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Chemistry Faculty Publications

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Articles 1081 - 1110 of 1129

Full-Text Articles in Chemistry

Refinement Of The Solution Structure Of A Branched Dna Three-Way Junction, Neocles B. Leontis, Igor V. Ouporov Jan 1995

Refinement Of The Solution Structure Of A Branched Dna Three-Way Junction, Neocles B. Leontis, Igor V. Ouporov

Chemistry Faculty Publications

We have refined the structure of the DNA Three-Way Junction complex, TWJ- TC, described in the companion paper by quantitative analysis of two 2D NOESY spectra (mixing times 60 and 200 ms) obtained in D2O solution. NOESY crosspeak intensities extracted from these spectra were used in two kinds of refinement procedure: 1) distance-restrained energy minimization (EM) and molecular dynamics (MD) and 2) full relaxation matrix back calculation refinement. The global geometry of the refined model is very similar to that of a published, preliminary model (Leontis, 1993). Two of the helical arms of the junction are stacked. These are Helix …

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Helical Stacking In Dna 3-Way Junctions Containing 2 Unpaired Pyrimidines - Proton Nmr-Studies, Neocles B. Leontis, Michael T. Hills, Martial Piotto, Igor V. Ouporov, Arun Malhotra, David G. Gorenstein Jan 1995

Helical Stacking In Dna 3-Way Junctions Containing 2 Unpaired Pyrimidines - Proton Nmr-Studies, Neocles B. Leontis, Michael T. Hills, Martial Piotto, Igor V. Ouporov, Arun Malhotra, David G. Gorenstein

Chemistry Faculty Publications

The proton NMR spectra of DNA three-way junction complexes (TWJ) having unpaired pyrimidines, 5'-TT- and 5'-TC- on one strand at the junction site were assigned from 2D NOESY spectra acquired in H2O and D2O solvents and homonuclear 3D NOESY-TOCSY and 3D NOESY-NOESY in D2O solvent. TWJ are the simplest branched structures found in biologically active nucleic acids. Unpaired nucleotides are common features of such structures and have been shown to stabilize junction formation. The NMR data confirm that the component oligonucleotides assemble to form conformationally homogeneous TWJ complexes having three double-helical, B-form arms. Two of the helical arms stack upon …

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Cs2ga2o(Bo3)2, Robert W. Smith Jan 1995

Cs2ga2o(Bo3)2, Robert W. Smith

Chemistry Faculty Publications

The structure of dicaesium digallium diorthoborate oxide constitutes a new type of oxide borate. It consists of a three-dimensional gallium-oxide-orthoborate lattice with Cs atoms occupying large cavities in the lattice. This lattice is made from pairs of Ga atoms connected through a shared O atom along the [001] direction; these Ga dimers are interconnected through shared O vertices to trigonal BO3 groups along the [010], [110] and [i10] directions, completing the tetrahedral coordination environment of each Ga atom.

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Three-Body Analytical Potential For Interacting Helium Atoms, Carol A. Parish, Clifford E. Dykstra Nov 1994

Three-Body Analytical Potential For Interacting Helium Atoms, Carol A. Parish, Clifford E. Dykstra

Chemistry Faculty Publications

Large basis set ab initio calculations have been carried out for a dense grid of points on the He, potential energy surface. Three-body contributions were extracted at every point, and a number of concise functional representations for the three-body potential surface were then examined. Three-body multipolar dispersion terms and other radial and angular terms were used in the representations, and an assessment of relative importance of the different terms is presented. Combined with a two-body He-He potential, the results of this work should offer a high quality interaction potential for simulations of aggregated helium.

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Dissection Of An Antibody-Catalyzed Reaction, Jon D. Stewart, Joseph F. Krebs, Gary Siuzdak, Anthony J. Berdis, David B. Smithrud, Stephen J. Benkovic Aug 1994

Dissection Of An Antibody-Catalyzed Reaction, Jon D. Stewart, Joseph F. Krebs, Gary Siuzdak, Anthony J. Berdis, David B. Smithrud, Stephen J. Benkovic

Chemistry Faculty Publications

Antibody 43C9 accelerates the hydrolysis of a p-nitroanilide by a factor of 2.5 x 10(5) over the background rate in addition to catalyzing the hydrolysis of a series of aromatic esters. Since this represents one of the largest rate accelerations achieved with an antibody, we have undertaken a series of studies aimed at uncovering the catalytic mechanism of 43C9. The immunogen, a phosphonamidate, was designed to mimic the geometric and electronic characteristics of the tetrahedral intermediate that forms upon nucleophilic attack by hydroxide on the amide substrate. Further studies, however, revealed that the catalytic mechanism is more complex and involves …

