Open Access. Powered by Scholars. Published by Universities.®

Physical Sciences and Mathematics Commons™

Open Access. Powered by Scholars. Published by Universities.®

Chemistry

Institution
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 29551 - 29580 of 34577

Full-Text Articles in Physical Sciences and Mathematics

Thermodynamic Properties Of Chlorocarbons And Kinetic Analysis For A- And B -Addition Of Oh+C2h3cl, Li Zhu Jan 1998

Thermodynamic Properties Of Chlorocarbons And Kinetic Analysis For A- And B -Addition Of Oh+C2h3cl, Li Zhu

Theses

Thermodynamic properties, ΔHf°298, S°298 and Cp(T) 300≤T/K≤1500, for C1, C2 chlorocarbons are calculated by AM1 and PM3 in MOPAC6, then compared with the literature data. AM1- and PM3-derived S°298 and Cp(T) (300≤T/K≤1500) are found to be consistent with the literature (Rd ≤ ± 5%). ΔHf°298 of CH2Cl2, CH2ClCH2Cl, CH2ClCHCl2, CHCl2CHCl2, and C2Cl4 and C2Cl2 calculated by PM3 as well as ΔHf°298 of CCl4, C2HCl3, …

Go to article

High-Performance Liquid Chromatographic Separation Of Enantiomers Of Unusual Amino Acids On A Teicoplanin Chiral Stationary Phase, Antal Péter, Gabriella Török, Daniel W. Armstrong Jan 1998

High-Performance Liquid Chromatographic Separation Of Enantiomers Of Unusual Amino Acids On A Teicoplanin Chiral Stationary Phase, Antal Péter, Gabriella Török, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

A glycopeptide antibiotic, teicoplanin, was used as chiral stationary phase for the high-performance liquid chromatographic (HPLC) separation of enantiomers of more than 30 unnatural amino acids, such as phenylalanine and tyrosine analogues and analogues containing 1,2,3,4-tetrahydroisoquinoline, tetraline, 1,2,3,4-tetrahydro-2-carboline, cyclopentane, cyclohexane, cyclohexene, bicyclo[2.2.1]heptane or heptene skeletons. Excellent resolutions were achieved for most of the investigated compounds by using a hydro-organic mobile-phase system. The effects of organic modifier content, temperature and flow-rate on the resolution were investigated and the conditions of separation were optimized.

Go to article

Studies On The Preparation Of Protomycinolide Iv: Enantioselective Synthesis Of The C3–C9 Segment, James Thomas Wasicak, William Donaldson Jan 1998

Studies On The Preparation Of Protomycinolide Iv: Enantioselective Synthesis Of The C3–C9 Segment, James Thomas Wasicak, William Donaldson

Chemistry Faculty Research and Publications

The C3–C9 segment, (−)-16, of the polyene macrolide antibiotic protomycinolide IV (1a) was prepared in optically pure form from commercially available methyl (S)-2-methyl-3-hydroxypropionate in 12 steps giving 17% yield.

Go to article

Radical Ion Probes. 8. Direct And Indirect Electrochemistry Of 5,7-Di-Tert-Butylspiro[2.5]Octa-4,7-Dien-6-One And Derivatives, J. Paige Phillips, Jason G. Gillmore, Phillip Schwartz, Larry E. Brammer Jr., Daniel J. Berger, J. M. Tanko Jan 1998

Radical Ion Probes. 8. Direct And Indirect Electrochemistry Of 5,7-Di-Tert-Butylspiro[2.5]Octa-4,7-Dien-6-One And Derivatives, J. Paige Phillips, Jason G. Gillmore, Phillip Schwartz, Larry E. Brammer Jr., Daniel J. Berger, J. M. Tanko

