A gas phase approach for glycan analysis: Combining ultrahigh-resolution ion mobility spectrometry with cryogenic vibrational spectroscopy

The last decades have been punctuated by the development of revolutionary analytical technologies that have enabled the analysis of biomolecular structures and unraveled the roles they play in biological systems. However, certain classes of biomolecules remain less understood than others. In fact, despite being among the most abundant molecules on our planet, glycans remain among the least understood class of biological macromolecules due to their highly complex structure. The complexity of glycan molecules arises from their isomeric nature, which poses a significant challenge to classical analytical tools. The advent of ionization methods such as ESI and MALDI has led to an unprecedented expansion of gas phase techniques for the analysis of biomolecules. Compared to condensed phase approaches, gas phase analysis allows for isolating specific molecules and collecting highly accurate and specific structural information. In this work, we present an analytical approach for the analysis of glycan molecules based on the combination of different gas phase techniques. A central part of this thesis is the development, design, and characterization of two new instruments that have the capabilities to identify glycan isomers unambiguously. Our experimental approach is based on the combination of high-resolution ion mobility spectrometry with cryogenic IR spectroscopy. Ion mobility spectrometry allows to separate charged molecules in the gas phase according to their overall shape, serving as an isomer-selective prefilter to the IR spectroscopic interrogation process. While IMS provides a way to separate glycan isomers, vibrational spectroscopy is used to identify the mobility-separated molecules. The IR absorptions characteristic of glycan molecules lead to distinct spectroscopic fingerprints, which are perfectly suited for the identification of glycan isomers. In the first part of this work, we report the modification of an existing instrument that combined drift tube IMS with IR spectroscopy. We replaced the drift tube section by IMS device employing a relatively novel technique called SLIM, which provides the highest mobility resolution reported to date while ensuring a minimum loss of ions. This prototype instrument was used in a series of proof-of-concept experiments where we successfully demonstrate that our approach provides highly accurate results, comparable to sophisticated double-resonance spectroscopic schemes. We also describe an analytical protocol that serves to identify the isomeric content of disaccharide and tetrasacharide mixtures unambiguously, using a database approach. Furthermore, we report a series of experiments in which we separate and identify the anomers of disaccharides. In the second part of the thesis, we describe a second-generation instrument based on the same approach. The design of this instrument was aimed at maximizing its sensitivity and throughput while adding more analytical functionalities. It includes a CID section, as well as a cryogenic multi-trap allowing for the multiplexed spectroscopic analysis of glycan isomers. We hereby report the characterization results highlighting the instrument capabilities in terms of ion transmission and IMS resolution. We also report the first rapid, multiplexed, IR spectral acquisition of two tetrasacharide isomers, which emphasizes the unique capabilities of this home-built instrument.