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The Thermodynamics Of Formation Of A Three-Strand, Dna Three-Way Junction Complex, John E. Ladbury, Julian M. Sturtevant, Neocles B. Leontis Jun 1994

The Thermodynamics Of Formation Of A Three-Strand, Dna Three-Way Junction Complex, John E. Ladbury, Julian M. Sturtevant, Neocles B. Leontis

Chemistry Faculty Publications

Isothermal titration calorimetry (ITC) is used to study the thermodynamics of assembly of the three DNA oligonucleotides S1 (5'GCCTGCCACCGC), S2 (5'-GCGGTGCGTCCG), and S3AA (5'-CGGACGAAGCAGGC) to form a three-way junction (TWJ) complex consisting of three double-helical arms radiating from a junction region having two unpaired adenosines in one strand (S3AA). The thermodynamics of assembly were measured for three different orders of addition of the component oligonucleotides at four temperatures between 10 and 25 degrees C. At each temperature studied, the overall values of Delta H, Delta S degrees, and Delta G degrees for assembly of the complex from the component single …

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An Ultra-Sensitive Electrochemical Enzyme Immunoassay For Thyroid Stimulating Hormone In Human Serum, Zhengrong Yu, Yan Xu, Michael P.C. Ip Jun 1994

An Ultra-Sensitive Electrochemical Enzyme Immunoassay For Thyroid Stimulating Hormone In Human Serum, Zhengrong Yu, Yan Xu, Michael P.C. Ip

Chemistry Faculty Publications

A sensitive heterogeneous electrochemical enzyme immunoassay has been developed for thyroid stimulating hormone (TSH) by modifying a commercially available two-site immunoenzymometric assay. p-Aminophenyl phosphate (PAPP) was used as the substrate of alkaline phosphatase, and hydrolysed to p-aminophenol (PAP). The amount of PAP produced from the assay was proportional to the amount of TSH in the sample. Detection of PAP was done by oxidative amperometry in a flow injection system. The working electrode was a glassy carbon electrode whose potential was held at +325 mV (vs Ag/AgCl). The amperometric detection of PAP required only 1 μl of sample (the range of …

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Electrochemical Enzyme Immunoassay Using Sequential Saturation Technique In A 20-Μl Capillary: Digoxin As A Model Analyte, Noriaki Kaneki, Yan Xu, Anu Kumari, H. Brian Halsall, William R. Heineman, Peter T. Kissinger Mar 1994

Electrochemical Enzyme Immunoassay Using Sequential Saturation Technique In A 20-Μl Capillary: Digoxin As A Model Analyte, Noriaki Kaneki, Yan Xu, Anu Kumari, H. Brian Halsall, William R. Heineman, Peter T. Kissinger

Chemistry Faculty Publications

Capillary enzyme immunoassay with flow-injection analysis for digoxin using the sequential saturation technique has been developed. Glass capillary tubes (10 cm × 0.53 mm i.d.) with immobilized digoxin antibody were used as the immunoassay reactor. The product of enzymatic reaction. 4-aminophenol, was detected amperometrically. The digoxin and the labeled digoxin binding reaction with the immobilized digoxin antibody were completed in 2 and 10 min, respectively. Digoxin was determined in a 20-μl sample with a detection limit of 10 pg ml−1 (200 fg or 260 attomoles) and a 3 orders of magnitude range.

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Effects Of Unpaired Bases On The Conformation And Stability Of Three-Arm Dna Junctions, Min Zhong, Michael S. Rashes, Neocles B. Leontis, Neville R. Kallenbach Mar 1994

Effects Of Unpaired Bases On The Conformation And Stability Of Three-Arm Dna Junctions, Min Zhong, Michael S. Rashes, Neocles B. Leontis, Neville R. Kallenbach

Chemistry Faculty Publications

Three-arm DNA junctions, in which three double helices intersect at a branch, have unique structure and reactivity of bases at and near the branch. Their solution conformation is asymmetric in the presence of Mg2+, while bases at the branch are sensitive to single-strand-specific agents. Following the surprising report that unpaired bases at the branch stabilize three-arm junctions, we have investigated the geometry and thermodynamics of three-arm junctions containing pendant T and A bases. The results are consistent with additional structure formation in junctions containing up to four pendant bases at the branch: relative to the tight junction, the …

