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Articles 151 - 180 of 2524

Full-Text Articles in Physical Sciences and Mathematics

Visualization Of Surface Acoustic Waves By Means Of Synchronous Amplitude Modulated Illumination, Bradley Duncan Nov 2015

Visualization Of Surface Acoustic Waves By Means Of Synchronous Amplitude Modulated Illumination, Bradley Duncan

Bradley D. Duncan

A simple technique for visualizing two-dimensional traveling surface acoustic wave (SAW) phenomena in real time was developed. The technique requires illumination of a SAW carrying substrate with a collimated, sinusoidally amplitude-modulated laser beam. Though at first the technique may appear to be stroboscopic in nature, it in fact has its foundations in spatiotemporal correlation theory. It is shown that if the modulation frequency of the illumination beam is equal to, or an integer fraction of, the SAW frequency (i.e., if they are temporally correlated) then, after simple spatial filtering, high-visibility stationary fringes can be produced. In fact, it is shown …

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A Technique For Removing Platform Vibration Noise From A Pulsed Ladar Vibration Sensor, Troy Sturm, R. Richmond, Bradley Duncan Nov 2015

A Technique For Removing Platform Vibration Noise From A Pulsed Ladar Vibration Sensor, Troy Sturm, R. Richmond, Bradley Duncan

Bradley D. Duncan

A technique has been developed for removing platform-induced vibration noise from a pulsed ladar vibration sensor. Deriving the vibrational characteristics of the platform is accomplished by simulating ambient atmospheric aerosols as a stationary reference target. Using a pulsed coherent detection ladar, the instantaneous Doppler frequency shifts from both aerosols and a distant hard target are measured and recorded, while the data acquisition is range gated so that both Doppler measurements are made from a single pulse. Periodic measurements are then made to develop a time history of the fluctuations in the Doppler signals, after which two vibration spectra are derived …

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Real-Time Frequency-Translated Holographic Visualization Of Saw Interactions With Surface-Breaking Defects, James Blackshire, Shamachary Sathish, Bradley Duncan, Mike Millard Nov 2015

Real-Time Frequency-Translated Holographic Visualization Of Saw Interactions With Surface-Breaking Defects, James Blackshire, Shamachary Sathish, Bradley Duncan, Mike Millard

Bradley D. Duncan

A real-time, frequency-translated holographic imaging system has been developed by use of bacteriorhodopsin film. The system provides a capability for imaging surface acoustic waves and has been utilized to detect and characterize surface-breaking defects through near-field ultrasonic scattering effects. Frequency-plane filtering was used to discriminate between ultrasonic standing-wave and near-field scattering features, dramatically enhancing the holographic visualization of the defect sites. A detailed description of the system is presented, along with representative holographic images showing the interaction of surface acoustic waves with surface-breaking cracks and small notches in aluminum and titanium substrates.

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High-Speed Shack-Hartmann Wave-Front Sensor Design Utilizing Commercial-Off-The-Shelf Optics, Jeffrey Widiker, Scott Harris, Bradley Duncan Nov 2015

High-Speed Shack-Hartmann Wave-Front Sensor Design Utilizing Commercial-Off-The-Shelf Optics, Jeffrey Widiker, Scott Harris, Bradley Duncan

Bradley D. Duncan

Several trade-offs relevant to the design of a two-dimensional high-speed Shack–Hartmann wavefront sensor are presented. Also outlined are some simple preliminary experiments that can be used to establish critical design specifications not already known. These specifications include angular uncertainty, maximum measurable wavefront tilt, and spatial resolution. A generic design procedure is then introduced to enable the adaptation of a limited selection of CCD cameras and lenslet arrays to the desired design specifications by use of commercial off-the-shelf optics. Although initially developed to aid in the design of high-speed (i.e., megahertz-frame-rate) Shack–Hartmann wavefront sensors, our method also works when used for …

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Real-Time Optical Holography Using A Spatial Light Modulator, Ting-Chung Poon, Bradley Duncan, Ming Hsien Wu, K. Shinoda, Y. Suzuki Nov 2015

Real-Time Optical Holography Using A Spatial Light Modulator, Ting-Chung Poon, Bradley Duncan, Ming Hsien Wu, K. Shinoda, Y. Suzuki

Bradley D. Duncan

Paper proposes a real-time technique for recording and reconstructing optical holograms. Holographic recording is accomplished by scanning an object with two superposed light beams of different temporal frequencies. For reconstruction, the scanned information is transferred to an electron beam addressed spatial light modulator for coherent processing and optically read out to reconstruct an image of the scanned object.

