(9:00-9:15)
[29]: Kinetics of a novel dual sequential release hydrogel
Magnus Damborg†★, Sandra Ward†Department of Chemistry and Biochemistry, †Frost Support, ★Speaker
Dual release stimuli hydrogels capable of slow and controlled release of encapsulated payloads offer various functions in many fields from agriculture to medicine. There is a large gap in knowledge on kinetic data regarding hydrogels with step-by-step kinetics and we wish to address this gap. We designed a vesicle crosslinked hydrogel for controlled stimuli responsive sequential release. Through a dynamic covalent thiol-disulfide exchange, a 4-arm thiolated polyethylene glycol (PEG) containing a silyl ether core “crosslinks” vesicles into a hydrogel. To combat this, commercially available 4-arm PEG thiol was used to create hydrogels of different PEG chain lengths and weight percentages. This commercially available compound is used to establish protocols and probe the non-responsive release kinetics. Kinetic data was collected and fitted to a variety of commonly used mathematical kinetic models allowing for new information regarding the hydrogel’s release capabilities and its future role as a drug delivery system. |
(9:15-9:30)
[30]: Effect of dithiocarboxylate containing ligands on the electronic and optical properties of CuInS$_2$ quantum dots
Samantha L. Lansky†★, Riley Ramos, Isabella A. Landeros, Erin M. Drew, Varsha Chandrasekaran, Kaitlyn L. Rockwood, Parvathi Nair, Bella R. Chabot, M. Taylor Haynes II, Eric Jones, David F. ZiglerDepartment of Chemistry and Biochemistry, †Frost Support, ★Speaker
Quantum dots (QDs) have the ability to deliver a molecular payload to a target following photoactivation. The high toxicity of well-studied QDs, including CdSe, limits their applicability for biomedical use, while the use of less toxic QD materials, like CuInS$_2$, may be biocompatible when paired with the appropriate surface ligands. CuInS$_2$ QDs were synthesized using a one-pot method and isolated via precipitation and centrifugation. UV-Vis and fluorescence spectroscopies were used to determine the optical and electronic properties of the QDs, and dynamic light scattering was used to measure QD size. The surface ligands of CuInS$_2$ QDs were exchanged for various dithiocarboxylate containing ligands to tune the optical and electronic properties of the QDs. The fluorescence of unmodified and ligand modified QDs were compared to each other, which showed quenching of the QDs by dithiocarboxylates. In addition, the QDs catalyzed dithiocarboxylate photodecomposition. Thus, dithiocarboxylate modified CuInS$_2$ QDs show promise for the photoinduced delivery of a reducing payload. |
(9:30-9:45)
[31]: Effect of Functionalized Graphene Oxide on Anticorrosion Polyurethane Coatings
Caleb Nashner★, Aaron Van Horn★, Shanju ZhangDepartment of Chemistry and Biochemistry, ★Speaker
Corrosion of metal structures results in significant repair costs and safety concerns. Traditional anticorrosion methods such as anodic and cathodic protection often require expensive maintenance. Polymer coatings, particularly polyurethane (PU), offer a more cost-effective alternative with inherent barrier properties. However, the anticorrosion performance of PU can be further enhanced through the incorporation of nanofillers such as graphene oxide (GO), which also improve mechanical and thermal properties. A key challenge in GO nanocomposites is its tendency to agglomerate due to strong intermolecular interactions. This study aimed to synthesize and improve the dispersion of GO in PU coatings by functionalizing GO with mono- and difunctional isocyanates. The corrosion resistance of the resulting coatings was evaluated using electrochemical impedance spectroscopy (EIS), while mechanical properties were assessed through dynamic mechanical analysis (DMA). EIS results showed that GO incorporation significantly increased impedance at low frequencies, indicating improved barrier properties and corrosion protection. DMA revealed enhancements in both modulus and tensile strength, confirming the reinforcing effect of GO. These findings demonstrate that isocyanate-functionalized GO can be effectively dispersed in PU matrices to develop high-performance, corrosion-resistant coatings. |
(9:45-10)
[32]: Heavy metal detection using low-cost portable diagnostic devices
Gabriel Ribeiro★, Andres W. Martinez†Department of Chemistry and Biochemistry, †Frost Support, ★Speaker
