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Articles 121 - 150 of 384
Full-Text Articles in Chemistry
Electron Transfer To Nitrogenase In Different Genomic And Metabolic Backgrounds, Saroj Poudel, Daniel R. Colman, Kathryn R. Fixen, Rhesa N. Ledbetter, Yanning Zheng, Natasha Pence, Lance C. Seefeldt, John W. Peters, Caroline S. Harwood, Eric S. Boyd
Electron Transfer To Nitrogenase In Different Genomic And Metabolic Backgrounds, Saroj Poudel, Daniel R. Colman, Kathryn R. Fixen, Rhesa N. Ledbetter, Yanning Zheng, Natasha Pence, Lance C. Seefeldt, John W. Peters, Caroline S. Harwood, Eric S. Boyd
Chemistry and Biochemistry Faculty Publications
Nitrogenase catalyzes the reduction of dinitrogen (N2) using low-potential electrons from ferredoxin (Fd) or flavodoxin (Fld) through an ATP-dependent process. Since its emergence in an anaerobic chemoautotroph, this oxygen (O2)-sensitive enzyme complex has evolved to operate in a variety of genomic and metabolic backgrounds, including those of aerobes, anaerobes, chemotrophs, and phototrophs. However, whether pathways of electron delivery to nitrogenase are influenced by these different metabolic backgrounds is not well understood. Here, we report the distribution of homologs of Fds, Flds, and Fd-/Fld-reducing enzymes in 359 genomes of putative N2 fixers (diazotrophs). Six distinct lineages …
Implications Of Monomer Deformation For Tetrel And Pnicogen Bonds, Wiktor Zierkiewicz, Mariusz Michalczyk, Steve Scheiner
Implications Of Monomer Deformation For Tetrel And Pnicogen Bonds, Wiktor Zierkiewicz, Mariusz Michalczyk, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
A series of TF4 and ZF5 molecules (T = Si, Ge, Sn and Z = P, As, Sb) were allowed to engage in tetrel and pnicogen bonds, respectively, with NH3, pyrazine, and HCN. The interaction energies are quite large, approaching 50 kcal mol-1 in some cases. The formation of each complex is accompanied by substantial geometrical deformation of the Lewis acid to accommodate the approaching base. The energy associated with this monomer rearrangement is the largest for the smaller central atoms Si and P, where it exceeds 20 kcal mol-1. The total reaction …
Steric Crowding In Tetrel Bonds, Steve Scheiner
Steric Crowding In Tetrel Bonds, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The tetravalent character of tetrel atoms leaves only limited room for an incoming nucleophile to approach and engage in a noncovalent bond with a tetrel atom. Any such approach can only occur at the expense of internal geometric distortions. The balance between attractive forces and repulsive steric crowding was studied for a series of Lewis acids of the type FTR3 (T = Si, Ge, Sn, Pb) which were allowed to interact with various bases. The strength and other properties of the tetrel bond are examined as the R groups are made progressively larger, varying from H and CH3 …
Chemical Characterization Of Fine Particulate Matter Emitted By Peat Fires In Central Kalimantan, Indonesia, During The 2015 El Niño, Thilina Jayarathne, Chelsea E. Stockwell, Ashley A. Gilbert, Kaitlyn Daugherty, Mark A. Cochrane, Kevin C. Ryan, Erianto I. Putra, Bambang H. Saharjo, Ati D. Nurhayati, Israr Albar, Robert J. Yokelson, Elizabeth A. Stone
Chemical Characterization Of Fine Particulate Matter Emitted By Peat Fires In Central Kalimantan, Indonesia, During The 2015 El Niño, Thilina Jayarathne, Chelsea E. Stockwell, Ashley A. Gilbert, Kaitlyn Daugherty, Mark A. Cochrane, Kevin C. Ryan, Erianto I. Putra, Bambang H. Saharjo, Ati D. Nurhayati, Israr Albar, Robert J. Yokelson, Elizabeth A. Stone
Chemistry and Biochemistry Faculty Publications
Fine particulate matter (PM2:5) was collected in situ from peat smoke during the 2015 El Niño peat fire episode in Central Kalimantan, Indonesia. Twenty-one PM samples were collected from 18 peat fire plumes that were primarily smoldering with modified combustion efficiency (MCE) values of 0.725-0.833. PM emissions were determined and chemically characterized for elemental carbon (EC), organic carbon (OC), water-soluble OC, water-soluble ions, metals, and organic species. Fuel-based PM2:5 mass emission factors (EFs) ranged from 6.0 to 29.6 g kg1 with an average of 17:36:0 g kg1. EC was detected only in 15 plumes and comprised 1% of PM mass. …
Nepal Ambient Monitoring And Source Testing Experiment (Namaste): Emissions Of Particulate Matter From Wood-And Dung-Fueled Cooking Fires, Garbage And Crop Residue Burning, Brick Kilns, And Other Sources, Thilina Jayarathne, Chelsea E. Stockwell, Prakash V. Bhave, Puppala S. Praveen, Chathurika M. Rathnayake, Robiul Md Islam, Arnico K. Panday, Sagar Adhikari, Rashmi Maharjan, J. Douglas Goetz, Peter F. Decarlo, Eri Saikawa, Robert J. Yokelson, Elizabeth A. Stone
