Dr. Robert Kennedy | University of Michigan

Professors Rebecca Pompano and Jill Venton

The Nanoliter Lab: Droplet Microfluidics for Screening and Sensing

Manipulating samples as droplets within microfluidic devices has emerged as an interesting approach for chemical analysis and screening. In segmented flow, one embodiment of this technology, nanoliter samples are manipulated in microfluidic channels as plugs separated by an immiscible fluid, such as air or fluorinated oil. These plugs serve as miniature test-tubes in which reactions can be performed at high throughput. Microfluidic tools have been developed to split, dilute, extract, and filter such plugs at rates >10 samples/s. We have developed methods to analyze plug content by electrophoresis and mass spectrometry (MS). A natural application of this technology is for high throughput screening. By coupling droplet manipulation with MS detection, it is possible to greatly reduce reagent consumption and eliminate the need for fluorescent labels or coupled reactions. The technology and application to screens of deacetylase reactions and protein-protein interactions will be presented. A more involved screening allows for monitoring reactions of enzyme variants to identify new biocatalysts. Droplet technology can also be used for chemical monitoring or sensing applications. In this approach samples emerging from a miniaturized sampling device are segmented for later analysis. We have used this method to monitor neurotransmitter dynamics in the brain. The technology and application to studies of neurotransmission in a Huntington’s disease models will be demonstrated. 

Graduate Visitation Weekend 3/18 - 3/19

Dr. Dan Mindiola | University of Pennsylvania

Professor Robert Gilliard

Metal-Ligand Multiple Bonds: Catalytic Dehydrogenation of Volatile Alkanes, Methane Olefination, and Super Bases

Abstract. Converting natural resources such as methane and ethane, the main components of natural and shale gas, into more value-added materials under mild conditions and using base metals, is one of the main objectives in my research program. I will start by presenting the reactivity of a transient titanium alkylidyne (PNP)Ti≡C^tBu (pincer PNP = N[2-P(CHMe₂)₂-4-methylphenyl]₂^–), specifically how this species forms and engages in intermolecular C-H activation and functionalization reactions.  Such a system can dehydrogenate methane, and react with C2-C8 alkanes selectively by activating at the a- and b-positions. In the case of linear alkanes C4-C8, we only observe formation of the terminal olefin adduct.  A new catalytic cycle for transfer dehydrogenation of alkanes will be also introduced in addition to unique platforms to form kinetically stable Ti=CH₂ moieties (titanium methylidene) that are relevant to our proposed catalytic cycle. I will also discuss a new transformation involving the room temperature conversion of methane to an olefin using a titanium alkylidene in cooperation with a redox-active ligand and how it compares to an electrophilic iridium system that can convert methane to ethylene with the aid of a phosphorus ylide reagent. The last component, if time permitted, will present the synthesis and reactivity of group 4 transition metal nitrides and how one can tune the basicity of the nitride ligand by shifting down the group. 

Chemical Engineering Approaches for Catalytic Reduction of CO2

Dr. Jingguang Chen | Columbia University

Professor Sen Zhang

Rising atmospheric concentration of CO2 is forecasted to have potentially disastrous effects on the environment from its role in global warming and ocean acidification.  Converting CO2 into valuable chemicals and fuels is one of the most practical routes for reducing CO2 emissions while fossil fuels continue to dominate the energy sector.  In the past few years our group has investigated the catalytic reduction of CO2 using a combination of kinetic studies, in situ characterization and density functional theory calculations.  In this talk we will present several examples on (1) CO2 conversion by thermocatalysis, (2) CO2 reduction by electrocatalysis, and (3) simultaneous upgrading of CO2 and shale gas. We will use these examples to highlight the importance of using fundamental chemical engineering principles to guide the selection of reaction conditions and catalyst compositions.

