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Electrospinning has recently emerged as a promising technique for tissue engineering because of its ability to produce nanofibers with differing porosities, surface area, fiber diameter, and fiber alignment. These properties of nanofibers can be altered through the use of varying parameters during the electrospinning process such that biomimetic nanofibers similar to the extracellular matrix (ECM) found in biological systems are obtained. Although these biomimetic nanofibers have multiple applications throughout tissue engineering, the potential application for this project is the formation of ligament scaffolds. The parameters used throughout the electrospinning process must first be determined in order to obtain nanofibers similar to those found in the ECM of natural ligaments. The objective of this study was to investigate the effects of fiber alignment on the mechanical properties and molecular structures of 3 electrospun polyurethanes: Tecoflex®, Carbothane 3575®, and Carbothane 3585®. Fiber alignment can be manipulated by varying the rotational speeds of the fibers’ collection. Three differing speeds were used (798 rpm, 4462 rpm, and 5900 rpm) in order to obtain nonaligned, semialigned, and completely aligned nanofibers. The alignment was confirmed using scanning electron microscopy (SEM), while mechanical testing was used to determine the effects of alignment on the enhancement of mechanical properties of the nanofibers.
EXTERNAL ELECTRIC FIELD MEDIATED ADSORPTION OF GLUCOSE OXIDASETomas Benavidez, Rhianna Velasquez, Carlos Garcia.
University of Texas at San Antonio, San Antonio, TX.
Enzyme adsorption to solid surfaces constitutes one of the immobilization processes used in the development of new platforms for biosensors in analytical chemistry. The advantage of enzyme adsorption to a solid substrate is that less biological activity will be lost when compared with the enzyme in solution. This work describes the effect of external applied potentials (500 mV, 650 mV, 800 mV, and 950 mV) on both the adsorption of glucose oxidase (GOD) to optically transparent carbon electrodes (OTCE) and the biological activity of the enzyme. Adsorption experiments were followed in real time by a variable-angle spectroscopic ellipsometer as a function of the potential applied, solution pH, ionic strength, and protein concentration. The potential applied at the interface resulted in 2 different behaviors. On the one hand, the effect of the electric fields at 800 and 950 mV significantly increased the adsorbed amount of GOD (ΓGOD) on the OTCE but caused the loss of the enzyme activity. On the other hand, the ΓGOD did not change the amount of enzymes adsorbed to the OTCE at open circuit potential (OCP). However, the enzymatic activity reached a maximum value after switching the potential from OCP to 500 mV. In conclusion, high potentials increased the amount of enzymes adsorbed to the OTCE but decreased the activity of the enzymes. At 500 mV, the adsorption levels did not change but the enzymatic activity was increased. These preliminary results show a good potential for the development of more sensitive biosensors. (This research was partially supported by UTSA MBRSRISE GM060655.) SAT-22
A NEW METHOD TO QUANTIFY HOMOCYSTEINEEscat Jimenez Leon, Mian Jiang.
University of Houston-Downtown, Houston, TX.
Homocysteine is a nonprotein amino acid. High levels of homocysteine have been linked to cardiovascular disease, Alzheimer’s disease, neural tube defects, and osteoporosis. To determine homocysteine levels is therefore significant in preventive medicine and neurotoxicity. In this work, we presented a new analytical method for determining homocysteine levels by using voltammetry. In alkaline media, homocysteine exhibits anodic oxidation. This oxidation is significantly enhanced when aliquot amounts of transition metal ions are introduced. Especially when cobalt (II) ions are present, homocysteine oxidation displays a well-defined anodic peak that showed concentration dependence. We present a new assay for homocysteine based on this discovery. Various factors, including transition metal ions, other sulfur- and nitrogen-containing amino acids and surfactants were examined for their possible impact on this response.
Our study revealed that homocysteine possesses the most sensitive and selective response in the proposed media.
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Optimization of the analytical system and calibration with various standards of homocysteine was performed.
Development of a real sample application is currently under way. [This work was supported by NASA-TSGC-NIP, SACP-UARP, Starter-award of UARP, and Welch Grant (BJ-0027 ).] FRI-18
N-HETEROCYCLIC CARBENE SUPPORTED IRON CATALYSTSMonica Kiewit, Jake Przyojski, Zachary Tonzetich.