Nepal Ambient Monitoring And Source Testing Experiment (Namaste): Emissions Of Particulate Matter From Wood-And Dung-Fueled Cooking Fires, Garbage And Crop Residue Burning, Brick Kilns, And Other Sources, Thilina Jayarathne, Chelsea E. Stockwell, Prakash V. Bhave, Puppala S. Praveen, Chathurika M. Rathnayake, Robiul Md Islam, Arnico K. Panday, Sagar Adhikari, Rashmi Maharjan, J. Douglas Goetz, Peter F. Decarlo, Eri Saikawa, Robert J. Yokelson, Elizabeth A. Stone
Chemistry and Biochemistry Faculty Publications
The Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) characterized widespread and under-sampled combustion sources common to South Asia, including brick kilns, garbage burning, diesel and gasoline generators, diesel groundwater pumps, idling motorcycles, traditional and modern cooking stoves and fires, crop residue burning, and heating fire. Fuel-based emission factors (EFs; with units of pollutant mass emitted per kilogram of fuel combusted) were determined for fine particulate matter (PM2.5), organic carbon (OC), elemental carbon (EC), inorganic ions, trace metals, and organic species. For the forced-draft zigzag brick kiln, EFPM2.5 ranged from 12 to 19gkg-1 with major contributions from OC (7%), sulfate …
Investigating Biomass Burning Aerosol Morphology Using A Laser Imaging Nephelometer, Katherine M. Manfred, Rebecca A. Washenfelder, Nicholas L. Wagner, Gabriela Adler, Frank Erdesz, Caroline C. Womack, Kara D. Lamb, Joshua P. Schwarz, Alessandro Franchin, Vanessa Selimovic, Robert J. Yokelson, Daniel M. Murphy
Investigating Biomass Burning Aerosol Morphology Using A Laser Imaging Nephelometer, Katherine M. Manfred, Rebecca A. Washenfelder, Nicholas L. Wagner, Gabriela Adler, Frank Erdesz, Caroline C. Womack, Kara D. Lamb, Joshua P. Schwarz, Alessandro Franchin, Vanessa Selimovic, Robert J. Yokelson, Daniel M. Murphy
Chemistry and Biochemistry Faculty Publications
Particle morphology is an important parameter affecting aerosol optical properties that are relevant to climate and air quality, yet it is poorly constrained due to sparse in situ measurements. Biomass burning is a large source of aerosol that generates particles with different morphologies. Quantifying the optical contributions of non-spherical aerosol populations is critical for accurate radiative transfer models, and for correctly interpreting remote sensing data. We deployed a laser imaging nephelometer at the Missoula Fire Sciences Laboratory to sample biomass burning aerosol from controlled fires during the FIREX intensive laboratory study. The laser imaging nephelometer measures the unpolarized scattering phase …
Pi Tetrel Bonds, And Their Influence On Hydrogen Bonds And Proton Transfers, Yuanxin Wei, Qingzhong Li, Steve Scheiner
Pi Tetrel Bonds, And Their Influence On Hydrogen Bonds And Proton Transfers, Yuanxin Wei, Qingzhong Li, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The positive region that lies above the plane of F2TO (T=C and Si) interacts with malondialdehyde (MDA), which contains an intramolecular H‐bond. The T atom of F2TO can lie either in the MDA molecular plane, forming a T⋅⋅⋅O tetrel bond, or F2TO can stack directly above MDA in a parallel arrangement. The former structure is more stable than the latter, and in either case, F2SiO engages in a much stronger interaction than does F2CO, reaching nearly 200 kJ mol−1. The π‐tetrel bond strengthens/weakens the MDA H‐bond when the bond is formed to the hydroxyl/carbonyl group of MDA, and causes an …
Aerogen Bonds Formed Between Aeof2 (Ae = Kr, Xe) And Diaziness: Comparisons Between Σ-Hole And Π-Hole Complexes, Wiktor Zierkiewicz, Mariusz Michalczyk, Steve Scheiner
Aerogen Bonds Formed Between Aeof2 (Ae = Kr, Xe) And Diaziness: Comparisons Between Σ-Hole And Π-Hole Complexes, Wiktor Zierkiewicz, Mariusz Michalczyk, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The interaction between KrOF2 or XeOF2 and the 1,2, 1,3, and 1,4 diazines is characterized chiefly by a Kr/Xe···N aerogen bond, as deduced from ab initio calculations. The most stable dimers take advantage of the σ-hole on the aerogen atom, wherein the two molecules lie in the same plane. The interaction is quite strong, as much as 18 kcal mol-1. A second class of dimer geometry utilizes the π-hole above the aerogen atom in an approximate perpendicular arrangement of the two monomers; these structures are not as strongly bound: 6-8 kcal mol-1. Both sorts of dimers contain auxiliary CH···F H-bonds …