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Direct Visualization Of Spruce Budworm Antifreeze Protein Interacting With Ice Crystals: Basal Plane Affinity Confers Hyperactivity, Natalya Pertaya, Christopher Marshall, Yeliz Celik, Peter Davies, Ido Braslavsky Nov 2015

Direct Visualization Of Spruce Budworm Antifreeze Protein Interacting With Ice Crystals: Basal Plane Affinity Confers Hyperactivity, Natalya Pertaya, Christopher Marshall, Yeliz Celik, Peter Davies, Ido Braslavsky

Yeliz Celik

Antifreeze proteins (AFPs) protect certain organisms from freezing by adhering to ice crystals, thereby preventing their growth. All AFPs depress the nonequilibrium freezing temperature below the melting point; however AFPs from overwintering insects, such as the spruce budworm (sbw) are 10–100 times more effective than most fish AFPs. It has been proposed that the exceptional activity of these AFPs depends on their ability to prevent ice growth at the basal plane. To test the hypothesis that the hyperactivity of sbwAFP results from direct affinity to the basal plane, we fluorescently tagged sbwAFP and visualized it on the surface of ice …

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Diosphenol-Based Approach To The A-Ring Functionalization Of Advanced Taxol Precursors., John Hofferberth Nov 2015

Diosphenol-Based Approach To The A-Ring Functionalization Of Advanced Taxol Precursors., John Hofferberth

John E Hofferberth

Several different approaches to the A-ring functionalization of an advanced, highly functionalized diosphenol precursor to Taxol are described. The first phase of the undertaking consists of an assessment of those reagents conducive to reaction at the enolic oxygen (silylation, methylation, allylation, and acylation). Transformations involving an alternative attack at the enol carbon center (bromination, selenation) have also been defined. Sodium borohydride reduction operates from the beta-face of C-14 as long as the C-1 hydroxyl is not protected so as to offer steric exclusion. Complications associated with various aspects of these methodological undertakings are addressed. The most advanced oxygenation achievements were …

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A Divergent Approach To The Diastereoselective Synthesis Of Several Ant-Associated Iridoids, John Hofferberth Nov 2015

A Divergent Approach To The Diastereoselective Synthesis Of Several Ant-Associated Iridoids, John Hofferberth

John E Hofferberth

The ant-associated iridoids nepetalactol, actinidine, dolichodial, isoiridomyrmecin, and dihydronepetalactone were prepared from citronellal using a divergent approach. Key features include a three-step synthesis of the individual antipodes of actinidine by a novel tandem cycloaddition/pyridine formation and a facile diastereoselective synthesis of both enantiomers of dolichodial.

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Lactide Cyclopolymerization Kinetics, X-Ray Structure, And Solution Dynamics Of (Tbu-Salamee)Al And A Cautionary Tale Of Polymetalate Formation, Yutan Getzler Nov 2015

Lactide Cyclopolymerization Kinetics, X-Ray Structure, And Solution Dynamics Of (Tbu-Salamee)Al And A Cautionary Tale Of Polymetalate Formation, Yutan Getzler

Yutan D.Y.L. Getzler

The complex (tBu-SalAmEE)Al (tBu-SalAmEEH3 = N,N-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-2-(2-aminoethoxy)ethanol, 1) catalyzes the ring-expansion polymerization of lactide to form cyclic poly(lactide) (cPLA). The X-ray structure of 1 was determined, its polymerization kinetics were examined and its interactions with Lewis bases were observed. The data from these experiments are consistent with a coordination–insertion mechanism whose rate-determining step is catalyst rearrangement by loss of a hemilabile, datively bound, bridging ligand ether. cPLA was examined by thermogravimetric analysis and found more stable than its linear counterpart. In the course of these studies, we unexpectedly observed the formation of polymetalate (AlMe(tBu-SalAmEE)AlMe2)2 (6), which was characterized (X-ray, EA, and …

