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Chemistry

Series

2014

Chemistry and Biochemistry Faculty Publications

Articles 1 - 26 of 26

Full-Text Articles in Physical Sciences and Mathematics

Chalcogen Bonds In Complexes Of Soxy (X, Y = F, Cl) With Nitrogen Bases, Luis Miguel Azofra, Ibon Alkorta, Steve Scheiner Dec 2014

Chalcogen Bonds In Complexes Of Soxy (X, Y = F, Cl) With Nitrogen Bases, Luis Miguel Azofra, Ibon Alkorta, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

SOF2, SOFCl, and SOCl2 were each paired with a series of N bases. The potential energy surface of the binary complexes were characterized by MP2 calculations with double and triple-ξ basis sets, extrapolated to complete sets. The most stable configurations contained a S···N chalcogen bond with interaction energies as high as 6.8 kcal/mol. These structures are stabilized by a Nlp→σ*(S−Z) electron transfer (Z = O, F, Cl), complemented by Coulombicattraction of N to theσ-hole opposite the Z atom. N···S−F and N···S−Cl chalcogen bonds are stronger than N···S = O interactions.Formation of each chalcogen bond elongates all of the internalcovalent bonds …

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Investigating The Links Between Ozone And Organic Aerosol Chemistry In A Biomass Burning Plume From A Prescribed Fire In California Chaparral, M. J. Alvarado, C. R. Lonsdale, Robert Yokelson, S. K. Akagi, H. Coe, J. S. Craven, E. V. Fischer, G. R. Mcmeeking, J. H. Seinfeld, T. Soni, J. W. Taylor, D. R. Weise, C. E. Wold Dec 2014

Investigating The Links Between Ozone And Organic Aerosol Chemistry In A Biomass Burning Plume From A Prescribed Fire In California Chaparral, M. J. Alvarado, C. R. Lonsdale, Robert Yokelson, S. K. Akagi, H. Coe, J. S. Craven, E. V. Fischer, G. R. Mcmeeking, J. H. Seinfeld, T. Soni, J. W. Taylor, D. R. Weise, C. E. Wold

Chemistry and Biochemistry Faculty Publications

Within minutes after emission, rapid, complex photochemistry within a biomass burning smoke plume can cause large changes in the concentrations of ozone (O3) and organic aerosol (OA). Being able to understand and simulate this rapid chemical evolution under a wide variety of conditions is a critical part of forecasting the impact of these fires on air quality, atmospheric composition, and climate. Here we use version 2.1 of the Aerosol Simulation Program (ASP) to simulate the evolution of O3 and secondary organic aerosol (SOA) within a young biomass burning smoke plume from the Williams prescribed burn in chaparral, …

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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 Dec 2014

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 …

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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 Dec 2014

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 …

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Designed Supramolecular Filamentous Peptides: Balance Of Nanostructure, Cytotoxicity And Antimicrobial Activity, Dawei Xu, Linhai Jiang, Anju Singh, Derek Dustin, Miao Yang, Ling Liu, Reidar Lund, Timothy J. Sellati, He Dong Nov 2014

Designed Supramolecular Filamentous Peptides: Balance Of Nanostructure, Cytotoxicity And Antimicrobial Activity, Dawei Xu, Linhai Jiang, Anju Singh, Derek Dustin, Miao Yang, Ling Liu, Reidar Lund, Timothy J. Sellati, He Dong

Chemistry and Biochemistry Faculty Publications

This work demonstrates a design strategy to optimize antimicrobial peptides with an ideal balance of minimal cytotoxicity, enhanced stability, potent cell penetration and effective antimicrobial activity, which hold great promise for the treatment of intracellular microbial infections and potentially systemic anti-infective therapy.

