Department of Chemistry and Biochemistry
Organic/Inorganic/Materials Seminar Series

Professor Pier Alexandre Champagne, New Jersey Institute of Technology
Tuesday March 4, 2025 
3:00 pm in 117 Education 

Hosted by Mike Pluth

Computational and Experimental Approaches to Understand and (Eventually) Control Reactive Sulfur Species

Reactive sulfer species (RSS) are a class of sulfur-based functional groups including H₂S, persulfides (RS₂H), polysulfides (R₂S_n, n>2), nitrosothiols (RSNO), and others, which are now recognized as important biological intermediates with various physiological and pathological effects. This versatile chemistry is due to sulfur’s unique properties, including the stability of all its oxidation states (-2 to +6) and its catenation behavior, leading to a variety of structures with important roles throughout chemistry. Notably, RSS are involved in the H₂S signaling pathways and in the protection of cells against oxidative insult, while polysulfides are also common intermediates in materials science and organic synthesis. Despite the proven importance of RSS and polysulfides, their intrinsic reactivity under organic or biological conditions is still poorly understood due to their thermodynamic and kinetic instability, making experimental characterization, probing, and isolation of individual RSS challenging.

This presentation will showcase our group’s recent efforts in advancing the chemical understanding of RSS, through the application of computational tools (e.g. Density Functional Theory (DFT) calculations) and the development of novel photoactivated small-molecule donors. Various examples of importance for inorganic chemistry, organic synthesis, and chemical biology will be discussed, highlighting the general rules of RSS reactivity that have been uncovered throughout. Overall, our work opens up new possibilities for the study and, eventually, control of polysulfides and RSS in various settings, despite their complicated behavior.

Department of Chemistry and Biochemistry
Physical Chemistry Seminar Series

Professor Achille Giacometti, Ca’ Foscari University, Venice, Italy
March 3, 2024 —2:00pm
Tykeson 140

Phase behaviour and self-assembly properties of semiflexible polymers in solution

This presentation explores the phase behaviour and self-assembly properties of semiflexible polymers in solution, focusing on temperature dependence and bending constraints. The talk is structured in two parts. In the first part, I will examine the phase behaviour of a single semiflexible polymer, comparing two types of bending constraints. The first is the traditional elastic penalty used in the worm-like chain model, while the second is an entropic constraint arising from steric effects introduced by a side sphere. I will demonstrate that these constraints lead to markedly different phase behaviours at low temperatures.

In the second part, I will extend the analysis to multiple polymer chains in solution, investigating their self-assembly properties under each bending constraint. Although the detailed low-temperature behaviour differs between the two constraints, the general self-assembly mechanism appears to exhibit universal characteristics.

Department of Chemistry and Biochemistry
Organic/Inorganic/Materials Seminar Series

Professor Julie Rorrer, University of Washington
Friday, February 28, 2025
3:00 pm, 110 Willamette Hall
Hosted by Teresa Rapp

Advancing the Catalytic Recycling of Polyolefin Waste

Single-use plastics such as polyolefins provide lightweight and effective packaging and materials for food, medicine, and many other consumer products. This has led to massive global generation of plastic waste which is accumulating in landfills and the environment, causing harm to the ecosystem and human health. While a small amount of plastic waste is mechanically recycled, the material quality is diminished compared to virgin polymers. Chemical recycling with heterogeneous catalysis can lower the energy required to selectively break apart polyolefins into higher value fuels, chemicals, and monomers. Emerging methods which can be performed at relatively low temperatures include hydrogenolysis and hydrocracking, solvent-based deconstruction, and tandem hydrogenolysis/aromatization. The scalability of these methods is limited by the high cost of reactants, the requirement for high pressure molecular hydrogen or solvents, and the high cost of catalytic materials. This talk will start by discussing advances in the catalytic depolymerization of waste plastics via hydrogenolysis and hydrocracking, followed by progress in hydrogen-free depolymerization pathways. The talk will close with a discussion on emerging frameworks for the chemical recycling of mixed plastic waste feedstocks and an outlook on remaining technical challenges in polymer upcycling, redesign, and circularity.