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Catalytic Carbonylation Of Β-Lactones To Succinic Anhydrides, Yutan Getzler Nov 2015

Catalytic Carbonylation Of Β-Lactones To Succinic Anhydrides, Yutan Getzler

Yutan D.Y.L. Getzler

A well-defined, highly active and selective catalyst for the synthesis of succinic anhydrides from CO and β-lactones is reported. At 200 psi of CO, the catalyst [(N,N‘-bis(3,5-di-tert-butylsalicylidene)phenylenediamino)Al(THF)2][Co(CO)4] carbonylates β-propiolactones to succinic anhydrides in high yield. (R)-β-Butyrolactone is carbonylated to (S)-methylsuccinic anhydride with clean inversion of stereochemistry, while cis-2,3-dimethyl-β-propiolactone yields exclusively trans-2,3-dimethylsuccinic anhydride. These data are consistent with a mechanism involving nucleophilic attack by [Co(CO)4]- on the β carbon of the lactone, followed by CO insertion and anhydride formation.

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Lactide Cyclopolymerization By An Alumatrane-Inspired Catalyst, Yutan Getzler Nov 2015

Lactide Cyclopolymerization By An Alumatrane-Inspired Catalyst, Yutan Getzler

Yutan D.Y.L. Getzler

Control of molecular structure is an enduring motivation for chemists. From total synthesis(1) to self-assembly(2) to crystal growth,(3) the pursuit continues unabated. Polymer synthesis, in particular, has seen a revolution in control. It is now possible to precisely predetermine chain length, extent of cross-linking, comonomer incorporation, block length, stereochemistry and topology.(4) There has even been success in sequence control,(5) previously achieved only in biological systems. The difficulties inherent in the synthesis of pure macrocycle(6) have limited their availability, despite their compelling predicted properties. A variety of strategies have been employed but only two avoid …

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The Mechanism Of Epoxide Carbonylation By [Lewis Acid]+[Co(Co)4]- Catalysts, Yutan Getzler Nov 2015

The Mechanism Of Epoxide Carbonylation By [Lewis Acid]+[Co(Co)4]- Catalysts, Yutan Getzler

Yutan D.Y.L. Getzler

A detailed mechanistic investigation of epoxide carbonylation by the catalyst [(salph)Al(THF)2]+ [Co(CO)4]- (1, salph = N,N‘-o-phenylenebis(3,5-di-tert-butylsalicylideneimine), THF = tetrahydrofuran) is reported. When the carbonylation of 1,2-epoxybutane (EB) to β-valerolactone is performed in 1,2-dimethoxyethane solution, the reaction rate is independent of the epoxide concentration and the carbon monoxide pressure but first order in 1. The rate of lactone formation varies considerably in different solvents and depends primarily on the coordinating ability of the solvent. In mixtures of THF andcis/trans-2,5-dimethyltetrahydrofuran, the reaction is first order in THF. From spectroscopic and kinetic data, the catalyst resting state was assigned to be the neutral …

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Synthesis Of An Epoxide Carbonylation Catalyst: Exploration Of Contemporary Chemistry For Advanced Undergraduates, Yutan Getzler Nov 2015

Synthesis Of An Epoxide Carbonylation Catalyst: Exploration Of Contemporary Chemistry For Advanced Undergraduates, Yutan Getzler

Yutan D.Y.L. Getzler

This lab presents an opportunity for advanced students of organic or inorganic chemistry to prepare a compound that belongs to a recently introduced class of catalyst that are active for the carbonylation of epoxides and related substrates to β-lactones and related products. Epoxides are inexpensive and readily available while β-lactones are not and have broad utility in both small molecule and polymer synthesis. Consequently, these catalysts, and related systems, have been the subject of intense investigation recently. The ability to work with a contemporary system was a major source of excitement and satisfaction to undergraduates at Cornell University who performed …

