2004 Beckman Scholars at Carnegie Mellon-Department of Biological Sciences - Carnegie Mellon University

2004 Beckman Scholars at Carnegie Mellon

Jamie Conklin

Jamie Conklin, Department of Biological Sciences, Carnegie Mellon University
(Mentor: Dr. Javier Lopez)

New Conductive Elastomers with Potential Applications in Electronics
The goal of this project is to synthesize poly(3-hexylthiophene)- b -polydiene conductive elastomers. An elastomer is a polymer that recovers its shape after being stretched or deformed. Polydienes are well-known elastomers, which are extensively used in the production of tires. The novelty of poly(3-hexylthiophene)- b -polydiene copolymers consists in combining the conductive properties of regioregular poly(3-hexylthiophene) with the elastic behavior of polydienes. The work is significant because conducting elastomers would be ideally suited for applications such as flexible electronic circuits. These circuits can be used as electronic identification tags or antitheft stickers into product wrappings for soft packages. There are no reports in the literature with regard to the synthesis of such copolymers. I envisaged a multi-step method for the synthesis of poly(3-hexylthiophene)- b -polydiene copolymers. The proposed synthesis of poly(3-hexylthiophene)- b -polydiene block copolymers consists of five reaction steps. In step one, 2,5-dibromo-3-hexylthiophene is first reacted with t -butyl magnesium chloride followed by [1,3-bis(diphenylphosphino)propane]-dichloronickel (II) (Ni(dppp)Cl 2 ) generating regioregular poly(3-hexythiophene) (PHT) (>98% head-to-tail coupling). The next step allows the quantitative formation of hydroxyethyl terminated PHT. Step three involves the conversion of hydroxyethyl terminated PHT to bromoethyl terminated PHT. Anionic polymerization of butadiene or isoprene is performed in the fourth step. Finally in Step five, coupling of living polydienyl lithium with bromoethyl terminated PHT will be performed. The block copolymer will be analyzed by 1H NMR, 13C NMR, IR spectroscopy and size exclusion chromatography (SEC).

Ashley Krankowski

Ashley Krankowski, Department of Chemistry, Carnegie Mellon University
(Mentor: Dr. Rick McCullough)

New Conductive Elastomers with Potential Applications in Electronics
The goal of this project is to synthesize poly(3-hexylthiophene)-b-polydiene conductive elastomers. An elastomer is a polymer that recovers its shape after being stretched or deformed. Polydienes are well-known elastomers, which are extensively used in the production of tires. The novelty of poly(3-hexylthiophene)-b-polydiene copolymers consists in combining the conductive properties of regioregular poly(3-hexylthiophene) with the elastic behavior of polydienes. There are no reports in the literature with regard to the synthesis of such copolymers. I envisaged a multi-step method for the synthesis of poly(3-hexylthiophene)-b-polydiene copolymers. The proposed synthesis of poly(3-hexylthiophene)-b-polydiene block copolymers consists of five reaction steps. In step one, 2,5-dibromo-3-hexylthiophene is first reacted with t-butyl magnesium chloride followed by [1,3-bis(diphenylphosphino)propane]-dichloronickel (II) (Ni(dppp)Cl 2 ) generating regioregular poly(3-hexythiophene) (PHT) (>98% head-to-tail coupling). The next step allows the quantitative formation of hydroxyethyl terminated PHT. Step three involves the conversion of hydroxyethyl terminated PHT to bromoethyl terminated PHT. Anionic polymerization of butadiene or isoprene is performed in the fourth step. Finally in Step five, coupling of living polydienyl lithium with bromoethyl terminated PHT will be performed. The block copolymer will be analyzed by 1 H NMR, 13 C NMR, IR spectroscopy and size exclusion chromatography (SEC). The work is significant because conducting elastomers would be ideally suited for applications such as flexible electronic circuits. These circuits can be used as electronic identification tags or antitheft stickers into product wrappings for soft packages.

