Chemistry Commons^™

Perfluoroalkyl Phosphonic And Phosphinic Acid Electrolytes For Proton Exchange Membrane Fuel Cells, Mahesha Herath

All Dissertations

Perfluorinated sulfonic acid polymers have been considered as the state-of-art membrane materials for proton exchange membrane fuel cells. A major technical issue with these polymers is that they do not function well at temperatures above 80 °C and at low humidities. Therefore, research has been focused on developing PEM materials that can operate independent of hydration requirements. The operation of fuel cells at high temperature (e.g. 120 oC) increases fuel cell system efficiency due to faster electrode kinetics and better CO tolerance. This dissertation will describe a study of proton-transport rates and mechanisms under anhydrous and aqueous conditions using a …

X-Ray Structure Of Mer-[Mo(Co)3(Pph3)(Κ2-Dppm)], Shishir Ghosh, Shariff E. Kabir, Faranza K. Camellia, Md. Kamal Hossain, Daniel T. Haworth, Sergey V. Lindeman, Tasneem A. Siddiquee, Dennis W. Bennett

Chemistry Faculty Research and Publications

Treatment of [Mo(CO)₃(NCMe)₃] with bis(diphenylphosphino)methane (dppm) and triphenylphosphine (PPh₃) at 50 °C afforded mer-[Mo(CO)₃(PPh₃)(κ²-dppm)] (1) in 55% yield which has been characterized by single crystal X-ray diffraction studies and spectroscopic measurements. Compound 1 crystallizes in the triclinic space group P−1 with a = 10.3449(6), b = 11.1570(6), c = 17.8961(10) Å, β = 80.8400(10)°, Z = 2 and V = 1959.8(2) ų.

Peroxisomal Plant 3-Ketoacyl-Coa Thiolase Structure And Activity Are Regulated By A Sensitive Redox Switch, Valerie E. Pye, Caspar E. Christensen, Jim Dyer, Susan Arent, Anette Henriksen

Department of Chemistry and Biochemistry Faculty Scholarship and Creative Works

The breakdown of fatty acids, performed by the β-oxidation cycle, is crucial for plant germination and sustainability. β-Oxidation involves four enzymatic reactions. The final step, in which a two-carbon unit is cleaved from the fatty acid, is performed by a 3-ketoacyl-CoA thiolase (KAT). The shortened fatty acid may then pass through the cycle again (until reaching acetoacetyl-CoA) or be directed to a different cellular function. Crystal structures of KAT from Arabidopsis thaliana and Helianthus annuus have been solved to 1.5 and 1.8 Å resolution, respectively. Their dimeric structures are very similar and exhibit a typical thiolase-like fold; dimer formation and …

Diels-Alder Chemistry Of Siloles And Their Transformation Into Cyclohex-2-Ene-1,4-Cis-Diols., Andrew C Stevens, Brian L Pagenkopf

Chemistry Publications

The synthesis of siloles with substitution patterns that are continuative toward natural product synthesis are described. Their reactivity in Diels-Alder chemistry was explored through thermal, Lewis acid, and high-pressure reactions. Furthermore, bicyclic adducts were oxidatively cleaved to reveal a highly functionalized cyclohexene core.

Ribosomal Synthesis Of N-Methylated Peptides, Sara Ahadi

Theses and Dissertations

Natural peptide products isolated from various organisms often contain N-methylated backbones. Such a modification of backbone of the peptide changes its conformational rigidity. This modification improves the biological properties of the peptide, such as improved target affinity, proteolytic stability or membrane permeability. Therefore synthesis of N-methylated peptide libraries is valuable in screening for drug-like peptides suitable for therapeutic uses. Protein synthesis using recombinant elements (PURE) and Flexizyme were used in order to reassign specific codons to N-methyl amino acids. mRNA-dependent translation system enable us to make our desired peptides with N-methyl amino acids. This technology is a convenient tool for …

