Date on Master's Thesis/Doctoral Dissertation

12-2023

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Degree Program

Chemistry, PhD

Committee Chair

Kozlowski, Pawl

Committee Co-Chair (if applicable)

Buchanan, Robert

Committee Member

Buchanan, Robert

Committee Member

Thompson, Lee

Committee Member

Sathitsuksanoh, Noppadon

Author's Keywords

intermediate omega; cobaloxime; Co-C bond dissociation; CASSCF/NEVPT2; dimethylamination of aromatic compounds; Fe-C bond dissociation

Abstract

The efficient application of DFT and TD-DFT has been harnessed to study bond-breaking processes in some molecules which play a prominent role in enzymatic reactions. The first application includes Radical S-adenosyl methionine (SAM) enzymes which are fundamentally important sources of organic radicals to initiate diverse radical reactions. Recently a bio-organometallic intermediate (Ω) that contains an Fe‒C bond has been characterized and shown to be a common feature of radical SAM enzymes. The strength of Fe‒C bond in Ω has been computed using broken-symmetry density functional theory (BS‒DFT). Additionally, Fe‒C bond dissociation energy (BDE) in Ω has been compared to that with S‒C bond in SAM and Co‒C bond in adenosylcobalamin (AdoCbl). The second application includes Ethyl(aqua)cobaloxime (Cbx) which is commonly used as a model compound to study vitamin B12 derivatives such as AdoCbl and methylcobalamin (MeCbl). The mechanism of Co‒C bond photodissociation in Cbx in presence of a benzophenone (acting as photocatalyst, PC) has been investigated by means of time-dependent density functional theory (TD-DFT). The calculation of low-lying singlet and triplet excited states of the substrate and PC reveal that the photodissociation process is mediated by a repulsive triplet state via Dexter energy transfer from PC to Cbx. Lastly, DFT and TD‒DFT have been applied to investigate photo-assisted cleavage of N, N-dimethylformamide (DMF). Potential energy surfaces (PES) have been constructed using DFT to investigate the cleavage of C‒F bond of perfluoronaphthalene (PFN) and simultaneous attachment of DMF N-atom to C-atom. Excited state PESs, which were calculated using TD‒DFT, reveals that the energy barrier for electron transfer from DMF to PFN is significantly reduced in presence of light. This enables a redistribution of the electronic charge between the DMF and PFN leading to accelerated reductive cleavage of the C‒F bond and subsequent quick reaction between radical ions to give amination products.

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