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

SPRING SEMINARS HAVE BEEN CANCELLED

ABSTRACT

Antisense Oligonucleotide Therapeutics for Neurological Diseases

Antisense oligonucleotides (ASOs) are synthetic, chemical modified nucleic acid analogs designed to bind to RNA by Watson-Crick base paring and upon binding, modulate the function of the targeted RNA. There are a variety of mechanisms by which ASOs can modulate RNA function dependent on the chemical design of the ASO, the type of RNA and where on the RNA the ASO is designed to bind. Both protein coding, as well as non-coding RNAs, can be targets of ASO based drugs, significantly broadening therapeutic targets for drug discovery compared to small molecules and protein-based therapeutics. The recent approval of nusinersen (Spinraza™) as a treatment for spinal muscular atrophy (SMA) and inotersen (Tegsedi) for polyneuropathy of hereditary transthyretin-mediated amyloidosis (hATTR)  validates the utility of antisense drugs for the treatment of neurological  diseases. A summary of the progress, lessons learned and future challenges applying antisense technology for neurological diseases will be provided.

SPRING SEMINARS HAVE BEEN CANCELLED

SPRING SEMINARS HAVE BEEN CANCELLED

A Designer's Toolkit for Constructing Complex Nanoparticle Libraries

Dr. Raymond Schaak | Penn State University

Professor Sen Zhang

ABSTRACT

Multi-component nanoparticles offer unique opportunities to combine different properties in a single construct, enabling both multi-functionality and the emergence of new synergistic functions. Synthesizing such multi-component nanoparticles requires simultaneous control over size, shape, composition, and structure, as well as interfaces and spatial arrangements. We have been developing two complementary strategies for synthesizing multi-component nanoparticles. The first approach involves heterogeneous seeded growth, where interfaces and asymmetry are introduced by sequentially growing new nanoparticles off of the surfaces of existing nanoparticles. Complex hybrid nanoparticles of a growing number of materials, configurations, and morphologies can now be synthesized. The second approach involves sequential partial cation exchange reactions, where interfaces and asymmetry are introduced by compositional modifications that are made within an existing nanoparticle. A growing library of complex heterostructured metal sulfide nanoparticles can now be rationally designed and then readily synthesized.

Systematic Methods for Learning Complex Mechanisms from Molecular Dynamics Simulations

Dr. Aaron Dinner | University of Chicago

Professor Kateri DuBay

ABSTRACT 

Computers and algorithms are now sufficiently powerful that many complex molecular processes can be simulated at atomic resolution.  Yet it remains challenging to describe dynamics when processes are stochastic and proceed by multiple pathways.  In this talk, I will illustrate these issues with simulations of insulin dimer dissociation, which serves as a paradigm for coupled (un)folding and (un)binding.  Then I will present recent work that we have done to advance methods for efficiently estimating kinetic statistics and systematically learning complex reaction mechanisms from molecular dynamics data.

Specific Inhibition of Heparanase by Glycopolymers for Cancer and Diabetic Therapeutics

Dr. Hien Nguyen | Wayne State University

Professor Clifford Stains

ABSTRACT

Specific Inhibition of Heparanase by Glycopolymers for Cancer and Diabetic Therapeutics

Heparanase has been illustrated to regulate aggressive tumor behavior and to play important roles in autoimmune diabetes. Heparanase cleaves polymeric heparan sulfate (HS) molecules into smaller chain length oligosaccharides, allowing for release of angiogenic growth factors promoting tumor development and autoreactive immune cells to reach the insulin-producing b cells. Interaction of heparanase with HS chains is regulated by substrate sulfation sequences, and only HS chains with specific sulfation patterns are cleaved by heparanase. Therefore, heparanase has become a potential target for anticancer and antidiabetic drug development. Several molecules have been developed to target heparanase activity, but only carbohydrate molecules have advanced to clinical trials. However, the carbohydrate-based heparanase inhibitors are heterogeneous in size and sulfation pattern leading to nonspecific binding and unforeseen adverse effects, thus halting their translation into clinical use.

Our group has recently discovered that the sulfation pattern of pendant disaccharide moiety on synthetic glycopolymers could be synthetically manipulated to achieve optimal heparanase inhibition. We have determined that glycopolymer with 12 repeating units was the most potent inhibitor of heparanase (IC50 = 0.10 ± 0.36 nM). This glycopolymer was further examined for cross-bioactivity, using a solution based competitive biolayer interferometry assay, with other HS-binding proteins (growth factors, P-selectin, and platelet factor 4) which are responsible for mediating angiogenic activity, cell metastasis, and antibody-inducedthrombocytopenia. The synthetic glycopolymer has low affinity for these HS-binding proteins in comparison to natural heparin. In addition, the glycopolymer possessed no proliferative properties towards human umbilical endothelial cells (HUVEC) and a potent antimetastatic effect against 4T1 mammary carcinoma cells. Furthermore, our recent results illustrated that treatment of cultured mouse pancreatic b cells with heparanase significantly reduced their survival. In stark contrast, the b cells treated with heparanase plus the synthetic glycopolymer exhibited a survival rate comparable to the b cells treated with the vehicle PBS. In addition, we treated insulin-secreting human pancreas islets with heparanase in the presence or absence of the glycopolymer inhibitor. Alcian blue staining of HS contents indicated that the the glycopolymer inhibitor protected the human islets from destruction of extracellular HS contents caused by elevation of heparanse. The extracellular HS contents play important roles in preserving pancreas β cell function and protecting β cells from destruction by heparanase.