Virtual Faculty Seminar Series

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Virtual Faculty Seminar Series

NOBCChE Collaborative's Faculty Seminar Series

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Date and time

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About this event

NOBCChE Collaborative is proud to announce our Faculty Seminar Series. These seminars will highlight faculty’s scientific expertise and will cover a wide range of topics. Each seminar is free and open to the public, but registration is required.

NOBCChE Collaborative Faculty Seminar Series Zoom Lin

January 27th - Mary Jo Ondrechen, PhD

Title: How do enzymes impart catalytic superpowers to amino acids?

Abstract: Enzymes catalyze reactions under mild conditions that would otherwise require extreme conditions such as high temperature or strong acidity or basicity. To achieve this, enzymes often impart reactive chemical properties to amino acid sidechains that are far less reactive in the absence of the protein environment. In the enzymatic environment, active site amino acid sidechains that are weak Brønsted acids or bases in a small peptide can transform into a strong acid or base. The primary amine side chain of lysine, which would normally be protonated at neutral pH, can be deprotonated to serve as a nucleophile. We present a set of 20 enzymes that represent all six major EC classes and a variety of fold types for which experimental studies of the catalytic residues' mechanistic roles have been reported in the literature. For these 20 enzymes the computed electrostatic and proton transfer properties are investigated. The catalytic aspartates and glutamates are shown to be strongly coupled to at least one other aspartate or glutamate residue, and frequently to multiple other carboxylate residues, with intrinsic pKa differences less than ~1 pH unit. These catalytic acidic residues are sometimes coupled to a histidine, wherein the intrinsic pKa of the acid is higher than that of the His. Anion-forming residues, Tyr or Cys, with intrinsic pKa higher than that of the lysine, are found strongly coupled to all catalytic lysines in the set. Some catalytic lysines are also coupled to other lysines with intrinsic pKas within ~1 pH unit. Some basic principles about the design of enzyme active sites are discussed. The interactions described here provide important clues about how side chain functional groups that are weak Brønsted acids or bases for the free amino acid can become strong acids, bases, or nucleophiles in the enzymatic environment. Supported by NSF CHE-1905214.

January 27th - John Herbert, PhD

Title: “Neat, Simple, and Wrong: Electrostatic Fallacies Regarding Non-Covalent Interactions”

Abstract: Multiple moments such as charge, dipole, and quadrupole are often invoked to rationalize intermolecular phenomena, but a low-order multipole expansion is rarely a valid description of electrostatics at the length scales that characterize non-bonded interactions. I will illustrate how several common explanations of steric repulsion, pi-stacking interactions, and hydrogen bonding do not stand up to close scrutiny based on detailed electronic structure calculations. These examples present a compelling case that electrostatic explanations based on low-order multipole moments are very often counterfactual for non-bonded interactions at close range and should not be taken seriously in the absence of additional justification.

February 24th - Stephen Leffler Buchwald, PhD

Title: Palladium-Catalyzed Carbon-Heteroatom Bond Formation

Description: The history of the development of Pd-Catalyzed Carbon-Heteroatom Bond Formation as well as a description of the basic mechanistic considerations, recent examples and an application to the modification of proteins will be described.

February 24th - Christo Sevov, PhD

Title: Mediator-Assisted Strategies for Electrocatalytic C–C and C–N Bond Forming Reactions

