coordination chemistry of Cy-Pip-phos depended on the Cy-Pip-phos:Pd ratio. At ≤1:1 Cy-Pip-phos:Pd ratio, rapid formation of L₂Pd(0) occurred. At higher L:Pd ratios, initial formation of trans-(Cy-Pip-phos)₂PdCl₂ was observed followed by slow reduction to the Pd(0) complex.
2005. "A Multispectrum Analysis of the v2 Band of H12C14N: Part I. Intensities, Broadening and Shift Coefficients." Journal of Molecular Spectroscopy 231(2005):66-84. Abstract Absolute intensities, self- and air-broadening coefficients, self- and air-induced shift coefficients and their temperature dependences have been determined for lines belonging to the P and R branches of the v2 band of H12C14N centered near 712 cm-1. Infrared spectra of HCN in the 14- vm region were obtained at high resolution (0.002-0.008 cm-1) using two different Fourier transform spectrometers (FTS), the McMath-Pierce FTS at the National Solar Observatory on Kitt Peak and the Bruker IFS 120HR FTS at the Pacific Northwest National Laboratory. Spectra were recorded with 99.8% pure HCN as well as lean mixtures of HCN in air at various temperatures ranging between +26ºC and –60ºC. A multispectrum nonlinear least squares technique was used to fit selected intervals of 36 spectra simultaneously to obtain the line positions, intensities, broadening and shift parameters. The measured line intensities were analyzed to determine the vibrational band intensity and the Herman-Wallis coefficients. The measured self-broadening coefficients vary between 0.2 and 1.2 cm-1 atm-1 at 296 K, and the air broadening Absolute intensities, self- and air-broadening coefficients, self- and air-induced shift coefficients and their temperature dependences have been determined for lines belonging to the P and R branches of the v2 band of H12C14N centered near 712 cm-1. Infrared spectra of HCN in the 14- vm region were obtained at high resolution (0.002-0.008 cm-1) using two different Fourier transform spectrometers (FTS), the McMath-Pierce FTS at the National Solar Observatory on Kitt Peak and the Bruker IFS 120HR FTS at the Pacific Northwest National Laboratory. Spectra were recorded with 99.8% pure HCN as well as lean mixtures of HCN in air at various temperatures ranging between +26ºC and –60ºC. A multispectrum nonlinear least squares technique was used to fit selected intervals of 36 spectra simultaneously to obtain the line positions, intensities, broadening and shift parameters. The measured line intensities were analyzed to determine the vibrational band intensity and the Herman-Wallis coefficients. The measured self-broadening coefficients vary between 0.2 and 1.2 cm-1 atm-1 at 296 K, and the air broadening coefficients range from 0.08 to 0.14 cm-1 atm-1 at 296 K. The temperature dependence exponents of self-broadening range from 1.46 to –0.12 while the corresponding exponents for air broadening vary between 0.58 and 0.86. The present measurements are the first known determination of negative values for the temperature dependence exponents of HCN broadening coefficients. We were able to support our self-broadening measurements with appropriate theoretical calculations. Our present measurements are compared, where possible, with previous measurements for this and other HCN bands, as well as the parameters that are included in the 2000 and 2004 editions of the HITRAN (HIgh-resolution TRANsmission) database.
2005. "Application of Equation-of-Motion Coupled-Cluster Methods to Low-Lying Singlet and Triplet Electronic States of HBO and BOH." Journal of Chemical Physics 122:Article No. 234316. doi:10.1063/1.1927078 Abstract There is no abstract currently available for this article.
2005. "Application of equation-of-Motion Coupled-Cluster Methods to Low-LyingSinglet and Triplet Electronic States of HBO and BOH." Journal of Chemical Physics 122(9):234316. doi:10.1063/1.1927078 Abstract An abstract is not available for this article at this time.
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.