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Acidity Fractions In Acid Sulfate Soils And Sediments: Contributions Of Schwertmannite And Jarosite, Chamindra Vithana, Leigh Sullivan, Richard Bush, Edward Burton Nov 2015

Acidity Fractions In Acid Sulfate Soils And Sediments: Contributions Of Schwertmannite And Jarosite, Chamindra Vithana, Leigh Sullivan, Richard Bush, Edward Burton

Chamindra Vithana

In Australia, the assessment of acidity hazard in acid sulfate soils requires the estimation of operationally defined acidity fractions such as actual acidity, potential sulfidic acidity, and retained acidity. Acid–base accounting approaches in Australia use these acidity fractions to estimate the net acidity of acid sulfate soils materials. Retained acidity is the acidity stored in the secondary Fe/Al hydroxy sulfate minerals, such as jarosite, natrojarosite, schwertmannite, and basaluminite. Retained acidity is usually measured as either net acid-soluble sulfur (SNAS) or residual acid soluble sulfur (SRAS). In the present study, contributions of schwertmannite and jarosite to the …

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Liberation Of Acidity And Arsenic From Schwertmannite: Effect Of Fulvic Acid, Chamindra Vithana, Leigh Sullivan, Edward Burton, Richard Bush Nov 2015

Liberation Of Acidity And Arsenic From Schwertmannite: Effect Of Fulvic Acid, Chamindra Vithana, Leigh Sullivan, Edward Burton, Richard Bush

Chamindra Vithana

Schwertmannite is one of the major components that produces acidity in acid mine drainage (AMD) and acid sulfate soils (ASS) and is also known to be an effective scavenger of Arsenic (As) in such environments. Fulvic acid (FA) is an active component of natural organic matter (NOM) and is known to interact strongly with both schwertmannite and As. Two main environmental hazards related to schwertmannite are acidity liberation and potential re-mobilization of adsorbed or co-precipitated As upon hydrolysis. This study focused on understanding the behaviour of As-substituted schwertmannite with regard to the potential of acidity liberation, the effect of FA …

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Jarosite Quantification In Soils: An Enhanced Sequential Extraction Procedure, Chamindra Vithana, Leigh Sullivan, Richard Bush, Edward Burton Nov 2015

Jarosite Quantification In Soils: An Enhanced Sequential Extraction Procedure, Chamindra Vithana, Leigh Sullivan, Richard Bush, Edward Burton

Chamindra Vithana

A two-step sequential extraction procedure established for the quantification of acidity producing ferric and ferrous sulfate minerals such as melanterite and jarosite in acid mine wastes was evaluated for quantification of jarosite spiked in soils. The procedure involves in sequence anoxic water extraction, roasting the solid residue after anoxic water extraction at 550 °C for 1 h, and 4 M HCl extraction of the roasted solid. Soil and quartz samples were spiked with known amounts of synthetic and natural jarosite and their recovery was measured using the suggested two-step sequential extraction procedure. The recoveries of synthetic and natural jarosite were …

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Assessment And Behaviour Of Secondary Iron(Iii) Minerals In Acid Sulphate Soil Materials, Chamindra Vithana Nov 2015

Assessment And Behaviour Of Secondary Iron(Iii) Minerals In Acid Sulphate Soil Materials, Chamindra Vithana

Chamindra Vithana

This study examined two aspects of acidity generating secondary Fe(III) minerals (i.e. schwertmannite and jarosite) in acid sulfate soils (ASS) environments: i) accurate identification and quantification, and ii) improving our understanding of their behaviour in ASS.The study showed that current assessment methods have a number of limitations and are not reliable for accurate estimation of both minerals in ASS environments. The study also showed that in natural environments, these minerals can behave in a manner different to current conceptual understanding. The broad implication of this study was identification of the need for development of improved management techniques for ASS.