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Use Of Pyocin To Select A Haemophilus Ducreyi Variant Defective In Lipooligosaccharide Biosynthesis, A A. Campagnari, R Karalus, M A. Apicella, William Melaugh, A J. Lesse, B W. Gibson Jan 1994

Use Of Pyocin To Select A Haemophilus Ducreyi Variant Defective In Lipooligosaccharide Biosynthesis, A A. Campagnari, R Karalus, M A. Apicella, William Melaugh, A J. Lesse, B W. Gibson

Chemistry Faculty Publications

Haemophilus ducreyi, a cause of genital ulcer disease in developing countries, appears to facilitate the heterosexual transmission of the human immunodeficiency virus in Africa. Despite an increase in studies of this gram-negative human pathogen, little is known about the pathogenesis of chancroid. Our studies have shown that the lipooligosaccharides (LOS) of H. ducreyi may play an important role in ulcer formation. Monoclonal antibody and mass spectrometric analyses identified a terminal trisaccharide present on H. ducreyi LOS that is immunochemically similar to human paragloboside. This epitope is present on the LOS of Neisseria gonorrhoeae, and it may be the site of …

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The 2′-Phosphate Of Nadp Is Critical For Optimum Productive Binding To 6-Phosphogluconate Dehydrogenase From Candida Utilis, Anthony J. Berdis, Paul F. Cook Sep 1993

The 2′-Phosphate Of Nadp Is Critical For Optimum Productive Binding To 6-Phosphogluconate Dehydrogenase From Candida Utilis, Anthony J. Berdis, Paul F. Cook

Chemistry Faculty Publications

Initial velocity studies obtained with alternative dinucleotide substrates for the 6-phosphogluconate dehydrogenase reaction suggest that the 2′-phosphate is critical for the optimum productive binding of the dinucleotide substrate. Initial velocity patterns obtained by varying 6-phosphogluconate at different fixed levels of NAD are nearly parallel with apparent competitive substrate inhibition by 6-phosphogluconate at pH 7 and below but intersect to the left of the ordinate at pH 8 and above. Dead-end inhibition studies indicate that the mechanism is random at all pH values. Data are interpreted in terms of a random mechanism with marked antagonism in the binding of NAD and …

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Investigation Of The Structural Heterogeneity Of Lipooligosaccharides From Pathogenic Haemophilus And Neisseria Species And Of R-Type Lipopolysaccharides From Salmonella Typhimurium By Electrospray Mass Spectrometry, B W. Gibson, William Melaugh, Nancy J. Phillips, M A. Apicella, A A. Campagnari, J M. Griffiss Jan 1993

Investigation Of The Structural Heterogeneity Of Lipooligosaccharides From Pathogenic Haemophilus And Neisseria Species And Of R-Type Lipopolysaccharides From Salmonella Typhimurium By Electrospray Mass Spectrometry, B W. Gibson, William Melaugh, Nancy J. Phillips, M A. Apicella, A A. Campagnari, J M. Griffiss

Chemistry Faculty Publications

Heterogeneity in the lipooligosaccharides (LOS) of pathogenic Haemophilus and Neisseria species is evident from the multiplicity of components observed with electrophoretic analyses. Knowledge of the precise structures that make up these diverse LOS molecules is clearly the key to reaching an understanding of pathogenic processes such as phase variation and molecular mimicry. Except for a few cases, little is known about the specific structural features of LOS that underlie phase variation and molecular mimicry, partly because of the inherent difficulties in the structural elucidation of these complex glycolipids. In the lipopolysaccharides (LPS) from Salmonella typhimurium and Escherichia coli, rough, or …

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A-Helical Polypeptide Monolayers, Erwin P. Enriquez Jan 1993

A-Helical Polypeptide Monolayers, Erwin P. Enriquez

Chemistry Faculty Publications

In efforts to utilize the a-helical structural motif as a basic building block in the formation of supramolecular assemblies, a study of the self-assembly of a-helical poly(glutamate)s from dilute solution onto a solid support was initiated. In particular, poly(y-benzyl-L-glutamate) [PBLG], which has an unusually robust a-helical conformation, was functionalized at the amino terminus with a disulfide-containing moiety (lipoic acid), which in turn has a specific and strong chemisorptive interaction with gold surfaces. The same end group functionalization was used with the /i-alkyl side chain analogs of PBLG. The resulting self-assembled monolayers were characterized by grazing angle reflection infrared (GIR-IR) spectroscopy, …