A Comparison Of Gc-Fid And Ptr-Ms Toluene Measurements In Ambient Air Under Conditions Of Enhanced Monoterpene Loading, Jesse L. Ambrose, K. Haase, R. S. Russo, Y. Zhou, M. L. White, E. K. Frinak, C. Jordan, Howard R. Mayne, Robert W. Talbot, B. C. Sive

Chemistry

Toluene was measured using both a gas chromatographic system (GC), with a flame ionization detector (FID), and a proton transfer reaction-mass spectrometer (PTR-MS) at the AIRMAP atmospheric monitoring station Thompson Farm (THF) in rural Durham, NH during the summer of 2004. Simultaneous measurements of monoterpenes, including alpha- and beta-pinene, camphene, Delta(3)-carene, and d-limonene, by GC-FID demonstrated large enhancements in monoterpene mixing ratios relative to toluene, with median and maximum enhancement ratios of similar to 2 and similar to 30, respectively. A detailed comparison between the GC-FID and PTR-MS toluene measurements was conducted to test the specificity of PTR-MS for atmospheric …

Measurement Of Hono, Hnco, And Other Inorganic Acids By Negative-Ion Proton-Transfer Chemical-Ionization Mass Spectrometry (Ni-Pt-Cims): Application To Biomass Burning Emissions, J. M. Roberts, P. Veres, C. Warneke, J. A. Neuman, R. A. Washenfelder, S. S. Brown, M. Baasandorj, J. B. Burkholder, I. R. Burling, T. J. Johnson, Robert J. Yokelson, J. De Gouw

Chemistry and Biochemistry Faculty Publications

A negative-ion proton-transfer chemical ionization mass spectrometric technique (NI-PT-CIMS), using acetate as the reagent ion, was applied to the measurement of volatile inorganic acids of atmospheric interest: hydrochloric (HCl), nitrous (HONO), nitric (HNO(3)), and isocyanic (HNCO) acids. Gas phase calibrations through the sampling inlet showed the method to be intrinsically sensitive (6-16 cts/pptv), but prone to inlet effects for HNO(3) and HCl. The ion chemistry was found to be insensitive to water vapor concentrations, in agreement with previous studies of carboxylic acids. The inlet equilibration times for HNCO and HONO were 2 to 4s, allowing for measurement in biomass burning …

Carbonate Control Of H(2) And Ch(4) Production In Serpentinization Systems At Elevated P-Ts, L. Camille Jones, Robert Rosenbauer, Jonas I. Goldsmith, Christopher Oze

Chemistry Faculty Research and Scholarship

Serpentinization of forsteritic olivine results in the inorganic synthesis of molecular hydrogen (H(2)) in ultramafic hydrothermal systems (e. g., mid-ocean ridge and forearc environments). Inorganic carbon in those hydrothermal systems may react with H(2) to produce methane (CH(4)) and other hydrocarbons or react with dissolved metal ions to form carbonate minerals. Here, we report serpentinization experiments at 200 degrees C and 300 bar demonstrating Fe(2+) being incorporated into carbonates more rapidly than Fe(2+) oxidation (and concomitant H(2) formation) leading to diminished yields of H(2) and H(2)-dependent CH(4). In addition, carbonate formation is temporally fast in carbonate oversaturated fluids. Our results …

Chemical Reasoning Based On An Invariance Property: Bond And Lone Pair Pictures In Quantum Structural Formulas, Joseph D. Alia

Chemistry Publications

Chemists use one set of orbitals when comparing to a structural formula, hybridized AOs or NBOs for example, and another for reasoning in terms of frontier orbitals, MOs usually. Chemical arguments can frequently be made in terms of energy and/or electron density without the consideration of orbitals at all. All orbital representations, orthogonal or not, within a given function space are related by linear transformation. Chemical arguments based on orbitals are really energy or electron density arguments; orbitals are linked to these observables through the use of operators. The Valency Interaction Formula, VIF, offers a system of chemical reasoning based …

