Organic Seminar
Monday, April 23, 3:30-4:30pm, WEL 2.122
Assistant Professor
Univ. of North Carolina Chapel Hill
Abstract: The polymer backbone is fundamental to the polymer’s identity and properties. My seminar will focus on the development of metathesis mechanisms to access heteroatom-rich polymer backbones, new editing tools to transform existing polymer backbones into different ones, and both strategies and tactics to depolymerize commodity polymeric materials into valuable small molecules. Specifically, I will discuss iridium-guanidinate catalyzed ring-opening metathesis of cyclic carbodiimides and the current directions toward diazene metathesis, as well as an array of rearrangement transformations—including Ireland-Claisen and aza-Cope—applied to edit the backbones of polymers. Besides the focus on polymer backbones, retrosynthetic logic applied to polymeric materials will be another common thread woven throughout this seminar, as it is a central element of the research in the Zhukhovitskiy group.
Inorganic Seminar
Wednesday, April 24, 3:30-4:30pm, WEL 2.122
Professor
Texas A&M
Abstract: After a brief summary of the group’s diverse research directions, this presentation will focus on our recent endeavors in the chemistry of ambiphilic platforms featuring a carbenium ion as the electron-poor functionality. Our investigations of such platforms as ligands for transition metals will showcase their capacity to not only support unusual metal-to-carbon dative interactions but also influence the catalytic properties of the transition metal center. The principles gleaned from these studies will be extrapolated to chalcogen-containing system systems, wherein the carbenium center can be leveraged to modulate the redox reactivity of the main group element. The presentation will also include examples of systems in which the carbenium unit is reversibly neutralized through the coordination of a Lewis base. The reversibility of this motif, established both in solution and in the solid state, will be correlated with the ability of such systems to serve as photoredox catalysts.
Publishing Seminar
Thursday, April 25, 10:00-11:00AM, NHB 1.720
Editor in Chief, Chem Catalysis
Dr. Cianchetta is Editor-in-Chief for the Cell Press journal, Chem Catalysis, a sister journal of Chem. Chem Catalysis is a high impact - low volume type journal and publishes catalysis work spanning biological catalysis, homogeneous catalysis and heterogeneous catalysis. All are invited to attend and learn about how to most effectively prepare a submission for the journal, or to ask any questions.
Analytical & Physical Seminar
Thursday, April 25, 3:30-4:30pm, WEL 2.122
Assistant Professor
Florida State University
Abstract: Imaging the chemical flux of various analytes around living cells is of importance for understanding cell communication, cell response to external stimuli and heterogeneity within a cell population. Electrochemical imaging using scanned probe microscopy can achieve high spatial resolution chemical mapping of cells, but lacks chemical specificity in complex media and is susceptible to electrode fouling. In this talk, thiolated single-stranded DNA aptamers are used as the biorecognition elements of specific biosensors fabricated on both gold electrodes and gold coated glass nanopipettes. These aptasensors for small molecules such neurotransmitters, have been fabricated on probes that are designed for chemical imaging, and include nanostructured microscale biosensors with enhanced sensing performance, electrode arrays used for simultaneous multiplexed sensing of analytes, and nanoscale probes that offer fast temporal resolution measurements.
Organic Seminar
Monday, April 29, 3:30-4:30pm, WEL 2.122
Assistant Professor
UNC Chapel Hill
Abstract: The remarkable functions of proteins, from refined binding profiles to efficient catalysis, are currently unrivaled by synthetic macromolecules due to complex hierarchical structure in natural systems. Inspired by this grand challenge, the Knight group is at the interface of chemical biology and polymer science, developing synthetic strategies to control hierarchical structure and high-throughput platforms to understand fundamental design principles underlying macromolecule conformation. These research efforts are motivated by the need for innovative strategies to address global health and environmental challenges, where our foundational work informs the de novo design and development of functional polymeric materials.
Inorganic / ChemBio Seminar
Wednesday, May 1, 3:30-4:30pm, WEL 2.122
Assistant Professor
University of Minnesota
Abstract: From respiration to nitrogen fixation, iron containing enzymes drive key biological processes in all forms of life. Bhagi-Damodaran lab seeks to uncover the structural and mechanistic basis of iron enzyme function, and design small-molecule and computational protein design approaches to engineer their biological activity. Such enzyme engineering studies, while fundamentally relevant to the fields of biological and inorganic chemistry, are posed to have significant implications on biological redox signaling and chemical catalysis. In this talk, Prof. Bhagi-Damodaran will discuss her lab’s research towards (A) reprograming heme and non-heme iron enzyme driven oxygen signaling pathways in human cells and microbes, and (B) developing non-heme iron enzyme based bio-catalysts that enable direct and modular C-H halogenation reactions. The research talk will be of broad interests to Biological, Inorganic, Computational, and Inorganic Chemists.