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Schwertmannite In Soil Materials: Limits Of Detection Of Acidified Ammonium Oxalate Method And Differential X-Ray Diffraction, Chamindra Vithana, Leigh Sullivan, Richard Bush, Edward Burton Nov 2015

Schwertmannite In Soil Materials: Limits Of Detection Of Acidified Ammonium Oxalate Method And Differential X-Ray Diffraction, Chamindra Vithana, Leigh Sullivan, Richard Bush, Edward Burton

Chamindra Vithana

Schwertmannite is a secondary iron mineral, found in acid mine drainage (AMD) and acid sulfate soils (ASS), that generates acidity when it transforms to stable mineral phases. Acidity liberated during schwertmannite transformation can seriously diminish water quality and soil health. Acidified ammonium oxalate (AAO) extraction in the dark coupled with differential X-ray diffraction (DXRD) analysis is routinely used to identify and to quantify poorly crystalline iron oxide phases such as schwertmannite in AMD environments. However, management of ASS environments is largely impacted due to lack of reliable methods to identify/quantify schwertmannite in soil materials. Our study aimed to evaluate the …

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Stability Of Schwertmannite And Jarosite In An Acidic Landscape: Prolonged Field Incubation, Chamindra Vithana, Leigh Sullivan, Edward Burton, Richard Bush Nov 2015

Stability Of Schwertmannite And Jarosite In An Acidic Landscape: Prolonged Field Incubation, Chamindra Vithana, Leigh Sullivan, Edward Burton, Richard Bush

Chamindra Vithana

Schwertmannite and jarosite are two of the main secondary iron(III) minerals commonly found in acidic, iron and sulfate-rich environments such as acid mine drainage and coastal acid sulfate soils (CASS). Both minerals exert major influence on the water and soil quality in these environments.While there are many studies conducted on the stability of these two minerals under controlled laboratory conditions, the behaviour of schwertmannite and jarosite under field conditions and the factors influencing their behaviour have not been investigated directly. In the present study, we examined the net transformation of introduced schwertmannite and jarosite samples incubated in a typical acidic …

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Synthesis And Flammability Testing Of Epoxy Functionalized Phosphorous-Based Flame Retardants, Vladimir Benin, Xuemei Cui, Alexander Morgan, Karl Seiwert Nov 2015

Synthesis And Flammability Testing Of Epoxy Functionalized Phosphorous-Based Flame Retardants, Vladimir Benin, Xuemei Cui, Alexander Morgan, Karl Seiwert

Vladimir Benin

Several potential new phosphorus-containing flame retardant molecules were evaluated for heat release reduction potential by incorporation of the molecules into a polyurethane, generated from methylene diphenyl diisocyanate and 1,3-propane diol. The heat release reduction potential of these substances was evaluated using the pyrolysis combustion flow calorimeter (PCFC). The polyurethanes were prepared in the presence of the potential flame retardants via solvent mixing and copolymerization methods to qualitatively evaluate their potential reactivity into the polyurethane prior to heat release testing. The functionality of the flame retardants was epoxide based that would potentially react with the diol during polyurethane synthesis. Flammability testing …

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Synthesis, Structural Studies And Desilylation Reactions Of Some N-2-(Trimethylsilyl)Ethyl-N-Nitrosocarbamates, Arpitha Thakkalapally, Vladimir Benin Nov 2015

Synthesis, Structural Studies And Desilylation Reactions Of Some N-2-(Trimethylsilyl)Ethyl-N-Nitrosocarbamates, Arpitha Thakkalapally, Vladimir Benin

Vladimir Benin

The present report describes the preparation and characterization of several N-2-(trimethylsilyl)ethyl-N-nitrosocarbamates, designed as precursors to thermally unstable secondary N-nitrosocarbamate anions via fluoride-assisted cleavage. X-ray structural studies demonstrate that the core N-nitrosocarbamate moiety has a nearly planar geometry, with an s-E orientation at the N–N bond. DFT calculations (B3LYP/6-31+G(d)) reproduce accurately the structural features of the title compounds and detailed conformational analysis at the same level of theory addresses the long-standing issue of preferred geometries for three classes of related structures: N-nitrosocarbamates, N-nitrosoureas and N-nitrosoamides. Desilylation studies demonstrate that both the …

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Nanomolar Binding Of Peptides Containing Noncanonical Amino Acids By A Synthetic Receptor, Leigh Logsdon, Christopher Schardon, Vijayakumar Ramalingam, Sharon Kwee, Adam Urbach Nov 2015

