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«Strengthening the Nation through Diversity, Innovation & Leadership in STEM San Antonio,Texas · October 3-6, 2013 Get Connected! Connect with the ...»

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Due to the difficulty in directly observing the process by which these lipid rafts form, we believe that using coarsegrained molecular dynamics simulations of a lipid bilayer model containing cholesterol is the most feasible approach for determining the mechanism of domain formation. We speculate that cholesterol in one leaflet of the lipid bilayer may influence behavior of cholesterol in the opposite leaflet. In order to probe this proposition, we will use the Martini force field coarse-grained lipid model to construct lipid bilayers containing cholesterol in both leaflets in order to run the molecular dynamics simulations. We will then analyze the simulation in order to measure correlations of cholesterol motion within and across leaflets.

SAT-10

ANALYSIS OF SURFACE PLASMONS USING NANOWIRES INCORPORATED INTO FIELD EFFECT

TRANSISTORS

Christopher Siefe, Jose Navarrete.

University of California, Santa Barbara, Santa Barbara, CA.

Surface plasmon resonance is a phenomenon which causes electron oscillations via the propagation of electromagnetic waves at a metal-dielectric interface. In a nanoscale material where the surface area-volume ratio is high, these surface plasmons can decay into hot electrons, which can be used for various means. This research aims to better understand the fundamental science behind surface plasmons for applications of a number of devices.

By assembling tin(IV) oxide nanowires decorated with gold nanoparticles into a back gate field-effect transistor, we can analyze the current density on the nanowire’s surface when illuminated with different wavelengths of light (400 to 1200 nm) and biased with various gate potentials. We will also be investigating the effects of nanowire lengths on the current. We can determine any current that runs through the nanowire in our field effect transistor as a result of the surface plasmon resonance in the gold nanoparticles on the nanowires. By finding which wavelengths receive the highest current reading for this interface, we can compare our values to other known environments. We expect to see that the current density on the surface of the nanowires will be most affected by wavelengths of light that match surface plasmon resonance in gold and by greater gate bias. With this research, we can apply the concepts of surface plasmons to improve current devices and find new applications for surface plasmons.

246 UNDERGRADUATE POSTER ABSTRACTS

SAT-12

QUANTUM MECHANICAL STUDIES OF GADOLINIUM(III) LIGANDS USED IN MRI CONTRAST AGENTS

Rafael de la Flor, Maria Benavides.

University of Houston-Downtown, Houston, TX.

Determining the structure and the chemical stability of polydentate coordinate complexes used in MRI contrast agents is essential in the field of diagnostic medicine. Chelation complexes using gadolinium(III) metal, a paramagnetic lanthanide, produce ideal signal intensities in diagnostics (MRI) that have made their use in radiology a staple and also justifies their importance for computational research. Gadolinium(III) complexes show variable imaging qualities depending on the ligands attached to the central atom and the diagnostic application for which they are used. Our study focuses on determining the structures and molecular properties of three ligands, MS-325-L, COPTA, and EOBDTPA, used in the preparation of the three Gd(III) complexes already used in commercial clinical applications. Our calculations were performed using density functional theory (DFT) with the B3LYP functional applied in conjunction with two basis sets (3-21G and 6-31G) to obtain the equilibrium geometries, vibrational frequencies, and IR spectra for the ligands. The highest occupied molecular orbital (HOMO) – lowest occupied molecular orbital (LUMO) energy gap values for all compounds are greater than 4 eV suggesting that the ligands are chemically stable. The ligands exhibit hydrogen bonding which can account for the significant chemical stability. The ligands possess significant dipole moments with values greater than 8 Debye, consistent with their chemical polar character. Our computed vibrational frequencies were found to be in excellent agreement with the experimental values, suggesting our proposed models are good representations of the actual molecular structures.

SAT-13

STRUCTURAL ANALYSIS OF BACTERIOPHYTOCHROMES ON GRAPHITE AND MICA USING SCANNING

PROBE MICROSCOPY

Justin Thomas, Blaire Sorenson, Daniel Westcott, Brian Lampert, Alexandra Sakols, Emina A. Stojkovic, Stefan Tsonchev, Kenneth Nicholson.

Northeastern Illinois University, Chicago, IL.

