PROBING THE STRUCTURAL CHANGES AND REACTIVITY OF IONS ON WELL-DEFINED INTERFACES PREPARED USING ION SOFT LANDING
Creators: name: Oviedo, Hugo Yuset Samayoa
Publisher: name: Purdue University Graduate School
Year: 2024
Subjects: classificationCode: 340199
subject: Analytical chemistry not elsewhere classified
classificationCode: 340699
subject: Physical chemistry not elsewhere classified

description: Interfaces play an important role in a broad range of physical, chemical, and biochemical processes. For example, nutrient transport from and to cells happens at the cellular membrane interface, the corrosion of metals occurs due to chemical reactions at the solid/air interface, and the development of waterproof clothing relies on the modification of the clothing surface with hydrophobic species. The importance and complexity of interfaces make a detailed understanding of the interfacial physicochemical processes central to both the fundamental science and the development of new technologies. Specifically in the fields of energy storage/production and heterogeneous catalysis, understanding the transformations of the active species on surfaces leads to the development of high-performance, stable interfaces. In the thesis presented herein, ion soft landing was used as a preparative technique to understand the chemical changes that ions undergo on surfaces. Ion soft landing is a mass spectrometry technique in which polyatomic ions are deposited onto surfaces while preserving their chemical structure and charge state. The advantage of using ion soft landing to study interfaces is that it enables the preparation of well-defined ionic interfaces by the deposition of mass-selected ions on a defined surface area with high control over the amount of deposited material. Because ion soft landing uses purified ion beams formed in the gas phase, it also allows to study the chemical properties of the analytes in the absence of counterions or solvent molecules. Collectively, these capabilities make ion soft landing a powerful approach for preparing ionic interfaces and studying their chemical properties. A new direction in ion soft landing research takes advantage of gas phase ion chemistry techniques, such as collision-induced dissociation, to generate well-defined reactive fragment ions as unique building blocks for studying chemistry at interfaces. <b>Chapter 2 </b>of this thesis discusses the development of an ion soft landing instrument that enables high transmission of fragment ions for their deposition onto surfaces. Ion soft landing of reactive fragment ions opens up possibilities for studying their stability and reactivity on surfaces providing a path to the controlled preparation of unique ionic interfaces. <b>Chapters 3 </b>and <b>4 </b>describe an unusual spontaneous ligand loss observed for soft landed [Ni(bpy)<sub>3</sub>]<sup>2+0</sup>, an ion of interest in the field of catalysis, and its stabilization by codeposition with anions. We compared the reactivity of [Ni(bpy)<sub>3</sub>]<sup>2+ </sup>on surfaces against that of [Ni(bpy)<sub>2</sub>]<sup>2+ </sup>and [Ni(bpy)]<sup>+ </sup>species (both formed by ligand removal in the gas phase). This comparison indicates that the dissociation of [Ni(bpy)<sub>3</sub>]<sup>2+</sup> occurs both due to its reorganization on a surface and by charge-reduction. Both processes substantially reduce ligand binding energy and facilitate ligand loss from the complex.<b>Chapter 5 </b>diverges from ion soft landing and instead presents a gas-phase ion chemistry study on the stability of cucurbituril-viologen host-guest complexes to better understand the intrinsic properties that influence the strength of their interaction. We found that there is a “perfect fit” size of the host that maximizes interactions with the guest thus increasing its stability. In addition, guests of smaller sizes that are better incorporated into the host have a substantial stability compared to those that have functional groups extending outside of the protecting cavity of the host. The results of this work reveal a strategy to stabilize viologens in the gas phase for the preparation of functional interfaces using ion soft landing.Finally, <b>Chapter 6 </b>shows the results of a work at the teaching/learning interface, specifically regarding an undergraduate research project developed for the Analytical Chemistry I course (CHM323) at Purdue University. The goal of this project was to further develop students’ scientific skills on planning, problem-solving, and critical thinking to assess the performance of two analytical techniques. Specifically, the project described in <b>Chapter 6 </b>was designed in such a way that students had to do research on appropriate analytical techniques to quantify ascorbic acid in an unknown sample, propose an experimental protocol, perform it in the laboratory, and concisely summarize the results of their work in a lab report.In summary, the work presented in this thesis encompasses three areas. First, it shows the advantages of using fragment ions produced in the gas phase to study the complex physicochemical processes occurring at interfaces. Second, it presents a study on the gas-phase stability of viologen-based host-guest complexes with the prospect of making viologens accessible for the preparation of functional interfaces using ion soft landing. Finally, it describes an undergraduate laboratory project aimed at developing the scientific skills of students in an analytical chemistry course.