Computational Assessment Of An Elusive Aromatic N3p3 Molecule, Alyona A. Starikova, Natalia M. Boldyreva, Ruslan M. Minyaev, Alexander I. Boldyrev, Vladimir I. Minkin
Computational Assessment Of An Elusive Aromatic N3p3 Molecule, Alyona A. Starikova, Natalia M. Boldyreva, Ruslan M. Minyaev, Alexander I. Boldyrev, Vladimir I. Minkin
Chemistry and Biochemistry Faculty Publications
We computationally proved that the planar aromatic hexagonal isomer N3P3 with the alteration of N and P is the second most stable structure for the N3P3 stoichiometry. We found that the aromatic isomer has high barriers for transition into the global minimum structure or into the three isolated NP molecules, making this structure kinetically stable. We showed that the sandwich N3P3CrN3P3 molecule corresponds to a minimum on the potential energy surface; thus, the aromatic N3P3 molecule has a potential to be a new ligand …
Comparison Of Various Means Of Evaluating Molecular Electrostatic Potentials For Noncovalent Interactions, Steve Scheiner
Comparison Of Various Means Of Evaluating Molecular Electrostatic Potentials For Noncovalent Interactions, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The various heterodimers formed by a series of Lewis acids with NH3 as Lewis base are identified. Lewis acids include those that can form chalcogen (HSF and HSBr), pnicogen (H2PF and H2PBr), and tetrel (H3SiF and H3SiBr) bonds, as well as H‐bonds and halogen bonds. The molecular electrostatic potential (MEP) of each Lewis acid is considered in a number of ways. Pictorial versions show broad regions of positive and negative MEP, on surfaces that vary with respect to either the value of the chosen isopotential, or their distance from the nuclei. Specific points are identified where the MEP reaches a …
Can Hcch/Hbnh Break B=N/C=C Bonds Of Single-Wall Bn/Carbon Nanotubes At Their Surface?, Tapas Kar, Peter Grüninger, Steve Scheiner, Holger F. Bettinger, Ajit K. Roy
Can Hcch/Hbnh Break B=N/C=C Bonds Of Single-Wall Bn/Carbon Nanotubes At Their Surface?, Tapas Kar, Peter Grüninger, Steve Scheiner, Holger F. Bettinger, Ajit K. Roy
Chemistry and Biochemistry Faculty Publications
The iminoborane (HBNH) molecule, which prefers cycloaddition reactions, selectively breaks a B=N bond of smaller diameter single-wall BNNTs and expands a ring at their surface, either at the edges or at the middle of the tube. Density functional theory (DFT) is used to test whether its organic counterpart HCCH can do the same with BNNTs. HCCH-BNNT complexes are identified and transition states located for these combination reactions. Also explored are possible reactions of HBNH with SWNTs and HCCH with SWNTs. Data suggest that B=N (C=C) bond breaking, followed by ring expansion at the surface may be possible. Although [2+2] cycloaddition …
Halogen Bonds Formed Between Substituted Imidazoliums And N Bases Of Varying N-Hybridization, Steve Scheiner
Halogen Bonds Formed Between Substituted Imidazoliums And N Bases Of Varying N-Hybridization, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Heterodimers are constructed containing imidazolium and its halogen-substituted derivatives as Lewis acid. N in its sp3, sp2 and sp hybridizations is taken as the electron-donating base. The halogen bond is strengthened in the Cl < Br < I order, with the H-bond generally similar in magnitude to the Br-bond. Methyl substitution on the N electron donor enhances the binding energy. Very little perturbation arises if the imidazolium is attached to a phenyl ring. The energetics are not sensitive to the hybridization of the N atom. More regular patterns appear in the individual phenomena. Charge transfer diminishes uniformly on going from amine to imine to nitrile, a pattern that is echoed by the elongation of the C-Z (Z=H, Cl, Br, I) bond in the Lewis acid. These trends are also evident in the Atoms in Molecules topography of the electron density. Molecular electrostatic potentials are not entirely consistent with energetics. Although I of the Lewis acid engages in a stronger bond than does H, it is the potential of the latter which is much more positive. The minimum on the potential of the base is most negative for the nitrile even though acetonitrile does not form the strongest bonds. Placing the systems in dichloromethane solvent reduces the binding energies but leaves intact most of the trends observed in vacuo; the same can be said of ∆G in solution.
