Nitric Oxide Reactivity at Biomimetic Copper and Zinc Complexes and Metal-free Frustrated Lewis Pairs
Cardenas, Allan Jay Pascasio
Warren, Timothy H.
Since the discovery of nitric oxide (NO) in 1772, this simplest, stable free radical with one unpaired electron has been a target of ongoing research as an industrial intermediate, environmental pollutant, and more recently, an important signaling molecule in biology. Nitric oxide is a very important intermediate for synthesis of nitric acid with an estimated annual global production of 10 million metric tons. Despite this massive scale of production, there are relatively few direct uses of NO in synthesis. Nitric oxide is also well known as a toxic gas from cars, factories and tobacco. It leads to photochemical smog and can cause acid rain. Nonetheless, over the last 3 decades, the reputation of NO has changed dramatically: NO and its biochemical relatives are central to a number of biochemical signaling pathways and are involved in many physiological response such as vasodilation.This thesis centers on reactivity of nitric oxide and several of its congeners such as nitroxyl (HNO), nitrite (NO2-), nitrous oxide (N2O) and nitrogen dioxide (NO2) with biomimetic models of copper and zinc enzymes. In addition, metal-free frustrated Lewis pairs are used to capture and activate NO. Tris(pyrazolyl)borate complexes of copper were employed to examine the coordination and NO reactivity of nitrosobenzene (PhNO), an HNO analogue stable towards irreversible dimerization, that provides insight into how HNO can bind to biologically relevant copper enzymes. Tris(pyrazolyl)borate complexes of zinc were used to model the reactivity of zinc bound nitrite (NO2-) with thiols RS-H that generates S-nitrosothiols RSNO that decompose to NO, outlining a new pathway for NO production from NO2-. Reaction of NO with two coordinate -diketiminato copper complexes was consistent with the production of oxidizing cis-hyponitrite intermediates subject to N2O loss to form copper-oxo species. These studies offer insight into mechanism of anaerobic oxidation of methane catalyzed by nitrite reductase and particulate methane monooxygenase which are both copper based enzymes. Lastly, a phosphorus and boron frustrated Lewis pair was used to capture and activate nitrogen oxides towards hydrogen atom abstraction and other reactions, illustrating new pathways for the metal-free NO reactivity.
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Varonka, Matthew Stephen (Georgetown University, 2009)Nitric oxide (NO) and biologically relevant sources of NO such as S-nitrosothiols (RSNOs) have become a topic of great interest due to their regulation of biological functions including vasorelaxation, neurotransmission, ...
Williams, Kamille D. (Georgetown University, 2016)The N-O functionality is ubiquitous endogenously. The wide range of oxidation states of the nitrogen atom, (+5 to -3), is attributed to the various biologically relevant congeners containing the NO functionality. The ...
Synthetic Models for Copper Electron Transfer Sites and Their Reactivity with Nitric Oxide and Dinitrogen Zhang, Shiyu (Georgetown University, 2015)Nitric oxide (NO) has been recently recognized as an important gaseous signal transmitter that participates in many biological processes, including vasorelaxation, neurotransmission, and immune responses. S-nitrosothiols ...