Towards an anthropogenic nitrogen cycle based on nitrite

Cioncoloni, Giacomo (2018) Towards an anthropogenic nitrogen cycle based on nitrite. PhD thesis, University of Glasgow.

Abstract

The overall goal of this thesis was to investigate the feasibility of a new route to anthropogenic nitrogen fixation based on the oxidation of nitrogen (to give primarily nitrite), and then electrocatalytic conversion of nitrite to other N-containing species of interest, such as nitrate and nitric oxide (NO). In pursuit of this goal, the synthesis of metal-ligand coordination complexes that could act as electrocatalysts for the oxidation of nitrite to nitrate was attempted, as was the synthesis of metal-ligand coordination complexes that could act as electrocatalysts for the reduction of nitrite to NO. As a corollary to this, routes for the initial fixation reaction were also investigated, of which the ultrasonic generation of nitrite from aerated aqueous solutions was found to be the most promising.
The work detailed in this thesis is organized in the following manner: In Chapter 1 we discuss coordination complexes that mimic the enzymes promoting the redox reactions of the nitrogen cycle involving nitrite as a substrate or product. During this introduction we will also give an overview of topics that are relevant to the following chapters, such as proton-coupled-electron transfer and basic kinetic treatment of catalytic reactions.
Chapter 2 is a description of the different techniques used throughout this thesis. Once having set the bases, we shall start with the actual research, which corresponds to Chapters 3 to 6.
Chapter 3 deals with the synthesis, characterization and catalytic properties of a copper coordination compound mimicking the active site of the copper nitrite reductase (CuNiR) class of enzymes. This chapter includes a detailed study of the kinetics and electrocatalytic properties of this complex towards the mono-electronic reduction of nitrite to nitric oxide.
Chapters 4 and 5 deal with the unusual structures and spectroscopic properties of a number of new cobalt complexes that we isolated whilst trying to develop Mo(bis-dithiolene) coordination complexes that might act as analogues of the molybdenum nitrite oxidoreductase (MoNiOR), which oxidises nitrite to nitrate in nature. Our original Mo-containing targets proved impossible to obtain and are not discussed in this thesis. However, we found that cobalt readily makes coordination complexes with these bis-dithiolene ligands, which allowed us to isolate the compounds we present in Chapters 4 and 5. Hence in Chapter 4 we show the synthesis and the solvatochromic properties of mixed-ligand mono-nuclear Co-diimine o-catecholato complexes and compare these complexes with the analogous compounds prepared with o-benzenedithiolato ligands. Chapter 5 then discusses the synthesis and redox properties of a mixed-ligand di-cobalt coordination complex in which the two cobalt centres have (unprecedented) inequivalent metal coordination environments.
Finally, in Chapter 6 we describe a much-underexplored way to fix nitrogen based on a sonochemical reaction. After a brief introduction we describe the optimisation of the procedure and comparisons with previous reports.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Nitrite, nitric oxide, PCET, electrocatalysis, nitrogen fixation, electrochemistry, sonochemistry, solvatochromism.
• Subjects: Q Science > Q Science (General); Q Science > QC Physics; Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Supervisor's Name: Symes, Dr. Mark D.
• Date of Award: 2018
• Depositing User: Giacomo Cioncoloni
• Unique ID: glathesis:2018-30717
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 07 Aug 2018 11:01
• Last Modified: 12 Oct 2018 07:36
• URI: https://theses.gla.ac.uk/id/eprint/30717

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