Fall 2013 Calendar of Events

Jennifer Kohler Seminar " Capturing glycoconjugate complexes with metabolically incorporated photo-sugars."

Jennifer Kohler Seminar

September 27, 20133:00 PM – 4:00 PM
Druckenmiller Hall, Room 020

Glycan-mediated interactions constitute the underlying molecular bases for a wide range of biological processes.  This class of interactions is particularly important in development, immunology, infection, and carcinogenesis.  Yet glycan-mediated interactions are difficult to detect and characterize, due to their low affinities and rapid dissociation kinetics.  To capture these ephemeral complexes, we make use of metabolic oligosaccharide engineering to incorporate photocrosslinking groups into cellular glycoconjugates.  In this presentation, I will describe our strategy for introducing photocrosslinkers into a variety of glycoconjugates, how we characterize which glycoconjugates are modified and the degree of modification, and the use of these photocrosslinkers to discover glycan-mediated interactions.  The utility of this approach will be demonstrated by describing the discovery of a novel receptor for cholera toxin.  

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John Dawson Seminar on Understanding Heme Enzyme Catalysis

John Dawson Seminar on Understanding Heme Enzyme Catalysis

October 16, 20134:00 PM – 5:30 PM
Druckenmiller Hall, Room 016

"Understanding Heme Enzyme Catalysis Starts with Their Active Site Coordination Structure: Identifying Heme Iron Axial Ligands Using Magnetic Circular Dichrosim Spectroscopy," by John Dawson of the University of South Carolina.
Magnetic circular dichroism (MCD) spectroscopy provides diagnostic spectral data sensitive to the identity of the axial ligands and to the spin and oxidation states of heme iron centers in proteins. In this effort, we have found the proximal ligand His93Gly myoglobin cavity mutant to be a remarkably versatile scaffold for preparation of model heme complexes of defined ligation. In particular, the difference in accessibility of the two sides of the heme iron center offers the advantage of forming ambient-temperature mixed-ligand heme model complexes, which are very difficult to prepare with model systems in organic solvents. Moreover, in the H93G Mb system, the protective environment provided by the protein allows for the formation of relatively stable oxyferrous and ferryl [Fe(IV)=O] complexes with variable ligands trans to the normally reactive dioxygen and oxo substituents. Ferrous, ferric and ferryl His93Gly Mb derivatives with various exogenous ligands have been prepared as models for native heme iron active sites ligated by proximal Lys (amines), Asp or Glu (carboxylates), Tyr (phenols), seleno-Cys (selenols), Cys (thiols) and Met (thioethers). Building upon this foundation, we have focused our attention on the use of the H93G Mb cavity mutant system to aid our investigation of the coordination structure of novel heme binding and transport proteins and heme-containing oxidative enzymes. (Funding NIH GM 26730)

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Daniel Schrag on Climate, Energy, and Innovation

Daniel Schrag on Climate, Energy, and Innovation

October 18, 201312:30 PM – 1:30 PM
Visual Arts Center, Kresge Auditorium

Common Hour with Dr. Daniel Schrag - Keynote for President's Science Symposium

Daniel P. Schrag will discuss "Climate, Energy and Innovation."

The increase in atmospheric CO2 due to burning coal, oil and natural gas represents an unprecedented experiment on the Planet Earth. Geologic records support the view that future climate change will have a profound impact both on human society and on natural ecosystems. A daunting challenge is the timescale of climate change. More than half of the carbon dioxide emitted to the atmosphere by burning fossil fuels will remain for hundreds of years, and roughly 20% will be there for tens of thousands of years. In this context, a variety of strategies will be discussed for meeting the world's energy needs, preserving economic prosperity and security, while protecting human and natural systems from climate impacts. In addition, we will explore what strategies might be required if the impacts of climate change are larger than we expect.

Daniel Schrag is the Director of the Harvard University Center for the Environment, the Sturgis Hooper Professor of Geology, and Professor of Environmental Science and Engineering at Harvard University. He currently serves on President Obama's Council of Advisors for Science and Technology. Among various honors, he was named a MacArthur Fellow in 2000. Schrag received a B.S. from Yale University and a Ph.D. in Geology from the University of California at Berkeley.

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President's Science Symposium: Student Talks

President's Science Symposium: Student Talks

October 18, 20131:35 PM – 2:45 PM
Visual Arts Center, Kresge Auditorium

Research conducted by faculty-mentored Bowdoin science and math students this past summer will be in the spotlight Friday, October 18, 2013, at the annual President's Science Symposium. All events are open to the Bowdoin community.

