Dissertation/Thesis Abstract

Investigating catalysis through quantum mechanical computations: An analysis of phosphoryl transfer enzymes and CCC-NHC pincer complexes
by Leigh, Katherine Nicholls, Ph.D., The University of Memphis, 2014, 714; 3728584
Abstract (Summary)

Chemical reactions are essential to the world we experience. Certain chemical reactions, though beneficial, occur at rates too slow to be practical. Catalysis, or the use of another species to increase the rate of a chemical reaction, is often utilized, allowing chemical reactions to become more beneficial. Catalysts increase reaction rates by lowering the amount of energy required to perform a reaction. Catalysis is abundant, as evidenced in nature in the form of enzymes, or in a myriad of non-biological processes such as chemical manufacturing and pharmaceutical materials.

Phosphoryl transfer is a fundamental step in numerous processes central to life, and its catalysis by enzymes is crucial to these processes occurring at biologically useful rates. Quantum mechanical computations have been employed to study mechanisms of phosphoryl transfer in four enzymes: β-phosphoglucomutase, phosphoserine phosphatase, cyclic AMP-dependent protein kinase, and phosphoglycerate kinase. Optimized geometries indicate that in each enzyme transfer of PO 3 is associative in nature and utilizes a five-coordinate trigonal bipyramidal phosphorane transition state. Metalfluoride species which act as analogues of the PO3 – species have been identified through X-ray crystallography and 19F NMR spectroscopy. Optimized geometries of the four enzymes containing these analogues indicate that BeF3 – behaves as a ground-state analogue of PO3 –, while MgF3 and AlF4 behave as transition-state analogues. Computationally-derived 19F NMR chemical shifts of the analogue-containing species closely resemble experimental spectra and demonstrate that each enzyme prioritizes constant charge (BeF3, MgF 3, or AlF4) over geometry (AlF3).

Hydroamination is an atom-economical method to produce alkylamines, an important component in biologically-relevant materials. The combination of an amine and an electron-rich unsaturated bond has a high energetic barrier, requiring catalysis to overcome it. Metal-based CCC N-heterocyclic pincer carbenes have successfully performed intramolecular hydroamination with various substituents, and plausible mechanisms for this process have been studied using quantum mechanical computations. Rh(III)-based hydroamination is proposed to occur by an alkene-bound mechanism, and possible Rh(I)-catalyzed mechanisms have also been investigated. Zr(IV)-based hydroamination is proposed to occur by a [2+2] cycloaddition type of mechanism, and the effects of halogen and substrate substitution have also been studied.

Indexing (document details)
School: The University of Memphis
Department: Chemistry
School Location: United States -- Tennessee
Source: DAI-B 77/03(E), Dissertation Abstracts International
Subjects: Organic chemistry
Keywords: Density functional theory, Hydroamination, Phosphoryl transfer, Quantum mechanics, Transition state analogue
Publication Number: 3728584
ISBN: 9781339140957
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