Prebiotic Astrochemistry in the "THz-Gap"

Dr. Susanna L. Widicus Weaver | University of Wisconsin-Madison

Professor Eric Herbst

Prebiotic Astrochemistry in the "THz-Gap"

Small reactive organic molecules are key intermediates in interstellar chemistry, leading to the formation of biologically-relevant species as stars and planets form.   These molecules are identified in space via their pure rotational spectral fingerprints in the far-IR or terahertz (THz) regime.  Despite their fundamental roles in the formation of life, many of these molecules have not been spectroscopically characterized in the laboratory, and therefore cannot be studied via observational astronomy.  The reason for this lack of fundamental laboratory information is the challenge of spectroscopy in the THz regime combined with the challenge of studying unstable molecules.  Our laboratory research involves characterization of astrophysically-relevant unstable species, including small radicals that are the products of photolysis reactions, organic ions formed via plasma discharges, and small reactive organics that form via O(1D) insertion reactions.  Our observational astronomy research seeks to examine the chemical mechanisms at play in a range of interstellar environments and to identify chemical tracers that can be used as clocks for the star-formation process.  In this seminar, I will present recent results from our laboratory and observational studies that examine prebiotic chemistry in the interstellar medium.  I will discuss these results in the broader context of my integrative research program that encompasses laboratory spectroscopy, observational astronomy, and astrochemical modeling.

Incorporating Metal-Ligand and Metal-Metal Cooperativity into First Row Transition Metal Complexes with Applications in Catalysis

Dr. Christine Thomas | Ohio State University

Professor Charlie Machan

Incorporating Metal-Ligand and Metal-Metal Cooperativity into First Row Transition Metal Complexes with Applications in Catalysis

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.

Graham Lecture | Repurposing the Blue Print of Life for Materials Design | 7:00 PM | Chemistry Zoom Meeting

Dr. Chad Mirkin | George B. Rathmann Professor of Chemistry, Northwestern University

Professor Charles Machan

 The materials-by-design approach to the development of functional materials requires new synthetic strategies that allow for material composition and structure to be independently controlled and tuned on demand. Although it is exceedingly difficult to control the complex interactions between atomic and molecular species in such a manner, interactions between nanoscale components can be encoded, independent of the nanoparticle structure and composition, through the ligands attached to their surface. DNA represents a powerful, programmable tool for bottom-up material design. We have shown that DNA and other nucleic acids can be used as highly programmable surface ligands (“bonds”) to control the spacing and symmetry of nanoparticle building blocks (“atoms”) in structurally sophisticated materials, analogous to a genetic code for materials assembly. The sequence and length tunability of nucleic acid bonds has allowed us to define a powerful set of design rules for the construction of nanoparticle superlattices with more than 50 unique lattice symmetries, spanning over one order of magnitude of interparticle distances, with several well-defined crystal habits. Furthermore, this control has enabled exploration of sophisticated symmetry breaking processes, including the body-centered tetragonal lattice as well as the clathrate lattice, the most structurally complex nanoparticle-based material to date (>20 particles per unit cell). The nucleic acid bond can also be programmed to respond to external biomolecular and chemical stimuli, allowing structure and properties to be dynamically tailored. Notably, this unique genetic approach to materials design affords functional nanoparticle architectures that can be used to catalyze chemical reactions, manipulate light-matter interactions, and improve our fundamental understanding of crystallization processes.

Dye-Sensitization for the Production of Electrical Power and Chemical Fuels from Sunlight

Dr. Jerry Meyer | University of North Carolina

Professor Charlie Machan

Dye-Sensitization for the Production of Electrical Power and Chemical Fuels from Sunlight

Gerald J. Meyer

Department of Chemistry,
University of North Carolina at Chapel Hill, Chapel Hill, NC, USA 27599-3290

E-mail: gjmeyer@email.unc.edu

Dye-sensitized solar cells have received considerable attention since the advent of mesoporous metal oxide thin films first described by Grätzel and O’Regan [1]. We have a fundamental interest in light driven interfacial electron transfer in these materials that is motivated by applications in electrical power generation and in solar fuels production [1,2]. Background on dye-sensitization and solar energy conversion will be provided that gives context for our most recent advances that suggest new directions for future research. An example includes the identification of a kinetic pathway for electron transfer from TiO2 to transition metal complexes with two redox active groups. [2,3] The distance between the two groups were held near parity yet electron transfer through an aromatic bridge that separated them was critically dependent on the degree of conjugation [3,4]. Electron transfer to acceptors positioned at variable distances from a conductive oxide surface revealed that the intrinsic barriers were dramatically decreased within the electric double layer [5]. Mechanistic study of core/shell oxide materials provided new insights into electron transport that were correlated with water oxidation efficiency [6]. Finally, an alternative approach to solar fuel production with small band gap semiconductors and tandem catalyst hybrids will be presented. This approach forms the basis of a new Department of Energy supported Solar Hub entitled the Center for Hybrid Approaches in Solar Energy to Liquid Fuels (CHASE) [7].       