Faculty Publications

Results pertaining to the direct and indirect electrochemistry of 5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1a), 1-methyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1b), and 1,1,-dimethyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1c) are reported. Product analyses reveal that reduction of all these substrates leads to cyclopropane ring-opened products; ring opening occurs with modest selectivity leading to the more substituted (stable) distonic radical anion. The direct electrochemistry of these compounds is characterized by rate limiting electron transfer (with α ≈ 0.5), suggesting that while ring opening is extremely rapid, the radical anions do have a discrete lifetime (i.e., electron transfer and ring opening are not concerted). Utilizing homogeneous redox catalysis, rate constants for electron transfer between 1a, …

Go to article

Chiral Separations Of Indan, Tetralin And Benzosuberan Derivatives By Capillary Electrophoresis, Kyung Hyun Gahm, Jauh Tzuoh Lee, Lisa W. Chang, Daniel W. Armstrong Jan 1998

Chiral Separations Of Indan, Tetralin And Benzosuberan Derivatives By Capillary Electrophoresis, Kyung Hyun Gahm, Jauh Tzuoh Lee, Lisa W. Chang, Daniel W. Armstrong

Chemistry Faculty Research & Creative Works

Several indan, tetralin and benzosuberan derivatives of diverse polarities were enantio-resolved by the use of sulfated β-cyclodextrins (CDs) or mixtures of sulfated β-CDs and γ-CD as chiral additives in capillary electrophoresis. Mixtures of sulfated 13-CDs and hydroxypropy1 β- CDs were also successfully utilized for enantiomeric and diastereomeric separations of some of the tetralin derivatives with two stereogenic centers. Both neutral and anionic analytes were resolved in the reversed electrophoretic polarity mode. Cationic amino derivatives of indan and tetralin were enantio-resolved in the conventional electrophoretic polarity mode.

Go to article

Mechanism Of Capillary Electrophoresis Enantioseparations Using A Combination Of An Achiral Crown Ether Plus Cyclodextrins, Daniel W. Armstrong, L. W. Chang, S. S.C. Chang Jan 1998

Mechanism Of Capillary Electrophoresis Enantioseparations Using A Combination Of An Achiral Crown Ether Plus Cyclodextrins, Daniel W. Armstrong, L. W. Chang, S. S.C. Chang

Chemistry Faculty Research & Creative Works

The addition of an achiral crown ether (18-crown-6) to a cyclodextrin- based separation can significantly affect the capillary electrophoresis (CE) enantioresolution of organic racemates that contain a primary amine functional group. In most cases an enhancement of the enantioseparation was observed. However, there are also cases where the addition of 18-crown-6 was detrimental to a cyclodextrin-based CE enantioseparation. The effect of concentration of the two complexing additives as well as the effect of pH and added potassium ion were examined. A specific three-body complex involving simultaneous, dual inclusion complex formation can be used to explain both the enhanced and diminished …

Go to article

Mechanistic Studies Of Cation Photogeneration, Mary Frances Clifton Jan 1998

Mechanistic Studies Of Cation Photogeneration, Mary Frances Clifton

Dissertations

No abstract provided.

Go to article

Biophysical Studies Of The Spectrin Sequence Motif, Denise M. Lusitani Jan 1998

Biophysical Studies Of The Spectrin Sequence Motif, Denise M. Lusitani

Dissertations

No abstract provided.

Go to article

Vibrational Sum Frequency Spectroscopy Of Surfactants And Phospholipids Monolayers At Liquid-Liquid Interfaces, B. L. Smiley, R. A. Walker, D. E. Gragson, T. E. Hannon, G. L. Richmond Jan 1998

Vibrational Sum Frequency Spectroscopy Of Surfactants And Phospholipids Monolayers At Liquid-Liquid Interfaces, B. L. Smiley, R. A. Walker, D. E. Gragson, T. E. Hannon, G. L. Richmond