Nanomolar Binding Of Peptides Containing Noncanonical Amino Acids By A Synthetic Receptor, Leigh Logsdon, Christopher Schardon, Vijayakumar Ramalingam, Sharon Kwee, Adam Urbach

Adam R Urbach

This paper describes the molecular recognition of phenylalanine derivatives and their peptides by the synthetic receptor cucurbit[7]uril (Q7). The 4-tert-butyl and 4-aminomethyl derivatives of phenylalanine (tBuPhe and AMPhe) were identified from a screen to have 20–30-fold higher affinity than phenylalanine for Q7. Placement of these residues at the N-terminus of model tripeptides (X-Gly-Gly), resulted in no change in affinity for tBuPhe-Gly-Gly, but a remarkable 500-fold increase in affinity for AMPhe-Gly-Gly, which bound to Q7 with an equilibrium dissociation constant (Kd) value of 0.95 nM in neutral phosphate buffer. Structure–activity studies revealed that three functional groups work in a positively cooperative …

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Charge-Mediated Recognition Of N-Terminal Tryptophan In Aqueous Solution By A Synthetic Host, Meghan Bush, Nicole Bouley, Adam Urbach Nov 2015

Charge-Mediated Recognition Of N-Terminal Tryptophan In Aqueous Solution By A Synthetic Host, Meghan Bush, Nicole Bouley, Adam Urbach

Adam R Urbach

The molecular recognition of peptides and proteins in aqueous solution by designed molecules remains an elusive goal with broad implications for basic biochemical research and for sensors and separations technologies. This paper describes the recognition of N-terminal tryptophan in aqueous solution by the synthetic host cucurbit[8]uril (Q8). Q8 is known to form 1:1:1 heteroternary complexes with methyl viologen (MV) and a second aromatic guest. Here, the complexes of Q8·MV with (i) the four natural aromatic α-amino acids, (ii) four singly charged tryptophan derivatives, and (iii) four tryptophan-containing tripeptides were characterized by isothermal titration calorimetry, mass spectrometry, and UV−visible, fluorescence, and …

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Molecular Recognition Of Insulin By A Synthetic Receptor, Jordan Chinai, Alexander Taylor, Lisa Ryno, Nicholas Hargreaves, Christopher Morris, P Hart, Adam Urbach Nov 2015

Molecular Recognition Of Insulin By A Synthetic Receptor, Jordan Chinai, Alexander Taylor, Lisa Ryno, Nicholas Hargreaves, Christopher Morris, P Hart, Adam Urbach

Adam R Urbach

The discovery of molecules that bind tightly and selectively to desired proteins continues to drive innovation at the interface of chemistry and biology. This paper describes the binding of human insulin by the synthetic receptor cucurbit[7]uril (Q7) in vitro. Isothermal titration calorimetry and fluorescence spectroscopy experiments show that Q7 binds to insulin with an equilibrium association constant of 1.5 × 106 M−1 and with 50−100-fold selectivity versus proteins that are much larger but lack an N-terminal aromatic residue, and with >1000-fold selectivity versus an insulin variant lacking the N-terminal phenylalanine (Phe) residue. The crystal structure of the Q7·insulin complex shows …

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A Cucurbit[8]Uril Sponge, Vijayakumar Ramalingam, Sharon Kwee, Lisa Ryno, Adam Urbach Nov 2015

A Cucurbit[8]Uril Sponge, Vijayakumar Ramalingam, Sharon Kwee, Lisa Ryno, Adam Urbach

Adam R Urbach

This paper describes a convenient approach to quantitative removal of the synthetic host cucurbit[8]uril (Q8) from aqueous mixtures using a sepharose resin coated in memantine groups to selectively sequester Q8 in the presence of competing hosts and guests. The “Q8 sponge” can separate Q8 from Q6 and reverse the Q8-mediated dimerization of peptides.

