The research in our laboratory focuses on applying mass spectrometry, ion mobility spectrometry, and infrared ion spectroscopy to learn fundamental properties of various types of ions and clusters. These properties include ionization, clustering, and dissociation. We are especially interested in molecular systems with high societal importance, thus our research focuses on three application areas: (1) next-generation ionic liquid-based spacecraft propellants, (2) modified amino acids and peptides, and (3) molecules of significance to cultural heritage studies.
Next-Generation Ionic Liquid-Based Spacecraft Propellants
Room temperature ionic liquids—salts with melting points at or around room temperature have gained a lot of interest in many areas—being used as lubricants, solvents, catalysts, and spacecraft propellants. In general, ionic liquids have high space compatibility because they have a very low vapor pressure, but a wide liquid range. This means that they won’t evaporate into the vacuum of space, but that they can withstand the temperature swings of space without their performance being significantly hindered. One of the areas that ionic liquids are being applied to in the space industry is in the development of safer, “greener” fuels and as propellants in new propulsions systems with new capabilities and benefits. Electrospray thrusters are a new type of propulsion system that uses the same concepts of electrospray ionization and ion acceleration as are used in mass spectrometry ionization sources, but instead of generating an analytical beam, these thrusters generate small amounts of thrust on the spacecraft in the opposite direction as the acceleration of the ejected charged ionic liquid clusters.
The gold standard of fundamental research on the clustering and dissociation of the ionic liquids ejected from electrospray emitters is to be able to fully model these systems in silico. This would allow for novel proposed propellants to be easily and quickly screened and, hopefully eventually, allow for ideal propellants to be found and, eventually, synthesized, tested, and implemented. However, at the current stage of development, it is of utmost importance to produce rigorous experimental data to confirm and evaluate the behaviors of these systems, so that computational methods can be benchmarked against them. Generating some of this benchmarking experimental data is one of the goals of our group.
Determining the ultimate fate of the ionic liquid clusters, cations, and anions once they have been ejected into the vacuum of space is also a problem that needs addressing. Thus, a second goal of this line of work is to evaluate the dissociation channels of these species. The understanding found from this line of work should also have transitional relevance to the analytical and environmental analysis community.
Post-Translational Modifications of Amino Acids and Peptides
In addition to the 20 proteinogenic amino acids, many peptides and proteins contain post-translational modifications to alter their structure and/or function. Often these modifications play significant roles in maintaining normal biological function and/or inducing specific disease states. While the primary structure of proteins and peptides has become rather straightforward to determine using mass spectrometric methods (proteomics, ladder sequencing), post-translational modifications remain much more challenging to identify, localize, and quantify. Our laboratory is especially interested in the analysis of isomers, cases in which “more than mass” is required for positive identification. Thus, our focus is on (1) the differentiation of isobaric modifications (such as differentiating sulfation from phosphorylation) and (2) the characterization of modification site isomers (e.g., sulfopeptides with multiple potential sites of modification, differing only in the site of modification). Since mass alone is usually not enough to make these differentiations confidently, we apply allied techniques—namely ion mobility spectrometry and infrared ion spectroscopy—to try and characterize these species. At this time, we are in the proof-of-principle stages for these technologies applied to these problems. However, the goal of the group is to transition these approaches into routine proteomics analyses, so that the biology community can benefit from the increased specificity provided by these allied techniques.
Molecules of Cultural Heritage Relevance
A third area of focus for our laboratory is on the increased knowledge of the gas-phase behavior of molecules of cultural heritage relevance and on method development for screening and analysis protocols for ancient animal bone samples. The hypothesis is that increased fundamental knowledge of these molecules’ behaviors within mass spectrometers will lead, eventually, to improved analytical approaches to their detection and characterization. Molecule classes of current interest include dyes and collagens. As with the other projects, mass spectrometry, infrared ion spectroscopy, and ion mobility spectrometry will be applied to these questions and challenges.