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Pairwise And Many-Body Contributions To Interaction Potentials In He(N) Clusters, Carol A. Parish, Clifford E. Dykstra Jan 1993

Pairwise And Many-Body Contributions To Interaction Potentials In He(N) Clusters, Carol A. Parish, Clifford E. Dykstra

Chemistry Faculty Publications

High level ab initio calculations have been carried out to assess the pairwise additivity of potentials in the attractive or well regions of the potential surfaces of clusters of helium atoms. A large basis set was employed and calculations were done at the Brueckner orbital coupled cluster level. Differences between calculated potentials for several interacting atoms and the corresponding summed pair potentials reveal the three‐body and certain higher order contributions to the interaction strengths. Attraction between rare gas atoms develops from dispersion, and so helium clusters provide the most workable systems for analyzing nonadditivity of dispersion. The results indicate that …

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Dispiro- 1,2,4,5-Tetraoxanes: A New Class Of Antimalarial Peroxides, Jonathan L. Vennerstrom, Hong-Ning Fu, Walter Reed Army Institute Of Research, Arba L. Ager Jr., James K. Wood Aug 1992

Dispiro- 1,2,4,5-Tetraoxanes: A New Class Of Antimalarial Peroxides, Jonathan L. Vennerstrom, Hong-Ning Fu, Walter Reed Army Institute Of Research, Arba L. Ager Jr., James K. Wood

Chemistry Faculty Publications

Dispiro-l,2,4,5tetraoxanes2 -4 were synthesized as potential peroxide a n t h a l a* d drugs. They had curative activity against Plasmodium berghei in vivo at single doses of 320 and 640 mg/kg which confirms earlier unpublished data Moreover, artemisinin (1) and 4 had equivalent ED”s against P. berghei in vivo in the multiple-dose Thompson tat; neither showed any evidence of acute toxicity at total doses of more than 12 g/kg. Dispiro-l,2,4,5-tetraoxane 4 had IC50’s comparable to those of 1 against Plasmodium falciparum clones in vitro. These results confirm the potential of dispiro-l,2,4,5-tetraoxanes as a new class of …

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Partial Characterization Of The Major Lipooligosaccharide From A Strain Of Haemophilus Ducreyi, The Causative Agent Of Chancroid, A Genital Ulcer Disease, William Melaugh, Nancy J. Phillips, A A. Campagnari, R Karalus, B W. Gibson Jan 1992

Partial Characterization Of The Major Lipooligosaccharide From A Strain Of Haemophilus Ducreyi, The Causative Agent Of Chancroid, A Genital Ulcer Disease, William Melaugh, Nancy J. Phillips, A A. Campagnari, R Karalus, B W. Gibson

Chemistry Faculty Publications

The first preliminary structure of a surface lipooligosaccharide from Haemophilus ducreyi has been determined. The major oligosaccharide was released by mild acid hydrolysis and analyzed by liquid secondary ion and tandem mass spectrometry. The mass spectral data combined with composition and methylation analysis yielded the most probable structure; Gal1----4GlcNAc1----3Gal1----4Hep1----6Glc1----( Hep1----2Hep1----)3,4Hep1---- KDO, where the reducing terminal 3-deoxy-D-manno-octulosonic acid (or KDO) exists in an anhydro form. This anhydro species results from the elimination of a phosphate from C-4 of KDO during mild acid hydrolysis. The core heptose trisaccharide consists of L-glycero-D-manno-heptose, but analysis of the peracetylated sugars indicated that the 1,4-linked heptose …

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Liquid Phase Electrochemistry At Ultralow Temperatures, Royce W. Murray, Stanton Ching, John T. Mcdevitt, Stephen R. Peck Aug 1991

Liquid Phase Electrochemistry At Ultralow Temperatures, Royce W. Murray, Stanton Ching, John T. Mcdevitt, Stephen R. Peck

