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Articles 91 - 120 of 202
Full-Text Articles in Biochemistry
Synthesis And Characterization Of Polymer (Sulfonated Poly-Ether-Ether-Ketone) Based Nanocomposite (H-Boron Nitride) Membrane For Hydrogen Storage, Naresh Muthu, S. Rajashabala, R. Kannan
Synthesis And Characterization Of Polymer (Sulfonated Poly-Ether-Ether-Ketone) Based Nanocomposite (H-Boron Nitride) Membrane For Hydrogen Storage, Naresh Muthu, S. Rajashabala, R. Kannan
Chemistry and Biochemistry Faculty Publications
The development of light weight and compact hydrogen storage materials is still prerequisite to fuel-cell technology to be fully competitive. The present experimental study reports the hydrogen storage capability of sulfonated poly-ether-ether-ketone (SPEEK)-hexagonal boron nitride (h-BN) (SPEEK-h-BN) nanocomposite membranes. The nanocomposite membranes are prepared by considering various amount of h-BN (0, 1, 3 and 5 wt. %) by phase inversion technique. The degree of sulfonation of the PEEK (SPEEK) is found to be 65% by Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy. Hydrogen adsorption studies have been carried out using a Seiverts-like hydrogenation setup. The membranes are characterized …
Antifungal Amphiphilic Aminoglycoside K20: Bioactivities And Mechanism Of Action, Sanjib K. Shrestha, Cheng-Wei Tom Chang, Nicole Meissner, John Oblad, Jaya P. Shrestha, Kevin N. Sorensen, Michelle M. Grilley, Jon Y. Takemoto
Antifungal Amphiphilic Aminoglycoside K20: Bioactivities And Mechanism Of Action, Sanjib K. Shrestha, Cheng-Wei Tom Chang, Nicole Meissner, John Oblad, Jaya P. Shrestha, Kevin N. Sorensen, Michelle M. Grilley, Jon Y. Takemoto
Chemistry and Biochemistry Faculty Publications
K20 is a novel amphiphilic antifungal aminoglycoside that is synthetically derived from the antibiotic kanamycin A. Reported here are investigations of K20′s antimicrobial activities, cytotoxicity, and fungicidal mechanism of action. In vitro growth inhibitory activities against a variety of human and plant pathogenic yeasts, filamentous fungi, and bacteria were determined using microbroth dilution assays and time-kill curve analyses, and hemolytic and animal cell cytotoxic activities were determined. Effects on Cryptococcus neoformans H-99 infectivity were determined with a preventive murine lung infection model. The antifungal mechanism of action was studied using intact fungal cells, yeast lipid mutants, and small unilamellar lipid …
Cold Magnetically Trapped 2DG Scandium Atoms. I. Interaction Potential, Tijs Karman, Xi Chu, Gerrit C. Groenenboom
Cold Magnetically Trapped 2DG Scandium Atoms. I. Interaction Potential, Tijs Karman, Xi Chu, Gerrit C. Groenenboom
Chemistry and Biochemistry Faculty Publications
We present a first principles description of the interaction of two ground-state scandium atoms. Scandium has a 2Dg ground state. Thirty molecular states correlate to the lowest dissociation limit of the dimer. In the short range, potential energy curves are calculated using second-order n-electron valence state perturbation theory. The first-order long-range interaction is calculated at the complete active space self-consistent field level. We determine the second-order long-range dispersion interaction from atomic dynamic polarizabilities at imaginary frequencies. These polarizabilities are calculated using time-dependent density functional theory. We merge the short-range approach with the long-range model to obtain a physical …
Aerosol Emissions From Prescribed Fires In The United States: A Synthesis Of Laboratory And Aircraft Measurements, A. A. May, G. R. Mcmeeking, T. Lee, J. W. Taylor, J. S. Craven, I. R. Burling, A. P. Sullivan, Sheryl Kashi Akagi, J. L. Collett Jr., M. Flynn, H. Coe, S. P. Urbanski, J. H. Seinfeld, Robert Yokelson, S. M. Kreidenweis
Aerosol Emissions From Prescribed Fires In The United States: A Synthesis Of Laboratory And Aircraft Measurements, A. A. May, G. R. Mcmeeking, T. Lee, J. W. Taylor, J. S. Craven, I. R. Burling, A. P. Sullivan, Sheryl Kashi Akagi, J. L. Collett Jr., M. Flynn, H. Coe, S. P. Urbanski, J. H. Seinfeld, Robert Yokelson, S. M. Kreidenweis
Chemistry and Biochemistry Faculty Publications
Aerosol emissions from prescribed fires can affect air quality on regional scales. Accurate representation of these emissions in models requires information regarding the amount and composition of the emitted species.Wemeasured a suite of submicron particulatematter species in young plumes emitted from prescribed fires (chaparral and montane ecosystems in California; coastal plain ecosystem in South Carolina) and from open burning of over 15 individual plant species in the laboratory. We report emission ratios and emission factors for refractory black carbon (rBC) and submicron nonrefractory aerosol and compare field and laboratory measurements to assess the representativeness of our laboratory-measured emissions. Laboratory measurements …
Airborne Characterization Of Smoke Marker Ratios From Prescribed Burning, A. P. Sullivan, A. A. May, T. Lee, G. R. Mcmeeking, S. M. Kreidenweis, S. K. Akagi, Robert Yokelson, S. P. Urbanski, J. L. Collett Jr.
