Applications of Density Functional Theory and Absolutely Localized Molecular Orbital Energy Decomposition Analysis: Intermolecular Interactions in Rhenium-Alkane s-Complexes and in Water Clusters and Reaction Energy Profiles of Methane Hydroxylation Mediated by Quantum Models of p-MMO Active Sites
- Author(s): Cobar, Erika Ann
- Advisor(s): Bergman, Robert G
- Head-Gordon, Martin
- et al.
Quantum chemical methods, particularly density functional theory (DFT), have become increasingly important tools in the study of transition-metal-mediated reactions. In the first part of this work, we use DFT to construct small models of the various candidates for the active site of the copper-containing metalloenzyme particulate methane monooxygenase (p-MMO). p-MMO mediates the conversion of methane to methanol at ambient temperature and pressure in nature--a feat which has not yet been achieved by synthetic transition metal complexes in the laboratory. Using these small models of the potential active sites of p-MMO, we study possible mechanisms employed by the enzyme, investigating the effects of complex charge, ligand identity, and coordination number on the energetics of the methane hydroxylation reactions they mediate.
Energy decomposition methods, which decompose intermolecular interaction energies into their component energy terms, are also becoming increasingly popular in the study of a wide range of chemical systems. In this work, we apply the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA) method to two very different kinds of intermolecular interactions. One is the interaction between an alkane C-H sigma-bond and a transition metal center, which is presumed to occur in the intermediates of transition-metal-mediated C-H activation reactions. The other is perhaps one of the most important intermolecular interactions on earth--the water-water hydrogen bond. We study water clusters between the dimer and 17-mer, examining total cluster interaction energies as well as local two- and three-body interactions.