8 results on '"Amy L. Graham"'
Search Results
2. Chemisorption of microcystins to a thiol and amine functionalized organosilica
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Paul L. Edmiston, Amy L. Graham, Kimberly A. Carter, and Emily J. Gleason
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chemistry.chemical_classification ,Addition reaction ,Chemistry ,Metal ions in aqueous solution ,Filtration and Separation ,02 engineering and technology ,010501 environmental sciences ,021001 nanoscience & nanotechnology ,01 natural sciences ,Analytical Chemistry ,Adsorption ,Nucleophile ,Chemisorption ,Polymer chemistry ,polycyclic compounds ,Michael reaction ,Thiol ,Amine gas treating ,0210 nano-technology ,0105 earth and related environmental sciences - Abstract
Microcystins are cyclic heptapeptide toxins produced by cyanobacteria that are frequently detected in surface waters during seasonal blooms. Chemisorption of microcystin through covalent bond formation to the acryloyl group common to all congeners was hypothesized to be a high affinity adsorption mechanism. Sol-gel derived organosilica materials were synthesized as sorbents that could potentially facilitate a Michael addition reaction between an immobilized thiol group on the adsorbent and the acryloyl group of microcystin. Amine groups were also added to the organosilica to catalyze the thiol addition reaction at neutral pH. Adsorption isotherms of microcystin-LR, -LA, and –RR were measured for sol–gel derived sorbents and compared to adsorption by wood-based powdered activated carbon, which has been demonstrated to be an effective adsorbent for microcystin. The amine/thiol containing organosilica demonstrated a broad specificity to remove all three congeners from water. Adsorption capacities for MC-LR from natural water were reduced compared to deionized water, especially for the thiol-amine organosilica media. Adsorption of Cu(II) ions by the amine/thiol organosilica was measured which indicated metal ions were bound, however, the degree of metal ion binding was insufficient to significantly decrease adsorption microcystin. Overall, the reaction of microcystin with a surface thiol appeared to be promoted by an initial physical adsorption event and thiol deprotonation by the amines to create a better nucleophile for the Michael addition reaction. more...
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- 2018
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Catalog
3. Function and structural stability of protein adsorbed to swellable organosilica
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Duc Pham, Paul L. Edmiston, Sarah E. Pitell, and Amy L. Graham
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biology ,Chemistry ,Inorganic chemistry ,Acid phosphatase ,02 engineering and technology ,General Chemistry ,Buffer solution ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Small molecule ,0104 chemical sciences ,Catalysis ,chemistry.chemical_compound ,Isoelectric point ,Adsorption ,Myoglobin ,Mechanics of Materials ,biology.protein ,General Materials Science ,0210 nano-technology ,Mesoporous material - Abstract
Swellable organically modified silica (SOMS) is a mesoporous sol-gel derived material that spontaneously swells >6 mL/g upon addition organic liquids. Adsorption of 8 different proteins to swollen-state SOMS was studied as a function of adsorbate molecular size and solution pH. Adsorption capacity was dependent on molecular size with the highest capacity of 690 mg/g measured for wheat germ acid phosphatase (58 kDa), a mid-size protein. Adsorption capacities were generally independent of pH suggesting protein-protein interactions do not play a major role in the adsorption mechanism. Rate of adsorption was measured at different protein loadings and fit to a pseudo second-order rate equation. Adsorption rates were independent of loading state when the pH was near a protein's isoelectric point (pI), but varied when the pH differed from the pI of adsorbate. Adsorption was found to irreversible for all proteins when rinsed with buffer solution or ethanol. Infrared spectroscopy of adsorbed cytochrome c and myoglobin indicated that both proteins maintain a native folded state that is stabilized to thermal denaturation. Adsorbed streptavidin was found to bind FITC-biotin (63% binding site saturation) suggesting that adsorbed proteins are accessible to small molecules in bulk solution. Acid phosphatase showed catalytic activity when adsorbed to swollen SOMS, however, specific activity of the bound enzyme was 10-fold lower compared to free enzyme in solution. Adsorption to SOMS appears to be a one-step, reagent-free method to irreversibly immobilize small to mid-sized proteins. Data supports an adsorption mechanism where protein molecules become sterically entrapped in the flexible mesoporous material. more...