Airborne Characterization Of Smoke Marker Ratios From Prescribed Burning, A. P. Sullivan, A. A. May, T. Lee, G. R. Mcmeeking, S. M. Kreidenweis, S. K. Akagi, Robert Yokelson, S. P. Urbanski, J. L. Collett Jr.
Chemistry and Biochemistry Faculty Publications
A Particle-Into-Liquid Sampler – Total Organic Carbon (PILS-TOC) and fraction collector system was flown aboard a Twin Otter aircraft sampling prescribed burning emissions in South Carolina in November 2011 to obtain smoke marker measurements. The fraction collector provided 2 min time-integrated offline samples for carbohydrate (i.e., smoke markers levoglucosan, mannosan, and galactosan) analysis by high-performance anion-exchange chromatography with pulsed amperometric detection. Each fire location appeared to have a unique 1levoglucosan /1water-soluble organic carbon (WSOC) ratio (RF01/RF02/RF03/RF05 = 0.163± 0.007 μg C μg−1 C, RF08 = 0.115 ± 0.011 μg C μg−1 C, RF09A = 0.072 ± 0.028 μgC μg−1 C, …
Trace Gas Emissions From Combustion Of Peat, Crop Residue, Domestic Biofuels, Grasses, And Other Fuels: Configuration And Fourier Transform Infrared (Ftir) Component Of The Fourth Fire Lab At Missoula Experiment (Flame-4), C. E. Stockwell, R. J. Yokelson, S. M. Kreidenweis, A. L. Robinson, P. J. Demott, R. C. Sullivan, J. Reardon, K. C. Ryan, D. W.T. Griffith, L. Stevens
Trace Gas Emissions From Combustion Of Peat, Crop Residue, Domestic Biofuels, Grasses, And Other Fuels: Configuration And Fourier Transform Infrared (Ftir) Component Of The Fourth Fire Lab At Missoula Experiment (Flame-4), C. E. Stockwell, R. J. Yokelson, S. M. Kreidenweis, A. L. Robinson, P. J. Demott, R. C. Sullivan, J. Reardon, K. C. Ryan, D. W.T. Griffith, L. Stevens
Chemistry and Biochemistry Faculty Publications
During the fourth Fire Lab at Missoula Experiment (FLAME-4, October-November 2012) a large variety of regionally and globally significant biomass fuels was burned at the US Forest Service Fire Sciences Laboratory in Missoula, Montana. The particle emissions were characterized by an extensive suite of instrumentation that measured aerosol chemistry, size distribution, optical properties, and cloud-nucleating properties. The trace gas measurements included high-resolution mass spectrometry, one-and two-dimensional gas chromatography, and open-path Fourier transform infrared (OP-FTIR) spectroscopy. This paper summarizes the overall experimental design for FLAME-4-including the fuel properties, the nature of the burn simulations, and the instrumentation employed-and then focuses on …
Identification And Quantification Of Gaseous Organic Compounds Emitted From Biomass Burning Using Two-Dimensional Gas Chromatography/Time-Of-Flight Mass Spectrometry, L. E. Hatch, W. Luo, J. F. Pankow, Robert Yokelson, C. Stockwell, K. C. Barsanti
Identification And Quantification Of Gaseous Organic Compounds Emitted From Biomass Burning Using Two-Dimensional Gas Chromatography/Time-Of-Flight Mass Spectrometry, L. E. Hatch, W. Luo, J. F. Pankow, Robert Yokelson, C. Stockwell, K. C. Barsanti
Chemistry and Biochemistry Faculty Publications
The current understanding of secondary organic aerosol (SOA) formation within biomass burning (BB) plumes is limited by the incomplete identification and quantification of the non-methane organic compounds (NMOCs) emitted from such fires. Gaseous organic compounds were collected on sorbent cartridges during laboratory burns as part of the fourth Fire Lab at Missoula Experiment (FLAME-4), with analysis by two-dimensional gas chromatography/time-of-flight mass spectrometry (GC×GC/TOFMS). The sensitivity and resolving power of GC×GC/TOFMS allowed the acquisition of the most extensive data set of BB NMOCs to date, with measure ments for 722 positively or tentatively identified compounds. Estimated emission factors (EFs) are presented …
Effects Of Charge And Substituent On The S∙∙∙N Chalcogen Bond, U. Adhikari, Steve Scheiner