Chemistry and Biochemistry

Work from our laboratory on vibrational sum frequency spectroscopic investigations of molecular ordering at the carbon tetrachloride-water interface is reviewed. Simple charged surfactants adsorbed at the liquid-liquid interface are seen to induce alignment of interfacial water molecules to a degree which is dependent on the induced surface potential. Saturation of water molecule alignment occurs at a surfactant surface concentration corresponding to a calculated surface potential of approximately 160 mV. In complementary studies, the relative degree of hydrocarbon chain ordering within monolayers of symmetric phosphatidylcholines of different chain lengths is inferred by the relative signal contributions of the methyl and methylene …

Go to article

D/H Exchange In Nitro Diastereomers, Charles A. Kingsbury Jan 1998

D/H Exchange In Nitro Diastereomers, Charles A. Kingsbury

Chemistry Department: Faculty Publications

The two diastereomers of 4-nitro-1,3-diphenylpentan-1-one behave differently in deuterium for hydrogen exchange in DMSO-d6/D2O solutions using various bases as catalyst. Reaction of the erythro diastereomer gives largely the same diastereomer upon D/H exchange (retention), i.e., exchange exceeds epimerization. Pyridine and acetonitrile as solvents lead to faster epimerization than exchange. In the threo diastereomer (DMSO-d6 solution), epimerization exceeds exchange, and the anion to some extent regains the same hydrogen originally removed by the base on the opposite face. 2-Bromo-4-nitro-1,3-diphenylbutan-1-one undergoes ring closure to the cyclopropane faster than exchange (within seconds). The cyclopropane shows faster exchange than equilibration, i.e., retention of configuration, …

Go to article

Dissociation Energies Of The Ga2, In2, And Gain Molecules, G Balducci, G Gigli, Giovanni Meloni Jan 1998

Dissociation Energies Of The Ga2, In2, And Gain Molecules, G Balducci, G Gigli, Giovanni Meloni

Chemistry Faculty Publications

The group III metal dimers Ga2 and In2 and the newly identified intermetallic molecule GaIn were investigated in a Knudsen cell-mass spectrometric study of the vapors over gallium–indium alloys. From the all-gas equilibria analyzed by the second-law and third-law methods the following dissociation energies were derived; D00 (Ga2)=110.8±4.9 kJ mol−1, D00 (In2)=74.4±5.7 kJ mol−1, D00 (GaIn)=90.7±3.7 kJ mol−1. The value here measured for the dissociation energy of In2 is discussed and compared with a previous experimental determination and with the results of more recent theoretical investigations.

Go to article

Petrographic And Chemical Properties Of Carboniferous Resinite From The Herrin No. 6 Coal Seam, John C. Crelling, Michael A. Kruge Jan 1998

Petrographic And Chemical Properties Of Carboniferous Resinite From The Herrin No. 6 Coal Seam, John C. Crelling, Michael A. Kruge

Department of Earth and Environmental Studies Faculty Scholarship and Creative Works

Resinite is a naturally occurring substance found in coal and derived from original plant resins. It is ubiquitous in North American coals and comprises 1 to 4% by volume of most Illinois coals. It has been commercially exploited in the western USA for use in adhesives, varnishes and thermal-setting inks. The major objectives of this study were: (1) to separate resinite macerals from the Herrin No. 6 coal seam and to carefully verify, by petrographic and fluorescence microspectrophotometric methods, that the separated material was indeed resinite; (2) to characterize the chemical composition of the separated resinite by Py–GC–MS techniques; and …

Go to article

Environmental And Botanical Controls On Peatification - A Comparative Study Of Two New Zealand Restiad Bogs Using Py-Gc/Ms, Petrography And Fungal Analysis, Tomasz K. Kuder, Michael A. Kruge, J C. Shearer, S L. Miller Jan 1998

Environmental And Botanical Controls On Peatification - A Comparative Study Of Two New Zealand Restiad Bogs Using Py-Gc/Ms, Petrography And Fungal Analysis, Tomasz K. Kuder, Michael A. Kruge, J C. Shearer, S L. Miller

Department of Earth and Environmental Studies Faculty Scholarship and Creative Works