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- 2020
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4. Photoemission Spectroscopy of Tethered CdSe Nanocrystals: Shifts in Ionization Potential and Local Vacuum Level As a Function of Nanocrystal Capping Ligand
- Author
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Amy L. Graham, Neal R. Armstrong, Andrea M. Munro, and Brian Zacher
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Specific orbital energy ,Materials science ,Nanocrystal ,Photoemission spectroscopy ,Chemical physics ,General Materials Science ,Fermi energy ,Work function ,Self-assembled monolayer ,Vacuum level ,Ionization energy ,Atomic physics - Abstract
We report the characterization of the frontier orbital energies and interface dipole effects for bare and ligand-capped 3.6 and 6.0 nm diameter CdSe nanocrystals (NC) tethered to smooth gold substrates, using He(I) and He(II) UV photoemission spectroscopy. Changes in the ionization potential (IP) of the NCs and local effective work function of the films were explored as a function of the dipolar nature of the NC capping ligands. The addition of thiol-capping ligands 1-hexanethiol, 1-benzenethiol, and 4-fluorothiophenol to both sizes of NCs produces negligible shifts in energy offset between the high kinetic energy edge of the CdSe NCs and the gold substrate Fermi energy. However, the local vacuum level and IP of the nanocrystal layer are altered by as much as 0.3 eV. We demonstrate the importance of determining both the local vacuum level and the high kinetic energy edge of a tethered NC sample. These studies demonstrate a method that can be used in the future to characterize the frontier orbital energy offsets for modified or unmodified nanocrystalline films, in which the NCs are incorporated into host materials, for applications ranging from photovoltaics to light-emitting diodes. more...
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- 2010
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5. High-Performance Hole-Transport Layers for Polymer Light-Emitting Diodes. Implementation of Organosiloxane Cross-Linking Chemistry in Polymeric Electroluminescent Devices
- Author
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Guennadi Evmenenko, Neal R. Armstrong, Pulak Dutta, Paul A. Lee, He Yan, Tobin J. Marks, and Amy L. Graham
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chemistry.chemical_classification ,Fabrication ,Chemistry ,General Chemistry ,Polymer ,Electroluminescence ,Biochemistry ,Catalysis ,Indium tin oxide ,Colloid and Surface Chemistry ,Chemical bond ,Chemical engineering ,Covalent bond ,Monolayer ,Polymer chemistry ,Diode - Abstract
This contribution describes an organosiloxane cross-linking approach to robust, efficient, adherent hole-transport layers (HTLs) for polymer light-emitting diodes (PLEDs). An example is 4,4'-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPDSi(2)), which combines the hole-transporting efficiency of N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl)-4,4-diamine) (TPD, prototypical small-molecule HTL material) and the strong cross-linking/densification tendencies of organosilanol groups. Covalent chemical bonding of TPDSi(2) to PLED anodes (e.g., indium tin oxide, ITO) and its self-cross-linking enable fabrication of three generations of insoluble PLED HTLs: (1) self-assembled monolayers (SAMs) of TPDSi(2) on ITO; (2) cross-linked blend networks consisting of TPDSi(2) + a hole transporting polymer (e.g., poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl))diphenylamine), TFB) on ITO; (3) TPDSi(2) + TFB blends on ITO substrates precoated with a conventional PLED HTL, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS). PLED devices fabricated using these new HTLs exhibit comparable or superior performance vs comparable devices based on PEDOT-PSS alone. With these new HTLs, current efficiencies as high as approximately 17 cd/A and luminances as high as approximately 140,000 cd/m(2) have been achieved. Further experiments demonstrate that not only do these HTLs enhance PLED anode hole injection but they also exhibit significantly greater electron-blocking capacity than PEDOT-PSS. The present organosiloxane HTL approach offers many other attractions such as convenience of fabrication, flexibility in choosing HTL components, and reduced HTL-induced luminescence quenching, and can be applied as a general strategy to enhance PLED performance. more...