Abstract: The seminar will describe our efforts towards the development of scalable, mild, and general electrosynthetic methodologies for C–C and C–N coupling reactions. These electrosynthetic methodologies are possible because of a synergy between conventional transition metal catalysts for cross-coupling and redox-active mediators developed by the battery community. It will be shown that yields from electrocatalytic reactions are dramatically improved with the incorporation of co-catalytic quantities of soluble battery compounds and other redox mediators that serve to assist in electron transfer with the coupling catalyst, protect the coupling catalyst from over-oxidation/reduction and degradation, or promote in the formation of highly-reactive intermediates. A particular focus will be placed on the discussion of a previously-unknown pathway for electrochemically-generating highly-reactive Ni(0) complexes at mild potentials through a choreographed series of ligand exchange reactions. Electroreductive access to Ni(0) intermediates enables selective activation of unreactive aryl electrophiles (e.g. Ar–Cl/OTf) even in the presence of highly-reactive alkyl electrophiles (e.g. 3° alkyl bromides). We leverage this unique mechanism towards coupling of 3° alkyl bromides, aryl chlorides, aryl triflates, vinyl triflates, and alkyl-aryl combinations therein. Each of these combinations represents a previously-unknown reaction, and the discovered reaction pathway represents a new strategy for Ni redox catalysis.

March 31st - Christine Thomas, PhD

Title: Incorporating Metal-Ligand and Metal-Metal Cooperativity into Catalysis

Abstract: The formation and cleavage of chemical bonds in catalytic reactions relies on accessible two-electron redox processes that are often challenging for base metals such as first row and early transition metals. Metal-ligand and metal-metal cooperativity provide a potential solution to this challenge by enabling heterolytic bond cleavage processes and/or facilitating redox processes. Both strategies will be discussed, showcasing the many ways that metal-ligand and bimetallic cooperativity can operate and the methods by which cooperativity can be built into catalyst design. A tridentate pincer ligand featuring a reactive N-heterocyclic phosphido fragment is found to be both redox active and an active participant in bond activation across the metal-phosphide bond, with catalytic applications in alkene hydroboration. A tetradentate bis(amido)bis(phosphide) ligand has been coordinated to iron and it has been shown that the resulting complex can activate two σ bonds across the two iron-amide bonds in the molecule without requiring a change in the formal metal oxidation state. In the context of metal-metal cooperativity, phosphinoamide-linked early/late heterobimetallic frameworks have been shown to support metal-metal multiple bonds and facilitate redox processes across a broad range of metal-metal combinations and the resulting complexes have been shown to activate small molecules and catalyze organic transformations.

March 31st - Gabriela Schlau-Cohen, PhD

Title: Why don't plants get sunburn?

Abstract: In green plants, chlorophyll-containing proteins known as light-harvesting complexes (LHCs) capture solar energy and feed it to downstream molecular machinery. Under high light (i.e., sunny days), excess absorbed energy can cause damage. Thus, LHCs have evolved a feedback loop that triggers photoprotective energy dissipation, solving the so-called “intermittency problem” in solar energy. A long-standing proposal has been that conformational changes of the LHCs activate dissipative photophysical pathways among the chlorophyll. First, we use single-molecule spectroscopy to identify the conformational states of the LHCs, uncovering parallel conformational dynamics that regulate fast and slow changes in sunlight. Second, we use 2D electronic spectroscopy to map out the corresponding photophysics, revealing dissipative chlorophyll-to-carotenoid energy transfer, a hypothesized yet previously unobserved pathway. Collectively, these multi-timescale measurements elucidate the multi-timescale dynamics of photoprotection.

Daniel Suess, PhD

Title: The Ins and Outs of the Graduate School Admissions Process

Abstract: In this talk, Dr. Suess will discuss several aspects of the graduate school admissions process: how to choose a graduate school, how the application review process works, and what to look for during the various recruiting events for admitted students. Although some of the details will pertain most directly to chemistry graduate programs, the main takeaways will apply equally well to chemical engineering programs and related programs in the physical/life sciences and engineering.

April 28th - Mohammad Movassaghi, PhD

Title: Complex Alkaloid Total Synthesis

Abstract: Representative enantioselective alkaloid total syntheses and related methodologies will be discussed. The focus of this research program is the development of new synthetic strategies for rapid generation of molecular complexity guided by biogenetic considerations. These syntheses feature new stereo- and chemoselective reactions that enable maximum use of the inherent chemistry of key intermediates.

https://www.nobcche.org/nobcche-collaborative

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