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Cold Magnetically Trapped 2DG Scandium Atoms. I. Interaction Potential, Tijs Karman, Xi Chu, Gerrit C. Groenenboom Nov 2014

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 …

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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 Oct 2014

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 …

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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. Oct 2014

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, …

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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 Sep 2014

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 …

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The Interplay Between Charge Transfer, Rehybridization, And Atomic Charges In The Internal Geometry Of Subunits In Noncovalent Interactions, Steve Scheiner Sep 2014

The Interplay Between Charge Transfer, Rehybridization, And Atomic Charges In The Internal Geometry Of Subunits In Noncovalent Interactions, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

When a noncovalent bond is formed, there is frequently some charge transfer from one subunit to the other. The interaction also causes changes in the atomic charges and hybridization patterns of bonding orbitals. The manner in which these various effects combine to cause elongations or contractions of bonds within the individual subunits is examined. In both the cases of CH···O H-bonds and P···N pnicogen bonds, the bond length changes are consistent with the guiding principles generally known as Bent’s rules.

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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 Sep 2014

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 …

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Cyanide Toxicokinetics: The Behavior Of Cyanide, Thiocyanate And 2-Amino-2-Thiazoline-4-Carboxylic Acid In Multiple Animal Models, Raj K. Bhandari, Robert P. Oda, Ilona Petrikovics, David E. Thompson, Matthew Brenner, Sari B. Mahon, Vikhyat S. Bebarta, Gary A. Rockwood, Brian A. Logue May 2014

Cyanide Toxicokinetics: The Behavior Of Cyanide, Thiocyanate And 2-Amino-2-Thiazoline-4-Carboxylic Acid In Multiple Animal Models, Raj K. Bhandari, Robert P. Oda, Ilona Petrikovics, David E. Thompson, Matthew Brenner, Sari B. Mahon, Vikhyat S. Bebarta, Gary A. Rockwood, Brian A. Logue

Chemistry and Biochemistry Faculty Publications

Cyanide causes toxic effects by inhibiting cytochrome c oxidase, resulting in cellular hypoxia and cytotoxic anoxia, and can eventually lead to death. Cyanide exposure can be verified by direct analysis of cyanide concentrations or analyzing its metabolites, including thiocyanate (SCN−) and 2-amino-2-thiazoline-4-carboxylic acid (ATCA) in blood. To determine the behavior of these markers following cyanide exposure, a toxicokinetics study was performed in three animal models: (i) rats (250–300 g), (ii) rabbits (3.5–4.2 kg) and (iii) swine (47–54 kg). Cyanide reached a maximum in blood and declined rapidly in each animal model as it was absorbed, distributed, metabolized and …

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Less Cookbook And More Research! Synthetic Efforts Toward Jbir-94 And Jbir-125: A Student-Designed Research Project In A Sophomore Organic Chemistry Lab, Mike A. Christiansen, C. L. Crawford, C. D. Mangum Feb 2014

Less Cookbook And More Research! Synthetic Efforts Toward Jbir-94 And Jbir-125: A Student-Designed Research Project In A Sophomore Organic Chemistry Lab, Mike A. Christiansen, C. L. Crawford, C. D. Mangum

Chemistry and Biochemistry Faculty Publications

In light of the meaningful learning gains that can be obtained through a genuine research experience, chemistry educators have had a longstanding interest in making teaching labs less “cookbook-like” and more research-driven [1]. With this mindset, we recently restructured our two-semester sophomore organic chemistry lab course to include a synthesis project that was chosen, designed, and carried out by students. This led to progress toward the syntheses of JBIR-94 and JBIR-125, two antioxidative/anticancer natural products that have yet to be assembled through organic chemistry. The major drawback of our course redesign is that it requires close supervision by an instructor …

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Simultaneous High-Performance Liquid Chromatography-Tandem Mass Spectrometry (Hplc-Ms-Ms) Analysis Of Cyanide And Thiocyanate From Swine Plasma, Raj K. Bhandari, Erica Manandhar, Robert P. Oda, Gary A. Rockwood, Brian A. Logue Jan 2014

Simultaneous High-Performance Liquid Chromatography-Tandem Mass Spectrometry (Hplc-Ms-Ms) Analysis Of Cyanide And Thiocyanate From Swine Plasma, Raj K. Bhandari, Erica Manandhar, Robert P. Oda, Gary A. Rockwood, Brian A. Logue