Inhibition Studies Of Serine Hydrolases By Cyclic Phosphates And Phosphonates, Supratik Dutta

Dissertations

The serine hydrolase superfamily is one of the largest known enzyme families comprising approximately 1% of the predicted protein product in human genome. This family of enzymes contains a catalytic triad that is mainly consists of serine, aspartic acid/glutamic acid and histidine residues in their active sites. It has been proposed that the potential drug targets for Alzheimer’s disease and diabetes type 2 are enzymes that belong to this enzyme family. Acetylcholinesterase is an enzyme that catalyses the breakdown of acetylcholine, a neurotransmitter that helps transport information from one nerve cell to another. Breakdown of acetylcholine in Alzheimer’s disease patients …

Adsorption Studies By Pulsed Streaming Potentials In Microfluidic Channels, Thutrang Nguyen

Theses and Dissertations

In this work, an instrument for measuring pulsed streaming potentials was constructed and optimized for analytical and teaching applications. This thesis is divided in three chapters, the first one deals with the construction of the instrument, the second describes a microfluidic experiment designed for undergraduate and high school students using this instrument, and the third one shows an application of pulsed streaming potential measurements in the detection of heparin. Streaming potential is the electric field generated when a liquid is forced to flow by a pressure gradient through a channel or other stationary charged surfaces.1,2 These measurements were done in …

2,4,6-Triphenyl­Aniline, Onome Ugono, Stephanie Cowin, Alicia Beatty

Chemistry & Biochemistry Faculty Works

Individual mol­ecules of the title compound, C24H19N, do not participate in hydrogen-bonding inter­actions due to the steric bulk of the phenyl rings ortho to the amine. The dihedral angles between the central ring and the pendant rings are 68.26 (10), 55.28 (10) and 30.61 (11)°.

Synthesis, Functionalization And Characterization Of Dual Mode Nanoparticles For Biomedical Applications, Farah Radwan

Theses and Dissertations

Three different approaches were used to prepare dual mode nanoparticles using a previously described reverse micelle technique. Superparamagnetic Fe@FeOx core shell nanoparticles were chosen to be the magnetic component for all three dual mode systems. In the first type of particles, 2- amino-1,3- propane diol (APD) was used as a functionalization ligand to stabilize the surface of the particles and its functional amino group also provided a binding site for the attachment of a fluorescent probe. The TEM analysis showed that the APD coated particles have a size range of 8-13 nm while XPS and MALDI measurements confirmed the presence …

The Nature Of The O-2/O-5 Cooperative Effect And Its Role In Chemical Glycosylation, Laurel Kathryn Mydock

Dissertations

Since carbohydrates were first discovered, understanding the structure, reactivity, and function of these bioorganic compounds has remained of great priority. However, as the appreciation for the biological roles of carbohydrates intensifies, a growing demand for efficient and scalable methods towards the synthesis of these challenging molecules has become even more imperative. While modern synthetic techniques have allowed us to readily achieve most glycosidic linkages, it is the inability to effectively predict and control the stereoselectivity of the glycosylation reaction that has remained the synthetic hurdle. Herein, much effort has been placed in the investigation of “mixed-patterned” glycosyl donors as they …

Core-Shell Nanoparticles: Synthesis, Design, And Characterization, Kyler Carroll

Theses and Dissertations

The design of core/shell nanoparticles is of great interest for a wide range of applications. The primary focus of this dissertation is on the design and optimization of two synthetic routes. The first one is an aqueous reduction method using sodium borohydride and sodium citrate. This method was extended to design two types of core/shell nanoparticles, both of which have many applications in bio-sensing, magnetic resonance imaging, and magnetically guided SERS for the identification of environmental threats. The first, Fe/Ag core/shell nanoparticles were designed using a novel one-pot method by varying the AgNO₃ addition time in the system. For …

