2012 Summer Symposium Program - Middlebury College

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Page 16 18 Lauren Pincus ‘14 Major: CHEM, GEOL Gretchen Augat Reilly ‘60 Environmental Studies Fund Peter Ryan Professor of Geology 19 Nathan Rudd ‘13 Major: CHEM National Science Foundation (Larrabee) Jim Larrabee William R. Kenan Jr. Professor of Chemistry Middlebury Summer Research Symposium 2012 Phosphorus Abundance and Reactivity in Champlain Valley Sediments: Implications for Nutrient Transport to Lake Champlain Lauren Pincus and Peter Ryan Department of Geology, Middlebury College, Middlebury VT 05753 Phosphorus is the main limiting nutrient responsible for eutrophication and toxic algal blooms in Lake Champlain, and in order to model P transport from the basin to the lake, a better understanding of P concentrations across the basin is necessary. Research and modeling efforts thus far have mainly focused on the release of phosphorus from point sources such as sewage treatment plants and from agricultural non-point sources; however, data is needed on P release from natural sources, especially eroding stream beds and lake shore deposits in order to accurately model the transport of P to Lake Champlain. This project seeks to collect data on P abundance in non-point sources such as river floodplains, eroding cut banks, and forest soils. Soil, sand, and clay samples have been collected at sites along multiple tributaries to the southern and central parts of Lake Champlain. X-ray diffraction was used to understand the mineralogical composition of collected samples. Relative amounts of the minerals were measured with particular importance placed on minerals with the potential to adsorb P such as smectite and iron hydroxides. This data provides insight into which minerals are present in clays, sands, and soils to release phosphorus or hold it in an insoluble form. Comparisons between weathered and unweathered samples can also potentially indicate which minerals may be preferentially weathering to release phosphorus. Research will continue with measurements of total P using LiBO 2 fusion and ICP-AES analysis of the samples. Additionally available P will be extracted and measured using sodium bicarbonate or another extractant. Characterization of 4- and 5-coordinate Co(II) Model Complexes by Magnetic Circular Dichroism Spectroscopy Nathan Rudd and Jim Larrabee Department of Chemistry & Biochemistry, Middlebury College, Middlebury VT 05753 The determination of zero-field splitting (ZFS) parameters provides valuable insight into the geometric and electronic structure of metalloenzyme active sites. Variable-temperature, variable-field magnetic circular dichroism (VTVH MCD) sheds light on the phenomenon of ground-state zero-field splitting, as well as a basis for investigating paramagnetic metal-containing enzyme active sites to see how structure correlates with mechanisms. VTVH MCD spectroscopy has been applied
20 Juliet Ryan-Davis ‘13 Major: GEOL John M. White ‘52 Memorial Fund and Northeastern GSA Undergraduate Research Grant Ray Coish Robert R. Churchill Professor of Geosciences Will Amidon Assistant Professor of Geology Middlebury Summer Research Symposium 2012 to eight mononuclear, high spin (S=3/2) Co(II) model complexes with coordination numbers of four or five. These complexes vary with skeletal structure and bound ligands. VTVH MCD has been used to investigate the ground state electronic structure of each species. The MCD spectra for the four-coordinate complexes have positive and negative transition bands between 500-750 nm, while the fivecoordinate Co(Et 4 dien)Cl 2 complex spectrum has bands between the larger range of 200–900 nm. Axial (D) and rhombic (E) zero-field splitting values—as well as spin Hamiltonian parameters—are determined computationally through a Fortranbased fitting program. Analysis of only the complex Co(L1)N 3 [L1: HB(3-tertbutylpyrazole) 3 ] is finished to date (average D and E values of 8.6188 and 0.1872 cm -1 , respectively). Future work will include fitting for the additional model complexes, as well as elucidating connections between computational parameters and enzyme active site structure and function. Origin of the Moretown Formation, Vermont: A Detrital Zircon Study Juliet Ryan-Davis, Ray Coish, and Will Amidon Department of Geology, Middlebury College, Middlebury VT 05753 Vermont’s geology reveals a series of collisional and rifting events, evidence for which is preserved in the various geologic belts. Detailed studies of these belts provide insight into the complex history of the northeastern Appalachian Mountains. U-Pb age analysis of detrital zircons from the Moretown Formation, part of the Rowe-Hawley belt, Vermont, will be used to determine the age of deposition of the formation and constrain its sedimentary provenance. The formation, mainly quartzrich granofels, phyllite and quartzite, with minor volcanogenic material as well as regions of greenstone and other metamorphosed mafic rocks, is currently interpreted to have been deposited in an arc-trench gap, likely a forearc basin, between the > 900 Ma Laurentian continental rocks and the approaching Shelburne Falls Arc, active between ~485 and 460 Ma. That arc is preserved in the highly deformed Barnard Volcanic unit in Vermont, which extends southward into the Hawley Formation in Massachusetts. In constraining the age of the sedimentary source of the Moretown Formation, we will determine whether it was formed by erosion of the young Shelburne Falls volcanic arc, or from older Laurentian continental material. Seven samples, 25 or more kilograms each, were collected from the Montpelier quadrangle, three quartzites and two phyllites from the Dumpling Hill belt, and two quartzites from the Wrightsville belt. Zircons were extracted from those samples using standard mineral separation procedures. Roughly 20 kilograms of rock was crushed using a large jaw crusher, and sifted into several size components, of which the finest grain size, less than 208 nm, was used. Samples were rinsed and panned in a standard gold pan to separate rock powder and fine sheet minerals from the sample. The sample was run through a Frantz magnetic separator up to 1.2 amps to Page 17
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Page 7 and 8: 3 Samouel Beguin ‘13 Major: ENVS,
Page 9 and 10: 6 Nicholas Dragone ‘14 Major: BIO
Page 11 and 12: 8 Aden Forrow ‘13 Major: PHYS, MA
Page 13 and 14: 11 Jacob Hobbie ‘15 Major: PHYS E
Page 15 and 16: 15 Poomirat Nawarat ‘14 Major: PH
Page 17: 17 Lucia Perez ‘14 Major: Astroph
Page 21 and 22: 22 Garron Sanchez ‘13 Major: MBB
Page 23 and 24: 25 Meghan Stang ‘13 Major: MBBC N
Page 25 and 26: 27 Karl Wetterhorn ‘13 Major: BIO
Page 27: Monomers: Middlebury Summer Researc

2012 Summer Symposium Program - Middlebury College

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