Organic / ChemBio Seminar
Vista Chemical Company Regents Endowed Memorial Lectureship in Organic Chemistry
Friday, May 3, 3:30-4:30pm, WEL 2.122
Professor
UCLA
Abstract: Nature performs challenging synthetic transformations using powerful enzymes. These enzymes are frequently found in the biosynthetic pathways of natural products, many of which have served as inspirations for generations of synthetic chemists over the last fifty years. With recent advances in our abilities to manipulate the biosynthetic pathways, many powerful enzymes in novel natural product biosynthetic pathways have been revealed and characterized. In this talk, I will present a selection of recent work in the identification, characterization and engineering of structurally interesting new natural products and functionally diverse enzymes. I will present the use of different genome mining approaches to identify novel natural product scaffolds and biological activities, including resistance-guided, biosynthon-guided and unknown enzyme-guided mining. Our work demonstrates there is significant potential in discovering new chemistry from fungi.
Inorganic / ChemBio Seminar
Wednesday, May 8, 3:30-4:30pm, WEL 2.122
Professor
Indiana University
Abstract: Metalloenzymes perform some of the most remarkable transformations in nature under ambient conditions in complex cellular milieu, but their native reactivity is limited to biologically-relevant reactions. Non-native enzyme catalysis brings the exquisite selectivity of enzymes to bear on chemical reactions that did not happen to emerge in nature. This capability can be revealed by exposing an enzyme to substrates, reagents, or conditions that are distinct from those associated with its native activity but that enable mechanistically feasible pathways involving its active site residues and cofactors. The possibility of further leveraging molecular recognition and evolution for non-biological metal catalysts has driven efforts to engineer artificial metalloenzymes (ArMs), hybrid catalysts comprised of synthetic metal cofactors linked to protein scaffolds. In this talk, I will discuss efforts from my group in both of these areas. I will first focus on efforts to evolve natural enzymes containing B12 and non-heme iron cofactors to control the selectivity of non-native radical carbon-carbon and carbon-heteroatom bond forming reactions. I will then show how the same principles at work in these systems can be extended to ArMs and how ArM engineering efforts are increasing our understanding of the complex interplay between organometallic complexes and the unique steric and electronic properties of enzyme active sites.
Analytical & Physical Seminar
Thursday, May 9, 3:30-4:30pm, WEL 2.122
Assistant Professor
Lehigh University
Abstract: Photoreactions are often unpredictable and unwanted reactions are hard to control because of the large driving force of light. Modern supercomputers allow chemists to predict the photochemistry of molecules. We explore multidimensional potential energy surfaces of the photoreactivity of molecular catalysts and photoswitches using quantum mechanics to build mechanistic understanding. In particular, we have developed a new computational pump-probe absorption method that produces transient spectra that can be directly compared to experimental ultrafast transient absorption spectroscopy (TAS). TAS measures the complex landscape of relaxation paths of photoexcited states which are difficult to untangle in general. This new method uses the same standard linear response time-dependent density functional theory (LR-TDDFT) of more traditional stead-state approaches. Through simple post-processing of a typical LR-TDDFT output, the energy differences between various excited states are approximated and their corresponding oscillator strengths are resolved from the transition dipole moments between the LR-TDDFT wavefunctions. By coupling multiple excited state features, computational difference spectra can be directly compared to experimental TAS at various time delays. Pump-probe TDDFT captures all relevant excited state absorption features of photoisomerization of azobenzene.
Organic / ChemBio Seminar
Friday, April 19, 3:30-4:30pm, WEL 2.122
Professor
University of Notre Dame
Abstract: The pathologic phenotype of numerous sporadic and hereditary neurodegenerative disorders is the presence of amyloid deposits the brain. Neurotoxic aggregates of the tau protein have the capacity to spread in a prion-like fashion from diseased to healthy cells causing normal tau to become misfolded. Parallel β-sheet stacking in fibrillar tau is characterized by hydrophobic interactions between sidechains on unique and distant β-strand modules within each protomer. While short aggregation-driving β-strand peptides have been widely employed as models of amyloid propagation, relatively little attention has been paid to the diversity of cross-β modules that interact with these sequences. Recent structural elucidation of tau fibrils isolated from patient-derived extracts also suggests that the conformations of misfolded tau, and the associated intramolecular cross-β interactions, vary by disease. Here, we describe a diversity-oriented approach toward peptide macrocycles that feature both the aggregation-prone PHF6 sequence and the cross-β interacting modules observed in solid-state structures of tau. Using a combination of biophysical techniques, we demonstrate that several of our β-arch tau mimics form higher-order assemblies reminiscent of those in pathological states. Moreover, we show that backbone N-amination of these macrocycles affords soluble inhibitors that modulate aggregation and cellular seeding in a sequence-specific manner. These and other studies in our lab demonstrate N-amination to be a subtle yet remarkably effective strategy toward soluble and stable β-strand/sheet mimics. Finally, we detail the structure-based design and synthesis of seed-competent s-arch proteomimetic based on a particularly infective 4R tauopathy fold. We anticipate that our novel approach to amyloid mimicry will enable the development of strain-selective ligands, synthetic nucleators, and minimalist models of physiologically relevant amyloid folds.
