Fall Student Research Posters



Margaret E Broz


Synthesis of Useful Block Copolymers Using Nitroxide Initiated Living Free Radical Polymerization

Margaret Broz, Gustavus Adolphus College

Advisor: Dr. Frank Bates, U of MN

Reactive diblock copolymers have been used to modify epoxy resins. These copolymers form ordered microstructures when blended with epoxy precursors before cure, and the microstructures are retained after curing. Specifically we will synthesize these reactive diblock copolymers using nitroxide-mediated living free radical polymerization. One example of these copolymers is one in which the miscible block is a random copolymer of glycidyl methacrylate and methyl acrylate, while the immiscible block is made of isoprene. A variety of copolymers will be made with differing reactive monomer units. Eventually these copolymers will be made into blends with the epoxy precursors. The effects of the incorporation of these block copolymers on the epoxy composite physical properties will be studied.

Timothy M. Sonbuchner

Balanced Atomic Charge Accounts: Extrication of Accurate Partial Atomic Charges from Quantum Mechanical Wave Functions

The study of neurological systems at the molecular level using quantum mechanics requires the inclusion of solvent effects. The SM5.42 solvation model incorporates long range solvent effects by treating the solute as a set of atom-centered point charges and the solvent as a dielectric continuum surrounding the solute. The purpose of this work was to derive accurate partial atomic charges for use with the SM5.42 model. These are obtained by parameterizing a function of quantum mechanical quantities to reproduce experimental charge-dependent observables. The database used for parameterization was extended over 400 molecules containing a diverse range of structures and organic functional groups and contains the elements H, C, N, O, F, Si, P, S, Cl, Br, and/or I. The current parameters of the CM2 model are more robust than previous implementations since they were derived from a larger set of molecules, and can now account for silicon-oxide and silicon-halide bonds.

Kelly Devine

Solvent Effects on the Molecular Spectroscopy of 7-diethylamino-4-methylcoumarin

In this particular investigation fluorescence spectroscopy was done on 7-diethylamino-4-methylcoumarin using solvents of varying dielectric constants. The shifting in the fluorescence emission and excitation spectrum due to the solvents polarity was investigated, and found that the major peak seen in the flourescence excitation and emission spectrum is due to a first excited state of the molecule. The minor peak has to be further investigated. The data if plotted dielectric constant vs. position of major peak on fluorescence, we do indeed see a straight line, showing that there is a relationship between the dielectric constant of the solvent and the shifting in the fluorescence spectrum.

Yong Soo Hoo and Alex Chan
Laser Raman and Fluorescence Study of Aromatic Systems
Mike Bradley

pH and Substrate Dependence of Inhibitor Interactions with Glutamate Dehydrogenase

The dynamic metabolic enzyme glutamate dehydrogenase (GDH) plays a pivotal role in numerous biochemical processes. This homohexameric enzyme reversibly catalyzes the conversion of the amino acid glutamate to the tricarboxylic acid cycle intermediate a-ketoglutarate, freeing ammonia in the process. In the reverse reaction, GDH can be thought of as mopping up excess ammonia and storing it in amino acid form. Thus this enzyme is a key player in both amino acid metabolism and the urea cycle. Additionally, glutamate is an important neurotransmitter and in pancreatic b-cells the activity of GDH partially regulates the release of insulin into the bloodstream. It has been shown that higher eukaryotic and especially mammalian GDH undergoes a high degree of regulation that includes negative cooperativity, substrate inhibition, and allosteric regulation. Such complex activity is likely facilitated by subunit interactions within the overall hexamer structure. Competitive inhibition, thermal activation, and thermal denaturation studies were utilized to determine potential mechanisms by which subunit interactions are transferred in bovine GDH. It was found that using the alternative substrate L-norvaline in place of glutamate and changing pH have large effects on GDH's activity and affinity for other substrate analogs. This data shows that subunit interactions are required for the effects observed and that such intersubunit communication is dependent on both pH and bound molecules. This data in combination with structural data and computational modeling will ultimately help us to characterize the key residues involved in transferring subunit interactions. Further study will include site-directed mutagenesis of a clone of human GDH to test the hypotheses formed from this investigation.




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Last modified: August 2000 by Jonathan M. Smith