Oral Presentations

Frustrated Lewis Paris (FLP) are sterically hindered acid-base pairs unable to form an adduct, generating enough “frustration energy” to break molecular hydrogen and transfer it to an unsaturated compound thus serving as efficient hydrogenating agents. Previous results from our lab have shown that microwave irradiation can dramatically reduce reaction time for FLP reduction aldehydes and ketones. The mechanism for this transformation is not fully understood. We intend to determine whether the reaction involves single electron transfer species by using radical clock molecules that can give definitive products if radicals are present. Preliminary data suggests a two-electron transfer, but optimized conditions for reaction completion and product characterization will be presented herein. 

N-substituted oligoglycines, referred to as peptoids, are a class of molecules whose structures and functions are controlled by side chain order and functional group diversity. A more robust understanding of peptoid structure would benefit materials or medicinal applications – however, few aqueous-phase studies of peptoids have been pursued. The focus of our research is to propose a comprehensive model of peptoid structure in aqueous environments. Our work examines structures of a set of isomeric hexamer peptoids we synthesized. Residues were selected to promote helicity through favorable electrostatic and aromatic interactions between side chains. Hexamer structure was studied primarily through circular dichroism (CD) spectroscopy. Analysis of CD spectra revealed exciton peaks in the 220-230 nm range in peptoids whose first and fourth  residues were aromatic, strongly indicating a helical structure in this subset of peptoids. This spectral feature did not diminish across a wide pH range, and variable-temperature CD spectroscopy of these peptoids is being conducted to assess the structural dynamics of these peptoids. In ongoing work, our lab is synthesizing new peptoids that comprise weaker helix-promoting residues. Structural evaluations of these will help us to deconvolute the origins of peptoid hexamer helicity. 

Magnetic resonance imaging (MRI) contrast agents are substances injected in patients before the procedure in order to improve the image quality and resolution, and improve diagnostic accuracy. Presently, the most commonly used MRI agents are GBCAs (gadolinium(III)-based contrast agents). However, GBCAs can cause unpleasant side effects with patients who have kidney disorders. This research aims to investigate the applicability of single stranded DNA (aptamers) as a chelating agent to GBCAs to improve their effectiveness and minimize their toxicity. To obtain aptamers with the highest binding affinity to Gadavist (a clinical GBCA), a selection procedure called SELEX (Systematic Evolution of Ligands by Exponential Enrichment) is performed. This is an iterative procedure where starting from a large combinatorial library of DNA aptamers (77 bases long), strands with sequences that do not bind to the target (Gadavist) are gradually eliminated. The selection progress is qualitatively monitored via electrophoresis and imaging until a final aptamer pool is isolated. To improve the binding selectivity, a counter-selection with potential interferents (such as the matrix) is carried out. Currently, 8 rounds of SELEX have been completed. In the initial rounds, 50 microM Gadavist was used. After 4 rounds, the concentration was reduced to 20 microM. 

Our research group aims to synthesize our own enzyme mimic, the “metallopolymer,” which incorporates secondary coordination sphere (SCS) interactions inspired by those of metalloenzymes through the use of a polymer scaffold. We hypothesize that the addition of a polymer as a mimic of the SCS will provide a microenvironment similar to that of an enzyme by producing steric effects and non-covalent interactions between the polymer and substrates bound to the metal center, improving the reactivity and tunability of our metallopolymer. We have reproduced the synthesis of two literature-based copper complexes and have modified each of the ligand precursors to include two vinyl moieties. These moieties allow our ligand precursors to be directly incorporated into a polymer scaffold via copolymerization. We used an arm-first approach to synthesize core crosslinked star polymers using reversible addition-fragmentation chain transfer polymerization. Metalation of the ligand precursors embedded within these star polymers with copper will form the desired supported copper-containing metallopolymers. Then, we will study the catalytic activity of these metallopolymers and compare them to catalysts without a polymer scaffold, allowing us to determine the effectiveness of our SCS mimics. 

Liquid Crystal Elastomers (LCE) are exciting new polymer materials that can repeatedly and elastically actuate in response to temperature. They have been proposed for applications in soft robotics, medicine, and artificial muscles. LCEs have also been developed to respond to light. However, it has not been clear how photoresponsive LCEs also respond to and are affected by temperature. We developed a setup to measure LCE photoresponsive while simultaneously regulating its temperature with a water bath. By controlling the temperature between 20 and 38 °C, we observed that liquid crystal elastomers produced by Yakacki et al.'s TAMAP method incorporating DR1 acrylate (an azobenzene containing photoresponsive dye) tend to display a larger bend at higher temperatures. Our samples probably have a glass transition temperature of around 19 °C(based on the reported values for a similar product), which could restrict the mobility of the samples at lower temperatures. However, because this temperature range is somewhat representative of typical environments in which such an actuator would be deployed, including the human body, the result still justifies further examination. 

One of the most common imaging techniques is Magnetic Resonance Imaging (MRI). An issue with MRI is its lack of sensitivity, due to the low polarization of nuclear spin states at thermal equilibrium, which can be mitigated by hyperpolarization methods. Some of these methods utilize parahydrogen (pH2), which is a spin isomer of hydrogen gas. In pH2 hyperpolarization methods, pH2 is associated with a target molecule and hyperpolarizes it, which leads to significant enhancements in signal. However, pH2 only exists in about a 1:3 ratio with orthohydrogen (oH2), therefore a method for converting oH2 to pH2 is required.

Our goal was to design and construct a pH2 generator to produce pH2, which provides the ability to explore pH2 based hyperpolarization methods in our low-field NMR. An open source pH2 generator design was found and adapted for our use. We constructed the generator, which involves slowly flowing hydrogen gas over a magnetic catalyst that is submerged in liquid nitrogen. Using a high-field Bruker NMR we can characterize the amount of pH2 being produced and tune the process to maximize our production capabilities. This allows us the possibility of utilizing pH2 hyperpolarization in future research.