Microsoft word - o1_5_-3_6_-chemistry.doc

Chemistry Oral Session Titles and Abstracts
Oral Session 1 9:15 - 10:45 am Saturday November 7th, 2009
Oral Session 3 11:00 - 12:30 pm Saturday November 7th, 2009

Oral Session 1
O1-1
Presenter: Yuyang Fan, Grinnell College
Title: Investigation of Succinate Dianion Structure, Dipolar and Scalar Couplings in Liquid-Crystal
Solution by Nuclear Magnetic Resonance (NMR)
Advisor: John D. Roberts, Division of Chemistry and Chemical Engineering, California Institute of
Technology
Coauthors: Andrew Mahon, Mrinmoy Nag
Succinate dianion is a simple four-carbon compound with a -C-C- bond that is free to rotate. Its dihedral
angle for gauche conformation is generally thought to have the classical value of 60°. However, quantum
mechanical calculations predict a dihedral angle of 46° in tetrahydrofuran (THF). In nematic phase, liquid
crystals are expected to have observable dipolar couplings, which it is hoped would elucidate the
intramolecular nuclear magnetic interactions. All the information should be determined by nuclear
magnetic resonance spectroscopy-a powerful method for probing the structure and conformation of
molecules from their electromagnetic properties. Poor substrate solubility of the dianion in liquid crystal
is the limiting factor for getting good signals and impurities can also bring complications to the spectra
and cause problems.
O1-2
Presenter: Erin Zimmerman, Carthage College
Title: Identifying the Intermolecular Interactions Responsible for Chiral Recognition in Drug:Micelle
Mixtures
Advisor: Kevin Morris, Department of Chemistry, Carthage College
NMR Spectroscopy was used to study the binding of two chiral β-blocker drugs to a chiral surfactant. β-
blocker drugs hinder the effects of adrenaline and reduce the force with which the heart contracts. The
surfactant investigated is sold by Waters, Inc. as EnantioSelect and is used as a chiral selector in
electrokinetic chromatography. Our study was undertaken to identify structural and thermodynamic
factors that lead to chiral resolution in chromatography experiments. All four diastereometric
drug:surfactant complexes (S:S, S:R, R:R, and R:S) were studied. NMR diffusion experiments with
atenolol showed that the binding constants were largest for the S:S and R:R drug:surfactant
diasteriomers. In contrast, binding constants for the propranolol:surfactant diastereomers were all very
large and did not differ significantly. Two-dimensional ROESY NMR experiments were used to establish
spatial relationships between drug and surfactant atoms in the bound state. This structural data was then
used in molecular modeling calculations to generate molecular structures and energies for the
drug:surfactant complexes. In the atenolol studies, the molecular modeling energies were consistent with
the association constant measurements.
O1-3
Presenter: Elissa Butler, Macalester College
Title: Dynamic Light Scattering: Analysis of Polydisperse Samples
Advisor: Thomas Varberg, Department of Chemistry, Macalester College
Dynamic Light Scattering (DLS) can be a useful analytical tool to measure the size of nanoparticles,
including gold nanospheres and protein aggregates. Because DLS measures the particle size using basic
principles, there is no calibration. However, parameter settings vary with type of particles and solutions. I
tested the validity of DLS polydisperse measurements. By mixing different concentrations of 20nm,
100nm, and 1000nm microspheres, I determined the accuracy in both the relative intensities of the peaks
and the reported average value of each peak. I also looked at two different distribution bases: volume and
scattering light intensity. Overall, in mixtures of the smaller particles, the relative intensities were much
more accurate than mixtures of larger particles, as expected by the breakdown of Raleigh scattering
theory as the size of the particle approaches the wavelength of the incident light. Also, the reported
average values of each peak for polydisperse samples were inaccurate up to 200%, especially with similar
numbers of each particle size. This shows us that DLS can be a useful tool in comparing polydisperse
samples qualitatively, but cannot be used to quantitatively measure the particle sizes.
O1-4
Presenter: William Hart-Cooper , Grinnell College
Title: Synthesis and Characterization of Mo(VI) Imido Complexes with N-Salicylidene-2-
aminothiophenol
Advisor: Martin Minelli, Department of Chemistry, Grinnell College
Coauthor: Guzei, Ilia
One new di-imido complex and four new mono-imido complexes have been synthesized and
characterized. By, reacting the di-imido complex Mo(NAr)2Cl2(dme) (Ar = 2,6-diisopropylphenyl, dme =
dimethoxyethane) with N-salicylidene-2-aminothiophenol (sma), Mo(NAr)2(sma) (1) was synthesized.