Chemistry Faculty Publications

Fluid electrolyte solutions based on mixtures of butyronitrile (PrCN) and ethyl chloride (EtCl) with or as electrolyte freeze below −180°C and provide excellent media for cryogenic electrochemical experiments. A 1:2 mixture of PrCN and EtCl exhibits the best combination of freezing point and ionic conductivity for ultralow temperature electrochemistry. Diffusion coefficients for bis(pentamethylcyclopentadienyl) iron are measurable by potential step chronoamperometry down to −160°C using a conventionally sized electrode, but the resistivity of the solvent mixture is such that potential sweep voltammetry benefits from the use of microdisk (10 and 25 μm diam Pt) or microband (0.2 μm wide Au) electrodes. …

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Nonlinear Optical Properties Of Bacteriorhodopsin: Assignment Of The Third-Order Polarizability Based On Two-Photon Absorption Spectroscopy, Robert R. Birge, Mark Masthay, Jeffery A. Stuart, Jack R. Tallent, Chian-Fan Zhang Jun 1991

Nonlinear Optical Properties Of Bacteriorhodopsin: Assignment Of The Third-Order Polarizability Based On Two-Photon Absorption Spectroscopy, Robert R. Birge, Mark Masthay, Jeffery A. Stuart, Jack R. Tallent, Chian-Fan Zhang

Chemistry Faculty Publications

The third-order (pi) -electron polarizability, (gamma) (pi), of bacteriorhodopsin in the 0.0 - 1.2 eV optical region is assigned based on an analysis of the experimental two-photon properties of the low-lying singlet state manifold. The following selected values of (gamma) (pi) (units of 10-36 esu) are observed: (gamma) (0;0,0,0) equals 2482 +/- 327; (gamma) (-3(omega) ;(omega) ,(omega) ,(omega) ) equals 2976 +/- 385 ((omega) equals 0.25 eV), 5867 +/- 704 ((omega) = 0.5 eV), 14863 +/- 1614 ((omega) = 0.66 eV), 15817 +/- 2314 ((omega) equals 1.0 eV), 10755 +/- 1733 ((omega) equals 1.17 eV). The third-order polarizability of this …

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Stability And Structure Of Three-Way Dna Junctions Containing Unpaired Nucleotides, Neocles B. Leontis, Wendy Kwok, Jennifer S. Newman Feb 1991

Stability And Structure Of Three-Way Dna Junctions Containing Unpaired Nucleotides, Neocles B. Leontis, Wendy Kwok, Jennifer S. Newman

Chemistry Faculty Publications

Non-paired nucleotides stabilize the formation of three-way helical DNA junctions. Two or more unpaired nucleotides located in the junction region enable oligomers ten to fifteen nucleotides long to assemble, forming conformationally homogeneous junctions, as judged by native gel electrophoresis. The unpaired bases can be present on the same strand or on two different strands. Up to five extra bases on one strand have been tested and found to produced stable junctions. The formation of stable structures is favoured by the presence of a divalent cation such as magnesium and by high monovalent salt concentration. The order-disorder transition of representative three-way …

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Photoinduced Electron Transfer In Self-Associated Complexes Of Several Uroporphyrins And Cytochrome C, J. S. Zhou, E. S. V. Granada, Neocles B. Leontis, M. A. J. Rodgers Jun 1990

Photoinduced Electron Transfer In Self-Associated Complexes Of Several Uroporphyrins And Cytochrome C, J. S. Zhou, E. S. V. Granada, Neocles B. Leontis, M. A. J. Rodgers

Chemistry Faculty Publications

Photoinduced electron transfer between cytochrome c and free base and metallouroporphyrin (Up, MUp) has been studied. Difference absorption spectrophotometry showed that the electrostatic interactions between Up and cytc(II1) result in their forming a self-associated 1:l complex in the ground state with a binding constant that depends upon the ionic strength. In the complex, the photoexcited uroporphyrin singlet state was quenched through a static interaction with the protein. Even under the most favorable quenching conditions, Le., when all porphyrin was complexed, residual fluorescence was noted. More significantly the excited singlet state of the complex was shown to undergo small, but significant, …

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Substituent Effects On The Electronic Spectroscopy Of Tryptophan Derivatives In Jet Expansions, John R. Cable, Michael J. Tubergen, Donald H. Levy Jan 1990

Substituent Effects On The Electronic Spectroscopy Of Tryptophan Derivatives In Jet Expansions, John R. Cable, Michael J. Tubergen, Donald H. Levy