Department of Chemistry Seminar
Thursday, April 18, 3:30-4:30pm, WEL 2.122
Professor
University of Pennsylvania
Abstract: Nature uses oxidative couplings to construct carbon-carbon, carbon-oxygen, and carbon-nitrogen bonds with a high degree of efficiency. The use of parallel microscale screening to discover selective and efficient catalysts for such processes using oxygen as the terminal oxidant will be discussed. With the desire to generate further large experimental data sets to drive machine learning, methods are needed to rapidly determine outcomes for a large numbers of diverse reactions. However, numerous technological and reproducibility hurdles limit the types of data sets that can be generated and their fidelity. Approaches to overcome these limitations will be discussed.
Organic Seminar
Friday, April 12, 3:30-4:30pm, WEL 2.122
Professor
Virginia Tech
Abstract: Our lab aims to understand and apply the process of self-assembly at a range of length scales. On the small side, we recently discovered a family of synthetic supramolecular polymers based on aromatic tetrapeptide amphiphiles that self-assembles into well-defined helical structures. Experimental characterization of the helical structures with a pitch of around 30 nm has led us to explore their utility in drug delivery, nanoparticle templation, and catalysis. We also study much larger amphiphiles, focusing on tapered (i.e., cone-shaped) bottlebrush block copolymers, where we use ring-opening metathesis polymerization (ROMP) strategies to synthesize these unique polymers with molecular weights approaching 1 Mg/mol. We ask questions regarding the fundamental self-assembly of these amphiphiles, probing the influence of cone-angle on self-assembled morphology of these materials in dilute solution.
Centennial Visiting Lectureship in Chemistry
Thursday, April 11, 3:30-4:30pm, WEL 2.122
Professor
University of Utah
Abstract: Analysis of molecular populations at liquid/solid interfaces is critical to the investigation, understanding, and optimization of interfacial chemical reactions, chemical separations, and surface-based biosensing. Quantifying interfacial molecular populations is challenging, however, because of the limited population of molecules that reside at a liquid/solid interface, the difficulty of preparing standards of known surface coverage to calibrate a measured response, and interferences from molecules in bulk solution. These challenges can be addressed through use of total-internal-reflection fluorescence microscopy to quantify interfacial populations by counting individual molecules. This measurement can also report reversible reaction kinetics at equilibrium by recording ‘movies’ of individual molecular-binding events. We have applied this methodology to investigate hybridization of individual immobilized DNA probe molecules. Despite the outstanding sensitivity of single-molecule fluorescence imaging, this technique requires that target molecules be labeled, and our recent work shows that labels can significantly perturb the reaction kinetics being investigated. A label-free approach to investigate molecular interactions at liquid/solid interfaces is confocal Raman microscopy, where small Raman-scattering cross sections can be overcome by interrogating interfacial chemistry within high surface-area porous supports. The internal surfaces of porous silica particles can be modified with DNA and used as substrates for investigating molecular-recognition within individual porous particles. When calibrated with measured scattering from internal standards, confocal-Raman microscopy can provide both structural information and absolute surface coverage of unlabeled molecules involved in interfacial molecular-recognition. We apply this method to investigate hybridization of immobilized DNA strands, the association of duplex DNA with a minor-groove-binding small-molecule, netropsin, at nanomolar concentrations, and the structure and interactions of a thrombin-binding DNA aptamer with its protein target.
Inorganic Seminar
Wednesday, April 10, 3:30-4:30pm, WEL 2.122
Professor
University of Pennsylvania
Abstract: The role of the partially-filled 4f shell in metal complexes of the lanthanides is typically considered to be non-bonding. And the degenerate set of 4f electrons confers unique, atomistic electronic- and magnetic-properties to complexes of the elements. In recent years, my research group has been working to expand the capabilities of lanthanide elements through fundamental studies of such complexes and their electronic structures. We have demonstrated that studies of cerium complexes, in terms of electronic structure, properties, and reactivity, are fruitful for discovery of both fundamental aspects of f-element chemistry, and new reactivity modalities, based on 4f-orbital participation. For this talk, recent results will be presented on our studies of organometallic complexes of cerium(IV) and related tetravalent metals showing unique participation of 4f-orbitals in bonding and reactivity. We have posited that 4f-orbital engagement can also alter reactivity of lanthanide complexes with properly designed ligand frameworks and reaction manifolds. Our efforts toward these goals, for the purposes of selective, inter-lanthanide reactive separations, will also be discussed.