"The President's Science Symposium is a time to showcase the extraordinary scientific research performed by Bowdoin faculty and students," note's the event's coordinator Michael Danahy, lecturer in the Department of Chemistry. "It's a unique event in that all the sciences and mathematics are represented in one place, so one gets a real sense of the breadth of the impressive work done at the College."

Four students will give talks about their research from 1:35 p.m. to 2:45 p.m. in Kresge Auditorium, Visual Arts Center. The student researchers are Justin Dury-Agri '15 from the mathematics department, Beatriz Malibiran '14 from the biochemistry program, Nicholas Wetzel '14 of the computer science department, and Adam Zhang '14 of the neuroscience program.

Following these talks, poster presentations by more than 90 student researchers in the sciences and math will be held from 3 p.m. to 4:30 p.m. in Morrell Lounge, David Saul Smith Union. Students will be on hand to discuss their projects.

"With the student poster presentations and student research talks, students take ownership of their research," says Danahy. "This event highlights the importance of research in science education."The symposium will kick off earlier in the day with a keynote address at Common Hour by guest speaker Daniel Schrag, an expert on climate change and a professor in the Department of Geology at Harvard University. Schrag's talk, titled "Climate, Energy and Innovation," will be given at 12:30 p.m. in Kresge Auditorium, Visual Arts Center.

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Dave Gorin Seminar "Methylation of Oxygen Nucleophiles with Safe, Stable Methylating Agents."

Dave Gorin Seminar

October 25, 20132:45 PM – 3:45 PM
Druckenmiller Hall, Room 020

Dave Gorin of Smith College gives a seminar on "Methylation of Oxygen Nucleophiles with Safe, Stable Methylating Agents."

Although methylation reactions are commonplace, currently used reagents are hazardous, toxic, and/or unstable. Dimethylcarbonate has been put forth as an inexpensive, non-toxic, and "green" potential methylating reagent. We have discovered a general, base-catalyzed methyl transfer from dimethylcarbonate to carboxylic acids. High selectivity for esterification is observed even in the presence of unprotected phenols and the mild reaction conditions enable conservation of stereochemistry at epimerizable stereocenters. Isotope-labeling studies suggest a mechanism proceeding by direct methyl transfer from dimethylcarbonate to the substrate.

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Graduate School Fair

Graduate School Fair

October 29, 20131:30 PM – 5:30 PM
David Saul Smith Union, Morrell Lounge

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Dinner with Chemists- INVITATION ONLY

Dinner with Chemists- INVITATION ONLY

November 7, 20136:00 PM – 9:00 PM
Cram Alumni House, Barn (Torrey Barn)

Enjoy dinner with the Chemistry Faculty!Fajita Buffet dinnerSalad VarietyMake your own fajitas, Chicken, veggies,Beans and Rice and cornbreadAssorted cookies, brownies and pastries.6:00pm Cram Alumni Barn83 Federal StreetSign in sheets available in class or in Room 157 at Penny's desk! Sign up NO LATER than Wednesday October 30th 4pm.The Chemistry Faculty look forward to seeing you there!

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From triclosan to dioxins: How handsoap leads to an environmental problem

From triclosan to dioxins: How handsoap leads to an environmental problem

November 8, 20133:00 PM – 4:00 PM
Druckenmiller Hall, Room 020

Seminar: "From triclosan to dioxins: How your handsoap leads to an unanticipated environmental problem" by William Arnold of the University of Minnesota

Pharmaceuticals and personal care products (PPCPs) are widely used and through their normal course of use, often find their way into the sewage system. Wastewater treatment plants are not designed to remove trace chemicals, but a large fraction of the PPCPs are removed. The small fraction that is released into the environment, however, may have adverse effects. 

One ubiquitous PPCP is triclosan, the antimicrobial ingredient in liquid handsoaps. For triclosan, the major route to the environment is via wastewater effluents discharged to surface waters. During the disinfection of wastewater, chlorinated triclosan derivatives are produced. The impact of triclosan and related compounds is, in part, determined by their persistence in aquatic environments. 

Photolysis (reaction initiated by sunlight) is an important loss process for triclosan, and triclosan and chlorinated triclosan derivatives produce specific dioxins (a class of known toxic chemicals) in 1-3% yield upon exposure to sunlight.

