Collaborative Research: Enantioselectivity in Heterogeneous Catalysts via the Addition of Chiral Modifiers

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Biomolecular building blocks can exhibit either right- or left-handed symmetries; such building blocks are known as enantiomers. All biomolecules found in living organisms have only one "handedness', that is, the molecules exist only in one enantiomeric form. Moreover, different enantiomers of the same molecule can interact with living organisms in completely different ways, sometimes beneficially and sometimes with catastrophic effects. As the wrong handedness can cause harm, pharmaceuticals and agrochemicals must be synthesized in enantiopure forms. This synthesis may be accomplished by purification after the drug has been synthesized, but that approach is often difficult and cumbersome. It is preferable to develop processes in which only one enantiomer of the drug is made. Enantiopure syntheses can be accomplished by using solid-phase catalysts with surfaces that are specifically modified to preferentially produce molecules with only one handedness. There have been a number of trial-and-error efforts to discover such heterogeneous catalysts, but success has so far been limited. Drs. Tysoe (University of Wisconsin-Milwaukee) and Zaera (University of California-Riverside) have considerable experience in studying the surface chemistry of catalytic systems under ideal conditions. Their research project focuses on understanding the molecular interactions that control enantio-selectivity in more complex and realistic systems for the advanced manufacturing of pharmaceuticals. Drs. Tysoe and Zaera are strongly committed to educating women and minorities, in particular, Hispanic students both in the laboratory and through formal courses. They participate in outreach programs at Milwaukee and Riverside, and are incorporating the research associated with this project into those activities. With funding from the Chemical Catalysis Program of the Chemistry Division, Drs. Tysoe and Zaera are studying the surface chemistry of model palladium(111) and platinum(111) chiral catalysts modified by a cinchonidine analog, 1-(1-naphthyl) ethylamine (NEA), using scanning tunneling microscopy (STM), infrared absorption spectroscopy, reactivity measurements, and first-principles density functional theory (DFT) calculations. This research provides a molecular-level understanding of the diastereomeric interactions between a number of prochiral reactants and NEA, and the forces that control them. They are investigating whether the detailed molecular understanding of the chiral surface chemistry from single-crystal studies in ultrahigh vacuum is relevant to the reaction pathways occurring under realistic conditions, that is, under atmospheric pressures and in the presence of a liquid phase. The resulting understanding may provide insights into how to improve catalytic selectivity. The research may facilitate the targeted design of supported heterogeneous enantioselective catalysts. Such an ability is expected to have a significant economic impact in the pharmaceutical and agrochemical industries. Drs. Tysoe and Zaera focus on educating women and minorities through their research and outreach programs as part of the broader impacts of the project.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.