Department of Chemistry and Biochemistry
Physical Chemistry Seminar Series

Professor Oliver L.A. Monti, University of Arizona
February 24, 2024 —2:00pm
Tykeson 140

Host: Elana Cope—PChem Student Group

What’s spin got to do with it?
Using organic semiconductors to manipulate spin for novel high-efficiency electronics                                     

The rapid growth of computing and communication capabilities creates enormous demand for power, and with that is beginning to make a sizeable contribution to global greenhouse gas emissions. To overcome this challenge, entirely novel concepts are needed for electronic devices whose power consumption is drastically reduced, if possible, by orders of magnitude. This will be impossible to accomplish within the existing framework of existing semiconductor technologies. One possible alternative might be to use spin as an information carrier. Though switching spin uses much less energy than switching e.g. voltages, it conventionally requires large magnetic fields which are difficult to miniaturize to the scale of conventional electronics.

In this talk, I will introduce new ideas of how one may achieve this without external magnetic fields. Instead, I will show how by appropriate choice of organic semiconductors and their interfaces with other materials one may control spin in transport, in the spin degrees of freedom of the electronic structure of a material, and on femtosecond timescales. I will showcase recent work from LabMontiTM how we achieve this at the single molecule level, in 2D materials and in quantum materials.

Department of Chemistry and Biochemistry
Organic/Inorganic/Materials Seminar Series

Professor Holger Bettinger, University of Tübingen
Monday – February 10, 2025
4:00 pm, 110 WIL
Hosted by Mike Haley

A Journey from Long Acenes to Cyclacenes

Acenes are a fundamentally and technologically important class of polycyclic aromatic hydrocarbons. Their small HOMO-LUMO gap is a blessing for materials properties but a curse for synthesis, characterization, and handling. My research group has achieved acenes of unprecedented lengths under the stabilizing conditions of matrix isolation and on-surface synthesis that allowed gaining an understanding of acene properties up to pentadecacene (15acene).[1] The key to success is the application of a protection group strategy that enables the release of acenes under these extreme conditions. The cyclic versions of acenes, cyclacenes, are unknown despite significant synthetic efforts since Edgar Heilbronner’s 1954 proposal. I will address expected properties of these zig-zag nanohoops and discuss strategies of their experimental realization using the low-temperature high-vacuum techniques in our laboratory.[2]

1. a) C. Tönshoff, H. F. Bettinger, Photogeneration of Octacene and Nonacene, Angew. Chem., Int. Ed. 2010, 49, 4125, 10.1002/anie.200906355; b) B. Shen, J. Tatchen, E. Sanchez-Garcia, H. F. Bettinger, Evolution of the Optical Gap in the Acene Series: Undecacene, Angew. Chem. Int. Ed. 2018, 57, 10506, 10.1002/anie.201802197; c) Z. Ruan, J. Schramm, J. B. Bauer, T. Naumann, H. F. Bettinger, R. Tonner-Zech, J. M. Gottfried, Synthesis of Tridecacene by Multistep Single-Molecule Manipulation, J. Am. Chem. Soc. 2024, 146, 3700, 10.1021/jacs.3c09392; d) Z. Ruan, J. Schramm, J. B. Bauer, T. Naumann, L. V. Müller, F. Sättele, H. F. Bettinger, R. Tonner-Zech, J. M. Gottfried, On-surface Synthesis and Characterization of Pentadecacene and its Gold Complexes, submitted for publication 2024.
2. a) D. Gupta, A. Omont, H. F. Bettinger, Energetics of Formation of Cyclacenes from 2,3-Didehydroacenes and Implications for Astrochemistry, Chem. Eur. J. 2021, 27, 4605, https://doi.org/10.1002/chem.202003045; b) J. B. Bauer, F. Diab, C. Maichle-Moessmer, H. Schubert, H. F. Bettinger, Synthesis of the [11]cyclacene framework by repetitive Diels-Alder cycloadditions, Molecules 2021, 26, 3047, 10.3390/molecules26103047; c) A. Somani, D. Gupta, H. F. Bettinger, Computational Studies of Dimerization of [n]-Cyclacenes, J. Phys. Chem. A 2024, 128, 6847, 10.1021/acs.jpca.4c02833.

