Brugia Malayi - Clark Science Center - Smith College

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Ion Transport of Extruded Liposomes as Cell Membranes Esther Hong Phospholipids are a type of lipids containing a hydrophilic polar head and hydrophobic tails. Phospholipids are important because they can be found in biological membranes. These lipids create a barrier for the passage of hydrophilic material, such as water and ions. In the presence of water, lipids form vesicles, or liposomes, which act as model cell membranes. This summer I examined a set of novel synthesized cyclic peptides and their ionophoric activity. 1 These cyclic peptides can form a flat ring structure that can stack to form dimers. I studied the ion transport of these cyclic peptides by preparing liposomes and examining the mediated ion transport using 23 Na Nuclear Magnetic Resonance (NMR). When first hydrated, most lipids form multilayered liposomes. I used extrusion to convert these mulilamellar structures into unilamellar, or bilayer, systems to model cell membranes found in nature. Ion channels and transporters facilitate the transport of material and signals in and out of the cell. These regulate the flow of metal ions across cellular lipid bilayers. Cyclic peptides were then added to these liposomes in varying amounts and tested using NMR. I used the prepared liposomes to test ionophores, including various cyclopeptides that can stack to form dimer ionophores and gramicidin, a known ion transporter as a standard by which to judge the efficiency of the cyclic peptides. 1 I compared changes over time in NMR peaks that indicate the concentration of ions in and out of the liposomes 2 . Increasing intracellular ion concentration indicates that the ionophore is effectively transporting ions from the higher extracellular concentration to the lower intracellular concentration. Initial tests show immediate concentration changes that plateau over time, suggesting that the tested cyclic peptides have an ion channel-like mechanism. 3 Discovering new compounds that have the ability to transport ions across cell membranes well can aid in the medical field, helping form new antibiotics that can have a faster effect on the human body. Determining if the tested cyclic peptides can be used as ion channels can lead us in a direction to possibly implement them for use in the future. I have presented my research to fellow students and will continue with my project in the fall. (Supported by the Howard Hughes Medical Institute) Advisor: Cristina Suarez References: 1 Amorin M., Castedo, Luis., Granja, J.R. (2008) Folding Control in Cyclic Peptides through N-Methylation Pattern Selection: Formation of Antiparallel β-Sheet Dimers, Double Reverse Turns and Supramolecular Helices by 3α,γ Cyclic Peptides. Chem.Eur.J. 14:2100. 2 Jin, T.; Kinjo, M.; Koyama, T.; Kobayashi, Y.; Hirata, H. Langmuir (1996) Selective Na + Transport through Phospholipid Bilayer Membrane by a Synthetic Calix[4] arene Carrier, 12: 2684-2689. 3 Herasymova, N. (2010) Gramicidin A and Cyclic Peptide Channel Conductances in Black Lipid Membranes. (Honors Thesis, Smith College, 2010). 2012 75
Energetic Comparison of S N 2 Self-Exchange Reactions on Pentacoordinate Carbon, Silicon, and Tin Sarah Kay Though carbons structures have been extensively studied in organic chemistry, relatively little is known about the analogous silicon or tin structures and whether these elements will behave similarly, given differences in size and nuclear charge. This project investigated the resultant energy changes when a ligand, XH n- , displaces an identical ligand from a methyl, silyl, or stannyl center via an S N 2 mechanism. Using ADF2012 1 many such systems were investigated, in which X is an element from rows 2-5, groups 14-17 of the periodic table. In each system, three structures were examined: the XH n - anion, the CH 3 XH n molecule (or Si or Sn), and the trigonal bipyramid [XH n —CH 3 —XH n ] - . The sum of total bonding energies (TBE) for the anion and molecule was subtracted from the TBE of the overall system, giving the reaction energy from infinite separation of the starting fragments. The most significant finding is that while the energy change for the methyl-centric system is nearly always positive (a barrier), the change in both silyl-centric and stannyl-centric systems is consistently negative (energy wells). I.e. the trigonal bipyramid for SiH 3 and SnHs self-exchange reactions (SER) are stabilizing, while the same structure for CH 3 SER’s is destabilizing. These results support a paper 2 published by Hoz; starting from a dipole attraction of the initial fragments (rather than infinite separation), Hoz found that the CH 3 systems are always uphill in energy. The trends observed show that elements farther to the right in the periodic table (i.e. halides) form the most stable pentacoordinate systems (for C, Si, and Sn). However, while silicon and tin favor the upper rows (C, N, O, F are best), carbon shows the smallest barriers with the largest elements (Sn, Sb, Te, I) as ligands. (Supported by Smith College Committee on Faculty Compensation and Development) Advisor: Robert Linck References: 1 ADF2012, SCM, Theoretical Chemistry, Vrije Universiteit, Amsterdam, The Netherlands, http://www.scm.com. E.J. Baerends, T. Ziegler, J. Autschbach, et al. 2 S. Hoz, H. Basch, J. L. Wolk, T. Hoz, E. Rozental, J. Am. Chem. Soc. 1999. 121, 7724-7725. 2012 76
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2012 Women in Science Clark Science
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We are pleased to recognize the gen
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Biological Sciences (continued) Nam
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Confirming a High-Redshift Galaxy C
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Effects of Surface Chemistry on Bio
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Hsp25 expression was quantified by
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Analyses of the Relationship betwee
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Function of Slit and Robo in Axon G
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Developing Forms and Maps for Data
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Smith College’s Bird Collection:
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Soil Seed Bank Exploration: Compari
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Landscape Field Studies Seneca Gray
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Distribution and Origin of Caliche
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The Statistical Sleuth in R Ruobing
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Patch-Clamp Investigation of the Mo
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The Effects of Isoflurane Pre-condi
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Pilot Testing of a Spanish Computer
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This graph shows a possible signifi
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