Margaret Young

Margaret Young, Department of Biological Sciences, Carnegie Mellon University
(Mentor: Dr. Jonathan Minden)

Proteomic Analysis of Cell Shape Changes during Gastrulation in Drosophila
Drosophila ventral furrow formation involves a series of cell shape changes that cause the formation of the mesoderm layer of the embryo. Mutational analysis has identified several genes which are involved in a signaling cascade that triggers the process, but this approach has not identified any cytoskeletal proteins or structural proteins involved. An important thing to remember here is that the embryo contains maternally contributed proteins, in addition to zygotically expressed genes, and that many proteins are regulated by post-translational modification. For this reason, a direct protein analysis may be more useful than genetic screens for identification of the protein changes that cause the furrow to form. The Minden lab has developed a new approach to identify protein changes between different cells, difference gel electrophoresis (DIGE). DIGE is a modified two-dimensional polyacrylamide gel electrophoresis method that allows two samples to be run on a single gel and protein differences between them can be identified through fluorescence. The spots that change are called "difference-proteins" and are identified by mass spectrometry. So far, over fifty difference-proteins have been found, and many of them have been identified. My project was to determine the function of four of these proteins in ventral furrow formation and cell shape change. The proteins that I studied were determined to be time-dependent in ventral furrow formation by DIGE; they were belle, eIF-4e, squid and a dynamin-like protein. I used time-lapse microscopy to confirm the roles of these proteins by reducing protein abundance with RNA interference. Squid and eIF-4E were shown to have the greatest effect on ventral furrow formation. Squid inhibition was analyzed further by using DIGE to compare squid-injected embryos with mock-injected embryos. Fifteen difference proteins were seen but have yet to be identified. Squid is known to play a major role in oogenesis for setting up the dorsal-ventral axis. These experiments may explain how squid functions in embryogenesis, giving a more complete picture of Drosophila development.

Mary Ellen Wiltrout

Mary Ellen Wiltrout, Department of Biological Sciences, Carnegie Mellon University
(Mentor: Dr. Chien Ho)

A Biophysical Investigation of Recombinant Hemoglobins (rHbs) with Mutations in the Distal Heme Pocket
This study focused on the effects of amino acid substitutions in the distal side of both the a- and b-chain heme pockets of normal human adult hemoglobin (Hb A) on the structural and functional properties of hemoglobin. Using our Escherichia coli expression system, four recombinant hemoglobins (rHbs), rHb (αL29F), rHb (αL29W), rHb (βL28F), and rHb (βL28W), were constructed and expressed. The α29 and β28 residues are located in the B10 helix of the α- and β-chains of Hb A, respectively. The B10 helix is an area of significance due to previous work showing the L29F mutation's ability to inhibit oxidation. Oxidation inhibition is an important feature because hemoglobin is only functional in the reduced state. Three of the rHbs, rHb (αL29W), rHb (βL28F), and rHb (βL28W), exhibit very low oxygen affinity and reduced cooperativity compared to Hb A, while the previously studied rHb (αL29F) exhibits high oxygen affinity. The effects of mutations in the B10 helix of both the α- and β-chains on the quaternary structure and the tertiary structure were studied using 1H NMR. The α1β1 and α1β2 subunit interfaces in both deoxy and liganded states are not perturbed, whereas the tertiary structures around the heme pockets of the mutated chains are perturbed in these four rHbs as expected. The rate constants for the autoxidation and azide-induced oxidation were measured by visible spectrophotometry. These experiments showed that rHb (αL29F) and rHb (αL29W) had equivalent or slower rates of oxidation compared to Hb A, but the β-chain rHbs had increased rates. The bimolecular rate constants for NO-induced oxidation have been determined through experiments involving a stopped-flow apparatus. The two α-chain rHbs in this study had notably decreased rates of NO-induced oxidation compared to Hb A as anticipated. The present and future results will provide new insights into the factors that affect the oxygen affinity, cooperativity, oxidation, and structure of hemoglobin in the interest of possible applications to research for hemoglobin-based oxygen carriers.