This study shows that chemical properties of two restiad species, Empodisma minus and Sporadanthus traversii, may contribute to their success as peat-formers in a climate of the North Island of New Zealand which is not conducive to raised mire development. Unlike Sphagnum, the equivalent northern hemisphere peat-former, restiads possess lignin in their tissues. In addition, the presence of non-lignin polyphenols (including tannins and phenolic acids) in restiads may be an important factor in peat formation due to the allelopathic decay retardation. Patterns of degradation of plant biopolymers have been examined and the pathway of degradation of monocotyledons (loss …

Go to article

A Molecular Evaluation Of Contaminants And Natural Organic Matter In Surface Sediments From Western Lake Ontario, Michael A. Kruge, Prasanta K. Mukhopadhyay, C.F. Michael Lewis Jan 1998

A Molecular Evaluation Of Contaminants And Natural Organic Matter In Surface Sediments From Western Lake Ontario, Michael A. Kruge, Prasanta K. Mukhopadhyay, C.F. Michael Lewis

Department of Earth and Environmental Studies Faculty Scholarship and Creative Works

Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) analysis of bottom sediment from Lake Ontario was shown to be effective in assessing organic contaminants, especially attractive as it is a rapid technique requiring little sample preparation. Pyrolyzates of samples richer in organic matter (OM) were relatively enriched in aliphatic hydrocarbons and pyrrolic nitrogen compounds, while leaner samples were more aromatic and pyridinic. Alkylbenzene and alkylphenol distributions in the pyrolyzates were most compatible with derivation from aquatic (algal, bacterial) OM. The organonitrogen compounds indicated the presence of degraded proteinaceous material from aquatic sources and/or sewage. Normal and polycyclic aromatic hydrocarbon distributions indicate, at least in …

Go to article

Effects Of Particle Size And Time On The Reliability Of Toxicity Characteristic Leaching Procedure Results, Michael A. Janusa Jan 1998

Effects Of Particle Size And Time On The Reliability Of Toxicity Characteristic Leaching Procedure Results, Michael A. Janusa

Faculty Presentations

No abstract provided.

Go to article

Designing A Better Matrix For Solidification/Stabilization Of Hazardous Waster With The Aid Of Bagasse (Lignin) As A Polymer Additive To Cement, Michael A. Janusa Jan 1998

Designing A Better Matrix For Solidification/Stabilization Of Hazardous Waster With The Aid Of Bagasse (Lignin) As A Polymer Additive To Cement, Michael A. Janusa

Faculty Presentations

No abstract provided.

Go to article

Effects Of Curing Temperature On The Leachability Of Lead Undergoing Solidification/Stabilization With Cement, Michael A. Janusa Jan 1998

Effects Of Curing Temperature On The Leachability Of Lead Undergoing Solidification/Stabilization With Cement, Michael A. Janusa

Faculty Publications

Curing temperature was found to dramatically affect the amount of waste leached from a solidified waste/cement matrix between 2 and 40°C. Using lead nitrate as a model waste, samples cured for 7,14, and 28 days at a cure temperature of 40°C leached very little lead (1-3 mg/liter), while at a cure temperature of 2°C samples leached approximately 25 times more lead (20-90 mg/liter). The results indicate that curing temperature is a very crucial variable to consider when solidifying waste with cement if maximum stabilization is to be achieved.

Go to article

Effects Of Particle Size And Contact Time On The Reliability Of Toxicity Characteristic Leaching Procedure For Solidified/Stabilized Waste, Michael A. Janusa Jan 1998

Effects Of Particle Size And Contact Time On The Reliability Of Toxicity Characteristic Leaching Procedure For Solidified/Stabilized Waste, Michael A. Janusa

Faculty Publications

Inconsistency in leaching results using the Toxicity Characteristic Leaching Procedure (TCLP)indicates that the procedure should contain specific guidance with respect to the following parameters: ( 1 ) minimum particle size, (2) contact time limit between leachant and waste. Experimental datas how that there is approximately a 50% decrease in the amount of waste leached when a minimum particle size of 8 mm is applied. Results indicate that as the contact time between leachant and waste increases, the amount of waste leached increases drastically. The results suggest that restrictions should be set on these two parameters for TCLP results to be …