Global Fire Emissions Estimates During 1997-2016, Guido R. Van Der Werf, James T. Randerson, Louis Giglio, Thijs T. Van Leeuwen, Yang Chen, Brendan M. Rogers, Mingquan Mu, Margreet J.E. Van Marle, Douglas C. Morton, G. James Collatz, Robert J. Yokelson, Prasad S. Kasibhatla
Global Fire Emissions Estimates During 1997-2016, Guido R. Van Der Werf, James T. Randerson, Louis Giglio, Thijs T. Van Leeuwen, Yang Chen, Brendan M. Rogers, Mingquan Mu, Margreet J.E. Van Marle, Douglas C. Morton, G. James Collatz, Robert J. Yokelson, Prasad S. Kasibhatla
Chemistry and Biochemistry Faculty Publications
Climate, land use, and other anthropogenic and natural drivers have the potential to influence fire dynamics in many regions. To develop a mechanistic understanding of the changing role of these drivers and their impact on atmospheric composition, long-term fire records are needed that fuse information from different satellite and in situ data streams. Here we describe the fourth version of the Global Fire Emissions Database (GFED) and quantify global fire emissions patterns during 1997-2016. The modeling system, based on the Carnegie-Ames-Stanford Approach (CASA) biogeochemical model, has several modifications from the previous version and uses higher quality input datasets. Significant upgrades …
Special Issue: Intramolecular Hydrogen Bonding 2017, Steve Scheiner
Special Issue: Intramolecular Hydrogen Bonding 2017, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Even after more than a century of study [1–6], scrutiny, and detailed examination, the H-bond continues [7–12] to evoke a level of fascination that surpasses many other phenomena. Perhaps it is the ability of the simple H atom, with but a single electron, to act as a glue that maintains contact between much more complicated species. Or it might be its geometry, which prefers to hold the bridging proton on a direct line between the two heavy atoms. Not to be ignored are the spectral features of the H-bond: the large red shift of the stretching frequency of the covalent …
Universal Surface Engineering Of Transition Metals For Superior Electrocatalytic Hydrogen Evolution In Neutral Water, Bo You, Xuan Liu, Guoxiang Hu, Sheraz Gul, Junko Yano, De-En Jiang, Yujie Sun
Universal Surface Engineering Of Transition Metals For Superior Electrocatalytic Hydrogen Evolution In Neutral Water, Bo You, Xuan Liu, Guoxiang Hu, Sheraz Gul, Junko Yano, De-En Jiang, Yujie Sun
Chemistry and Biochemistry Faculty Publications
The development of low-cost hybrid water splitting-biosynthetic systems that mimic natural photosynthesis to achieve solar-to-chemical conversion is of great promise for future energy demands, but often limited by the kinetically sluggish hydrogen evolution reaction (HER) on the surface of nonprecious transition metal catalysts in neutral media. It is thus highly desirable to rationally tailor the reaction interface to boost the neutral HER catalytic kinetics. Herein, we report a general surface nitrogen modification of diverse transition metals (e.g. iron, cobalt, nickel, copper, and nickel-cobalt alloy), accomplished by a facile low-temperature ammonium carbonate treatment, for significantly improved hydrogen generation from neutral water. …
Systematic Elucidation Of Factors That Influence The Strength Of Tetrel Bonds, Steve Scheiner
Systematic Elucidation Of Factors That Influence The Strength Of Tetrel Bonds, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Quantum calculations are used to examine the properties of heterodimers formed by a series of tetrel-containing molecules with NH3 as universal Lewis base. TH4 was taken as a starting point, with T= C, Si, Ge, and Sn. The H atoms were replaced by various numbers of F atoms: TH3F, TF3H, and TF4 so as to monitor the effects of adding electron-withdrawing substituents. Unsubstituted TH4 molecules form the weakest tetrel bonds, only up to about 2 kcal/mol. The bond is strengthened when the H opposite NH3 is replaced by F, rising up …
Assembly Of Effective Halide Receptors From Components. Comparing Hydrogen, Halogen, Tetrel Bonds, Steve Scheiner