Sediment cores serve as a record of contaminant release and accumulation in aquatic systems, and thus were collected across Minnesota to determine historical levels of triclosan and its degradation products. Analysis of sediment cores shows that while dioxins produced from incineration have been decreasing for the past thirty years, concentrations of dioxins derived from triclosan have been increasing and are correlated with triclosan concentrations/use.

The findings of this work suggest that the use of triclosan in consumer products merits additional scrutiny.

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Accurate Nonadiabatic Dynamics: Putting Your Best Foot Forward

Accurate Nonadiabatic Dynamics: Putting Your Best Foot Forward

November 22, 20133:00 PM – 3:55 PM
Druckenmiller Hall, Room 020

Chemistry Department Seminar

"Accurate Nonadiabatic Dynamics: Putting Your Best Foot Forward" by David Yarkony of Johns Hopkins University

Dr. Yarkony will review nonadiabatic processes, including their relevance to biological chemistry and solar energy storage, emphasizing the role of conical intersections and providing a historical perspective. He will present accurate simulations of nonadiabatic reactions and photodissociation, which rely on accurate representations of adiabatic potential energy surfaces coupled by conical intersections. He will also describe a new approach to accurately provide the requisite ab initio electronic structure data in a timely manner.

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Chemistry Department Seminar Christoph Aeppli "Where did all the oil go? The chemistry of oil weathering after the Deepwater Horizon oil spill"

Chemistry Department Seminar Christoph Aeppli

December 6, 20133:00 PM – 4:00 PM
Druckenmiller Hall, Room 020

The 2010 Deepwater Horizon oil spill led to the release of approx. 5 million barrels of oil in the Gulf of Mexico, making it the larges marine oil spill in US history. Whereas approx. 40% of the released hydrocarbons were burnt, recovered or evaporated, 45% dissolved in a deep plume in the water phase, and the remaining 15% formed surface slicks that ended up on beaches or formed near-shore submersed oil mats. These mats are a long-term source of oil and still today, oil-soaked sand aggregates are washed on beaches along the Gulf of Mexico. Analyzing these samples provides a unique opportunity to gain new insights in the fate of oil on time scales of years. Oil is a complex mixture of thousands of hydrocarbons with various physico-chemical properties. Recent analytical development, such as comprehensive two-dimensional gas chromatography now allows analyzing relative changes in the composition of petroleum on a molecular level. This technique allowed us to identify Deepwater Horizon oil on the sea surface and on beaches, based on relative amounts of various petroleum biomarker compounds (“oil fingerprinting”). Furthermore, we analyzed compositional changes in the petroleum hydrocarbon over time. This showed that abiotic (photooxidation) and biotic (biodegradation) oil degradation processes efficiently remove many – but not all – hydrocarbons on time scales of years. However, these degradation processes also led to the formation of highly oxygenated oil degradation products. These compounds are recalcitrant on the observed time scale, form a pool of compounds that are currently overlooked, and might contain products with ecotoxic effects. Overall, taking advantage of the complexity of oil allowed us to gain new knowledge about oil weathering processes. This knowledge will be useful to prepare for future potential oil spills.

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Chemistry Deparment Seminar Geoffrey Davies Northeastern University

Chemistry Deparment Seminar Geoffrey Davies Northeastern University

February 7, 20143:00 PM – 4:00 PM
Druckenmiller Hall, Room 020

Humic acids (HA) and fulvic acids (FA) are sequestered carbon compounds in soils that can bemeasured reliably with gravimetric and spectrophotometric methods, respectively. As part of theongoing National Soil Project at Northeastern University, this paper reports the HA and FA contentsof soil horizons from agricultural (potatoes in rotation with small grains and broccoli) and forestryland uses in northern Maine, USA. The agricultural fields are depleted in HA and FA compared tonearby woodland soils of similar provenance. We confirm that HA are better soil water retainersthan total organic matter (OM) components on an equal mass basis. Humification starts at the soilsurface and HA, FA, and dissolved organic carbon (DOC) contents drop sharply below the O andA horizons. The depleted OM, HA, FA, and DOC contents of spodosol horizons in soil profiles canbe quantified. Fulvic acids in the Maine soils investigated are in a solid-solution equilibrium witha HA·FA(s)/FA(aq) ratio of about 3.4:1. From the regression of DOC (g L-1) and FA(g L-1), FA in theMaine soil samples contain about 54% carbon. The HA and FA are long-lived soil components thatrepresent the baseline OM content of any soil. As such they are a sink in the carbon cycle that needsto be maintained in agricultural soils, including those in Aroostook and Piscataquis Counties of Maine.

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