2005. "The effect of cavitating ultrasound on the aqueous phase hydrogenation of cis-2-buten-1-ol and cis-2-penten-1-ol on Pd-black." Applied Catalysis. A, General 288(1-2):62-66. doi:10.1016/j.apcata.2005.04.040 Abstract We have studied the effect of cavitating ultrasound on the heterogeneous aqueous hydrogenation of cis-2-buten-1-ol (C4 olefin) and cis-2-penten-1-ol (C5 olefin) on Pd-black to form the trans-olefins (trans-2-buten-1-ol and trans-2-penten-1-ol) and saturated alcohols (1-butanol and 1-pentanol, respectively). Silent (and magnetically stirred) experiments served as control experiments. As described in an earlier publication by our group, we have added an inert dopant, 1-propanol, in the reaction mixture to ensure the rapid onset of cavitation in the ultrasound-assisted reactions that can lead to altered selectivity compared to silent reaction systems [R.S. Disselkamp, Ya-Huei Chin, C.H.F. Peden, J. Catal. 227 (2004) 552]. The motivation for this study is to examine whether cavitating ultrasound can reduce the [trans-olefin/saturated alcohol] molar ratio during the course of the reaction. This could have practical application in that it may offer an alternative processing methodology of synthesizing healthier edible seed oils by reducing trans-fat content.We have observed that cavitating ultrasound results in a [(trans-olefin/saturated alcohol)ultrasound/(trans-olefin/saturated alcohol)silent] ratio quantity less than 0.5 at the reaction mid-point for both the C4 and C5 olefin systems. This indicates that ultrasound reduces trans-olefin production compared to the silent control experiment. Furthermore, there is an added 30% reduction for the C5 versus C4 olefin compounds again at reaction mid-point. We attribute differences in the ratio quantity as a moment of inertia effect. In principle, the C4 versus C5 olefins has a ~52% increase in moment of inertia about C2 C3 double bond slowing isomerization. Since seed oils are C18 multiple cis-olefins and have a moment of inertia even greater than our C5 olefin here, our study suggests that even a greater reduction in trans-olefin content may occur for partial hydrogenation of C18 seed oils.
2005. "The Effect of Cavitating Ultrasound on the Aqueous Phase Hydrogenation of Cis-2-buten-1-ol and Cis-2-penten-1-ol on Pd-black." Applied Catalysis. A, General 288(1-2):62-66. Abstract We have studied the effect of cavitating ultrasound on the heterogeneous aqueous hydrogenation of cis-2-buten-1-ol (C4 olefin) and cis-2-penten-1-ol (C5 olefin) on Pd-black to form the trans-olefins (trans-2-buten-1-ol and trans-2-penten-1-ol) and saturated alcohols (1-butanol and 1-pentanol, respectively). Silent (and magnetically stirred) experiments served as control experiments. As described in an earlier publication by our group, we have added an inert dopant, 1-propanol, in the reaction mixture to ensure the rapid onset of cavitation in the ultrasound-assisted reactions that can lead to altered selectivity compared to silent reaction systems [Disselkamp et al., J. Catal., 227 (2004) 552]. The motivation for this study is to examine whether cavitating ultrasound can reduce the [trans-olefin/saturated alcohol] molar ratio during the course of the reaction. This could have practical application in that it may offer an alternative processing methodology of synthesizing healthier edible seed oils by reducing trans-fat content. We have observed that cavitating ultrasound results in a [(trans-olefin/saturated alcohol)ultrasound/(trans-olefin/saturated alcohol)silent] ratio quantity less than 0.5 at the reaction mid-point for both the C4 and C5 olefin systems. This indicates that ultrasound reduces trans-olefin production compared to the silent control experiment. Furthermore, there is an added 30% reduction for the C5 versus C4 olefin compounds again at reaction mid-point. We attribute differences in the ratio quantity as a moment of inertia effect. In principle, the C4 versus C5 olefins has a ~52% increase in moment of inertia about C2=C3 double bond slowing isomerization. Since seed oils are C18 multiple cis olefins and have an moment of inertia even greater than our C5 olefin here, our study suggests that even a greater reduction in trans-olefin content may occur for partial hydrogenation of C18 seed oils.
2005. "Ultrasound-Assisted Hydrogenation of Cinnamaldehyde." Ultrasonics Sonochemistry 12(4):319-324. Abstract They hydrogenation, employing hydrogen gas, of cinnamaldehyde was performed using Pd-black and Raney Ni catalysis at 298± K in a water-cooled (jacketed) reaction vessel. Sampling at pre-determined time intervals and GC/MS analysis yielded time-dependent product state distribution information. A kinetic modeling of the data revealed that cinnamaldehyde was both hydrogenated to the final product benzene propanal, as well as a fraction being converted to the intermediate benzene propanal, where the latter was subsequently hydrogenated to benzene propanal. Comparing the ultrasound-assisted and blank (stirred) experiments revealed that a higher maximum relative concentration of intermediate benzene propanal was formed in the ultrasound experiments compared to the stirred experiment. The activities of the ultrasound experiments compared to blank were 9-fold and 20-fold greater for the Pd-black and Raney Ni catalysts, respectively. Finally, an application of Polayni’s principle to yield an estimate of the ratio of rate coefficients for benzene propanal and benzene propanal formation was performed by considering chemical group energy differences and surface adsorption energy differences in the first mechanistic step of hydrogenation.