Assembly Of Effective Halide Receptors From Components. Comparing Hydrogen, Halogen, Tetrel Bonds, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Receptors for halide anions are constructed based on the imidazolium unit, and then replacing the H-bonding C-H group firstby halogen-bonding C-I and then by tetrel-bonding C-SnH3 and C-SiF3.Attaching a phenyl ring to any of these species has little effect on its ability to bind a halide, but incorporation of a second imidazolium to the benzene connector, forming a bidentate dicationic receptor, greatly enhances the binding. Addition of electron-withdrawing F atoms to each imidazolium adds a further increment. F- consistently binds more strongly to the various receptor models than does Cl-. Whereas replacement of the H atom on the imidazolium groups …
Relative Importance Of Black Carbon, Brown Carbon, And Absorption Enhancement From Clear Coatings In Biomass Burning Emissions, Rudra P. Pokhrel, Eric R. Beamesderfer, Nick L. Wagner, Justin M. Langridge, Daniel A. Lack, Thilina Jayarathne, Elizabeth A. Stone, Chelsea E. Stockwell, Robert J. Yokelson, Shane M. Murphy
Relative Importance Of Black Carbon, Brown Carbon, And Absorption Enhancement From Clear Coatings In Biomass Burning Emissions, Rudra P. Pokhrel, Eric R. Beamesderfer, Nick L. Wagner, Justin M. Langridge, Daniel A. Lack, Thilina Jayarathne, Elizabeth A. Stone, Chelsea E. Stockwell, Robert J. Yokelson, Shane M. Murphy
Chemistry and Biochemistry Faculty Publications
A wide range of globally significant biomass fuels were burned during the fourth Fire Lab at Missoula Experiment (FLAME-4). A multi-channel photoacoustic absorption spectrometer (PAS) measured dry absorption at 405, 532, and 660 nm and thermally denuded (250 °C) absorption at 405 and 660 nm. Absorption coefficients were broken into contributions from black carbon (BC), brown carbon (BrC), and lensing following three different methodologies, with one extreme being a method that assumes the thermal denuder effectively removes organics and the other extreme being a method based on the assumption that black carbon (BC) has an Ångström exponent of unity. The …
Solvation Enhances The Distinction Between Carboxylated Armchair And Zigzag Single-Wall Carbon Nanotubes (Swnt-Cooh), Tapas Kar, Upendra Adhikari, Steve Scheiner, Ajit K. Roy, Renato L. T. Parreira, Pedro A. De S. Bergamo, Giovanni F. Caramori, Felipe S. S. Schneider
Solvation Enhances The Distinction Between Carboxylated Armchair And Zigzag Single-Wall Carbon Nanotubes (Swnt-Cooh), Tapas Kar, Upendra Adhikari, Steve Scheiner, Ajit K. Roy, Renato L. T. Parreira, Pedro A. De S. Bergamo, Giovanni F. Caramori, Felipe S. S. Schneider
Chemistry and Biochemistry Faculty Publications
The effect of various solvents on the structures and properties of carboxylated SWNTs has been explored using the Same Level Different Basis Set approach (SLDB), where B3LYP functional of density functional theory (DFT) was applied. Armchair (4,4) and zigzag (8,0) and (9,0) tubes were considered as the test bed. In order to simulate varying concentration of –COOH groups, one to five acids groups were placed at one end of these tubes. These samples were placed in different solvents (namely, CS2, THF and water) with varying polarity and results were compared with gas-phase properties. Similar to the gas-phase, zigzag tubes also …
Comparison Of Halide Receptors Based On H, Halogen, Chalogen, Pnicogen, And Tetrel Bonds, Steve Scheiner
Comparison Of Halide Receptors Based On H, Halogen, Chalogen, Pnicogen, And Tetrel Bonds, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
A series of halide receptors are constructed and the geometries and energetics of their binding to F-, Cl-, and Br- assessed by quantum calculations. The dicationic receptors are based on a pair of imidazolium units, connected via a benzene spacer. The imidazoliums each donate a proton to a halide in a pair of H-bonds. Replacement of the two bonding protons by Br leads to binding via a pair of halogen bonds. Likewise, chalcogen, pnicogen, and tetrel bonds occur when the protons are replaced, respectively, by Se, As, and Ge. Regardless of the binding group considered, F- is bound much more …
Multi-Instrument Comparison And Compilation Of Non-Methane Organic Gas Emissions From Biomass Burning And Implications For Smoke-Derived Secondary Organic Aerosol Precursors, Lindsay E. Hatch, Robert J. Yokelson, Chelsea E. Stockwell, Patrick R. Veres, Isobel J. Simpson, Donald R. Blake, John J. Orlando, Kelley C. Barsanti