Microfluidic paper-based analytical devices (MicroPADs) can be used as portable diagnostic devices to detect and measure the concentration of toxic heavy metal ions in water. The heavy metal assay relies on two sequential steps. In the first step, the water sample is incubated with ?-galactosidase (?-gal), an enzyme that is inhibited by heavy metal ions even at part-per-billion (ppb) concentrations. In the second step, the incubated ?-gal activity is measured by adding a yellow substrate, chlorophenol red ?-galactopyranoside (CPRG), that is hydrolyzed by ?-gal to a red product. Our group has developed a MicroPAD capable of automating the two steps of the assay by relying on a combination of traditional capillary action and evaporation-driven capillary action. The device includes a sample addition zone, a CPRG storage zone, an assay channel with ?-gal, and an evaporation zone. Solutions of silver ion (Ag$^+$) of known concentrations ranging from 40-10,000 ppb were tested, and the degree of inhibition of the ?-gal was found to correlate with the concentration of silver ion in the sample. Our current devices can detect concentrations of Ag$^+$ down to 40 ppb, but the precision of the assay is poor. This talk will describe the development of the assay and the methods we are exploring to improve the precision of the devices to ensure the MicroPADs can deliver accurate, precise, and consistent results. Low-cost MicroPADs that can detect Ag$^+$ and other heavy metal ions could have potential future applications in food and water testing. |
(10-10:15)
[33]: Studying the photochemistry of dithiocarboxylates in aerated solutions
Riya Nigudkar†★, Karalee Webb†, Elizabeth Manis†, Kelsey Blechen†, Reiden Emery†, Julia Mcdonald, David Zigler†, M. Taylor Haynes†Department of Chemistry and Biochemistry, †Frost Support, ★Speaker
Among thiocarbonyls, dithiocarboxylate chromophores have been studied in metal coordination and electrochemistry. Recent work from our group established that organic soluble dithiocarboxylate salts have a higher density of excited electronic states than their thiocarbonyl analogs. As a result, we continued our investigation into the photochemical decomposition of dithiocarboxylates in aerated solutions. Experiments testing the effects of concentration and substituents have narrowed our understanding of possible excited state relaxation pathways. Using quantum yields measured from UV-Vis data, a major photoproduct was identified and then characterized with $^{13}$C-NMR, IR, and LC-MS. Additionally, mass spectrometry provided evidence for the production of at least one intermediate. Evidence collected from both experiments thus far suggests that a photo-redox pathway is followed during the photodecomposition. |
(10:15-10:30)
[34]: Investigating the Electronics of the Fragmentation of Ylidenenorbornadienes
Danilo Alamillo†★, Dan Bercovici†Department of Chemistry and Biochemistry, †Frost Support, ★Speaker
Our method of “click-and-clip” chemistry is exemplified in the synthesis and then fragmentation of Ylidenenorbornadiene (YND) systems. A YND substrate prepared from 6,6’-dimethylfulvene and DMAD was reacted with a set of 4-substituted thiophenols, to yield a mixture of three diastereomers.? These diastereomers after chromatographic separation were characterized and identified. Hammett studies investigated the electronic effects of the retro-[4+2] fragmentations typical of YND-thiol adducts. The goal of this research is to explain the electronic effects of a range of substituents attached to the pendant aryl rings of the thiol nucleophile on the rates of retro-[4+2] fragmentation of YND-thiol adducts. A dual substituent parameter (DSP) method was utilized to examine the effects of aryl substituents and evaluate the influence of field effects versus resonance. Electron-withdrawing groups on the thiophenol stabilize the partial negative charge buildup associated with carbon alpha to the sulfur and accelerate fragmentation. |
(10:30-10:45)
[35]: Linear Free-Energy Relationships of Nucleophile-Induced retro-[4+2] Cycloaddition Fragmentations of Ylidenenorbornadienes
Ashley Freeman★, Daniel BercoviciDepartment of Chemistry and Biochemistry, ★Speaker
“Click” and “Clip” reactions have become new and exciting fields of research within the study of Chemistry. With the simple addition or simple cleavage of two molecules, substrates can be easily connected or removed. Our method of “click-and-clip” chemistry is exemplified in the synthesis and then fragmentation of Ylidenenorbornadiene (YND) systems. YND substrates with pendant aryl substituents have been synthesized by [4+2] cycloaddition reactions between 6,6’-diarylfulvenes and dimethylacetylene dicarboxylate (DMAD). Subsequent conjugate addition with propanethiol as a nucleophile leads to a mixture of four diastereomers. These diastereomers after chromatographic separation were characterized and identified by NOESY correlations. The goal of this research is to explain the electronic effects of a range of substituents attached to the pendant aryl rings on the ylidene bridge of the YND on the rates of retro-[4+2] fragmentation of YND-propanethiol adducts. It was observed that electron-donating groups on the aryl rings attached to the ylidene bridge stabilize the buildup of partial positive-charge on the bridgehead carbon and accelerate fragmentation. |