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Multivalent Recognition Of Peptides By Modular Self-Assembled Receptors, Joseph Reczek, Aimee Kennedy, Brian Halbert, Adam Urbach Nov 2015

Multivalent Recognition Of Peptides By Modular Self-Assembled Receptors, Joseph Reczek, Aimee Kennedy, Brian Halbert, Adam Urbach

Adam R Urbach

Developing nontraditional approaches to the synthesis and characterization of multivalent compounds is critical to our efforts to study and interface with biological systems and to build new noncovalent materials. This paper demonstrates a biomimetic approach to the construction of discrete, modular, multivalent receptors via molecular self-assembly in aqueous solution. Scaffolds presenting 1−3 viologen groups recruit a respective 1−3 copies of the synthetic host, cucurbit[8]uril, in a noncooperative manner and with a consistent equilibrium association constant (Ka) value of 2 × 106 M−1 per binding site. The assembled mono-, di-, and trivalent receptors bind to their cognate target peptides containing 1−3 …

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Solid-Phase Synthesis Of Peptide−Viologen Conjugates, Joseph Reczek, Elisa Rebolini, Adam Urbach Nov 2015

Solid-Phase Synthesis Of Peptide−Viologen Conjugates, Joseph Reczek, Elisa Rebolini, Adam Urbach

Adam R Urbach

This paper presents a robust method for the conjugation of viologens to peptides using an amide coupling strategy that is compatible with standard Fmoc solid-phase peptide synthesis. Methodology is presented for monitoring the milligram scale process quantitatively by UV spectroscopy. This chemistry enables the synthesis of a broad range of asymmetric viologens in high yield at room temperature and is compatible with a wide range of functional groups, including amine, guanidinyl, thiol, carboxylic acid, phenol, and indole.

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Sequence-Specific Inhibition Of A Nonspecific Protease, Leigh Logsdon, Adam Urbach Nov 2015

Sequence-Specific Inhibition Of A Nonspecific Protease, Leigh Logsdon, Adam Urbach

Adam R Urbach

A nonspecific exopeptidase, aminopeptidase N (APN), is inhibited sequence-specifically by a synthetic host, cucurbit[7]uril (Q7), which binds with high affinity and specificity to N-terminal phenylalanine (Phe) and 4-(aminomethyl)phenylalanine (AMPhe) and prevents their removal from the peptide. Liquid chromatography experiments demonstrated that in the presence of excess Q7, APN quantitatively converts the pentapeptides Thr-Gly-Ala-X-Met into the dipeptides X-Met (X = Phe, AMPhe). The resulting Q7-bound products are completely stable to proteolytic digestion for at least 24 h. Structure–activity studies revealed a direct correlation between the extent of protection of an N-terminal amino acid and its affinity for Q7. Therefore, Q7 provides …

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Effects Of Sequence Context On The Binding Of Tryptophan-Containing Peptides By The Cucurbit[8]Uril-Methyl Viologen Complex, Omar Ali, Eric Olson, Adam Urbach Nov 2015

Effects Of Sequence Context On The Binding Of Tryptophan-Containing Peptides By The Cucurbit[8]Uril-Methyl Viologen Complex, Omar Ali, Eric Olson, Adam Urbach

Adam R Urbach

This paper describes a novel assay for measuring the relative extent of peptide binding in a large parallel format and the use of this assay to explore the effects of sequence context on the binding of tryptophan (Trp)-containing peptides by the synthetic receptor comprising the noncovalent complex between cucurbit[8]uril and methyl viologen (i.e. Q8√MV). The extent of quenching of Trp fluorescence upon binding to Q8√MV was used to measure the relative extent of binding and thus the relative affinities of 104 Trp-containing peptides, in parallel, using a fluorescence plate reader. This study resulted in the remarkable observation that the identity …

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Supramolecular Chemistry: A Capstone Course, Adam Urbach, Christopher Pursell, John Spence Nov 2015

Supramolecular Chemistry: A Capstone Course, Adam Urbach, Christopher Pursell, John Spence

Adam R Urbach

A fourth-year capstone course offers students an opportunity to integrate topics covered in the core disciplinary courses, to learn an advanced interdisciplinary topic, and to approach unfamiliar problems and literature. This article describes a fourth-year capstone course designed to incorporate components of faculty lectures, student seminars, and original, hands-on research projects in order to cover the topic of supramolecular chemistry in one semester with unusual depth. This approach should be applicable to other advanced topics in chemistry.

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