Multi-Instrument Comparison And Compilation Of Non-Methane Organic Gas Emissions From Biomass Burning And Implications For Smoke-Derived Secondary Organic Aerosol Precursors, Lindsay E. Hatch, Robert J. Yokelson, Chelsea E. Stockwell, Patrick R. Veres, Isobel J. Simpson, Donald R. Blake, John J. Orlando, Kelley C. Barsanti
Chemistry and Biochemistry Faculty Publications
Multiple trace-gas instruments were deployed during the fourth Fire Lab at Missoula Experiment (FLAME- 4), including the first application of proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOFMS) and comprehensive two-dimensional gas chromatography-time-offlight mass spectrometry (GC×GC-TOFMS) for laboratory biomass burning (BB) measurements. Open-path Fourier transform infrared spectroscopy (OP-FTIR) was also deployed, as well as whole-air sampling (WAS) with onedimensional gas chromatography-mass spectrometry (GCMS) analysis. This combination of instruments provided an unprecedented level of detection and chemical speciation. The chemical composition and emission factors (EFs) determined by these four analytical techniques were compared for four representative fuels. The results demonstrate that the instruments are …
Comparison Of Tetrel Bonds In Neutral And Protonated Complexes Of Pyridinetf3 And Furantf3 (T = C, Si, And Ge) With Nh3, Mingxiu Liu, Qing-Zhong Li, Steve Scheiner
Comparison Of Tetrel Bonds In Neutral And Protonated Complexes Of Pyridinetf3 And Furantf3 (T = C, Si, And Ge) With Nh3, Mingxiu Liu, Qing-Zhong Li, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
Ab initio calculations have been performed for the complexes H+–PyTX3⋯NH3 and H+–furanTF3⋯NH3 (T = C, Si, and Ge; X = F and Cl) with focus on geometries, energies, orbital interactions, and electron densities to study the influence of protonation on the strength of tetrel bonding. The primary interaction mode between α/β-furanCF3/p-PyCF3 and NH3 changes from an F⋯H hydrogen bond to a C⋯N tetrel bond as a result of protonation. Importantly, the protonation has a prominent enhancing effect on the strength of tetrel bonding with an increase in binding energy from 14 to 30 kcal mol−1. The tetrel bonding becomes stronger …
Flipped Learning In Synchronously-Delivered, Geographically-Dispersed General Chemistry Classrooms, Michael A. Christiansen, Louis Nadelson, Lianna K. Etchberger, Marilyn M. Cuch, Trish A. Kingsford, Leslie O. Woodward
Flipped Learning In Synchronously-Delivered, Geographically-Dispersed General Chemistry Classrooms, Michael A. Christiansen, Louis Nadelson, Lianna K. Etchberger, Marilyn M. Cuch, Trish A. Kingsford, Leslie O. Woodward
Chemistry and Biochemistry Faculty Publications
In synchronously-delivered, multi-site classrooms, the physical separation between distance students and instructors may create a perceived divide that negatively affects learning. Building on prior experience in flipping organic chemistry in single-site face-to-face (F2F) classes, we decided to extend our approach to multi-site, synchronously-delivered general chemistry courses. Our thought was to narrow the perceived instructor-student divide in distance teaching by using the flexible in-class time that flipping affords to increase the number of positive teacher/distance-student interactions. In this effort, we gradually developed a technique called “bridging questions,” through which the instructor becomes more familiar with student interests and then connects those …
Airborne Measurements Of Western U.S. Wildfire Emissions: Comparison With Prescribed Burning And Air Quality Implications, Xiaoxi Liu, L. Gregory Huey, Robert J. Yokelson, Vanessa Selimovic, Isobel J. Simpson, Markus Müller, Jose L. Jimenez, Pedro Campuzano-Jost, Andreas J. Beyersdorf, Donald R. Blake, Zachary Butterfield, Yonghoon Choi, John D. Crounse, Douglas A. Day, Glenn S. Diskin, Manvendra K. Dubey, Edward Fortner, Thomas F. Hanisco, Weiwei Hu, Laura E. King, Lawrence Kleinman, Simone Meinardi, Tomas Mikoviny, Timothy B. Onasch, Brett B. Palm, Jeff Peischl, Ilana B. Pollack, Thomas B. Ryerson, Glen W. Sachse, Arthur J. Sedlacek, John E. Shilling, Stephen Springston, Jason M. St. Clair