Go to article

Radicals, Metals And Magnetism, David J R Brook Jan 1998

Radicals, Metals And Magnetism, David J R Brook

Faculty Publications

The interaction between unpaired electrons governs many physical properties of materials. Although in a fundamental sense the interaction is simple, a full understanding of the interaction in molecular systems is complicated by the presence of other bonding and non-bonding electrons. The resulting many body problem is very challenging. Nevertheless, much qualitative understanding can be obtained from applying simple molecular orbital theory and considering only the partly filled orbitals. The resulting model can be used to describe existing diradical and metal-radical systems and also has predicative value in the search for molecular magnets and design of nanoscale devices.

Go to article

Mass Transfer With Chemical Reaction In The Process Of Ammonia Desorption From Aqueous Solutions Containing Carbon Dioxide, Wojciech M. Budzianowski Jan 1998

Mass Transfer With Chemical Reaction In The Process Of Ammonia Desorption From Aqueous Solutions Containing Carbon Dioxide, Wojciech M. Budzianowski

Wojciech Budzianowski

No abstract provided.

Go to article

Archiv Der Pharmazie, Philadelphia University Jan 1998

Archiv Der Pharmazie, Philadelphia University

Philadelphia University, Jordan

No abstract provided.

Go to article

Simulation And Fpga Implementation Of A Simple Computer, Philadelphia University Jan 1998

Simulation And Fpga Implementation Of A Simple Computer, Philadelphia University

Philadelphia University, Jordan

No abstract provided.

Go to article

Computational Evidence For A Free Silylium Ion, Thomas Müller, Yan Zhao, Joseph B. Lambert Jan 1998

Computational Evidence For A Free Silylium Ion, Thomas Müller, Yan Zhao, Joseph B. Lambert

Yan Zhao

Ab initio calculations are the method of choice to gain an insight into the structure and properties of silylium ions, especially when an X-ray structure cannot be obtained, as in the case of trimesitylsilylium (1). The computed structures and properties of triarylsilylium ions suggest that 1 is the first free silylium ion prepared in the condensed phase.

Go to article

33. Noburo Yamazaki, Otto Vogl, Seiichi Nakahama Jan 1998

33. Noburo Yamazaki, Otto Vogl, Seiichi Nakahama

Otto Vogl

No abstract provided.

Go to article

Ionic Hydrogen Bonds In Bioenergetics. 3. Proton Transport In Membranes, Modeled By Ketone/Water Clusters, Michael Meot-Ner, Steve Scheiner, Edward Yu Jan 1998

Ionic Hydrogen Bonds In Bioenergetics. 3. Proton Transport In Membranes, Modeled By Ketone/Water Clusters, Michael Meot-Ner, Steve Scheiner, Edward Yu

Edward Yu

Hydrogen bond networks in protonated acetone/water clusters are stabilized by H3O+(Me2CO)2 centers, and the stabilizaton increases with further acetone content. For example, proton transfer from neat water (H2O)6H+ clusters to form mixed (Me2CO)3(H2O)3H+ clusters is exothermic by 80 kJ/mol (19 kcal/mol), due to strong hydrogen bonding of the carbonyl groups; in a series of mixed clusters B3(H2O)3H+, the stability of the hydrogen bond network correlates with the proton affinities PA(B). In diketone models of adjacent peptide links, the proton is stabilized by internal hydrogen bonds between the carbonyl groups. The internal bonds can be significant, for example, 31 kJ/mol (7 …

Go to article

Radicals, Metals And Magnetism, David J R Brook Jan 1998

Radicals, Metals And Magnetism, David J R Brook

Faculty Publications, Chemistry

The interaction between unpaired electrons governs many physical properties of materials. Although in a fundamental sense the interaction is simple, a full understanding of the interaction in molecular systems is complicated by the presence of other bonding and non-bonding electrons. The resulting many body problem is very challenging. Nevertheless, much qualitative understanding can be obtained from applying simple molecular orbital theory and considering only the partly filled orbitals. The resulting model can be used to describe existing diradical and metal-radical systems and also has predicative value in the search for molecular magnets and design of nanoscale devices.

