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MECHANISTIC PROBING OF COMPOUNDS OF BIOLOGICAL AND PHARMACEUTICAL INTEREST BY AMBIENT IONIZATION MASS SPECTROMETRY

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thesis
posted on 28.07.2020 by Tsdale F Mehari

This thesis covers the four topics discussed in each of the following paragraphs. It is unified by the dual ability of ambient ionization mass spectrometry as a useful analytical tool allowing for monitoring of chemical reactions, in addition to its capability to accelerate reaction rates using the same equipment under accelerating or non-accelerating conditions. The ability to manipulate reactions and monitor the subsequent effects to the rate of the reactions can provide vital information for many industrial arenas. Current process analytical technology (PAT) is extremely time-consuming, and typically costly due to dependence on analysis conducted at the end stage of production. Additionally, many chemical reactions found to be useful in pharmaceutical or manufacturing industries are labor intensive and require harsh conditions such as heat or expensive catalysts. Several methods have been developed to overcome these current limitations, while providing vital information on short-lived intermediates, degradation products, and accelerated reaction rates. A sampling device was developed and coupled with nESI allowing for monitoring of heterogeneous chemical reactions by mass spectrometry without the additional requirement of separation (filters, chromatography, etc.) In addition, this technique maintains the high sensitivity, specificity, speed and structural elucidation provided by mass spectrometry analysis. The analysis provided kinetic profiles of all reactants, intermediates, products and coproducts throughout the course of the reaction.

The ability to effectively control chemical reactions and their rates is a priority across several fields of study. Several factors affecting reaction rates, such as heat and catalysts selected, have been well studied. However, there has been recent interest in exploring the capabilities for reaction acceleration in charged microdroplets. It is known that reaction rates on the surface of a droplet greatly differ from reactions occurring in the droplet. The Katritzky transamination reaction was used as a model to identify the effects of the air-solution interface on reaction acceleration by varying the air-liquid surface to volume ratio. The significant increase in reaction rate constants was further enhanced by solid–solution interfacial effects observed after addition of glass nanoparticles.

The effective degradation of non-polar hydrocarbons is an environmental concern as they are the main composition of waste generated from petroleum processing. Saturated alkanes are relatively stable molecules which present a challenge for analysis by mass spectrometry without the use of extreme experimental conditions. A rapid analysis method by paper spray ionization was developed that allows for the oxidation products of saturated alkanes to be monitored by MS in under two minutes. This method relies on the generation of a hydroxyl radical by reacting iron (III) chloride with aqueous hydrogen peroxide on the principle of Fenton’s chemistry. The presence of this radical in direct contact with an alkane produces several oxidation products which can be easily monitored by MS. The reagents are added to a paper triangle sequentially, creating a thin film which allows reaction acceleration in relatively small volumes analyzed directly from paper at atmospheric pressure.

The dimerization of 4-ethynylaniline derivatives in acetonitrile was monitored by nano electrospray ionization mass spectrometry. Dimer products formed by electrocyclization and radical processes were observed that are not detected as a corresponding bulk reaction. This gas-phase reaction has been interrogated in a solution phase analog with radical initiators and characterized by 1H NMR. This work demonstrates that compounds can be synthesized by the electrospray process. Future studies may reveal how this observation affects the interpretation of the MS results involving electrospray.

Funding

National Science Foundation

National Cancer Institute

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History

Degree Type

Doctor of Philosophy

Department

Chemistry

Campus location

West Lafayette

Advisor/Supervisor/Committee Chair

Dr. R. Graham Cooks

Additional Committee Member 2

Dr. Scott McLuckey

Additional Committee Member 3

Dr. Hilkka Kenttamaa

Additional Committee Member 4

Dr. Kavita Shah

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