Airborne Measurements Of Western U.S. Wildfire Emissions: Comparison With Prescribed Burning And Air Quality Implications, Xiaoxi Liu, L. Gregory Huey, Robert J. Yokelson, Vanessa Selimovic, Isobel J. Simpson, Markus Müller, Jose L. Jimenez, Pedro Campuzano-Jost, Andreas J. Beyersdorf, Donald R. Blake, Zachary Butterfield, Yonghoon Choi, John D. Crounse, Douglas A. Day, Glenn S. Diskin, Manvendra K. Dubey, Edward Fortner, Thomas F. Hanisco, Weiwei Hu, Laura E. King, Lawrence Kleinman, Simone Meinardi, Tomas Mikoviny, Timothy B. Onasch, Brett B. Palm, Jeff Peischl, Ilana B. Pollack, Thomas B. Ryerson, Glen W. Sachse, Arthur J. Sedlacek, John E. Shilling, Stephen Springston, Jason M. St. Clair
Chemistry and Biochemistry Faculty Publications
Wildfires emit significant amounts of pollutants that degrade air quality. Plumes from three wildfires in the western U.S. were measured from aircraft during the Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) and the Biomass Burning Observation Project (BBOP), both in summer 2013. This study reports an extensive set of emission factors (EFs) for over 80 gases and 5 components of submicron particulate matter (PM1) from these temperate wildfires. These include rarely, or never before, measured oxygenated volatile organic compounds and multifunctional organic nitrates. The observed EFs are compared with previous measurements of temperate …
A Dual-Chamber Method For Quantifying The Effects Of Atmospheric Perturbations On Secondary Organic Aerosol Formation From Biomass Burning Emissions, Daniel S. Tkacik, Ellis S. Robinson, Adam Ahern, Rawad Saleh, Chelsea Stockwell, Patrick Veres, Isobel J. Simpson, Simone Meinardi, Donald R. Blake, Robert J. Yokelson, Albert A. Presto, Ryan C. Sullivan, Neil M. Donahue, Allen L. Robinson
A Dual-Chamber Method For Quantifying The Effects Of Atmospheric Perturbations On Secondary Organic Aerosol Formation From Biomass Burning Emissions, Daniel S. Tkacik, Ellis S. Robinson, Adam Ahern, Rawad Saleh, Chelsea Stockwell, Patrick Veres, Isobel J. Simpson, Simone Meinardi, Donald R. Blake, Robert J. Yokelson, Albert A. Presto, Ryan C. Sullivan, Neil M. Donahue, Allen L. Robinson
Chemistry and Biochemistry Faculty Publications
Biomass burning (BB) is a major source of atmospheric pollutants. Field and laboratory studies indicate that secondary organic aerosol (SOA) formation from BB emissions is highly variable. We investigated sources of this variability using a novel dual-smog-chamber method that directly compares the SOA formation from the same BB emissions under two different atmospheric conditions. During each experiment, we filled two identical Teflon smog chambers simultaneously with BB emissions from the same fire. We then perturbed the smoke with UV lights, UV lights plus nitrous acid (HONO), or dark ozone in one or both chambers. These perturbations caused SOA formation in …
In Situ Measurements Of Water Uptake By Black Carbon-Containing Aerosol In Wildfire Plumes, Anne E. Perring, Joshua P. Schwarz, Milos Z. Markovic, David W. Fahey, Jose L. Jimenez, Pedro Campuzano-Jost, Brett D. Palm, Armin Wisthaler, Tomas Mikoviny, Glenn Diskin, Glen Sachse, Luke Ziemba, Bruce Anderson, Taylor Shingler, Ewan Crosbie, Armin Sorooshian, Robert Yokelson, Ru Shan Gao
In Situ Measurements Of Water Uptake By Black Carbon-Containing Aerosol In Wildfire Plumes, Anne E. Perring, Joshua P. Schwarz, Milos Z. Markovic, David W. Fahey, Jose L. Jimenez, Pedro Campuzano-Jost, Brett D. Palm, Armin Wisthaler, Tomas Mikoviny, Glenn Diskin, Glen Sachse, Luke Ziemba, Bruce Anderson, Taylor Shingler, Ewan Crosbie, Armin Sorooshian, Robert Yokelson, Ru Shan Gao
Chemistry and Biochemistry Faculty Publications
Water uptake by black carbon (BC)-containing aerosol was quantified in North American wildfire plumes of varying age (1 to ~40 h old) sampled during the SEAC4RS mission (2013). A Humidified Dual SP2 (HD-SP2) is used to optically size BC-containing particles under dry and humid conditions from which we extract the hygroscopicity parameter, κ, of materials internally mixed with BC. Instrumental variability and the uncertainty of the technique are briefly discussed. An ensemble average κ of 0.04 is found for the set of plumes sampled, consistent with previous estimates of bulk aerosol hygroscopicity from biomass burning sources. The temporal evolution of …