2005. "Heats of Formation of Xenon Fluorides and the Fluxionality of XeF₆ from High Level Electronic Structure Calculations." Journal of the American Chemical Society 127(24):8627-8634. doi:10.1021/ja0423116 Abstract Atomization energies at 0ºK and heats of formation at 0ºK were obtained for XeF⁺, XeF⁻, XeF₂, XeF₄, XeF₅⁻, and XeF₆ from coupled cluster theory including noniterative, quasi-perturbative triple excitations (CCSD(T)) calculations with new correlation-consistent basis sets for Xe up through aug-cc-pV5Z in some cases. In order to achieve near chemical accuracy (± 1 kcal/mol) in the thermodynamic properties, up to four corrections were added to the estimated complete basis set binding energies based on frozen core coupled cluster theory energies: (1) a correction for core-valence effects, (2) a correction for scalar relativistic effects, (3) a correction for first order atomic spin-orbit effects, and (4), in some cases, a second order spin-orbit correction. Vibrational zero point energies were computed at the coupled cluster level of theory. The structure of XeF6 is difficult to obtain. The C₃v and Oh structures for XeF₆ are essentially degenerate with the Oh structure below the C₃v structure by 0.19 kcal/mol at the CCSD(T)/CBS level based on an approximate geometry for the C₃v structure. The two structures are probably isoenergetic with the C₃v slightly lower. The calculated heats of formation are: ΔHf0 (XeF⁺) = 255.8, ΔHf0(XeF⁻) = -66.3, ΔHf0(XeF2) = -23.3, ΔHf0(XeF4) = -42.5, ΔHf0(XeF5⁻) = -160.6, and ΔHf0(XeF6) = -55.9 kcal/mol. The calculated heats of formation for the neutral XeFn fluorides are higher (less stable) than the experimental values from equilibrium measurements by 2.0, 7.7, and 12.2 kcal/mol for n =2, 4, and 6 respectively. The calculated values are even higher as compared to the heats of formation from photoionization measurements. The calculated results suggest that the experimental heats of formation need to be revised. The fluxional nature of the stereoactive lone pair in XeF6 is noted.
2005. "Methyl Cation Affinities of Rare Gases and Nitrogen and the Heat of Formation of Diazomethane." Journal of Physical Chemistry A 109(18):4073-4080. doi:10.1021/jp044561e Abstract The methyl cation affinities of the rare gases have been calculated at 0 K and 298 K by using coupled cluster theory including noniterative, quasi-perturbative triple excitations level with the new correlation-consistent basis sets for Xe up through aug-cc-pV5Z in some cases. In order to achieve near chemical accuracy (± 1 kcal/mol) in the thermodynamic properties, we add to the estimated complete basis set valence binding energies based on frozen core coupled cluster theory energies two corrections: (1) a core/valence correction and (2) a scalar relativistic correction. Vibrational zero point energies were computed at the coupled cluster level of theory at the CCSD(T)/aug-cc-pVDZ level. The calculated rare gas methyl cation affinities (MCA) at 298 K are: MCA(He) = 1.7, MCA(Ne) = 2.5, MCA(Ar) = 16.9, MCA(Kr) = 25.5, and MCA(Xe) = 36.6 kcal/mol. Because of the importance of the MCA(N₂) in the experimental measurements of the MCA scale, we calculated a number of quantities associated with CH₃N₂⁺ and CH₂N₂. The calculated values for diazomethane at 298 K are: ΔHf(CH₂N₂) = 65.3, PA(CH₂N₂) = 211.9, and MCA(N₂) = 43.2 kcal/mol.
2005. "Thermodynamic Properties of Molecular Borane Amines and the [BH4-][NH4+] salt for Chemical Hydrogen Storage Systems from Ab Initio Electronic Structure Theory." Journal of Physical Chemistry A 109(23):5129-5135. doi:10.1021/jp0445627 Abstract The heats of formation for the boron amines BH3NH3, BH2NH2, and HBNH, tetrahedral BH4-, and the BN molecule have been calculated by using ab initio molecular orbital theory. Coupled cluster calculations with perturbative triples (CCSD(T)) were employed for the total valence electronic energies. Correlation consistent basis sets were used, up through the augmented quadruple zeta, to extrapolate to the complete basis set limit. Core/valence, scalar relativistic, and spin-orbit corrections were included in an additive fashion to predict the atomization energies. Geometries were calculated at the CCSD(T) level up through at least aug-cc-pVTZ and frequencies were calculated at the CCSD(T)/aug-cc-pVDZ level. The heats of formation at 0K in the gas phase are ΔHf(BH3NH3) = -9.1, ΔHf(BH2NH2) = -15.9, ΔHf(BHNH) = 13.6, ΔHf(BN) = 146.4, and ΔHf(BH4-) = -11.6 kcal/mol. The reported experimental value for ΔHf(BN) is clearly in error. The heat of formation of the salt [BH4-]NH4+] (s) has been estimated by using an empirical expression for the lattice energy and the calculated heats of formation of the two component ions. The calculations show that both BH3NH3(g) and [BH4-]NH4+](s) can serve as good hydrogen storage systems which release H2 in a slightly exothermic process. The hydride affinity of BH3 is calculated to be 72.2 kcal/mol in excellent agreement with the experimental value at 298K of 74.2 ± 2.8 kcal/mol.