Effects Of Charge And Substituent On The S∙∙∙N Chalcogen Bond, U. Adhikari, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Neutral complexes containing a S···N chalcogen bond are compared with similar systems in which a positive charge has been added to the S-containing electron acceptor, using high-level ab initio calculations. The effects on both XS···N and XS+···N bonds are evaluated for a range of different substituents X = CH3, CF3, NH2, NO2, OH, Cl, and F, using NH3 as the common electron donor. The binding energy of XMeS···NH3 varies between 2.3 and 4.3 kcal/mol, with the strongest interaction occurring for X = F. The binding is strengthened by a factor of 2–10 in charged XH2S+···NH3 complexes, reaching a maximum of …
Competition Between Lone Pair-Π, Halogen Bond, And Hydrogen Bond In Adducts Of Water With Perhalogenated Alkenes C2clnf4-N (N = 0-4), U. Adhikari, Steve Scheiner
Competition Between Lone Pair-Π, Halogen Bond, And Hydrogen Bond In Adducts Of Water With Perhalogenated Alkenes C2clnf4-N (N = 0-4), U. Adhikari, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
A thorough search of the potential energy surface is carried out for heterodimers of water with C2ClnF4−n. Three different types of interactions are observed. Structures dominated by a lone pair–π interaction have the highest binding energies, and are stabilized by charge transfer from O lone pairs of H2O to the Csingle bondC π* antibonding orbital of the alkene. Halogen-bonded O⋯Cl complexes are slightly less strongly bound, followed by OH⋯X hydrogen bonds. The replacements of Cl by F atoms have only small effects upon binding energies. Inclusion of vibrational and entropic effects removes the clear energetic superiority of lp–π binding energies. …
Complexation Of N So2 Molecules (N=1,2,3) With Formaldehyde And Thioformaldehyde, L. M. Azofra, Steve Scheiner
Complexation Of N So2 Molecules (N=1,2,3) With Formaldehyde And Thioformaldehyde, L. M. Azofra, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio and density functional theory calculations are used to examine complexes formed between H2CO and H2CS with 1, 2, and 3 molecules of SO2. The nature of the interactions is probed by a variety of means, including electrostatic potentials, natural bond orbital, atoms in molecules, energy decomposition, and electron density redistribution maps. The dimers are relatively strongly bound, with interaction energies exceeding 5 kcal/mol. The structures are cyclic, containing both a O/S⋯S chalcogen bond and a CH⋯O H-bond. Addition of a second SO2 molecule leads to a variety of heterotrimer structures, most of which resemble the original dimer, where …
Complexes Containing Co2 And So2. Mixed Dimers, Trimers And Tetramers, L. M. Azofra, Steve Scheiner
Complexes Containing Co2 And So2. Mixed Dimers, Trimers And Tetramers, L. M. Azofra, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Mixed dimers, trimers and tetramers composed of SO2 and CO2 molecules are examined by ab initio calculations to identify all minimum energy structures. While AIM formalism leads to the idea of a pair of C···O bonds in the most stable heterodimer, bound by some 2 kcal mol(-1), NBO analysis describes the bonding in terms of charge transfer from O lone pairs of SO2 to the CO π* antibonding orbitals. The second minimum on the surface, just slightly less stable, is described by AIM as containing a single O···O chalcogen bond. The NBO picture is that of two transfers in opposite …
Interaction Between Temozolomide And Water: Preferred Binding Sites, O. E. Kasende, A. Matondo, M. Muzomwe, J. T. Muya, Steve Scheiner
Interaction Between Temozolomide And Water: Preferred Binding Sites, O. E. Kasende, A. Matondo, M. Muzomwe, J. T. Muya, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Computational methods are used to predict the most favorable site of temozolomide towards attack by a water molecule. The energetics of the various complexes are presented as well as their geometries, including perturbations of each subunit caused by the presence of the other. Molecular electrostatic potential and Natural Bond Orbital (NBO) data are used to understand the interactions which conclude the terminal amide group is the preferred attack site where water can act as simultaneous proton donor and acceptor. Other potential proton acceptor N atoms within the aromatic ring structure represent weaker binding sites. Some of the less strongly bound …