References:

[1] “A Low- Cost, High Efficiency Solar Cell Based on the Dye- Sensitized Colloidal TiO2 Films” O’Regan, B.; Grätzel, M. Nature 1991, 353, 737.

[2] “Perspectives in Dye Sensitization of Nanocrystalline Mesoporous Thin Films” Hu, K.; Sampaio, R.N.; Schneider, J.; Troian-Gautier, L.; Meyer, G.J. J. Am. Chem. Soc. 2020, in press.

[3] “A Kinetic Pathway for Interfacial Electron Transfer from a Semiconductor to a Molecule” Hu. K.; Blair, A.D.; Piechota, E.J.; Schauer, P.A.; Sampaio, R.N.; Parlane, F.; Meyer, G.J.; Berlinguette, C.P. Nature Chem. 2016, 8, 853-859.

[4] “Kinetics Teach That Equilibrium Constants Shift Toward Unity with Increased Electronic Coupling” Sampaio, R.N.; Piechota, E.J.; Troian-Gautier, L.; Maurer, A.B.; Berlinguette, C.P., Meyer, G.J. Proc. Nat. Acad. Sci. USA 2018, 115, 7248-7253.

[5] “Kinetic Evidence that the Solvent Barrier for Electron Transfer is Absent in the Electric Double Layer” Bangle, R.E.; Schneider, J.; Conroy, D.T.; Aramburu-Troselj, B.M.; Meyer, G.J. J. Am. Chem. Soc. 2020, 142, 14940-14946. 

[6] “Electron Localization and Transport in SnO2/TiO2 Mesoporous Thin Films: Evidence for a SnO2/SnxTi1- xO2/TiO2 Structure” James, E.M.; Bennett, M.T.; Bangle, R.E.; Meyer, G.J. Langmuir 2019, 39, 12694-12703.

[7] https://uncnews.unc.edu/2020/07/31/department-of-energy-funds-milestone-north-carolina-led-initiative-to-advance-solar-energy-research/

Borane Lewis Acids and B-N Lewis Pairs: From Molecules to Materials

Dr. Frieder Jaekle | Rutgers University, Newark

Professor Robert Gilliard

The incorporation of main group elements into conjugated materials is known to result in unusual properties and to enable new functions.[1] In particular, the ability of tricoordinate boron to participate in p-delocalization can have a dramatic effect on the optoelectronic properties of conjugated materials by selectively lowering the LUMO orbital levels. The electron-deficient character of boron also enables the reversible formation of Lewis pairs (LPs) by interaction of Lewis acids with Lewis bases.

In our recent work, we have explored the incorporation of boron into conjugated oligomers, macrocycles, and polymers for optoelectronic applications.[2] We have also demonstrated that base-directed electrophilic aromatic C-H borylation provides an effective means to generate luminescent B-N containing conjugated materials with unusual properties such as self-sensitized singlet oxygen generation.[3]

On the other hand, the judicious decoration of polymers with organoborane Lewis acid sites can be exploited in sensory and stimuli-responsive materials, as well as the development of supported catalysts that rely on the ability of Lewis acids to activate small molecules.[4] In addition, we have discovered that “smart” dynamic materials can be generated by embedding both Lewis acid and base sites into polymer networks.[5]

In this talk I will discuss some of these discoveries and highlight their impact in diverse application fields ranging from organic electronic materials and chemosensors to reprocessible elastomers and supported catalysts.