Chemistry Faculty Publications

Electronic excitation spectra of seven tryptophan derivatives entrained in a supersonic expansion have been recorded using both resonantly enhanced two-photon ionization and laser induced fluorescence. Two derivatives, tryptophan amide and tryptophan methyl amide, were found to have substantial low frequency vibrational progressions in their excitation spectra, yet in both compounds this behavior was apparent in only one conformer. Other derivatives did not display as much vibronic activity. Conformers which had vibrational progressions were found to emit in a broad band far to the red of excitation. All other conformers were found to fluoresce most strongly in resonance with excitation. The …

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Structure Of Ba2cu(Bo3)2, Robert W. Smith, Douglas A. Keszler Jan 1990

Structure Of Ba2cu(Bo3)2, Robert W. Smith, Douglas A. Keszler

Chemistry Faculty Publications

As part of our program in the synthesis and characterization of new solid-state borates, we recently synthesized the polymorphic compound Sr2Cu(BO3)2 (Smith & Keszler, 1989) which undergoes a first-order phase transition from a low-temperature form to a high-temperature form at 1073 K. The high-temperature beta form exhibits larger coordination numbers for the Sr atoms and a substantial rearrangement of the copper borate network relative to that of the low-temperature... form.

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Stress-Induced Infrared Frequency Shifts In Polyethylene, George A. Pfeffer, Donald W. Noid Jan 1990

Stress-Induced Infrared Frequency Shifts In Polyethylene, George A. Pfeffer, Donald W. Noid

Chemistry Faculty Publications

The molecular dynamics technique is used to study the spectral response of a polyethylene chain in a crystal environment under a mechanical deformation. The MUSIC method, which was previously shown to accurately compute dispersion curves from the time-dependent structure factor, is used. A complete characterization of frequency shifts is presented for various lamellar thickness, temperatures, stress (or pressure), and mass defects.

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Insecticides Based On Differences In Metabolic Pathways, Richard T. Mayer, G N. Cunningham, John T. Gupton Jan 1990

Insecticides Based On Differences In Metabolic Pathways, Richard T. Mayer, G N. Cunningham, John T. Gupton

Chemistry Faculty Publications

Insects have been major pests of humankind at least since the beginning of recorded history. To this day insects continue to cause problems in domestic, agricultural, and health situations. It is no wonder that people have continually sought new solutions to controlling insect pests. Even when new control methods are discovered and established, insects evolve into resistant species so that the method is only of real value for a few brief years. Modern science and technology are now enabling scientists to tear away the fabric that has so long masked physiological and biochemical events critical to insects. Armed with this …

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Photocycloaddition Of 4,5',8-Trimethylpsoralen And Oleic Acid Methyl Ester: Product Structures And Reaction Mechanism, Kathleen G. Specht, W. Robert Midden, Miles R. Chedekel Aug 1989

Photocycloaddition Of 4,5',8-Trimethylpsoralen And Oleic Acid Methyl Ester: Product Structures And Reaction Mechanism, Kathleen G. Specht, W. Robert Midden, Miles R. Chedekel

Chemistry Faculty Publications

The stereochemical structures of the four adducts formed between oleic acid methyl ester (OAME) and 4,5',8-trimethylpsoralen (tmPso) have been determined. Assignment of the tmPso 'H NMR spectrum was accomplished by analogy to two coumarin model compounds and with the use of homonuclear decoupling and resonance enhancement. Assignment of the lH NMR spectra for the OAME-tmPso adducts was made by analogy to the spectra of OAME and tmPso and using 2D &resolved and COSY analyses. The configurations of the cyclobutyl rings in these adducts was determined by The stereochemical structures of the four adducts formed between oleic acid methyl ester (OAME) …

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Origins Of The Quantum Efficiency Duality In The Primary Photochemical Event Of Bacteriorhodopsin, Robert R. Birge, Leonore A. Findsen, Albert F. Lawrence, Mark Masthay, Chian-Fan Zhang May 1989

Origins Of The Quantum Efficiency Duality In The Primary Photochemical Event Of Bacteriorhodopsin, Robert R. Birge, Leonore A. Findsen, Albert F. Lawrence, Mark Masthay, Chian-Fan Zhang