Substituent Effects In The Noncovalent Bonding Of So2 To Molecules Containing A Carbonyl Group. The Dominating Role Of The Chalcogen Bond, L. M. Azofra, Steve Scheiner
Substituent Effects In The Noncovalent Bonding Of So2 To Molecules Containing A Carbonyl Group. The Dominating Role Of The Chalcogen Bond, L. M. Azofra, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The SO2 molecule is paired with a number of carbonyl-containing molecules, and the properties of the resulting complexes are calculated by high-level ab initio theory. The global minimum of each pair is held together primarily by a S···O chalcogen bond wherein the lone pairs of the carbonyl O transfer charge to the π* antibonding SO orbital, supplemented by smaller contributions from weak CH···O H-bonds. The binding energies vary between 4.2 and 8.6 kcal/mol, competitive with even some of the stronger noncovalent forces such as H-bonds and halogen bonds. The geometrical arrangement places the carbonyl O atom above the plane of …
An Exploration Of The Ozone Dimer Potential Energy Surface, L. M. Azofra, I. Alkorta, Steve Scheiner
An Exploration Of The Ozone Dimer Potential Energy Surface, L. M. Azofra, I. Alkorta, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The (O3)2 dimer potential energy surface is thoroughly explored at the ab initio CCSD(T) computational level. Five minima are characterized with binding energies between 0.35 and 2.24 kcal/mol. The most stable may be characterized as slipped parallel, with the two O3 monomers situated in parallel planes. Partitioning of the interaction energy points to dispersion and exchange as the prime contributors to the stability, with varying contributions from electrostatic energy, which is repulsive in one case. Atoms in Molecules analysis of the wavefunction presents specific O⋯O bonding interactions, whose number is related to the overall stability of each dimer. All internal …
Field Measurements Of Trace Gases Emitted By Prescribed Fires In Southeastern Us Pine Forests Using An Open-Path Ftir System, S. K. Akagi, I. R. Burling, A. Mendoza, T. J. Johnson, M. Cameron, David W. T. Griffith, C. Paton-Walsh, D. R. Weise, J. Reardon, Robert Yokelson
Field Measurements Of Trace Gases Emitted By Prescribed Fires In Southeastern Us Pine Forests Using An Open-Path Ftir System, S. K. Akagi, I. R. Burling, A. Mendoza, T. J. Johnson, M. Cameron, David W. T. Griffith, C. Paton-Walsh, D. R. Weise, J. Reardon, Robert Yokelson
Chemistry and Biochemistry Faculty Publications
We report trace-gas emission factors from three pine-understory prescribed fires in South Carolina, US measured during the fall of 2011. The fires were more intense than many prescribed burns because the fuels included mature pine stands not subjected to prescribed fire in decades that were lit following an extended drought. Emission factors were measured with a fixed open-path Fourier transform infrared (OP-FTIR) system that was deployed on the fire control lines. We compare these emission factors to those measured with a roving, point sampling, land-based FTIR and an airborne FTIR deployed on the same fires. We also compare to emission …
Aerosol Single Scattering Albedo Dependence On Biomass Combustion Efficiency: Laboratory And Field Studies, Shang Liu, Allison C. Aiken, Caleb Arata, Manvendra K. Dubey, C. Stockwell, Robert Yokelson, Elizabeth A. Stone, Thilina Jayarathne, Allen L. Robinson, Paul J. Demott, Sonia M. Kreidenweis
Aerosol Single Scattering Albedo Dependence On Biomass Combustion Efficiency: Laboratory And Field Studies, Shang Liu, Allison C. Aiken, Caleb Arata, Manvendra K. Dubey, C. Stockwell, Robert Yokelson, Elizabeth A. Stone, Thilina Jayarathne, Allen L. Robinson, Paul J. Demott, Sonia M. Kreidenweis