In-Class Versus At-Home Quizzes: Which Is Better? A Flipped Learning Study In A Two-Site Synchronously-Broadcast Organic Chemistry Course, Michael A. Christensen, Alyssia M. Lambert, Louis S. Nadelson, Kami M. Dupree, Trish A. Kingsford
In-Class Versus At-Home Quizzes: Which Is Better? A Flipped Learning Study In A Two-Site Synchronously-Broadcast Organic Chemistry Course, Michael A. Christensen, Alyssia M. Lambert, Louis S. Nadelson, Kami M. Dupree, Trish A. Kingsford
Chemistry and Biochemistry Faculty Publications
We recently shared our design of a two-semester flipped organic chemistry course, in which we gave students in-class quizzes to incentivize attendance and watching the lecture videos in advance. With a second iteration, we planned to make the video-watching experience more engaging. We accordingly hypothesized that if students completed short at-home quizzes while watching the videos, then attentiveness, engagement, and learning would increase. We tested this with a later section of the course, dividing the material into 13 units. For units 1-6, we gave in-class quizzes; for 7-13, quizzes were at home. Although units 1-6 and 7-13 covered different material, …
Assessment Of The Presence And Strength Of H-Bonds By Means Of Corrected Nmr, Steve Scheiner
Assessment Of The Presence And Strength Of H-Bonds By Means Of Corrected Nmr, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The downfield shift of the NMR signal of the bridging proton in a H-bond (HB) is composed of two elements. The formation of the HB causes charge transfer and polarization that lead to a deshielding. A second factor is the mere presence of the proton-accepting group, whose electron density and response to an external magnetic field induce effects at the position of the bridging proton, exclusive of any H-bonding phenomenon. This second positional shielding must be subtracted from the full observed shift in order to assess the deshielding of the proton caused purely by HB formation. This concept is applied …
Infrared Spectroscopy Of The Nitrogenase Mofe Protein Under Electrochemical Control: Potential-Triggered Co Binding, P. Paengnakorn, Philip A. Ash, Sudipta K. Shaw, Karamatullah Danyal, T. Chen, Dennis R. Dean, Lance C. Seefeldt, Kylie A. Vincent
Infrared Spectroscopy Of The Nitrogenase Mofe Protein Under Electrochemical Control: Potential-Triggered Co Binding, P. Paengnakorn, Philip A. Ash, Sudipta K. Shaw, Karamatullah Danyal, T. Chen, Dennis R. Dean, Lance C. Seefeldt, Kylie A. Vincent
Chemistry and Biochemistry Faculty Publications
We demonstrate electrochemical control of the nitrogenase MoFe protein, in the absence of Fe protein or ATP, using europium(III/II) polyaminocarboxylate complexes as electron transfer mediators. This allows the potential dependence of proton reduction and inhibitor (CO) binding to the active site FeMo-cofactor to be established. Reduction of protons to H2 is catalyzed by the wild type MoFe protein and Β-98Tyr→His and Β-99Phe→His variants of the MoFe protein at potentials more negative than -800 mV (vs. SHE), with greater electrocatalytic proton reduction rates observed for the variants compared to the wild type protein. Electrocatalytic proton reduction is strongly …
Highly Selective Halide Receptors Based Upon Chalcogen, Pnicogen, And Tetrel Bonds, Steve Scheiner
Highly Selective Halide Receptors Based Upon Chalcogen, Pnicogen, And Tetrel Bonds, Steve Scheiner
Chemistry and Biochemistry Faculty Publications
The interactions of halides with a number of bipodal receptors are examined via quantum chemical methods. The receptors are based upon a dithieno thiophene framework in which two S atoms can engage in a pair of chalcogen bonds with a halide. These two S atoms are replaced by P and As atoms to compare chalcogen with pnicogen bonding, and by Ge which engages in tetrel bonds with the receptor. Zero, one, and two O atoms are added to the thiophene S atom which is not directly involved in the interaction with the halides. Fluoride is bound the most strongly, followed …