Analytical & Physical / ChemBio Seminar
Thursday, April 4, 3:30-4:30pm, WEL 2.122
Assistant Professor
University of Florida
Abstract: Imaging mass spectrometry is a powerful analytical technique for analyzing the spatial lipidome. This technology enables the visualization of molecular pathology directly in tissues by combining the specificity of mass spectrometry with the spatial fidelity of microscopic imaging. This label-free methodology has proven exceptionally useful in research areas such as cancer diagnosis, diabetes, and infectious disease. However, state-of-the-art experiments stress the limits of current analytical technologies, necessitating improvements in molecular specificity and sensitivity in order to answer increasingly complicated biological and clinical hypotheses. Especially when studying lipids, many isobaric (i.e., same nominal mass) and isomeric (i.e., same exact mass) compounds exist that complicate spectral analysis, with each structure having a potentially unique cellular function. The Prentice Lab develops instrumentation and novel gas-phase reactions to provide unparalleled levels of chemical resolution. These gas-phase transformations are fast, efficient, and specific, making them ideally suited for implementation into imaging mass spectrometry workflows. For example, these workflows have enabled the identification of multiple sn-positional phosphatidylcholine isomers, the separation of isobaric phosphatidylserines and sulfatides, the identification of fatty acid double bond isomers, and the identification of sulfatide stereoisomers using a variety of charge transfer and covalent ion/ion reactions as well as ion/electron and ion/photon reactions. Working with biologists and clinicians, we then leverage these novel imaging technologies to understand the molecular events associated with important problems in human health, including infectious disease, diabetes, and neurodegenerative diseases.
Inorganic / ChemBio Seminar
Wednesday, April 3, 3:30-4:30pm, WEL 2.122
Professor
Northwestern University
Abstract: As chemists and materials scientists, it is our duty to synthesize and utilize materials for a multitude of applications that promote the development of society and the well-being of its citizens. Since the inception of metal-organic frameworks (MOFs), researchers have proposed a variety of design strategies to rationally synthesize new MOF materials, studied their porosity and gas sorption performances, and integrated MOFs onto supports and into devices. MOFs are a class of porous, crystalline materials composed of metal-based nodes and organic ligands that self-assemble into multi-dimensional lattices. In contrast to conventional porous materials, an abundantly diverse set of molecular building blocks allows for the realization of MOFs with a broad range of properties. Efforts have explored the relevance of MOFs for applications including, but not limited to, heterogeneous catalysis, guest delivery, water capture, destruction of nerve agents, gas storage, and separation. For example, we have developed an extensive understanding of how the physical architecture and chemical properties of MOFs affect material performance in applications such as catalytic activity for chemical warfare agent detoxification. Recently, start-up companies have undertaken MOF commercialization within industrial sectors. ION-X™ is used in this talk as an example to show case the way NuMat Technologies is innovating at the intersection of molecular design and precision engineering, to build the products driving the industries of tomorrow.
Organic Seminar
Monday, April 1, 3:30-4:30pm, WEL 2.122
Assistant Professor
University of Minnesota
Abstract: Research in the Roberts group involves looking at unsolved problems in organic synthesis through the perspective of organometallic/inorganic chemistry. One main area of interest for the group is the synthesis of heterocycles through aryne intermediates. Despite their useful reactivity, a number of challenges still remain in the use of arynes including problems with regioselectivity and the synthesis of N-heterocyclic arynes. Using fundamental principles of Ni chemistry, our group is the first to be able to access previously “inaccessible” 5-membered heterocyclic arynes for the first time since they were hypothesized to exist 120 years ago. We are also the first group to demonstrate catalyst controlled regioselectivity in arynes, where all previous examples operated under substrate control. Another challenge in organic synthesis lies in alkyl–alkyl cross-coupling. This is due to challenges with oxidative addition and off cycle pathways such as beta-hydride elimination. Our group has pioneered the use of Group 3 metal catalysts supported by redox-active ligands to overcome some of these challenges. Using 10 mol% of a Sc, Y, or Lu tris(amido) catalyst, coupling partners that both have beta-hydrogens can be successfully cross-coupled for the first time using early transition metals. These improvements related to organic synthesis can only be accessed using inorganic/organometallic chemistry.
Seminar tabs are listed in the order of upcoming dates, followed by past seminars (most recent first).
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