Chemistry and Biochemistry Faculty Publications
Single scattering albedo (ω) of fresh biomass burning (BB) aerosols produced from 92 controlled laboratory combustion experiments of 20 different woods and grasses was analyzed to determine the factors that control the variability in ω. Results show that ω varies strongly with fire-integrated modified combustion efficiency (MCEFI)—higher MCEFI results in lower ω values and greater spectral dependence of ω. A parameterization of ω as a function of MCEFI for fresh BB aerosols is derived from the laboratory data and is evaluated by field observations from two wildfires. The parameterization suggests that MCEFI explains 60% of …
Strongly Bound Noncovalent (So3)N:H2co Complexes (N = 1, 2), L. M. Azofra, I. Alkorta, Steve Scheiner
Strongly Bound Noncovalent (So3)N:H2co Complexes (N = 1, 2), L. M. Azofra, I. Alkorta, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The potential energy surfaces (PES) for the SO3:H2CO and (SO3)2:H2CO complexes were thoroughly examined at the MP2/aug-cc-pVDZ computational level. Heterodimers and trimers are held together primarily by SO chalcogen bonds, supplemented by weaker CHO and/or OC bonds. The nature of the interactions is probed by a variety of means, including electrostatic potentials, AIM, NBO, energy decomposition, and electron density redistribution maps. The most stable dimer is strongly bound, with an interaction energy exceeding 10 kcal mol(-1). Trimers adopt the geometry of the most stable dimer, with an added SO3 molecule situated so as to interact with both of the original …
Membrane Lipid-Modulated Mechanism Of Action And Non-Cytotoxicity Of Novel Fungicide Aminoglycoside Fg08, Sanjib Shrestha, Michelle Grilley, Marina Y. Fosso, Cheng-Wei Tom Chang, Jon Y. Takemoto
Membrane Lipid-Modulated Mechanism Of Action And Non-Cytotoxicity Of Novel Fungicide Aminoglycoside Fg08, Sanjib Shrestha, Michelle Grilley, Marina Y. Fosso, Cheng-Wei Tom Chang, Jon Y. Takemoto
Chemistry and Biochemistry Faculty Publications
A novel aminoglycoside, FG08, that differs from kanamycin B only by a C8 alkyl chain at the 4″-O position, was previously reported. Unlike kanamycin B, FG08 shows broad-spectrum fungicidal but not anti-bacterial activities. To understand its specificity for fungi, the mechanism of action of FG08 was studied using intact cells of the yeast Saccharomyces cerevisiae and small unilamellar membrane vesicles. With exposure to FG08 (30 µg mL−1), 8-fold more cells were stained with fluorescein isothiocyanate, cells had 4 to 6-fold higher K+ efflux rates, and 18-fold more cells were stained with SYTOX Green in comparison to exposure to kanamycin B …
Laboratory Characterization Of Pm Emissions From Combustion Of Wildland Biomass Fuels, S. Hosseini, S. P. Urbanski, P. Dixit, L. Qi, I. R. Burling, Robert J. Yokelson, T. J. Johnson, M. Shrivastava, H. S. Jung, D. R. Weise, J. W. Miller, D. R. Cocker Iii
Laboratory Characterization Of Pm Emissions From Combustion Of Wildland Biomass Fuels, S. Hosseini, S. P. Urbanski, P. Dixit, L. Qi, I. R. Burling, Robert J. Yokelson, T. J. Johnson, M. Shrivastava, H. S. Jung, D. R. Weise, J. W. Miller, D. R. Cocker Iii
Chemistry and Biochemistry Faculty Publications
[1] Particle emissions from open burning of southwestern (SW) and southeastern (SE) U.S. fuel types during 77 controlled laboratory burns are presented. The fuels include SW vegetation types: ceanothus, chamise/scrub oak, coastal sage scrub, California sagebrush, manzanita, maritime chaparral, masticated mesquite, oak savanna, and oak woodland, as well as SE vegetation types: 1 year, 2 year rough, pocosin, chipped understory, understory hardwood, and pine litter. The SW fuels burned at higher modified combustion efficiency (MCE) than the SE fuels resulting in lower particulate matter mass emission factor. Particle mass distributions for six fuels and particle number emission for all fuels …