Synthesis Of Glycolipids And Evaluation Of Their Nkt Cell Stimulatory Properties, Yang Liu

Theses and Dissertations

Natural killer T (NKT) cells are a subset of T cells that modify a variety of immune responses. NKT cells recognize glycolipid antigen presented by a molecule called CD1d, a nonclassical antigen-presenting molecule. The best known subset of CD1d-dependent NKT cells expresses an invariant T cell receptor Vα (TCR-α) chain. These are referred to as type I or invariant NKT (iNKT) cells. When stimulated by a glycolipid, NKT cells rapidly release large amounts of cytokines. Cytokines released by NKT cells can induce either Th1 or Th2 responses. Th1 cytokines are effective in regulating bacterial, parasitic, and viral infections. But Th1 …

Palladium(Ii)-Catalyzed Dicarboxymethylation Of Chiral Allylic Alcohols: Chirality Transfer Affording Optically Active Diesters Containing Three Contiguous Chiral Centers, Othman Hamed, Patrick M. Henry, Daniel P. Becker

Chemistry: Faculty Publications and Other Works

This manuscript describes the extension of Stille’s palladium-catalyzed olefin dicarbonylation reaction to chiral allylic alcohols with chirality transfer to afford the corresponding chiral alcohol functionalized with bis-carbomethoxy esters, containing three contiguous chiral centers, in good to excellent diastereoselectivities (78–98%).

Impact Of Nickel Doping On Hydrogen Storage In Porous Metal-Organic Frameworks, Tanushree Banerjee

Theses and Dissertations

A supply of clean, carbon neutral and sustainable energy is the most scientific and technical challenge that humanity is facing in the 21st century. Though there is enough fossil fuels available for a few centuries, their use would increase the level of CO2 in the atmosphere. This would lead to global warming and may pose serious threats such as rising of sea level, change in hydrological cycle, etc. Hence there is a need for an alternative source of fuel that is clean and sustainable. Among the many resources considered as an alternative power source, hydrogen is considered one of the …

2,4,6-Tri­Phenyl­Aniline, Onome Ugono, Stephanie Cowin, Alicia M. Beatty

Educator Preparation & Leadership Faculty Works

No abstract provided.

Modeling, Preparation, And Characterization Of A Dipole Moment Switch Driven By Z/E Photoisomerization, Alfonso Melloni, Riccardo Rossi Paccani, Donato Donati, Vinicio Zanirato, Adalgisa Sinicropi, Maria Laura Parisi, Elena Martin, Mikhail Ryazantsev, Wan Jian Ding, Luis Manuel Frutos, Riccardo Basosi, Stefania Fusi, Loredana Latterini, Nicolas Ferre, Massimo Olivucci

Chemistry Faculty Publications

We report the results of a multidisciplinary research effort where the methods of computational photochemistry and retrosynthetic analysis/synthesis have contributed to the preparation of a novel N-alkylated indanylidene-pyrroline Schiff base featuring an exocyclic double bond and a permanent zwitterionic head. We show that, due to its large dipole moment and efficient photoisomerization, such a system may constitute the prototype of a novel generation of electrostatic switches achieving a reversible light-induced dipole moment change on the order of 30 D. The modeling of a peptide fragment incorporating the zwitterionic head into a conformationally rigid side chain shows that the switch can …

Mechanism Of N(5)-Ethyl-Flavinium Cation Formation Upon Electrochemical Oxidation Of N(5)-Ethyl-4a-Hydroxyflavin Pseudobase, Vincent Sichula, Ying Hu, Ekaterina Mirzakulova, Samuel F. Manzer, Shubham Vyas, Christopher M. Hadad, Ksenija D. Glusac