Chemistry and Biochemistry Faculty Publications

An analytical procedure for the simultaneous determination of cyanide and thiocyanate in swine plasma was developed and validated. Cyanide and thiocyanate were simultaneously analyzed by high-performance liquid chromatography tandem mass spectrometry in negative ionization mode after rapid and simple sample preparation. Isotopically labeled internal standards, Na13C15N and NaS13C15N, were mixed with swine plasma (spiked and nonspiked), proteins were precipitated with acetone, the samples were centrifuged, and the supernatant was removed and dried. The dried samples were reconstituted in 10 mM ammonium formate. Cyanide was reacted with naphthalene-2,3-dicarboxaldehyde and taurine to form N-substituted …

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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 Jan 2014

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 …

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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 Jan 2014

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 …

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Complexation Of N So2 Molecules (N=1,2,3) With Formaldehyde And Thioformaldehyde, L. M. Azofra, Steve Scheiner Jan 2014

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 …

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Interaction Between Temozolomide And Water: Preferred Binding Sites, O. E. Kasende, A. Matondo, M. Muzomwe, J. T. Muya, Steve Scheiner Jan 2014

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 …

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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 Jan 2014

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 …

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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 Jan 2014

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. …

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Electrodeposited Nickel-Sulfide Films As Competent Hydrogen Evolution Catalysts In Neutral Water, N. Jiang, L. Bogoev, M. Popova, S. Gul, J. Yano, Y. Sun Jan 2014

Electrodeposited Nickel-Sulfide Films As Competent Hydrogen Evolution Catalysts In Neutral Water, N. Jiang, L. Bogoev, M. Popova, S. Gul, J. Yano, Y. Sun

Chemistry and Biochemistry Faculty Publications

The development of low-cost, efficient, and robust electrocatalysts of the hydrogen evolution reaction (HER) is a crucial step toward the conversion and storage of sustainable and carbon-neutral energy resources, such as solar energy. Not only the HER catalysts need to be composed of inexpensive elements, they are also desirable to be prepared at low energy cost. In this work, we report that nickel-sulfide (Ni-S) films prepared by facile potentiodynamic deposition are active HER catalysts in aqueous media. Notably, the Ni-S films showed catalytic activity in water with a wide range of pH values (0 to 14), as well as in …

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Complexes Containing Co2 And So2. Mixed Dimers, Trimers And Tetramers, L. M. Azofra, Steve Scheiner Jan 2014

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 …

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Effects Of Charge And Substituent On The S∙∙∙N Chalcogen Bond, U. Adhikari, Steve Scheiner Jan 2014

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 …

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An Exploration Of The Ozone Dimer Potential Energy Surface, L. M. Azofra, I. Alkorta, Steve Scheiner Jan 2014

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 …

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The Mtr4 Ratchet Helix And Arch Domain Both Function To Promote Rna Unwinding, Lacy L. Taylor, Ryan N. Jackson, Megi Rexhepaj, Alejandra Klauer King, Lindsey K. Lott, Ambro Van Hoof, Sean J. Johnson Jan 2014

The Mtr4 Ratchet Helix And Arch Domain Both Function To Promote Rna Unwinding, Lacy L. Taylor, Ryan N. Jackson, Megi Rexhepaj, Alejandra Klauer King, Lindsey K. Lott, Ambro Van Hoof, Sean J. Johnson

Chemistry and Biochemistry Faculty Publications

Mtr4 is a conserved Ski2-like RNA helicase and a subunit of the TRAMP complex that activates exosomemiated 3-5 turnover in nuclear RNA surveillance and processing pathways. Prominent features of the Mtr4 structure include a four-domain ring-like helicase core and a large arch domain that spans the core. The ‘ratchet helix’ is positioned to interact with RNA substrates as they move through the helicase. However, the contribution of the ratchet helix in Mtr4 activity is poorly understood. Here we show that strict conservation along the ratchet helix is particularly extensive for Ski2-like RNA helicases compared to related helicases. Mutation of residues …

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Strongly Bound Noncovalent (So3)N:H2co Complexes (N = 1, 2), L. M. Azofra, I. Alkorta, Steve Scheiner Jan 2014

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 …

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