Pitfalls With The Use Of Enhancement Ratios Or Normalized Excess Mixing Ratios Measured In Plumes To Characterize Pollution Sources And Aging, Robert J. Yokelson, Meinrat O. Andreae, S. K. Akagi
Pitfalls With The Use Of Enhancement Ratios Or Normalized Excess Mixing Ratios Measured In Plumes To Characterize Pollution Sources And Aging, Robert J. Yokelson, Meinrat O. Andreae, S. K. Akagi
Chemistry and Biochemistry Faculty Publications
Normalized excess mixing ratios (NEMRs), also known as enhancement ratios, are a common way to characterize plumes of pollution in atmospheric research. As single-source pollutant plumes disperse in the atmosphere, they are diluted by mixing with the adjacent background air. Changes in the composition of this background air can cause large changes to the NEMR that is subsequently measured by remote-sensing, airborne, or ground-based instruments. This scenario is common when boundary layer plumes enter the free troposphere and could also impact long-range transport or plumes near the top of the troposphere. We provide a context for these issues and an …
Mesobiliverdin Ixα Enhances Rat Pancreatic Islet Yield And Function, Taihei Ito, Dong Chen, Cheng-Wei Tom Chang, Takashi Kenmochi, Tomonori Saito, Satoshi Suzuki, Jon Y. Takemoto
Mesobiliverdin Ixα Enhances Rat Pancreatic Islet Yield And Function, Taihei Ito, Dong Chen, Cheng-Wei Tom Chang, Takashi Kenmochi, Tomonori Saito, Satoshi Suzuki, Jon Y. Takemoto
Chemistry and Biochemistry Faculty Publications
The aims of this study were to produce mesobiliverdin IXα, an analog of anti-inflammatory biliverdin IXα, and to test its ability to enhance rat pancreatic islet yield for allograft transplantation into diabetic recipients. Mesobiliverdin IXα was synthesized from phycocyanobilin derived from cyanobacteria, and its identity and purity were analyzed by chromatographic and spectroscopic methods. Mesobiliverdin IXα was a substrate for human NADPH biliverdin reductase. Excised Lewis rat pancreata infused with mesobiliverdin IXα and biliverdin IXα-HCl (1–100 μM) yielded islet equivalents as high as 86.7 and 36.5%, respectively, above those from non-treated controls, and the islets showed a high degree of …
The Role Of The Global Cryosphere On The Fate Of Organic Contaminants., Amanda M. Grannas, Christian Bogdal, Kimberly J. Hageman, Frank Wania
The Role Of The Global Cryosphere On The Fate Of Organic Contaminants., Amanda M. Grannas, Christian Bogdal, Kimberly J. Hageman, Frank Wania
Chemistry and Biochemistry Faculty Publications
The cryosphere is an important component of global organic contaminant cycles. Snow is an efficient scavenger of atmospheric organic pollutants while a seasonal snowpack, sea ice, glaciers and ice caps are contaminant reservoirs on time scales ranging from days to millennia. Important physical and chemical processes occurring in the various cryospheric compartments impact contaminant cycling and fate. A variety of interactions and feedbacks also occur within the cryospheric system, most of which are susceptible to perturbations due to climate change. In this article, we review the current state of knowledge regarding the transport and processing of organic contaminants in the …
Role Of Resonance-Enhanced Multiphoton Excitation In High-Harmonic Generation Of N-2: A Time-Dependent Density-Functional-Theory Study, Xi Chu, Gerrit C. Groenenboom
Role Of Resonance-Enhanced Multiphoton Excitation In High-Harmonic Generation Of N-2: A Time-Dependent Density-Functional-Theory Study, Xi Chu, Gerrit C. Groenenboom
Chemistry and Biochemistry Faculty Publications
A minimum at similar to 39 eV is observed in the high-harmonic-generation spectra of N-2 for several laser intensities and frequencies. This minimum appears to be invariant for different molecular orientations. We reproduce this minimum for a set of laser parameters and orientations in time-dependent density-functional-theory calculations, which also render orientation-dependent maxima at 23-26 eV. Photon energies of these maxima overlap with ionization potentials of excited states observed in photoelectron spectra. Time profile analysis shows that these maxima are caused by resonance-enhanced multiphoton excitation. We propose a four-step mechanism, in which an additional excitation step is added to the well-accepted …
