Fundamental Study of Gas Phase Ion/Ion Reactions and Mass Spectrometry Instrumentation

Jiexun Bu, Purdue University

Abstract

Bu, Jiexun Ph.D., Purdue University, May 2017. Fundamental Study of Gas Phase Ion/Ion Reactions and Mass Spectrometry Instrumentation. Major Professor: Scott A. McLuckey. Mass spectrometry (MS) is one of the most important analytical tools in various scientific fields, including chemistry, physics, biology, and geology. The work described here covers a set of projects ranging from mass spectrometry instrumentation to fundamental gas phase ion chemistry. Structural information acquired from tandem mass spectrometry is highly dependent on the precursor ion type. Ion/ion reactions have been developed as a widely used technique to convert ion type from one to another. Recently selective covalent ion/ion chemistry has been developed to modify the analyte in the gas phase. A series of calculations and experiments were done to probe the potential energy surface of ion/ion reactions, which leads to a better understanding of ion/ion reaction chemistry and has provided means to predict the reactivity of gas phase reagents. It also provides a theory to guide the experiment in order to achieve higher modification yield in the gas phase. Several projects have been carried out to explore novel ion/ion reactions. Triazoles have been developed as an electrophile to modify basic residues of biomolecules in the gas phase. It shows a higher reactivity compared to the previously developed NHS based reagents. This result matches well to the theoretical calculation. Cycloaddition between azide and alkynes, which is also known as Click Chemistry, is realized in the gas phase as well. Click chemistry is widely used in biological fields. The gas phase coupling provides a new way to probe azides or alkynes by mass spectrometry. The relationship between the solution phase analyte and the gas phase analyte ions is cause for debate. Solvated ions are a good subject to study in order to bridge the gap between the solution phase and the gas phase. Also, many reactions in the solution phase require solvent molecules to proceed, which indicates that solvated ions may have unique gas phase reactivity. These interests lead to an instrumentation project to facilitate the study of solvated ions. In order to trap the solvated ions long enough for an ion trap experiments (hundreds of milliseconds), cooling is required. A liquid nitrogen cooled ion trap was designed and built for this purpose. Preliminary results have been demonstrated. Aside from the ion type, activation methods can also change the structure information acquired via tandem mass spectrometry. Ultraviolet photo dissociation is one of the activation methods that has become a hot topic. A lot of reactions can also be activated by UV photons which meet the group's interest for ion/ion reaction. A series of experiments were done to generate peptide radical ion in the gas phase by UVPD and ion/ion reactions. Those radical ions can be subjected to collision induced dissociation and provide complimentary information compared to its protonated analog. A new instrument was also built to avoid noise problems associated with an older instrument design.

Degree

Ph.D.

Advisors

McLuckey, Purdue University.

Subject Area

Chemistry|Analytical chemistry

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