References:

1. (a) Main Group Strategies towards Functional Hybrid Materials, T. Baumgartner, F. Jäkle, Eds. John Wiley & Sons Ltd, Chichester, 2018; (b) F. Vidal, F. Jäkle, Angew. Chem. Int. Ed. 2019, 58, 5846.
2. (a) B. Meng, Y. Ren, J. Liu, F. Jäkle, L. Wan, Angew. Chem. Int. Ed. 2018, 57, 2183; (b) N. Baser-Kirazli, R. A. Lalancette, F. Jäkle, Angew. Chem. Int. Ed. 2020, 59, 8689.
3. (a) K. Liu, R. A. Lalancette, F. Jäkle J. Am. Chem. Soc. 2019, 141, 7453; (b) M. Vanga, R. A. Lalancette, F. Jäkle Chem. Eur. J. 2019, 25, 10133.
4. (a) F. Cheng, E. M. Bonder, F. Jäkle, J. Am. Chem. Soc. 2013, 135, 17286; (b) F. Vidal, J. McQuade, R. A. Lalancette, F. Jäkle, J. Am. Chem. Soc. 2020, 142, DOI: 10.1021/jacs.0c05454; (c) H. Lin, S. Patel, F. Jäkle, Chem. Eur. J. 2020, submitted.
5. F. Vidal, J. Gomezcoello, R. A. Lalancette, F. Jäkle, J. Am. Chem. Soc. 2019, 141, 15963.

Biography

Frieder Jäkle is a Distinguished Professor in the Department of Chemistry at the Newark Campus of Rutgers University. He received his Diploma in 1994 and Ph.D. in 1997 from TU München, Germany, under the direction of Prof. Wagner. After a postdoctoral stint with Prof. Manners at the University of Toronto he joined Rutgers University in 2000. His research interests revolve around main group chemistry as applied to materials and catalysis, encompassing projects on organoborane Lewis acids, conjugated hybrid materials, luminescent materials for optoelectronic and sensory applications, stimuli-responsive and supramolecular polymers. He is the recipient of an NSF CAREER award (2004), an Alfred P. Sloan fellowship (2006), a Friedrich Wilhelm Bessel Award of the Alexander von Humboldt Foundation (2009), the ACS Akron Section Award (2012), the Boron Americas Award (2012) and the Board of Trustees Research Award at Rutgers University (2017). In 2019 he was named a Fellow of the American Chemical Society. He has served on the editorial advisory boards of several journals, including Macromolecules, ACS Macro Letters, and Organometallics.

Expanding the Chemical Toolbox for Acoustic-based Imaging of Cancer

Dr. Jefferson Chan | University of Illinois, Urbana-Champaign

Professor Clifford Stains

Many disease states are characterized by molecular level changes that occur before detectable symptoms have begun to manifest. In order to maximize treatment outcomes it is essential to accurately detect such alterations at an early stage. Chemical probes designed to selectively image such molecular processes have the potential to not only aid in disease diagnosis but can also provide unique insights into disease progression. As an important step toward these goals we have developed a palette of activatable probes for photoacoustic imaging and apply these to visualize changes in the tumor microenvironment. Briefly, photoacoustic imaging is a state-of-the-art technique that generates ultrasound signals from light, which can be detected and converted into high-resolution 3D images. Since sound scattering is three orders of magnitude less than light in tissue, photoacoustic imaging can be employed to image up to 8 cm in depth while achieving micron resolution. To image deeper regions of the body in real-time, we have recently developed the first activatable ‘smart bubbles’ for ultrasound imaging. Like our photoacoustic probes, smart bubbles respond selectively to a disease property to provide signal enhancements via enhancement of their echogenic properties. In this seminar, we will discuss the strategies employed to construct both photoacoustic and ultrasound probes, as well as highlight notable examples from our laboratory.      

Brief Bio:

Professor Chan received his BSc degree in chemistry from the University of British Columbia in 2006 and his PhD from Simon Fraser University (Prof. Andrew Bennet) in 2011. For his graduate research, he received the Boehringer Ingelheim (Canada) Doctoral Research Award for the top Canadian thesis in the areas of organic and bioorganic chemistry. From 2011-2014 he was a Human Frontiers Science Program Postdoctoral Fellow at the University of California, Berkeley (Prof. Christopher Chang). In the fall of 2014 he joined the faculty at the University of Illinois, Urbana-Champaign.

SPRING SEMINARS HAVE BEEN CANCELLED