Coupling Field And Laboratory Measurements To Estimate The Emission Factors Of Identified And Unidentified Trace Gases For Prescribed Fires, Robert J. Yokelson, I. R. Burling, J. Gilman, C. Warneke, C. Stockwell, J. De Gouw, S. K. Akagi, S. P. Urbanski, P. Veres, J. M. Roberts, W. C. Kuster, J. Reardon, David W. T. Griffith, T. J. Johnson, S. Hosseini, J. W. Miller, D. R. Cocker Iii, H. Jung, D. R. Weise
Coupling Field And Laboratory Measurements To Estimate The Emission Factors Of Identified And Unidentified Trace Gases For Prescribed Fires, Robert J. Yokelson, I. R. Burling, J. Gilman, C. Warneke, C. Stockwell, J. De Gouw, S. K. Akagi, S. P. Urbanski, P. Veres, J. M. Roberts, W. C. Kuster, J. Reardon, David W. T. Griffith, T. J. Johnson, S. Hosseini, J. W. Miller, D. R. Cocker Iii, H. Jung, D. R. Weise
Chemistry and Biochemistry Faculty Publications
An extensive program of experiments focused on biomass burning emissions began with a laboratory phase in which vegetative fuels commonly consumed in prescribed fires were collected in the southeastern and southwestern US and burned in a series of 71 fires at the US Forest Service Fire Sciences Laboratory in Missoula, Montana. The particulate matter (PM2.5) emissions were measured by gravimetric filter sampling with subsequent analysis for elemental carbon (EC), organic carbon (OC), and 38 elements. The trace gas emissions were measured by an open-path Fourier transform infrared (OP-FTIR) spectrometer, proton-transfer-reaction mass spectrometry (PTRMS), proton-transfer ion-trap mass spectrometry (PIT-MS), negative-ion proton-transfer …
Measurements Of Reactive Trace Gases And Variable O-3 Formation Rates In Some South Carolina Biomass Burning Plumes, S. K. Akagi, Robert J. Yokelson, I. R. Burling, S. Meinardi, Isobel J. Simpson, Donald R. Blake, G. R. Mcmeeking, A. Sullivan, T. Lee, S. Kreidenweis, S. P. Urbanski, J. Reardon, David W. T. Griffith, T. J. Johnson, D. R. Weise
Measurements Of Reactive Trace Gases And Variable O-3 Formation Rates In Some South Carolina Biomass Burning Plumes, S. K. Akagi, Robert J. Yokelson, I. R. Burling, S. Meinardi, Isobel J. Simpson, Donald R. Blake, G. R. Mcmeeking, A. Sullivan, T. Lee, S. Kreidenweis, S. P. Urbanski, J. Reardon, David W. T. Griffith, T. J. Johnson, D. R. Weise
Chemistry and Biochemistry Faculty Publications
In October-November 2011 we measured trace gas emission factors from seven prescribed fires in South Carolina (SC), US, using two Fourier transform infrared spectrometer (FTIR) systems and whole air sampling (WAS) into canisters followed by gas-chromatographic analysis. A total of 97 trace gas species were quantified from both airborne and ground-based sampling platforms, making this one of the most detailed field studies of fire emissions to date. The measurements include the first emission factors for a suite of monoterpenes produced by heating vegetative fuels during field fires. The first quantitative FTIR observations of limonene in smoke are reported along with …
Characterization Of A Novel Fusion Protein Of Ipab And Ipad Of Shigella And Its Potential As A Pan-Shigella Vaccine, F. J. Martinez-Becerra, X. Chen, Nicholas E. Dickenson, S. P. Choudhari, K. Harrison, J. D. Clements, W. D. Picking, L. L. Van De Verg, R. I. Walker, W. L. Picking
Characterization Of A Novel Fusion Protein Of Ipab And Ipad Of Shigella And Its Potential As A Pan-Shigella Vaccine, F. J. Martinez-Becerra, X. Chen, Nicholas E. Dickenson, S. P. Choudhari, K. Harrison, J. D. Clements, W. D. Picking, L. L. Van De Verg, R. I. Walker, W. L. Picking
Chemistry and Biochemistry Faculty Publications
