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Chemistry

2007 Honors Recipients

Spring 2007

Group Photo Chicago Trip Six Bowdoin honors chemistry students recently presented posters on their original research at the 2007 National American Chemical Society Conference in Chicago. With support from the College, the seniors were able to join the more than 12,000 scientists in attendance at the meeting.

“I think it really opened their minds to many things, just to see the scale of things going on,” noted Associate Professor of Chemistry Dharni Vasudevan. “There are so many kinds of chemistry, and so many sub-disciplines within those.”

Among the students was chemistry major Ethan Van Arnam ’07, who flew directly to the conference from California, where he had been visiting potential graduate schools.

“I plan to get my Ph.D. in chemistry,” said Van Arnam, “and the conference gave me a chance to meet up with some of the professors I want to study with. It was neat to see them lay out their research in a big lecture format.”

The large-scale format also applied to poster presentations: The Bowdoin students were among over 500 undergraduate presenters at a conference poster session.

“They had a huge exhibition hall for us,” noted Van Arnam, who was attending a major scientific conference for the first time. “We were divided by sub-discipline and got to stand by our posters and explain our work, then walk around and see what other people had done.”

All six students have been working closely together in Bowdoin laboratories, where they have been conducting research with various Bowdoin faculty members during summers as well as the academic year.

Van Arnam was joined at the ACS conference by chemistry major Anthony Carrasquillo ’07; biochemistry majors Chris Cashman ’07 and Tim Cashman ’07; and biochemistry majors Michael Reutershan ’07 and Lauren Steffel ‘07.

“Somehow our professors trusted us to head off to Chicago for four days,” smiled Van Arnem, adding: “We behaved ourselves. For the most part.”

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Timothy Cashman, '07

Title: Disulfide-based beta-sheet peptidomimetics
Timothy Cashman Abstract: Small molecules that resemble beta-sheets may be capable of mimicking the behavior of naturally occurring beta-sheets without the added complexity of the protein in its entirety. These small molecules have become important tools in understanding molecular recognition, protein-protein interactions and protein folding. A cystine dimer is a simple and easily created molecule that exhibits such a structure. The disulfide bond between the cystines functions as an effective scaffold for hydrogen bond formation that is consistent with beta-sheet secondary structure. Extension of the peptide strands to increase the number of hydrogen bonds produces a structure that more closely resembles naturally occurring beta-sheets.

Lauren Steffel, '07

Title: The use of hydrogen bonds to control peptide structure
Lauren Steffel Abstract:
Peptidomimetics that exhibit specific hydrogen-bonding secondary structures were designed to mimic the folding found in larger proteins. The respective strengths of the hydrogen bonds in these structures were analyzed primarily via hydrogen-deuterium exchange rates. Specifically, this work focused on the hydrogen bonding patterns present in β-turns, Asx-turns, and γ-turns. The combination of these secondary protein structures in peptidomimetics elucidates the energetic variables involved in hydrogen-bonding and possibly broader factors that control protein folding.

Ethan B Van Arnam, '07

Title: Modified selecitivity of linear α-olefin dimerization to linear α-olefin products by cobalt catalysis
Ethan B. Van Arnam Abstract:
Dimerization of linear α-olefins to linear α-olefin products has recently been achieved by cobalt catalysis. Here we report modification of the selectivity of dimerization by manipulations to the catalyst's phosphine ligand. Cobalt catalysis of linear α-olefin oligomerization yields several branched and linear α-olefin products from insertion of one α-olefin into the agostic Co-alkyl complex of a second olefin. Consistent with the proposed insertion transition state orientations of the agostic Co-alkyl species, the cone angle of the catalyst's phosphine ligand correlates to the ratio of branched to linear oligomeric products. Phosphine ligands with small cone angles were selected to promote linear dimer formation by the improved catalyst. Thus, phosphabenzene was synthesized as a target phosphine ligand. Oligomerization by catalysts employing phosphines with smaller cone angles will be discussed

Anthony Carrasquillo, '07

Title: CHED 1122 - Influence of compound structure on the sorption of cationic amines to mineral surfaces
Anthony Carrasquillo Abstract:
Veterinary antibiotics and pesticides containing cationic amines are often detected in natural waters. The fate and bioaccessibility of these compounds are influenced by their retention onto mineral surfaces. This study examines the influence of molecular structure, specifically delocalization, inductive effects, and proximity effects, on the nature and extent of amine sorption to soil minerals. Sorption of oxytetracycline onto metal oxide exceeded that of ciprofloxacin, but the reverse was true of sorption to aluminosilicates. Sorption studies of methylated anilines suggested that the presence of methyl groups on the nitrogen did not cause a steric hindrance to oxytetracycline sorption. Instead, repulsion between an ortho-substituted anionic moiety and the negatively charged mineral surface likely decreased the extent of oxytetracycline sorption. Further insight into structural criteria influencing sorption was obtained by varying the extent of delocalization of charge and the identity of electron donating/withdrawing substituents on a series of structurally related heterocyclic amines.

Michael H. Reutershan, '07

Title: Beta-turn peptides as asymmetric catalysts
Michael H. ReutershanAbstract:
Asymmetric organocatalysts have been developed that catalyze the reaction of vinyl ketones with nitroalkane derivatives. The peptide catalysts were designed to contain both Bronsted basic and hydrogen-bonding residues located around a central beta-turn core. The mechanism for substrate binding and peptide catalysis will be examined. Additionally, the structural considerations for maximal selectivity will be discussed.

Christopher Cashman, '07

Title: C-Terminal histidine loss from orcokinin family neuropeptides: Implications for the identification of truncated neuropeptide variants by MALDI-FTMS
Christopher CashmanAbstract:
The orcokinins comprise a family of neuromodulatory peptides found in decapod crustaceans and insects. They are short (~13 residue) peptides characterized by a conserved N-terminal region, with a variable C-terminal sequence that identifies the orcokinin isoform. In this study, matrix assisted laser desorption/ionization-Fourier transform mass spectrometry (MALDI-FTMS) has been used to identify orcokinins in decapod crustaceans, making use of cleavages C-terminal to aspartate residues (Asp-Xxx cleavages) to flag novel orcokinins, coupled with SORI-CID to determine the orcokinin sequence. We have characterized tissue samples from over 30 species of decapod crustaceans, and have found that the detection of C-terminally truncated orcokinins correlates with the detection of orcokinins containing C-terminal histidine residues. In this study we show that orcokinins containing C-terminal histidine residues are susceptible to metastable decay via neutral loss of histidine and that methyl esterification eliminates this fragmentation process. Implications of this fragmentation process for neuropeptides analysis will be presented.