University of Texas at San Antonio, San Antonio, TX.
Established processes involving iron catalysis are currently known but not well understood. The development of well-defined iron catalysts will allow probing of relevant reaction mechanisms affording the necessary information to optimize processes of interest. Several N-heterocyclic carbene (NHC)-supported FeCl2 complexes and their alkylated derivatives have been synthesized under an inert atmosphere and characterized by NMR, UV-vis, X-ray crystallography, and cyclic voltammetry. The NHC ligand is chosen for its steric and electronic tunability. Experiments involving the chlorination or saturation of the backbone are used to influence the sigma-donor properties of the ligand.
However, saturating the backbone tends to affect the steric properties as well. Further investigations will explain the effects of these ligand modifications on catalytic activity. A primary focus will revolve around low coordination species stabilized by the bulk of the 2,6-diisopropylphenyl NHC derivative. These compounds are of particular interest for their binding site availability, and their functionality as a catalyst in Kumada-type couplings will be explored and reported.
(Partially supported by UTSA MARC-U*STAR GM007717.) SAT-24
OPTIMIZING THE LUMINESCENCE INTENSITY OF POROUS SI QUANTUM-DOT NANOPARTICLESJose Cruz, Jinmyoung Joo, Michael Sailor.
University of California, San Diego, La Jolla, CA.
Porous silicon (pSi) has many physical properties that can be exploited for very useful applications such as drug delivery, in vivo imaging, and chemical sensors. Porous silicon, through an electrochemical process, may be etched and processed to become photoluminescent. One activation step that is used in making pSi particles luminescent involves a 2-week long incubation period. The process by which the particles become luminescent is not very well understood and requires further investigation. Through optical spectroscopy measurements along with surface
RHENIUM AND MANGANESE PHOTOACTIVE CORMS SUPPORTING 2-PHENYLAZO PYRIDINE LIGANDSJoshua Alvarado, Samantha Carrington, Indranil Chakraborty, Pradip Mascharak.
University of California, Santa Cruz, Santa Cruz, CA.
Carbon monoxide (CO) has always carried a negative connotation as the silent killer. Surprisingly, it has recently been shown to elicit antiinflammatory, antiproliferative, and vasoregulatory effects. It is in our interest to synthesize photoactive CORMs (carbon monoxide releasing molecule) in order to administer CO in a controlled manner since targeted and controlled delivery of exogenous CO has been shown to aid in a plethora of ailments and maladies.
Although the mechanisms of these salutary effects are not well understood, the syntheses of CORMs has been underway as possible therapeutic agents. Using a “smart design approach”, we have recently synthesized photoactive CORMs that use metal-to-ligand charge transfer (MLCT) transitions to release CO on illumination with visible light.
The synthesis of 2 metal-based photoCORMs and their structural characterization through infrared spectroscopy, nuclear magnetic resonance, and electronic spectroscopy will be described in this report.
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MODIFICATION OF CONFORMATION, PACKING, AND ELECTRONIC STRUCTURE OF CONJUGATED
POLYMERS FOR ORGANIC SOLAR CELLS USING STRONG ELECTRON ACCEPTORSCody Aldaz, John Grey, Alan Thomas.
University of New Mexico, Albuquerque, Albuquerque, NM.
The focus of this research is to obtain a molecular-level understanding of the relationship between the conformation and packing of conjugated polymers and their ability to transport charge. This relationship plays a significant role in determining the overall power efficiency of an organic photovoltaic cell (OPV). However, the desired conformation and packing of a conjugated polymer for OPVs is very difficult to control using the current solution-based processing strategies where polymers are simply blended with an electron acceptor (i.e., fullerenes) to achieve the photovoltaic affect. This research takes a new approach to influence conformation and packing by using small molecule dopants that tune structure via charge transfer interactions with the polymer. We study the prototypical solar cell polymer poly[2-methoxy-5-(3,7-dimethyl-octyloxy-1,4 phenylene vinylene) (MDMO-PPV) doped with strong electron acceptor dichloro-dicyano-benzoquinone (DDQ). Resonance Raman spectroscopy is the primary physical technique used in our research to report changes in polymer ground- and excited-state structural characteristics. It is hypothesized that DDQ induces long-range order in MDMO-PPV which should favor enhanced charge transfer. Preliminary Raman data suggests that DDQ induces planarity in MDMO’s conformation, and future research will entail device studies to show how MDMO’s morphology and ability to transfer and transport charge is affected by small molecule doping.