Bacteriophytochromes (BphPs) are red-light photoreceptor proteins found in photosynthetic and nonphotosynthetic bacteria. Classical BphPs undergo reversible photoconversion between distinct red-light (Pr) and far red-light (Pfr) absorbing states. Our research group is studying RpBphP3 (P3) from Rhodopseudomonas palustris that Sciences Physical has unique photoconversion between Pr and near-red light (Pnr)-absorbing states. To investigate the structure of intact P3, we are using atomic force microscopy (AFM) and scanning tunneling microscopy (STM), two powerful surface analytic methods that can be used to take images of the macromolecule with individual domain resolution.





Proteins self assemble when deposited onto a surface due to protein-protein and protein-surface interactions.

We are using AFM and STM to image proteins on a hydrophobic graphite surface and a hydrophilic mica surface.

We have obtained images of the P3 dimers on the surface with nanoscale resolution for AFM and STM. The STM data has shown P3 assembling into periodic fibrous structures, while individual molecules as well as aggregates of multiple dimers have been observed via AFM on mica. Our goals are to gain insight into how the nature of the surface drives protein self assembly and how the surface impacts protein structure. We will compare our results with published cryogenic-electron microscopy data on related BphP from Deinnococcus radiodurans and determine quaternary organization of P3 dimers in the Pnr state. In the future, we plan to study adsorption and arrangement of P3 on N-hydroxysuccinimide-terminated self-assembled monolayers, which have been proposed in the literature as selectively binding individual proteins to the surface in a single orientation.

SAT-3

PH AND PHYSICAL PROPERTIES OF AMINO ACID-BASED SURFACTANTS

Mariela Vazquez, Fereshteh Billiot.

Texas A & M-Corpus Christi, Corpus Christi, TX.

The purpose of this research was to examine the effects of pH on the critical micelle concentration (CMC) and aggregation number of 2 amino acid (alanine and leucine) based surfactants. The amino acid-based surfactants were synthesized by reacting the respective amino acids with the N-hydroxysuccinimide ester of undecylenic acid in tetrahydrofuran and water to form undecyl alanine and undecyl leucine. The purity of the surfactants was confirmed by NMR and HPLC. Fluorescence spectroscopy with pyrene as the probe was used to measure the CMC and calculate the aggregation numbers for each of the surfactants from pH 6 to 12. A slight decrease in aggregation number from 70 to 65 was observed for undecyl leucine compared to undecyl alanine. It was further observed that the CMC of both

–  –  –

surfactants increased as pH increased from pH 6 to 8 and plateaued after reaching a pH of 8. It is also worth noting that no significant differences in CMC were observed for the surfactants at each of the respective pHs.

SAT-5

SYNTHESIS OF GUANIDYLATED AMPHIPHILES AND BOLAAMPHIPHILES FOR SIRNA ENCAPSULATION IN

GENE-SILENCING THERAPY

Audrey Ynigez-Gutierrez, Adelphe M. Mfuh, George R. Negrete.

University of Texas at San Antonio, San Antonio, TX.

Since its discovery by Fire and Mello, RNA interference (RNAi) has been established as a potential route for gene-silencing therapy and has been anticipated as a possible remedy for various diseases such as cancer, viral diseases, diabetes, and gene disorders. However, the development of RNAi therapies has been significantly impeded due to difficulties in the delivery of the nucleic acid into the cells. Recently, lipoplexes and stable nucleic acid lipid particles (SNALPs) have been shown to be effective at encapsulating siRNA for gene-silencing therapy. In particular, the presence of tertiary amines and unsaturated hydrocarbon chains in the lipid portion appear to assist in siRNA interaction and delivery. Our lab envisioned the use of guanidylated amphiphiles and bolaamphiphiles (long hydrophobic chains with polar heads at each end) in the formation of lipoplexes with RNA for delivery applications.

The use of guanidine in place of amines should increase the amount of H-bonding interactions to provide more stable complexes. Here, we report the progress towards the synthesis and characterization of a guanidylated amphiphile synthesized from oleyl alcohol and a guanidylated bolaamphiphile synthesied from 10-undecenoic acid using a Grubbs’ catalyst for olefin metathesis. These lipids will be combined with RNA to form nanoparticles, which will be investigated as siRNA delivery modalities. (This work was partially supported by NIGMS MARC U*STAR GM007717, NIGMS MBRS-RISE GM60655, and the Department of Chemistry at the University of Texas at San Antonio.) SAT-1

ON-CHIP SAMPLE PRECONCENTRATION OF THIOLS FOR SENSITIVE IN SITU EXTRATERRESTRIAL

ANALYSIS Matt Gordon1, Fernanda Mora2, Carlos Garcia1, Peter Willis2.

