Phoebe Aron ’13
Estuarine Sedimentary Sulfur as an Indicator of Drought in MidCoast Maine.
Sediment cores contain a continuous, high-resolution depiction of climate history and environmental conditions. Within a core, deeper sediments reflect older conditions and top sediments capture more recent records. Merrymeeting Bay (MMB), a freshwater tidal estuary in MidCoast Maine, provides a fertile site to investigate sedimentary records because the bay is exposed to both ocean input and freshwater rivers, many of which have a history of industrial use. Previous research in MMB has focused primarily on migratory fish populations and ecosystem degradation due to upriver industry; however, no studies have fully probed MMB sediments for a climate record. Therefore, the goal of this project was to evaluate a record of climate and environmental conditions in MidCoast Maine by measuring sedimentary sulfur and iron levels as a function of depth from two MMB sites. Specifically this project investigates the potential intrusion of sulfate-rich ocean water into MMB, which is likely to occur under drought conditions.
To evaluate the presence or absence of a drought record, two sediment cores were obtained from MMB, one from a lower site subject to ocean water intrusion and another from an upper site less exposed to ocean water intrusion. Sediment samples were digested by nitric acid microwave digestion and analyzed with ICP-OES to measure total sedimentary sulfur and iron concentrations. Elemental signatures were constructed by plotting sulfur and iron content (mass %) as a function of depth.
In both the upper and lower site cores, reference regions were defined as the oldest, deepest sediments where sulfur content is low and relatively constant with depth. Sulfur content in the upper site reference region (below 108 cm) is 0.2-0.8 m %. Sulfur content in the lower site reference region (below 85 cm) is 0.1-0.3 m %. We defined a reference region as the baseline against which we compared other regions and suggest that reference samples accumulated under standard climate conditions.
Above the reference regions, sediments were evaluated for a record of increased sulfur sequestration and anomalous environmental conditions. In the lower site core, enriched sulfur samples (0.3-0.6 m %) are present at 15-85 cm; in the upper site core enriched samples (0.3-0.8 m %) are present at 46-85 cm. Relative to reference samples, sulfur enrichment is more pronounced at the lower site than at the upper site. Additionally, Fe/S (mol/mol) amount ratios were calculated from elemental content and further indicate marked sulfur enrichment at the lower site. Only lower site Fe/S values decrease from reference levels (3-10 mol/mol) to enriched levels (2 mol/mol). In the upper site core, the Fe/S signature is relatively constant with depth (2 mol/mol) below 42 cm. Finally, MMB lower site signatures were compared with total sulfur and total iron signatures from the FOAM (Friends of Anoxic Mud), Long Island Sound, CT site. Both the lower MMB and FOAM sites are exposed to ocean water but only MMB is tidal. Therefore, a comparison of elemental signatures obtained at the two sites allows us to isolate and investigate the potential intrusion of sulfate-rich ocean water into MMB. This comparison indicates that lower site enrichment is unique to MMB and points to an intrusion of sulfate-rich ocean water under drought conditions as the source of additional sequestered sulfur.
Basyl Stuyvesant ’13
Structure Based Prediction of Substituted Pyridine Cation Exchange to Ca-Montmorrilonite
David Bean ’13
Improving the selectivity of a Cobalt α-Olefin Dimerization Catalyst: Studies on the Synthesis of a Phosphabenzene Derivative Ligand
The dimerization of short, linear α-olefins is a convenient pathway to synthesize longer linear α-olefins for their use in the production of surfactants and lubricants. We previously synthesized a cobalt catalyst, bis(h2-ethene) ( h5-pentamethylcyclopentadienyl) cobalt (I), for the dimerization of linear α-olefins.1 That catalyst is inefficient as the reaction is slow and produces a high proportion of branched α-olefin oligomers. We hypothesize that the selectivity of the cobalt catalyst can be improved by reducing the cone angle of the phosphine ligand using a substituted phosphabenzene ligand. The rotation of the ligand may be limited due to increased π-backbonding and may promote 2,1-insertion for the dimerization to a linear product. Synthesis of the improved catalyst was begun through the synthesis of phosphabenzene and its derivative 4-phenylphosphabenzene.
Advisor: Richard Broene
Zara Bowden ’13
Investigation of n → Π* interactions in peptoids and thiopeptoids
Daniel Dickstein ’13
Quantitative Evaluation of Nonlinear Sorption of Cationic Amines to Soils and Soil Minerals
Andrea Koenigsberg ’13
Monitoring Glycoprotein Dynamics in Helicobacter pylori
Margaret Lammert ’13
Preparation and Coordination Studies of Isocyanides as Potential Ligands for a Cobalt-Based Linear α-Olefin Dimerization Catalyst
Matthew Spring ’13
Development of a Peptoid Catalyst for the Enantioselective Trifluoromethylation of Aldehydes
The trifluoromethyl moiety (-CF3) is a useful functional group in pharmaceuticals because it increases drug stability and bioavailability. This group is often found at chiral centers in drugs, and the enantiopurity of these drugs can be crucial for their proper function. Therefore, an enantioselective catalyst that produces an excess of one enantiomer over the other is desirable. In addition to high enantioselectivity, an optimal catalyst should catalyze trifluoromethylation in high yield and with broad substrate scope. However, the primary catalyst for enantioselective trifluoromethylation of carbonyls, a cinchona alkaloid derivative, is quite limited in substrate scope and difficult to modify. Asymmetric peptide catalysts consisting of an achiral catalytic group attached to a chiral peptide scaffold have been shown to enantioselectively catalyze various transformations, but they are unsuitable for the trifluoromethylation conditions. Peptoids, a type of peptidomimetic that can fold into discrete 3-D structures and that are stable under many reaction conditions, could function as novel catalysts for enantioselective transformations. In fact, it was recently demonstrated that a peptoid catalyst was able to enantioselectively catalyze the transformation of an alcohol to a ketone. In this project, by attaching a catalytic amine N-oxide group, which activates –CF3 in the trifluoromethylation reaction, to a chiral peptoid scaffold, novel peptoid catalysts were generated for enantioselective trifluoromethylation.
Van Tra ’13
Synthesis of phosphine-PpIX-FLAG photosensitizer to target Helicobacter pylori by photodynamic therapy