Chemistry Faculty Publications

Experimental and theoretical evidence is presented which suggests that two distinct forms of light-adapted bacteriorhodopsin may exist. We propose that these two forms have characteristic photocycles with significantly different primary quantum yields. INDO-PSDCI molecular orbital procedures and semiempirical molecular dynamics simulations predict that one ground state geometry of bR undergoes photochemistry with a primary quantum yield, Φ1, of ~ 0.27, and that a second ground state geometry, with a slightly displaced counterion, yields Φ1 ~ 0.74. This theoretical model is supported by the observation that literature measurements of Φ1 tend to fall into one of two categories- those that observe …

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Solid-Phase Electrochemical Enzyme Immunoassay With Attomole Detection Limit By Flow Injection Analysis, Yan Xu, H. Brian Halsall, William R. Heineman Jan 1989

Solid-Phase Electrochemical Enzyme Immunoassay With Attomole Detection Limit By Flow Injection Analysis, Yan Xu, H. Brian Halsall, William R. Heineman

Chemistry Faculty Publications

A sandwich electrochemical enzyme immunoassay with flow injection analysis for the model antigen mouse IgG has been developed with alkaline phosphatase as the enzyme label. The enzyme substrate, 4-aminophenyl phosphate and its enzymatic reaction product, 4-aminophenol have been studied by cyclic and hydrodynamic voltammetry. The determination of 4-aminophenol by flow injection analysis with electrochemical detection (FIAEC) has a linear range of 5.0 × 10−8 to 1.0 × 10−5 M, a detection limit of 2.4 × 10−8 M, and a sample throughput of 72 samples/h. The detection limit is set by a background capacitance response, which depends on the ionic strength …

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Computer Simulation Of The Melting Process In Linear Macromolecules, Donald W. Noid, George A. Pfeffer, Stephen Z.D. Cheng, Bernhard Wunderlich Jan 1988

Computer Simulation Of The Melting Process In Linear Macromolecules, Donald W. Noid, George A. Pfeffer, Stephen Z.D. Cheng, Bernhard Wunderlich

Chemistry Faculty Publications

Polymer crystal melting kinetics is simulated by using molecular dynamics. A simplified molecular model of polyethylene crystal melting consisting of one extended chain on a polyethylene-like crystal surface is presented. The simulation data indicate that the end-to-end distance (eed) of radius of gyration (rg) has a simple exponential dependence on time. The rate constants for eed and rg are found to be temperature and molecular length dependent. A more detailed analysis of polymer crystal melting will be described.

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Applications Of The Semiclassical Spectral Method To Nuclear, Atomic, Molecular, And Polymeric Dynamics, M. L. Koszykowski, George A. Pfeffer, Donald W. Noid Jan 1987

Applications Of The Semiclassical Spectral Method To Nuclear, Atomic, Molecular, And Polymeric Dynamics, M. L. Koszykowski, George A. Pfeffer, Donald W. Noid

Chemistry Faculty Publications

Nonlinear dynamics plays a dominant role in a variety of important problems in chemical physics. Examples are unimolecular reactions,’ infrared multiphoton decomposition of molecules,’ the pumping process of the gamma ray laser,’ dissociation of vibrationally excited state-selected van der Waals’s complexes,’ and many other chemical and atomic processes. The present article discusses recent theoretical studies on the quasi-periodic and chaotic dynamical aspects of vibrational-rotational states of atomic, nuclear, and molecular systems using the semiclassical spectral method (SSM).’ We note that the coordinates, momenta, and so on, are found using classical mechanics in the studies included in this review. Consequently, certain …

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A Theoretical Investigation Of The One– And Two–Photon Properties Of Porphyrins, Mark Masthay, Leonore A. Findsen, Brian M. Pierce, David F. Bocian, James S. Lindsey, Robert R. Birge Jan 1986

A Theoretical Investigation Of The One– And Two–Photon Properties Of Porphyrins, Mark Masthay, Leonore A. Findsen, Brian M. Pierce, David F. Bocian, James S. Lindsey, Robert R. Birge

Chemistry Faculty Publications

The one‐ and two‐photon properties of free base porphin, free base porphin dianion, and the 2,4‐substituted diformyl and divinyl analogs of these molecules are studied using a semiempirical SCF‐MO formalism (CNDO‐π‐SCF‐MO‐PSDCI) including extensive single and double configuration interaction. Strongly two‐photon allowed states are predicted to lie in the Soret region as well as in the region between the Soret and visible bands. A number of the two‐photon allowed states in the Soret region are predicted to have two‐photon absorptivities exceeding 100×10−50 cm4 s molecule−1 photon−1. The calculations indicate that the visible (Q) states are well characterized by the …

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