Benjamin Rousseau Thesis Defense “Nuclear Quantum Effects and Proton Transfer Mechanisms in Molecular and Solid-Liquid Interface Systems”
Field: Theoretical Chemistry
Represented Lab: Hammes-Schiffer Group
Nuclear quantum effects are ubiquitous in chemistry and can change the behavior of chemical systems. In the first part of my talk, I will discuss the development of an affordable multicomponent wave function-based quantum chemistry method that accurately predicts proton densities and proton affinities and that automatically incorporates the nuclear quantum effects of select nuclei of interest. This method has significant potential for describing nuclear quantum effects in molecular systems, but alternative approaches are needed to describe tunneling effects in large systems that perform proton-coupled electron transfer (PCET) processes.
In the next section, I will discuss a recent study of hydrogen underpotential deposition (HUPD) on a Pt(111) electrode surface, which is the Volmer reaction at potentials more positive than the hydrogen evolution reaction (HER) and is thus central to the efficient large-scale production of hydrogen gas. In alkaline conditions the proton donor is assumed to be water, but its local chemical environment near the Pt electrode surface is unknown. We employ a theoretical model based on nonadiabatic PCET theory that accounts for hydrogen tunneling by treating the transferring hydrogen on the same quantum mechanical footing as the electrons, combined with periodic density functional theory (DFT), to provide theoretical insights into the nature of HUPD on Pt(111). We identify a single proton donor motif in the rigid water monolayer on the Pt(111) surface that reproduces experimental results. This study serves as a proof of concept of this theory in its application to HUPD on Pt(111), demonstrating the importance of considering nonadiabatic effects while modeling the Volmer reaction.
In the final section, I will discuss our work in understanding the mechanism by which a water- and blood-stable copper metal-organic framework (Cu-MOF) catalyzes the release of nitric oxide, a safe and effective vasodilator, from S-nitrosoglutathione (GSNO), which is endogenous in blood. As such, the Cu-MOF material has tremendous potential for application as a biomedical implant. A previously proposed PCET mechanism is shown to be thermodynamically inaccessible, and after evaluating numerous possible mechanisms, a single mechanism is identified that is consistent with experiment and in which a reductive elimination step occurs to form a Cu(I) intermediate. We suggest partial stabilization of this Cu(I) intermediate is already achieved by protonation of an organic linker, and we predict further stabilization of this Cu(I) intermediate will facilitate its usage in more alkaline conditions.
Thesis defense can be viewed online at:
https://yale.zoom.us/j/99637600121?pwd=eHp2bjNkYUhWaWlUR0JXYi8yK1p1UT09 Meeting ID: 996 3760 0121