Chemistry Faculty Publications

We investigated the oxidation behavior of 5-ethyl-4a-hydroxy-3-methy1-4a,5-dihydrolumitlavin (pseudobase Et-FlH) in acetonitrile with the aim of determining if the two-electron oxidized Et-FlOH(2+) undergoes a release of hydroxyl cation and the production of 5-ethyl-3methyllumiflavinium cation (Et-Fl(+)). The focus of this work is to investigate the possibility of using Et-FlOH as a catalyst for water oxidation. The cyclic voltammetry demonstrates that Et-FlOH exhibits two one-electron oxidation potentials at +0.95 and +1.4 V versus normal hydrogen electrode (NHE), with the second oxidation potential being irreversible. The production of Et-FY' is observed in the cyclic voltammetry of Et-FlOH and has been previously assigned to the …

Synthesis Of Pbs/Tio2 Colloidal Heterostructures For Photovoltaic Applications, Krishna P. Acharya, Nishshanka N. Hewa-Kasakarage, Taiwo R. Alabi, Ian Nemitz, Elena Khon, Bruno Ullrich, Pavel Anzenbacher Jr., Mikhail Zamkov

Chemistry Faculty Publications

We report on heteroepitaxial growth of nearly monodisperse PbS nanocrystals onto the surface of TiO2 nanoparticles via colloidal hot-injection routes. Fabricated PbS/TiO2 nanocomposites can be dispersed in nonpolar solvents, which enables an easy solution processing of these materials into mesoporous films for use as light-absorbing layers in nanocrystal-sensitized solar cells. High-temperature deposition of the sensitizer material allows controlling both the size and the number of PbS domains grown onto TiO2 nanoparticles, whereby providing synthetic means for tuning the absorbance spectrum of PbS/TiO2 nanocomposites and simultaneously enhancing their photocatalytic response in the visible and near-infrared. Compared with conventional ionic bath deposition …

Short-Chain Carboxylic Acids From Gray Catbird (Dumetella Carolinensis) Uropygial Secretions Vary With Testosterone Levels And Photoperiod, Rebecca J. Whelan, Tera C. Levin, Mary C. Garvin

Faculty & Staff Scholarship

The uropygial gland of birds produces secretions that are important in maintaining the health and structural integrity of feathers. Non-volatile components of uropygial secretions are believed to serve a number of functions including waterproofing and conditioning the feathers. Volatile components have been characterized in fewer species, but are particularly interesting because of their potential importance in olfactory interactions within and across species. We used solid-phase microextraction headspace sampling with gas chromatography-mass spectrometry to detect and identify volatiles in uropygial secretions of gray catbirds (Dumetella carolinensis), a North American migratory bird. We consistently detected the following carboxylic acids: acetic, …

Oxygen Isotopes As A Tracer Of Dom Processes In River-Estuary Systems, Joy Ashley Matthews

OES Theses and Dissertations

In the biogeochemical study of dissolved organic matter (DOM) in natural waters, stable isotopes are used to provide insight into both the sources of DOM and the processes affecting its alteration. Through the research presented here, oxygen isotopes are incorporated into the study of DOM through the adaptation of a pyrolysis elemental analysis isotope ratio mass spectrometer method, and sample preparation using two-stage ultrafiltration.

The application of oxygen isotopes to the study of DOM is demonstrated in two studies. First, natural abundance of δ¹⁸O in DOM is explored in the Delaware estuary. Using a two end-member mixing model, …

Effects Of Hydrogen Bonding On Vibrational Normal Modes Of Pyrimidine, Austin A. Howard, Gregory S. Tschumper, Nathan I. Hammer

Chemistry Faculty Research & Creative Works

The effects of weak intermolecular interactions on 10 vibrational normal modes of pyrimidine are investigated by Raman spectroscopy and electronic structure computations. Hydrogen-bonded networks of water induce a shift to higher energy in certain normal modes of pyrimidine with increasing water concentration, while other modes are relatively unaffected. Pyrimidine molecules also exhibit weak C-H⋯N interactions and shifted normal modes upon crystallization. The selective nature of the shifting of normal modes to higher energy allows for definitive assignments of the nearly degenerate ν8a and ν8b modes with polarized Raman spectroscopy. Natural bond orbital (NBO) analyses indicate that when water molecules donate …