Shigellosis is an important disease in the developing world, where about 90 million people become infected with Shigella spp. each year. We previously demonstrated that the type three secretion apparatus (T3SA) proteins IpaB and IpaD are protective antigens in the mouse lethal pulmonary model. In order to simplify vaccine formulation and process development, we have evaluated a vaccine design that incorporates both of these previously tested Shigella antigens into a single polypeptide chain. To determine if this fusion protein (DB fusion) retains the antigenic and protective capacities of IpaB and IpaD, we immunized mice with the DB fusion and compared …
The Magnitude And Mechanism Of Charge Enhancement Of Ch∙∙O H-Bonds, U. Adhikari, Steve Scheiner
The Magnitude And Mechanism Of Charge Enhancement Of Ch∙∙O H-Bonds, U. Adhikari, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Quantum calculations find that neutral methylamines and thioethers form complexes, with N-methylacetamide (NMA) as proton acceptor, with binding energies of 2–5 kcal/mol. This interaction is magnified by a factor of 4–9, bringing the binding energy up to as much as 20 kcal/mol, when a CH3+ group is added to the proton donor. Complexes prefer trifurcated arrangements, wherein three separate methyl groups donate a proton to the O acceptor. Binding energies lessen when the systems are immersed in solvents of increasing polarity, but the ionic complexes retain their favored status even in water. The binding energy is reduced when the methyl …
Time-Dependent Density-Functional-Theory Calculation Of High-Order-Harmonic Generation Of H-2, Xi Chu, Gerrit C. Groenenboom
Time-Dependent Density-Functional-Theory Calculation Of High-Order-Harmonic Generation Of H-2, Xi Chu, Gerrit C. Groenenboom
Chemistry and Biochemistry Faculty Publications
The observation of the isotope effect in the high-order-harmonic generation (HHG) of H-2 presents a challenge for time-dependent density-functional-theory (TDDFT) methods, since this effect is related to the dynamics of the ion created in the tunneling ionization step of HHG and it depends on the harmonic order. As an initial step toward describing this effect within current computational capacity, we benchmark a method in which the nuclear and electronic degrees of freedom are separated and both treated quantum mechanically. For the electrons two TDDFT formalisms are adopted. Although the ion-dynamics effect is not described in our method, it reproduces the …
Detailed Comparison Of The Pnicogen Bond With Chalcogen, Halogen And Hydrogen Bonds, Steve Scheiner
Detailed Comparison Of The Pnicogen Bond With Chalcogen, Halogen And Hydrogen Bonds, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The characteristics of the pnicogen bond are explored using a variety of quantum chemical techniques. In particular, this interaction is compared with its halogen and chalcogen bond cousins, as well as with the more common H-bond. In general, these bonds are all of comparable strength. More specifically, they are strengthened by the presence of an electronegative substituent on the electron-acceptor atom, and each gains strength as one moves down the appropriate column of the periodic table, for example, from N to P to As. These noncovalent bonds owe their stability to a mixture in nearly equal parts of electrostatic attraction …
First Steps In Growth Of A Polypeptide Toward Β-Sheet Structure, U. Adhikari, Steve Scheiner
First Steps In Growth Of A Polypeptide Toward Β-Sheet Structure, U. Adhikari, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The full conformational energy surface is examined for a molecule in which a dipeptide is attached to the same spacer group as another peptide chain, so as to model the seminal steps of β-sheet formation. This surface is compared with the geometrical preferences of the isolated dipeptide to extract the perturbations induced by interactions with the second peptide strand. These interpeptide interactions remove any tendency of the dipeptide to form a C5 ring structure, one of its two normally stable geometries. A C7 structure, the preferred conformation of the isolated dipeptide, remains as the global minimum in the full molecule. …