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- 2005
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6. Interface Dipoles Arising from Self-Assembled Monolayers on Gold: UV−Photoemission Studies of Alkanethiols and Partially Fluorinated Alkanethiols
- Author
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Ramon Colorado, Vicki H. Wysocki, Darrin L. Smith, Neal R. Armstrong, Paul A. Lee, Michael Hofmann, Nadine E. Gruhn, Dana M. Alloway, Amy L. Graham, and T. Randall Lee
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chemistry.chemical_classification ,Chemistry ,Analytical chemistry ,Self-assembled monolayer ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,Crystallography ,X-ray photoelectron spectroscopy ,Monolayer ,Materials Chemistry ,Work function ,Physical and Theoretical Chemistry ,Thin film ,Methylene ,Spectroscopy ,Alkyl - Abstract
Gold surfaces modified with C3−C18-alkanethiols (CH3(CH2)X-1SH; HXSH; x = 3, 8, 12, 16, 18) and C16-alkanethiols, fluorinated at the outer 1, 2, 4, and 10 methylene positions (CF3(CF2)Y-1(CH2)XSH; FyHxSH; y = 1, x = 15; y = 2, x = 14; y = 4, x = 12; y = 10, x = 6) were characterized by He(I) UV-photoelectron spectroscopy (UPS). (Detailed X-ray photoelectron spectroscopic characterization of the partially fluorinated thin films is given in the Supporting Information). Long incubation times of the gold surface with the alkanethiol solutions lead to compact monolayer films for all of the alkanethiols, as indicated by the exponential decrease in emission intensity versus alkyl chain length for both the gold Fermi edge (UPS data), and by a parallel decrease in Au(4f) photoemission intensity using X-ray photoelectron spectroscopy. Changes in the effective work function of these surfaces due to the presence of significant interfacial dipoles are observed (i) as alkyl chain length is increased, and (ii) as the fr... more...
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- 2003
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7. Critical interfaces in new solar cell materials: organic heterojunctions and heterojunctions involving semiconductor nanoparticles
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Dana M. Alloway, R. Clayton Shallcross, Neal R. Armstrong, Amy L. Graham, P. Alex Veneman, Weining Wang, Diogenes Placencia, and Michael T. Brumbach
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Materials science ,Organic solar cell ,Photoemission spectroscopy ,business.industry ,Nanoparticle ,Heterojunction ,law.invention ,Semiconductor ,X-ray photoelectron spectroscopy ,law ,Photovoltaics ,Solar cell ,Optoelectronics ,business - Abstract
The heterojunctions formed between different organic dyes (O/O' heterojunctions), organic dyes with contacting oxide or metal electrodes (O/I heterojunctions), and semiconductor nanoparticles with organic host polymers and ligands (SC-NP/ O heterojunctions) must be understood and optimized in order to enhance the energy conversion efficiencies of photovoltaics using these materials as their active components. We have used combinations of UV-photoelectron spectroscopy, and X-ray photoelectron spectroscopy (UPS/XPS) in the characterization of representative heterojunctions, and extrapolate these studies to the optimization of new photovoltaic and photoelectrochemical energy conversion devices. more...
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- 2008
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8. Development and characterization of molecularly imprinted sol-gel materials for the selective detection of DDT
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Amy L. Graham, Catherine A. Carlson, and Paul L. Edmiston
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Hydrogen bond ,Stereochemistry ,Chemistry ,Intermolecular force ,Molecular Conformation ,Fluorescence spectroscopy ,Analytical Chemistry ,DDT ,Covalent bond ,Molecular Probes ,Polymer chemistry ,Molecule ,Amine gas treating ,Molecular imprinting ,Gels ,Sol-gel - Abstract
Molecularly imprinting sol-gel materials for DDT using both a noncovalent and a covalent approach was examined. A nonpolar porous sol-gel network was created through the use of the bridged polysilsesquioxane, bis-(trimethoxysilylethyl)benzene (BTEB), as the principal sol-gel component. Noncovalent molecular imprinting was deemed unsuccessful, presumably because of the lack of strong intermolecular interactions that can be established between the DDT and the sol-gel precursor. A covalent imprinting strategy was employed by generating a sacrificial spacer through the reaction of two 3-isocyanatopropyltriethoxysilanes with one of two different template molecules: 4,4'-ethylenedianiline (EDA) or 4,4'-ethylidenebisphenol (EBP). After formation of the sol-gel, the bonds linking the spacer template to the matrix were cleaved in a manner that generated a pocket of the appropriate size bordered by amine groups that could aid in the binding of DDT through weak hydrogen bonding interactions. Experiments indicated that DDT could be bound selectively by such an approch. To generate a sensor, an environmentally sensitive fluorescent probe, 7-nitrobenz-2-oxa-1,3-diazole, (NBD) located adjacent to the DDT binding site was used to transduce the binding of analyte. EDA-imprinted sol-gels, deposited as films on glass microscope slides, were shown to quantitatively detect DDT in water to a limit-of-detection of 50 ppt with a response time of60 s. Repeat measurements could be made with the same sensing films after rinsing with acetone between each measurement. The EDA sensing material was selective for DDT and other structurally similar molecules. However, the sensing film design was limited by the relatively minor changes in fluorescence intensity upon binding DDT. This situation may be remedied by an alternative methodology that can facilitate attachment of the NBD fluorophore in an optimal position proximal to the binding pocket. more...
- Published
- 2002
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