Spring 2019 Seminars
|Lunch at 12 PM (Grote 401)/Seminar at 3 PM (Grote 411, Presentation 3-3:45 PM & Question Sesssion 3:45-4:00 PM)|
|January 11, 2019||First Day No Speaker||First Day No Speaker||First Day No Speaker||First Day No Speaker|
|January 18, 2019||Charles Machan:||University of Virginia||Pienkos||Inorganic|
|January 25, 2019||Elizabeth Papish: New proton responsive ligands for metal complexes as catalysts and for pH activated anticancer properties||University of Alabama||Lee||Inorganic|
|February 1, 2019||Sungwoo Yang:||UTC||Park||Chemical Engineering|
|February 8, 2019|
|February 15, 2019||Sharani Roy:||UTK||Albu||Physical|
|February 22, 2019|
|March 1, 2019|
|March 8, 2019|
|March 15, 2019||SPRING BREAK||SPRING BREAK||SPRING BREAK||SPRING BREAK|
|(Official: March 11-17)||(Official: March 11-17)||(Official: March 11-17)||(Official: March 11-17)|
March 22, 2019
2p.m. Grote 411
|March 29, 2019|
|April 5, 2019|
|April 12, 2019||BANQUET||BANQUET||BANQUET||BANQUET|
|April 19, 2019||SPRING HOLIDAY||SPRING HOLIDAY||SPRING HOLIDAY||SPRING HOLIDAY|
The steady increase in anthropogenic carbon dioxide (CO2) emissions and corresponding atmospheric concentrations continues to generate interest in its use as a liquid fuel and commodity chemical precursor. The conversion of CO2 has the dual benefit of addressing its associated negative environmental effects and the diminishing supply of petrochemical feedstocks. If these conversions are driven electrochemically using renewable energy sources like wind and solar, the overall process can be referred to as artificial photosynthesis: reduced carbon-containing compounds are produced from CO2 and water by storing electrical energy in chemical bonds as ‘solar fuels’. At the heart of reductive CO2 transformations are proton-coupled electron transfer (PCET) reactions, where electrons and protons move in a concerted way to mitigate kinetic and thermodynamic penalties. Catalytic selectivity and activity for specific products remains an ongoing challenge that can be understood and iteratively optimized through molecular design. The electrocatalytic reduction of dioxygen (O2) has relevance to biological systems and fuel cells and faces similar selectivity challenges in PCET reactions. We are investigating new molecular catalysts for the electrocatalytic reduction of CO2 and O2 using electrochemical and spectroelectrochemical measurements to extract information on the reaction parameters and elucidate important mechanistic details. Using this mechanistic information, we are developing methods to increase the scale of these molecular electrocatalytic reactions in a meaningful way.
We aim to apply bioinorganic and organometallic chemistry to problems that relate to green chemistry and sustainability. In particular, we are interested in exploring how protic groups and electron donor groups impact catalysis. Within these broad goals, we have pursued reactivity inspired by the need for energy storage, specifically carbon dioxide reduction. Recently, we designed a new pincer ligands using N-heterocyclic carbene (NHC) and pyridinol rings that can change their properties by protonation and deprotonation, rather than lengthy synthesis. The most active transition metal catalysts with these pincers use methoxy groups which balance electron donor ability with stability. This has allowed for formation of ruthenium and nickel complexes that perform catalytic and light driven carbon dioxide reduction, as shown by our collaborator Delcamp. We have also demonstrated that the OH derivatives can be switched on or off for catalysis with acid concentration. One of our ruthenium complexes is record setting in terms of reaction rates and selectivity. CO2 reduction is of fundamental importance to the impending global energy crisis, and carbon dioxide reduction (when coupled with water oxidation) can allow for a sustainable method of energy storage in solar fuels. Furthermore, we have studied our hydroxyl substituted bipyridine ligands as a part of ruthenium based anticancer metallo-prodrugs. The ruthenium complexes are light activated and show selective toxicity towards cancer cells (vs. normal cells). With collaborator Kim, we are studying the mode of action of these complexes towards cancer cells.
Sungwoo Yang: Engineered Porous Materials for Solar-Thermal Energy Conversion
Chemistry is an important key in controlling the structure of a material and its transport properties via photon, phonon, electron, ion, and molecule interactions. In this seminar, I will show how understanding and manipulating the underlying physics and chemistry of porous materials can greatly benefit sustainable energy technologies, including solar-thermal energy conversion and water harvesting from air. I will focus on three emerging porous materials: 1) metal organic frameworks (MOFs), 2) aerogels. MOFs are highly promising porous materials due to their exceptional water adsorption capacity and low regeneration temperatures with the ability to tailor their structure, sorption capacity and surface properties. 3dGR is a promising thermal additive to alleviate the problem of low thermal conductivity of porous materials without compromising their energy density. By combining MOFs and 3dGR, we have demonstrated high thermal energy density (495 Wh/kg and 218 Wh-L) in a thermal battery designed for electric vehicle applications. We have also demonstrated water harvesting (~2.8 L/kg) with MOFs at a surprisingly low relative humidity of 20% to address the increasing problem of water scarcity in arid regions around the world. Finally, I will discuss the design and synthesis of thermally insulating and optically transparent silica aerogels designed to suppress thermal losses in solar-thermal energy systems. We have demonstrated a prototype system with a working fluid temperature of 240 °C under un-concentrated solar illumination in ambient conditions, which can replace conventional heating systems based on fossil fuels. I will conclude by sharing my vision and future outlook on how we can develop new and exciting materials to address the most challenging problems in energy conversion, energy storage, and water harvesting.
The control of catalytic selectivity in olefin polymerization is a desirable ability. Redox-switchable polyethylene catalysis has recently been investigated for a Ni-diimine-based Brookhart-type catalyst. Both redox states of the catalyst, with and without an additional electron on the dipp-BIAN α-diimine ligand, can be activated by methylaluminoxane (MAO), with the reduced form yielding a decreased branch content. This work presents a detailed computational study that elucidates the transformations of this dipp-BIANNiBr2 catalyst after reduction and activation. Our calculations support the purported Ni(I) dipp-BIANNiBr2− species as the likely reduction product in solution, and subsequent methylations transfer the electron to the ligand. We propose distinct active catalyst forms for each redox state to explain how different polymer branching content is obtained. Finally, we present our computed reaction pathways for the reduced and non-reduced forms of the catalyst to explain why the reduced form of the catalyst produces a less-branched polyethylene.
Conventionally, transcription regulatory networks are first defined by first identifying co-regulated genes, determining DNA sequence homology in proximal control regions, and identifying transcription factor(s) responsible for their regulation. Alternatively, one may first determine the binding specificity of a putative transcription factor, map its consensus sequence to an organism’s genome, and identify those genes/operons potentially regulated by this transcription factor. We have used the alternative approach including the combinatorial selection method Restriction Endonuclease Protection, Selection, and Amplification (REPSA), massively parallel sequencing, and a variety of bioinformatics to determine the binding specificity and target genes for four previously investigated Thermus thermophilus HB8 transcription factors: FadR, PaaR, PfmR, and SbtR. We found superior consensus binding sequences and additional target genes than previously described for each of these transcription factors. These findings demonstrate that our alternative approach for transcription factor discovery is an effective means of obtaining information on transcription regulatory networks, especially in organisms lacking genetic tools for identifying co-regulated genes.