Department of Chemistry and Biochemistry
Organic/Inorganic/Materials Seminar Series

Professor Professor Renana Gershoni Poranne, Technion
February 7, 2025
3:00 pm, WIL 110
Hosted by Mike Haley

Data are a Girl’s Best Friend: From High-Throughput Computation to Generative Deep Learning

Chemical databases are an essential tool for data-driven investigation of structure-property relationships and design of novel functional compounds, and they are the crucial foundation for machine- and deep-learning techniques, which efficiently map the chemical space and allow discovery of new molecular motifs of molecules and materials for various uses. However, there is a lack of suitable databases of polycyclic aromatic systems (PASs).

To enable the application of such techniques to the design of novel functional PASs, we established the COMPAS Project — a COMputational database of Polycyclic Aromatic Systems. This new database already contains over 500k molecules in three datasets: cata-condensed polybenzenoid hydrocarbons (COMPAS-1),¹ cata-condensed hetero-PASs (COMPAS-2),² and peri-condensed polybenzenoid hydrocarbons (COMPAS-3).³

With this new data in hand, we demonstrate the first examples of interpretable learning models in the chemical space of PASs. To this end, we developed two types of molecular representation to enable efficient and effective machine- and deep-learning models to train on the new data: a) a text-based representation⁴ and b) a graph-based representation.⁵ Our dedicated representations not only achieve higher predictive ability with fewer data, but are also amenable to interpretation – thus allowing the extraction of chemical insight from the model.

Using the COMPAS database and our dedicated representations, we implemented the first guided diffused-based model for inverse design of PASs: GaUDI.⁶ Our model generates new PASs with defined target properties. In addition to its flexible target function and high validity scores, GaUDI also accomplishes design of molecules with properties beyond the distribution of the training data.

References

(1)  Wahab, A.; Pfuderer, L.; Paenurk, E.; Gershoni-Poranne, R. The COMPAS Project: A Computational Database of Polycyclic Aromatic Systems. Phase 1: Cata-Condensed Polybenzenoid Hydrocarbons. J. Chem. Inf. Model. 2022, 62 (16), 3704.

(2)  Mayo Yanes, E.; Chakraborty, S.; Gershoni-Poranne, R. COMPAS-2: A Dataset of Cata-Condensed Hetero-Polycyclic Aromatic Systems. Sci. Data 2024, 11 (1), 97.

(3)  Wahab, A.; Gershoni-Poranne, R. COMPAS-3: A Data Set of Peri-Condensed Polybenzenoid Hydrocarbons. ChemRxiv February 26, 2024.

(4)  Fite, S.; Wahab, A.; Paenurk, E.; Gross, Z.; Gershoni-Poranne, R. Text-Based Representations with Interpretable Machine Learning Reveal Structure-Property Relationships of Polybenzenoid Hydrocarbons. J. Phys. Org. Chem. 2022, e4458.

(5)  Weiss, T.; Wahab, A.; Bronstein, A. M.; Gershoni-Poranne, R. Interpretable Deep-Learning Unveils Structure–Property Relationships in Polybenzenoid Hydrocarbons. J. Org. Chem. 2023, 88 (14), 9645–9656. https://doi.org/10.1021/acs.joc.2c02381.

(6)  Weiss, T.; Mayo Yanes, E.; Chakraborty, S.; Cosmo, L.; Bronstein, A. M.; Gershoni-Poranne, R. Guided Diffusion for Inverse Molecular Design. Nat. Comput. Sci. 2023, 3 (10), 873–882. https://doi.org/10.1038/s43588-023-00532-0.

Department of Chemistry and Biochemistry
Organic/Inorganic/Materials Seminar Series

Professor Jonathan Kuo, Penn State
January 31, 2025
3:00 pm, WIL 110
Hosted by ADSE

Comparing Metalloenzymatic Active Sites to Synthetic Model Complexes: Expanding Views on Supporting Ligands

Organic ligands alter the electronic structure and properties of the transition metals that they bind to. But what other functions can be programmed into metal/ligand complexes? In this talk, we will discuss how dynamic ligand features “unlock” key steps in (a) aerobic oxygenation and (b) electrophilic olefin activation. These dynamic features replicate dynamics present in enzymatic active sites. Recently, comparisons to enzymatic active sites have drawn us to host-guest-type ligand-metalate complexes – where the supporting ligand is designed to bind polyatomic metal anions [MO4]2– or [MCl4]2– via hydrogen bonding.