We hope everyone is having a fun ACS week! Our next webinar will take place via the internet on Tuesday April 20th at 11AM EST/4PM GMT. Sign up on our mailing list to receive the Zoom link!
We look forward to continuing this series well into the future and hope to see/hear from you all at one of our sessions or as one of the next speakers. If you are an early career scientist and would like to present your research don't hesitate to submit an abstract today! For now, please learn more about our current speakers and their research below!
Our featured speakers this week are Rebeca Rodriguez (graduate student; University of Minnesota, USA), Cole Carter (graduate student; Northwestern University, USA), and Dr. Michelle Herridge (graduate student, University of Arizona, USA). The seminar will be guest moderated by Beza Tuga from the University of Minnesota!
LEARN MORE ABOUT THE SPEAKERS AND THEIR TALKS BELOW
REBECA RODRIGUEZ (on twitter @beck_ayeee)
Biography: Rebeca (Becky) Rodriguez received her undergraduate degree in Chemistry from American University in 2016. She received her M.S. in Chemistry (2018) and will graduate with her Ph.D. in Chemistry from the University of Minnesota in 2021 under the advisement of Dr. Christy Haynes. Her research is at the interface of analytical, polymer, and materials chemistry, with a focus on biosensor applications. She also completed an internship at the Naval Surface Warfare Center in Dahlgren, VA (2019) in the Chemical, Biological, and Radiological Defense Division. Becky spends her free time planning and performing science demos for kids, trying new restaurants, and exploring art museums.
Title of Talk: Detection of Food Contaminants via Linear Polymer Affinity Agents and Surface-Enhanced Raman Scattering
Abstract: There are a variety of small molecule toxins found in crops that can be extremely carcinogenic to humans, posing dangerous hazards in food production and consumption. This work exploits polymers, with commercially available monomers, as capture agents for various toxin targets such as mycotoxins. Mycotoxins are small molecule toxins produced from fungi, that contaminate a wide variety of crops. Detecting mycotoxins traditionally employs the use of specific affinity agents. However, those detection methods are expensive and do not offer the opportunity to detect a multitude of toxins in complex matrices. For this reason, we propose the use of a less specific affinity agent, like a linear polymer, to these small molecules. The capture agents can be immobilized on plasmonic substrates known as film over nanospheres (FONs), based on their end group reactivity whilst maintaining an affinity for a target. These FONs with short, anchored polymer chains serve as a novel sensing system when paired with surface-enhanced Raman spectroscopy (SERS). SERS is an attractive analytical technique due to its high enhancement factors and its ability to assign specific vibrational modes to certain molecules at very low concentrations. By providing fingerprint spectra for various targets, one can easily detect more than one target mycotoxin in relevant complex matrices. Pairing experimental SERS with computational modeling helps confirm hypotheses on binding and target/polymer interaction. Using density function theory (DFT) modeling, one can to attribute changes in vibrational spectra to particular interactions between the target and polymer. This promotes the use of multiplex detection of various targets in the same class of small molecules based on the adaptable nature of the polymer affinity agent. In this talk, two mycotoxins: deoxynivalenol and ochratoxin A are modeled with DFT to provide predictive Raman spectra. Multiplexing the two toxins to one respective methacrylamide-based polymer affinity agent (pAEMA29) experimentally and monitoring the binding with SERS, we can definitively attribute vibrational characteristics of both toxins based on the DFT calculations. This work demonstrates optimization of SERS sensing to achieve limits of detection comparable to current detection methods with a simpler and more flexible signal transduction mechanism, providing an opportunity for future applications in complex matrices where these toxins are traditionally found.
COLE CARTER (on twitter @coal_carter)
Biography: Cole is a California born 5th year graduate student in inorganic chemistry at Northwestern University with interests in weird ligands and even weirder complexes of those ligands. Cole graduated with a B.S. from the University of California, San Diego in 2016 (#westcoastbestcoast) after studying the mechanism of nitrogenase and gorging on tacos. He spends his time in Chicagoland cooking, rock climbing, and posting his cat on social media. His plant, Squirtle, is thriving which proves that even in the worst of years there is still growth.
Title of Talk: Orbital Legos: Constructing Switchable Mixed Valent Behavior
Abstract: A family of metal dichloride complexes having a bis-ferrocenyl-substituted pyridinediimine ligand was systematically synthesized ((Fc2PDI)MCl2, M = Mg, Zn, Fe, and Co) and characterized crystallographically, spectroscopically, electrochemically, and computationally. Electronic coupling between the ligand ferrocene units is switched on upon binding to a MCl2 fragment, as evidenced by both sequential oxidation of the ferrocenes in cyclic voltammetry (ΔEox ≈ 200 mV) and by Inter-Valence Charge Transfer electronic excitations in the near IR. Additionally, UV–vis spectra are used to directly observe orbital mixing between the ferrocenyl units and the imine π system since breaking of the orbital symmetry results in allowed transitions as well as broadening and red-shifting of the ferrocenyl transitions—indicating organic character in formerly pure metal-centered transitions. DFT analysis reveals that interaction between the ferrocenes and the MCl2 fragment is small and suggests that delocalization of Fe electrons is largely occuring in the LUMO; mediated by better energy matching of the organic and Fe orbitals when a lewis acid is coordinated to the ligand. Furthermore, single crystal diffraction data obtained from oxidation of one and both ferrocenes show distortions, introducing the empty dxy/dx2-y2 orbitals into the secondary coordination sphere of the MCl2 fragment. Such structural rearrangements provide insights for catalysis and for mixed valent compounds where internuclear distance is assumed equal between neutral and mixed valent states.
DR. MICHELLE HERRIDGE (on twitter @mdhh99)
Biography: Michelle Herridge just defended her PhD at the University of Arizona in chemistry, where she works with Dr. Vicente Talanquer. She has worked in chemistry education research since she was an undergrad at Clemson, where she got degrees in chemistry and sociology, and she obtained her masters in chemistry from Missouri State. Her graduate research explores assessment in chemistry education and how instructors evaluate student work. She is also a Mentor TA in the chemistry department and works with the Graduate College to create professional development materials and mentoring support for instructors across campus.
Title of Talk: Variation in Chemistry Instructors’ Approaches to the Evaluation and Grading of Student Written Responses
Abstract: Science faculty (FIs) and graduate student instructors (GSIs) regularly engage in the evaluation and grading of student responses in formal formative and summative assessments. In this study, we identified dimensions of variation in instructors' approaches to the evaluation and grading of students' answers. Using qualitative methods of research, we conducted individual interviews in which participating chemistry FIs and GSIs were asked to evaluate and grade the same set of students' responses to a typical exam prompt and justify their decisions. Our results indicate that observed variability in assigned grades emerged from the complex interaction of explicit and implicit decisions made and preferences manifested along various dimensions. Additional findings from this study show that individual instructors are generally consistent in their approach to the evaluation of different students’ answers, but major variations may exist from one instructor to another. Some of these differences have a significant impact on the assigned grades regardless of question type or content. Our findings highlight areas that need to be targeted during the professional development of chemistry instructors to reduce grading variability and increase fairness in the evaluation of student work.