Because the conformation and packing has a significant impact on determining the final OPV efficiency, this research will provide much needed data on the extent of tunability afforded by molecular doping approaches to control polymer conformation and ability to transport charge.
DEVELOPMENT OF AFFINITY MEMBRANES FOR THE PURIFICATION OF PLASMINOGEN ACTIVATOROsiris Martinez1, Vibha Bansal2, Ezio Fasoli1.
University of Puerto Rico at Humacao, Humacao, PR, 2University of Puerto Rico at Cayey, Cayey, PR.
1 Plasminogen activators (PAs) are important therapeutic proteins used as emergency thrombolytic agents for the treatment of thrombovascular disorders such as myocardial infarction and stroke. The separation and purification of these proteins from complex mixtures of cell cultures is a challenging task due to the lack of efficient and suitable processes available. In order to develop a new, efficient method for the purification of plasminogen activators, our research was directed toward the development of an effective and accessible affinity membrane-based isolation process that could selectively bind the molecule of interest in a single filtration step. Regenerated cellulose (RC) membranes were chemically modified with spacer arms carrying epoxide or aldehyde moiety, which reacted with the hydroxyl moiety of the cellulose membrane. Spacer arms of different length (5, 7, and 14 atoms) were tested in order to optimize the process. The spacers were further reacted with two different selective ligands for PAs (paraaminobenzamidine (pABA) and L-Lysine). The modified membranes were characterized in term of epoxide content, ligand density, and further used for the purification process. Results showed a 40-fold purification in a single-step separation of PA from cell lines HEK-293 conditioned media using these affinity membranes, irrespective of the length of the spacer arm. The system was also showed to be very stable and could be reused several times, achieving 90% of the PA binding capacity of the membranes even after 5 cycles of use.
N, N-DIMETHYLACRYLAMIDE-BASED HYDROGELS FOR RECEPTOR CONJUGATION ONTO GLASSNANOPORES Ace Galermo1, Nader Pourmand2.
University of California, Santa Cruz, Santa Cruz, CA, 2Jack Baskin School of Engineering, University of California, 1 Santa Cruz, Santa Cruz, CA.
Monomers containing carboxyl or boronic acid functional groups were incorporated into hydrogels, which were analyzed for their properties of hydrophobicity and covalent attachment onto a functionalized quartz surface. The purpose of these experiments was to fabricate a bench-top method for covalent attachment of various receptors that can be used in miniature electrical sensors. One device that can measure analyte-to-receptor interaction is a solid-state nanopore. Ion current through the device can be modulated by charge and physical blockage at the pore. Using radical polymerization, we have synthesized a copolymer of N,N-dimethylacrylamide (DMAA) with
either 2-carboxyethyl acrylate (CEA) or N-3-acrylamidophenylboronic acid (AAPBA), which can conjugate amine
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containing proteins or bind monosaccharides, respectively. By modulating polymer composition and initiator conditions, hydrophobicity of the gels and polymer chain length can be controlled. The gels were analyzed for their ability to covalently attach to quartz slides through measurements of their surface contact angles. Immobilization of biomolecules to the hydrogels was measured by fluorescence and by modulation of ionic current within a glass nanopore. The nanopores were fabricated using quartz capillary tubes, which offer many practical properties that include reproducibility, low-cost, miniature size, and sensitivity. Principally, fabrication of such a device can further benefit biomedical research regarding saccharide detection, protein-protein interactions, and intracellular sensing applications.
DEVELOPMENT OF PEPTIDES AS ISLET-NEOGENESIS STIMULATING DRUGS FOR THE TREATMENT OFDIABETES Michael Covington, Jing Su.
Northeastern Illinois University, Chicago, IL.