Summer Research 2012

Summer research 2012

Celebration of Summer Research September 6, 2012

Hannah Ryan was one of three student speakers at this event. Here are a few quotes from her reflection on her summer research experience.

Hannah R

 


"My summer research experience was truly impactful .... Research opened up my eyes to a world of creative and critical thinking."

I play the violin in the Westmont orchestra, and I realized that science is a lot like music. ...[R]esearch is the composing of science. It is the artistic expression of scientific minds... questioning, discovering, creating."

Confidence in my ability to think and explore has revolutionized the way I approach academics... and also my personal life. I am more engaged in my classes, and just have a general hunger for learning.


 

Abstracts of Chemistry student poster presentations at Celebration of Summer Research
September 6, 2012

FUNCTIONALIZED CHIRAL AUXILIARIES FROM CYCLIC CARBONATES USING THE WITTIG REACTION

Advantageous, organic compounds containing high stereoselctivity can be synthesized from Wittig reagents with chiral auxiliaries. The Wittig reaction can involve aldehydes or ketones to form carbon-carbon double bonds. The generated alkene can then be transformed in stereoselective ways to form useful, and functionalized, organic molecules. This project synthesized cyclic carbonates from readily available, optically active, and chiral diols, to be used in Wittig reactions in order to induce ester linkages with the chiral auxiliary. Terpene diols resulted in molecules showing primarily E-selectivity with 72% of compounds displaying trans conformations. Xylofuranose diols demonstrated similar results, however, the reacted compounds also indicated a higher selectivity towards less highly substituted sites, with primary configurations composing 94% of total material. Jennifer Davis ‘14; David Marten, Professor of Chemistry.

N-SUBSTITUTED OXAZOLIDINONES IN THE PREPARATION OF FUNCTIONALIZED CHIRAL AUXILIARIES USING WITTIG REAGENTS

Wittig reagents with chiral auxiliaries can be used to stereoselectively synthesize useful organic compounds. Wittig reagents are used in a reaction with aldehydes or ketones to form carbon-carbon double bonds. The resulting alkenes can be transformed in stereoselective ways using organometallic reagents to produce useful organic compounds. Three novel chiral N-substituted oxazolidinones were used to produce Wittig reagents with an ester linkage to a chiral auxiliary. The use of an N-mesitoyl group with a 5,5-dimethyl substituted oxazolidinone resulted in a 91:9 E/Z ratio in the chiral enoate. When an N-tosyl group was used with an unsubstituted oxazolidinone, the Wittig reaction occurred as expected to yield a chiral enoate with a 95:5 E/Z ratio. Using the N-mesitoyl substituted oxazolidinone, the Wittig olefination occurred with 99% E selectivity. Aleah Bond ‘14 and David Marten, Professor of Chemistry

RESONANCE ENERGY TRANSFER FROM NAPHTAHLENE TO FLUORENONE ON α-ALUMINA

Resonance energy transfer (RET) was observed among aromatic molecules on a dielectric surface. Molecules were vacuum deposited as bilayers on the surface of a crystal and electronically excited. The crystal was heated in a temperature programmed desorption experiment and molecular luminescence was recorded. The donor molecule, naphthalene (N), was shown to fluoresce with λmax ~ 420 nm, and the acceptor, fluorenone, absorbed this energy and emitted at a lower energy, λmax ~ 550 nm. Close to the desorption temperature of N, mixing of the layers resulted in the formation of a complex which facilitated RET. Hannah Ryan, Shanan Lau, Bradly B. Baer ‡Department of Chemistry, Westmont College, Santa Barbara, CA 9310‡ Department of Chemistry, Point Loma Nazarene University, San Diego, CA 92106

LAZER INDUCED FLUORESCENCE DECAY OF 1-METHYL-, 1-METHOXY- AND 1-ETHYLNAPTHALANE ON α-ALUMINA DURING TEMPERATURE PROGRAMMED DESORPTION

The laser induced fluorescence lifetimes of excited molecular films of several substituted naphthalene molecules were recorded as a function of temperature. 1-methylnaphthalene, 1-methoxynaphthalene, and 1-ethylnaphthalene were each vapor deposited as thin films on an α-alumina crystal as the surface was heated and the decays upon excitation with a Nd:YAG laser at 266 nm was monitored. The decays were assumed to be a first-order exponentials and were curve fit by least square regression routine. The slopes yielded the decay rate constants and were plotted during the temperature programmed desorption. The total decay was found to have long and short components, the values of which allowed the assigned to different excimers and traps that formed as the surface temperature was raised. Shanan Lau, Hannah Ryan, Bradly B. Baer‡, Department of Chemistry, Westmont College, Santa Barbara, CA 93108‡ Department of Chemistry, Point Loma Nazarene University, San Diego, CA 92106

IMPROVED SYNTHESIS AND CHARACTERIZATION OF N-FERROCENYL ISONICOTINAMIDE AND[Ru(bpy)2pyCONHphen]