University of Texas at San Antonio, San Antonio, TX, 2NASA, Jet Propulsion Lab, Pasadena, CA.

1 The search for signs of life on extraterrestrial planetary bodies is among NASA’s top priorities in solar system exploration. Because all life on Earth is based on common biochemical roots and genetic history, one essential astrobiological question is whether there is life elsewhere in the universe, and if so, whether it has a similar biochemical nature. Due to the anticipated complexity of extraterrestrial samples, identification and quantification of individual species is extremely challenging or impossible without a method to separate them prior to detection.

Microchip capillary electrophoresis (μCE) is a powerful separation technique that has progressed greatly in the last 2 decades and offers short analysis times, small sample and solvent consumption, and low waste generation. This technique has been successfully employed for analyses of a wide range of compounds in relatively simple samples (e.g., water) to highly complex ones (biological fluids), demonstrating its powerful analytical capabilities. We have designed a new microfluidic architecture that incorporates a preconcentration chamber into existing automated microfluidic technology. This preconcentration chamber encapsulates functionalized silica beads (40 µm) for the trapping of target molecules (thiols), which ultimately allows for ultralow levels of detection. While preconcentration methods have been demonstrated for a range of molecules, they have never been integrated into fully automated μCE devices. We have created a microfluidic device capable of completely automated end-to-end analysis of thiols following an initial preconcentration step. This device would allow detection of traces of sulfur-containing molecules in an automated, miniaturized fashion, which is crucial for planetary studies.

FRI-16

SIZE CONTROL IN MICROWAVE SYNTHESIS OF GERMANIUM NANOCRYSTALS

Marlene Amador, Elayaraja Muthuswamy, Susan Kauzlarich.

University of California Davis, Davis, CA.

Germanium (Ge) is a narrow band gap semiconductor and is considered a potential material in the nanoscale for solar energy conversion. Colloidal synthetic methods assist in the formation of size- and shape-controlled nanocrystals.

Our group developed a microwave assisted method to prepare colloidal Ge nanocrystals in oleylamine using Geiodides as precursors. The nanoparticle size was controlled by adjusting the precursor ratio (GeI2:GeI4). Our current efforts are focused on exploring the effect of additives such as SiI4 and I2 in the microwave reaction and determining

248 UNDERGRADUATE POSTER ABSTRACTS

the mechanism of formation. Preliminary experiments demonstrate the correlation between nanocrystal size with increasing additive quantity. The Ge nanocrystals were characterized by routine spectroscopic methods, powder X-ray diffraction for phase-purity and crystallinity, and electron microscopy for size and morphology. The results of the experiment along with characterization will be presented and the mechanism of formation proposed.

FRI-8

THE SYNTHESIS OF MIXED-BRIDGE DIQUINOXALINE CAPSULES

Ephraim Morado, Yanwei Cai, Linda Gutierrez-Tunstad.

California State University, Los Angeles, Los Angeles, CA.

Resorcin[4]arenes have been used as a primary scaffold in supramolecular chemistry to create a family of container molecules that adopt a bowl-shaped geometry, known as cavitands. The environmentally dependent and conformationally changeable structures of cavitands make them attractive compounds for capturing and releasing guest molecules. The main purpose of this research is to synthesize a fully enclosed capsule that is composed of a dimethylene bridged resorcin[4]arene and a diquinoxaline cavitand connected by 2 tetraazaanthracene linkers.

The cavitands were generated using well-established organic synthetic methodology. Also, the structure and binding studies of the cavitand capsules were determined using nuclear magnetic resonance analysis. So far, the dimethylene bridged resorcin [4] arene cap and the diquinoxaline cavitand base were synthesized in relatively high yields.

Modifications to the reaction conditions are being developed to incorporate tetraazaanthracene in the construction of our product: the molecular capsule. These molecular capsules have potential applications for toxin remediation and drug delivery. In toxic remediation, the cavitand capsules can potentially selectively bind toxins and extract them from the environment. Additionally, capsules could revolutionize how drugs are delivered into the human body and act as a transportation system for foreign molecules.



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