White Matter Diffusion Alterations In Normal Women At Risk Of Alzheimer's Disease, Charles D. Smith, Himachandra Chebrolu, Anders H. Andersen, David A. Powell, Mark A. Lovell, Shuling Xiong, Brian T. Gold

Neurology Faculty Publications

Increased white matter mean diffusivity and decreased fractional anisotropy (FA) has been observed in subjects diagnosed with mild cognitive impairment (MCI) and Alzheimer's disease (AD). We sought to determine whether similar alterations of white matter occur in normal individuals at risk of AD. Diffusion tensor images were acquired in 42 cognitively normal right-handed women with both a family history of dementia and at least one apolipoprotein E4 allele. These were compared with images from 23 normal women without either AD risk factor. Group analyses were performed using tract-based spatial statistics. Reduced FA was observed in the fronto-occipital and inferior temporal …

Rhodium-Catalyzed Hydroboration: Directed Asymmetric Desymmetrization, Judy L. Miska

Department of Chemistry: Dissertations, Theses, and Student Research

Rhodium-catalyzed asymmetric hydroboration in conjunction with directing groups can be used control relative and absolute stereochemistry. Hydroboration has the potential to create new C–C, C–O, and C–N bonds from an intermediate C–B bond with retention of stereochemistry. Desymmetrization resulting in the loss of one or more symmetry elements can give rise to molecular chirality, i.e., the conversion of a prochiral molecule to one that is chiral. Unsaturated amides and esters hold the potential for two-point binding to the rhodium catalyst and have been shown to direct the regiochemistry and impact stereochemistry in asymmetric hydroborations of acyclic β,γ-unsaturated substrates. In …

Fluorescent Chemosensors For Toxic Organophosphorus Pesticides: A Review, Sherine O. Obare, Chandrima De, Wen Guo, Tajay L. Haywood, Tova A. Samuels, Clara P. Adams, Noah O. Masika, Desmond H. Murray, Ginger A. Anderson, Keith Campbell, Kenneth Fletcher

Faculty Publications

Many organophosphorus (OP) based compounds are highly toxic and powerful inhibitors of cholinesterases that generate serious environmental and human health concerns. Organothiophosphates with a thiophosphoryl (P=S) functional group constitute a broad class of these widely used pesticides. They are related to the more reactive phosphoryl (P=O) organophosphates, which include very lethal nerve agents and chemical warfare agents, such as, VX, Soman and Sarin. Unfortunately, widespread and frequent commercial use of OP-based compounds in agricultural lands has resulted in their presence as residues in crops, livestock, and poultry products and also led to their migration into aquifers. Thus, the design of …

Excited State Geometry Of Photoactive Yellow Protein Chromophore: A Combined Conductorlike Polarizable Continuum Model And Time-Dependent Density Functional Study, Yali Wang, Hui Li

Hui Li Publications

Analytic gradient of the combined conductorlike polarizable continuum model (CPCM) and time-dependent density functional theory method is derived and implemented. Due to the use of the fixed points with variable areas tessellation scheme, the excited state potential energy surfaces (PESs) are rigorously continuous and smooth. The CPCM/TD-B3LYP method is used to study an analog of the photoactive yellow protein chromophore, anionic thiomethyl p-coumaric acid (TMpCA⁻). Although CPCM/TD-B3LYP method may not be accurate in predicting solvent effect on vertical excitation of TMpCA⁻, it may be used to predict redshiftings of emission maxima relative to absorption maxima with …

Hrc Enews — 2010 Summer, Megan K. Svarz

Publications (HRC)

This issue contains staff accomplishments and announcements, event listings, and a "new faces" listing for new staff, affiliates, and researchers.