A Quantum Embedding Approach to Understanding Biological N2 Fixation

California Institute Of Technology, Pasadena CA

Investigators

Abstract

With this award, the Chemistry of Life Processes Program in the Chemistry Division is funding Dr. Thomas Miller from the California Institute of Technology to investigate nitrogen fixation in biological and synthetic chemical systems. Understanding nitrogen fixation (breaking N2 into more useful forms) is a challenge of paramount scientific, industrial and societal importance. The predominant route for nitrogen fixation is the Haber-Bosch process, resulting in ammonia (NH3). Beyond this process few advances have been made to fix nitrogen, especially at mild temperatures and pressures. The search for other routes that operate under various conditions and understanding how they work are among the most elusive challenges in the chemical sciences. Recently developed computational quantum chemistry methods are employed in this research to achieve a detailed characterization of pathways involved in nitrogen fixation. Throughout this pursuit graduate students and postdoctoral fellows are acquiring specialized training in electronic structure theory and reaction dynamics of complex systems. New theoretical methods to advance the accuracy and efficiency of what is computationally obtainable, are being employed and developed in this research. This project is integrated into an outreach program to introduce high school students and high school science teachers to the science of computational chemistry. This research project is undertaken to characterize important catalytic pathways and reaction intermediates for the fixation of nitrogen via biological and synthetic catalysts. The research approach applies recently developed quantum embedding methods that enable high-level descriptions of the electronic wave-functions (such as CCSD(T) or CASPT2) in the reaction center of transition metal catalysts at dramatically reduced computational costs. The project involves the use of these powerful new theoretical methods to elucidate the catalytic pathways for nitrogen reduction in both single-site and two-site synthetic models of the FeMo-cofactor. In addition the project incorporates full-scale studies of the nitrogenase FeMo-cofactor with protein and solvent environment. The project addresses physical questions and methodological challenges that are at the forefront of biological, inorganic, and theoretical chemistry research. The project will yield critical insights into the catalytic pathways for nitrogen reduction, clear mechanistic insights into both model complexes that are testable in the synthetic laboratory, as well as characterizations and predictions for the nitrogenase enzyme in its full complexity. Furthermore, the project is synergistic with NSF research priorities related to catalytic activation of other small molecules (such as H2 and CO2), as well as with the Innovations at the Nexus of Food, Energy and Water Systems (INFEWS) initiative.