Go to article

Influences Of Acid Mine Drainage On Water Chemistry Of Blackwater River Watershed, Carla C. Morato-Lara Jan 1998

Influences Of Acid Mine Drainage On Water Chemistry Of Blackwater River Watershed, Carla C. Morato-Lara

Theses, Dissertations and Capstones

Acidic mine drainage flow from active and abandoned coal mines has been a major source of water pollution in the Appalachian Mountain region of the eastern USA. Water samples were collected and analyzed from Blackwater River watershed during 2 years (September 1996 - May 1998). The water quality measurements determined that the Beaver Creek and North Fork tributaries were affected by acid mine drainage but not Yellow Creek. Beaver Creek and North Fork stations had high sulfate and manganese markers of acid mine drainage, whereas Yellow Creek was slightly acidic with low sulfate and manganese. North Fork was the primary …

Go to article

Approaches To A Generalized Synthesis For Hexaphenylbutadiene, Karena Kaye Linkenhoger Robinson Jan 1998

Approaches To A Generalized Synthesis For Hexaphenylbutadiene, Karena Kaye Linkenhoger Robinson

Theses, Dissertations and Capstones

This study was concerned with the attempted development of a generalized synthesis of hexaphenylbutadiene. Three methods were attempted: Michael Addition of cyanide to -phenylcinnamate followed by organolithium or Grignard addition; reaction of benzil with two moles of the Wittig reagent prepared from bromodiphenylmethane; reaction of two moles of benzophenone with the bisphosphorane prepared from 1,2- dibromo-1,2-diphenylethane.

Go to article

Synthesis And Characterization Of A Trypsin Inhibitor, Eric L. Schneider Jan 1998

Synthesis And Characterization Of A Trypsin Inhibitor, Eric L. Schneider

Honors Theses, 1963-2015

Inhibitors of biological enzymes are frequently produced by mimicking the molecular structure of the enzyme's natural substrate. Because of the extensive studies that have already been performed on the trypsin enzyme, its natural substrates and its mode of interaction with them are well understood. By finding an easily synthesized molecule to inhibit the trypsin enzyme, college level laboratory experiments could be designed and integrated into organic chemistry and biochemistry courses. In this project, a possible trypsin inhibitor molecule, 4-fluorobenzylaimine, was chosen based on its similarity to the natural trypsin substrates and because it has been predicted through computational studies to …

Go to article

Arginine To Glutamine Substitutions In The Fourth Module Of Xenopus Interphotoreceptor Retinoid-Binding Protein, Mark S. Braiman, Claxton A. Baer, Ellen E. Van Niel, Jeffrey W. Cronk, Michael T. Kinter, Nicholas E. Sherman, Federico Gonzalez-Fernandez Jan 1998

Arginine To Glutamine Substitutions In The Fourth Module Of Xenopus Interphotoreceptor Retinoid-Binding Protein, Mark S. Braiman, Claxton A. Baer, Ellen E. Van Niel, Jeffrey W. Cronk, Michael T. Kinter, Nicholas E. Sherman, Federico Gonzalez-Fernandez

Chemistry - All Scholarship

Interphotoreceptor retinoid-binding protein (IRBP) is unusual for a lipid-binding protein in that its gene is expressed uniquely by cells of photoreceptor origin and consists of four homologous repeats, each coding for a module of~300 amino acid residues. All-trans retinol binding domains, which appear to be present in each module, are composed of conserved hydrophobic regions [Baer et al, Exp Eye Res 1998; 66:249-262]. Here we investigate the role of highly conserved arginines contained in these regions.

Go to article

First Prev Next Last