Complex 1 was then reacted with several bidentate aromatic ligands that replaced one imido ligand to
yield the six-coordinate complexes 2-5 (2-aminophenol, 2; 3,4-dimercaptotoluene, 3; catechol, 4; 3-
amino-2-naphthol, 5). All five compounds were characterized by 1H NMR spectroscopy and four through
cyclic voltammetry. Complexes 3, 4 and 5 show one reversible and one irreversible reduction, while 1
exhibits only an irreversible reduction. The structures of complexes 3 and 4 were determined by X-ray
crystallography.
O1-5
Presenter: Michael Lipschutz, Washington University in St. Louis
Title: Novel Oxapentadienyl Cobalt Complexes
Advisor: John Bleeke, Department of Chemistry, Washington University in St. Louis
The synthesis, structure and reactivity of novel Cobalt complexes with the oxapentadienyl ligand have
been investigated. The oxapentadienyl ligand is known to exhibit many different bonding modes taking
up varying numbers of coordination sites on the metal center, which makes it a promising ligand for the
creation of a catalytic system. Our research aims to characterize these systems, laying the groundwork for
a future catalytic cycle. Compounds and ligands are synthesized under inert atmosphere conditions with
dry solvents and are purified via crystallization. Characterization is performed by 1H, 13C and 31P NMR as
well as x-ray crystallography. We have characterized several novel oxapentadienyl cobalt phosphine
complexes and examined their reactivity with carbon monoxide. We have begun expanding our
investigations of reactivity into reactions with electrophilic reagents such as methyltriflate.
Oral Session 3
O3-1
Presenter: Christina Konecki, Carthage College
Title: The development of a facile approach for monitoring flash chromatography via fluorescence
Advisor: CJ Stephenson, Department of Chemistry, Carthage College
Flash chromatography is difficult to monitor since the identity of a compound can only be determined once it is removed from the column. The ability to monitor the column during the separation process would further increase the utility of flash chromatography. A fluorescein containing polymer that changes from non-fluorescent to fluorescent under specific environmental conditions was added to the stationary phase of the chromatography column. The addition of an environmentally sensitive fluorescent polymer will provide a novel method for monitoring a compound as it moves down the column. Fluorescein is a xanethene dye that can switch from a non-fluorescent lactone (off) to a fluorescent carboxylic acid form (on). The on form primarily exists under basic conditions. This property allows for fluorescein to be manipulated as a fluorimetric sensor when in the presence of basic analytes. Fluorescein isothiocyanate (FITC) was coupled with a polymerizable substituent to create an off/on colorimetric monomer. This monomer was used to form a polymer with an off/on colorimetric switch. The fluorescein polymer was dried and sized and added to the stationary phase of a silica gel column. A moderate color change was observed when basic compounds were run down a column containing the silica doped with the fluorescein polymer. We are currently exploring methods of enhancing the signal change. We are also are also investigating how the polymer affects the fidelity of the silica gel column.
O3-2
Presenter: Zach Wickens, Macalester College
Title: Conformational Analysis of N,N-Dimethylethylenediamine N-Oxide
Advisor: John D. Roberts, Department of Chemistry, California Institute of Technology
Molecular conformations influence reactivity, structure and ultimately function of organic molecules.
Chemists rely on fundamental principles to formulate qualitative guidelines and predict conformational
preferences. Unfortunately, these guidelines consider molecules as they were in the gas phase and most
chemistry occurs in condensed phases. The following is an investigation of hydrogen bonds in
disubstituted ethane systems to elucidate nitrogen-oxygen intramolecular hydrogen bonding in a variety
of solvents. The gauche preferences have been determined to better understand the overall influence of
the intramolecular hydrogen bond. Curves will be shown depicting 13C shift as a function of pH. These
curves were used to determine pK1, pK2 and the K1/K2 ratio of N,N-dimethylethylenediamine N-oxide in
D2O. The conformational preferences of each protonation state of N,N-dimethylethylenediamine N-oxide
have been calculated using the Karplus equation as modified by Altona et al. Acceptably high-resolution
spectra are simulated via gNMR 4.1 to extract accurate vicinal coupling constants. These coupling
constants are ultimately used to determine to conformational preferences of N,N-
dimethylethylenediamine N-oxide in D2O and DMSO.