We are developing metal salens with Ruthenium-modified and Iron-modified axial ligands as redox active catalysts for the oxygenation of organic substrates. This summer our goal was to improve the synthesis and complete the characterization of the axial ligands N-ferrocenyl Isonicotinamide and [Ru(bpy)2pyCONHphen]. The N-ferrocenyl isonicotinamide synthesis was improved from a 28% yield to a 61% yield by means of an HOBt/DCC coupling synthesis. Crystals of the product were grown for x-ray crystallography and the structure was found to be orthorhombic with the space group Pcba and an R value of 0.0357. Most of our attempts at an alternate synthesis of [Ru(bpy)2pyCONHphen] have been unsuccessful, but we were able to purify and obtain an improved 13C-NMR spectrum of a sample from the original synthesis. The alternate synthesis we have explored have proved difficult in the preparation of pyCONHphen, although recently we have discovered a promising DCC coupling synthesis for pyCONHphen. Currently we are working on purifying the product to obtain its 13C-NMR spectrum and to attach it to Ru(bpy)2(Cl)2 to complete the synthesis. Eric Patterson '13, Stephen Contakes, Assistant Professor of Chemistry

SPATIAL SENSITIVITY AND TIME DEPENDENCE OF EVANESCENT-WAVE CAVITY RING-DOWN SPECTROSCOPY

Evanescent-wave cavity ring-down spectroscopy (EW-CRDS) is a highly sensitive, absorption-based technique. The spatial sensitivity and time dependence of EW-CRDS may be demonstrated by measuring changes in absorption as substances adsorb to chemically modified silica surfaces. In this study, the adsorption of methyl red to a surface modified with (3-aminopropyl)trimethoxysilane (APTMS) was monitored as a function of both position and time. Allison Vander Wall ‘13 and Claire Berchiolli ’13. Dr. Michael Everest, Professor of Chemistry

SYNTHESIS AND PHOTOPHYSICAL CHARACTERIZATION OF RUTHENIUM-DIIMINE MODIFIED PAMAM DENDRIMERS

We are interested in developing Ruthenium modified PAMAM dendrimers that retain the ability to bind ions. In the present work we used HOBt/EDC coupling to attach sub-sotichiometric ratios of [Ru(bpy)2(dcbpy)](NO3)2 (dcbpy = 4,4’-dicarboxybipyridine) to G2.0 PAMAM dendrimers containing amine surface groups and [Ru(bpy)2(5-aminophen)](NO3)2 (5-aminophen = 5’-amino-1,10-phenanthroline) to G1.5 PAMAM dendrimers containing carboxy surface groups. The product Ru:dendrimer ratio increases nonlinearly with the Ru:dendrimer reactant ratio and approaches the 16:1 stoichimetric ratio, although high loadings could not be consistently achieved with the G1.5 dendrimer labeling reactions. The coupling yields for the reactions involving conjugation to the G2.0 dendrimers were consistently higher than those involving the G1.5 dendrimers, in part due to the use of an aromatic amine in the latter reactions. The conjugates’ absorbance and emission spectra indicate that the Ruthenium diimine complexes experience a relatively hydrophobic environment. Specifically, the conjugates’ MLCT bands are broadened and their emission spectra exhibit maxima at unusually long wavelengths that decrease with Ru:dendrimer ratio, eventually becoming closer to that for [Ru(bpy)2(phen)]2+. The low loading G2.0 conjugates exhibit anomalously large emission quantum yields of ~12% that decreases to ~2% as the Ru:dendrimer ratio is increased from 3 to10. These results are consistent with interior bound Ru-diimine groups that undergo increasing intergroup energy transfer at higher loadings. Garrett W. Johnson ‘12, Tamara Sparks ‘13, Jeffrey T. Kuwahara ‘11, Anneka Rienstra ‘15, Michelle Haas ‘11, Stephen M. Contakes, Assistant Professor of Chemistry

EXAMINING THE ROLE OF plrS in Bordetella bronchiseptica VIRULENCE GENE EXPRESSION

Bordetella bronchiseptica is a respiratory pathogen that uses two-component regulators (TCR) to control gene expression in order to colonize the respiratory tract of many mammals. A recently discovered TCR sensor kinase, plrS, is necessary for Bordetella to colonize rodent respiratory tracts. Microarray analysis was performed on wild type and plrS deficient cells, which indicated altered expression of several known virulence functions, including type III secretion (TTSS), cyaA, and nitrogen response genes. To determine the effect that plrS has on TTSS, cytotoxicity and hemolysis assays were performed. On macrophage-like J774 cells, plrS mutants showed statistically significant decreases both in cytotoxicity and hemolysis compared to the wild-type (normal) strain. Western blot analyses show less CyaA in plrS mutants, but CO2 levels do not appear to affect these differences. Finally, the expression of at least one protein is affected in plrS mutant strains in nitrogen-limiting conditions, and the difference is independent of a known regulatory system that governs the bacterial response to nitrogen stress. Dean LaBarba ‘13, Jeffrey Midgley ‘13, Michelle Wheeler ‘13 and Dr. Steve Julio, Associate Professor of Biology