2005. "Time-Dependent Density Functional Theory Predictions of the Vertical Excitation Energies of Silanones as Models for the Excitation Process in Porous Silicon." Journal of Physical Chemistry B 109(31):14830-14835. doi:10.1021/jp050538x Abstract Abstract is not available for this article at this time.
2005. "1H, 13C and 15N resonance assignments of URNdesign, a computationally redesigned RRM protein." Journal of Biomolecular NMR 33:135. doi:10.1007/s10858-005-1928-4 Abstract Protein design represents one of the great challenges of computational structural biology. The ability to successfully design new proteins would allow us to generate new reagents and enzymes, while at the same time providing us with an understanding of the principles of protein stability. Here we report 1H, 15N and 13C resonance assignments of a redesigned U1A protein, URNdesign. U1A has been studied extensively by our group and hence was chosen as a design target. For the assignments we sued 2D and 3D heteronuclearNMR experiments with uniformly 13C, 15N-labeled URNdesign. The assignments for the backbone NH, CO,Ca and Cb nuclei are 94%complete. Sidechain 1Hand13C, aromatic andQ/NNH2 resonances are essentially complete with guanidinium and K NH3 residues unassigned. BMRB deposit with accession number 6493
2005. "The Membrane-anchoring Domain of Epidermal Growth Factor Receptor Ligands Dictates Their Ability to Operate in Juxtacrine Mode." Molecular Biology of the Cell 16(6):2984-2998. Abstract All ligands of the epidermal growth factor receptor (EGFR) are synthesized as membrane-anchored precursors. Previous work has suggested that some ligands, such as EGF, must be proteolytically released to be active, whereas others, such as heparinbinding EGF-like growth factor (HB-EGF) can function while still anchored to the membrane (i.e., juxtacrine signaling). To explore the structural basis for these differences in ligand activity, we engineered a series of membrane-anchored ligands in which the core, receptor-binding domain of EGF was combined with different domains of both EGF and HB-EGF. We found that ligands having the N-terminal extension of EGF could not bind to the EGFR, even when released from the membrane. Ligands lacking an N-terminal extension, but possessing the membrane-anchoring domain of EGF still required proteolytic release for activity, whereas ligands with the membraneanchoring domain of HB-EGF could elicit full biological activity while still membraneanchored. Ligands containing the HB-EGF membrane anchor, but lacking an N-terminal extension, activated EGFR during their transit through the Golgi apparatus . However, cell-mixing experiments and fluorescence resonance energy transfer (FRET) studies showed that juxtacrine signaling typically occurred in trans at the cell surface, at points of cell-cell contact. Our data suggest that the membrane-anchoring domain of ligands selectively controls their ability to participate in juxtacrine signaling and thus, only a subclass of EGFR ligands can act in a juxtacrine mode.
2005. "Influence of Calcite and Dissolved Calcium on Uranium(VI) Sorption to a Hanford Subsurface Sediment." Environmental Science and Technology 39(20):7949-7955. doi:10.1021/es0505088 Abstract The influence of calcite and dissolved calcium on U(VI) adsorption was investigated using a calcite-containing sandy silt/clay sediment from the U. S. Department of Energy Hanford site. U(VI) adsorption to sediment, treated sediment, and sediment size fractions was studied in solutions that both had and had not been preequilibrated with calcite, at initial [U(VI)] ) 10-7-10-5 mol/L and final pH ) 6.0- 10.0. Kinetic and reversibility studies (pH 8.4) showed rapid sorption (30 min), with reasonable reversibility in the 3-day reaction time. Sorption from solutions equilibrated with calcite showed maximum U(VI) adsorption at pH 8.4 (0.1. In contrast, calcium-free systems showed the greatest adsorption at pH 6.0-7.2. At pH > 8.4, U(VI) adsorption was identical from calcium-free and calcium-containing solutions. For calcite-presaturated systems, both speciation calculations and laser-induced fluorescence spectroscopic analyses indicated that aqueous U(VI) was increasingly dominated by Ca2UO2(CO3)3 0(aq) at pH<8.4 and that formation of Ca2UO2(CO3)3 0(aq) is what suppresses U(VI) adsorption. Above pH 8.4, aqueous U(VI) speciation was dominated by UO2(CO3)3 4- in all solutions. Finally, results also showed that U(VI) adsorption was additive in regard to size fraction but not in regard to mineral mass: Carbonate minerals may have blocked U(VI) access to surfaces of higher sorption affinity.