O3-3
Presenter: Joshua Borycz, Hope College
Title: The Forensic Relevance of Mineral Identification with Cathodoluminescence Spectrometry
Advisor: Graham Peaslee, Department of Chemistry, Hope College
Coauthors: Brokus, Sarah, Silletti, Danielle, Lunderberg, Justin
In modern forensic analysis, trace evidence such as soil is often important. The current methods used to
determine the origins of trace geological evidence are limited in their provenance determination and are
time consuming. To address this problem, cathodoluminescence (CL) spectroscopy has the potential to
rapidly identify minerals provenance and basic makeup. By studying various CL spectra of minerals with
known origins, the reasons behind the spectral characteristics and consistencies could be determined.
To demonstrate the potential power of this method, several classes of minerals were studied from samples
collected from different, well-known locations around the US. Reflected light and CL images of single
mineral grains were digitally photographed, and spectral analysis performed on replicate grains from each
location. Color analysis of the CL photographs was done with different grain sizes, and spectra for each
sample were analyzed using commercial peak-fitting software. Results were compiled into spreadsheets
and trends in mineralogy noted. Local sand-dune samples were examined similarly to check for
consistency and distinctive CL signatures. Preliminary results indicate that minerals from the same
region have similar spectral features and that they remain distinct compared to samples from other
regions. Mineralogical and statistical analysis of sand and soil samples provide two types of
discriminatory tools that would be very useful in the development of a reliable forensic geology method
for provenance determination.
O3-4
Presenter: Meareg Amare, Lawrence University
Title: Synthesis of novel cobalt-alkyne drugs and evaluation of their anti-cancer activity
Advisor: Professor Stefan Debbert, Chemistry Department, Lawrence University
Most commonly used drugs are small organic compounds; however, the organometallic drug Cisplatin
has successfully been used to treat breast and ovarian cancer. We developed organometallic drugs of
Aspirin analogues containing a Co2(CO)6-alkyne complex. These compounds have been shown to be even
better at killing cancer cells than Cisplatin. However, the mechanism by which this is achieved is not well
understood.
One possible mechanism for this increased toxicity is that the cobalt complex stabilizes formation of a
propargyl cation, which makes an alkylating agent that targets DNA. This can be used in chemotherapy to
kill cancer cells. We used different analogues of salicylic acid such as those with electron-withdrawing or
electron-donating groups, to help us determine the relationship between cation formation and cytotoxicity.
Alkyne groups attached to the analogues were also varied to test for the same effect. We tested some of
these compounds for efficacy in killing cancer cells and we found that one compound, 2-acetoxy-4-
bromodicobalt alkyne complex has twice the cytotoxicity of Cisplatin in killing cancer cells. More tests
are going to be carried out to test the efficacy of other synthesized compounds.
O3-5
Presenter: Danielle Silletti, Hope College
Title: Forensic Identification of Neutron Irradiation Signatures
Advisor: Graham Peaslee, Chemistry, Hope College
Coauthors: Borycz, Joshua
Nuclear proliferation and the potential threat to national security from unsecured special nuclear materials
around the world have renewed our national interest in nuclear forensics. One important aspect to the
forensic identification of nuclear materials is to identify new methods to detect not only the presence of
special nuclear materials, but also the detection of materials pathways into this country. The only current
method to identify where special nuclear materials have been stored involves measuring induced radiation
in adjacent materials, which is typically short-lived. We have identified a permanent change to the
luminescent properties of certain common mineral that is due to neutron irradiation that could potentially
be developed into a nuclear forensics tool.
Feldspars, quartzes and carbonates are ubiquitous minerals that are known to luminesce under electron
bombardment. We have measured the UV-Vis light spectra of hundreds of feldspars and carbonates with
cathodoluminescence (CL) spectroscopy. CL spectroscopy uses an electron beam to induce fluorescence
in certain minerals due to their chemical composition and defects in their crystal lattice structure. By
comparing these measurements of natural minerals to a selection of minerals that have been exposed to
neutron irradiation, we can determine whether neutron bombardment permanently alters the CL spectra in
a predictable or quantifiable manner. Preliminary results from a source study and a reactor study will be
presented.
O3-6
Title: Superhydrophobic Polystyrene Nanotube Sheets
Presenter: Jamie Eversage, Beloit College
Advisor: George Lisensky, Chemistry Department, Beloit College
Polystyrene nanotubes are prepared by dissolving packing peanuts in xylene and coating the pores of an
alumina membrane. The filter is removed by etching with NaOH to produce sheets of superhydrophobic
tubes with a diameter of 200 nm. Water drops bead up on the open side and spread out on the closed side
of the sheet, demonstrating the importance of size and shape in determining properties. The procedure
was adapted from M. Jin, X. Feng, L. Feng, T. Sun, J, Zhai, T, Li, and L. Jiang, Adv. Mater., 17, 1977-
1981 (2005).

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