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Description
Lipids are essential for all forms of life. They constitute the scaffold of every cell membrane, act as hormones, secondary messengers, and energy storage for times of famine. The functional diversity of lipids goes hand in hand with a huge structural diversity and heterogeneity. One major challenge in the analysis of lipids is the existence of isomers – molecules with different structures even though being composed of identical atoms. Being able to distinguish between isomers is crucial because in many cases, each isomer fulfills a specific biological function.
Here, the potential of cryogenic gas-phase infrared spectroscopy to analyze lipid isomers is investigated. The technique is based on technology from the field of mass spectrometry and employs an infrared free-electron laser as a powerful light source. Irradiation of lipids in helium droplets with infrared light induces molecular vibrations that yield unique fingerprints for each molecule. An exceptionally high spectral resolution is achieved by the narrow bandwidth of the laser, the cryogenic temperatures, and by the fact that isolated lipids are investigated in the gas phase, which inhibits intermolecular interactions and thus spectral broadening.
The results show that gas-phase infrared spectroscopy is able to distinguish various kinds of isomers in different lipid classes that are difficult if not impossible to distinguish using established workflows for lipid analysis [1-3]. The hyphenation of spectroscopy with mass spectrometry can therefore significantly contribute to reliable identification of isomers. In addition, it can be employed to study lipid fragmentation mechanisms in the mass spectrometer [4]. The implementation of the technique into commercial instruments will be the next challenge in the rapidly developing field of gas-phase infrared spectroscopy for biomolecular analysis.
References:
[1] C. Kirschbaum, E. M. Saied, K. Greis, E. Mucha, S. Gewinner, W. Schöllkopf, G. Meijer, G. von Helden, B. L. J. Poad, S. J. Blanksby, C. Arenz, K. Pagel, Angew. Chem. Int. Ed. 59, 13638-13642 (2020).
[2] C. Kirschbaum, K. Greis, M. Lettow, S. Gewinner, W. Schöllkopf, G. Meijer, G. von Helden, K. Pagel, Anal. Bioanal. Chem. 413, 3643-3653 (2021).
[3] C. Kirschbaum, K. Greis, E. Mucha, L. Kain, S. Deng, A. Zappe, S. Gewinner, W. Schöllkopf, G. von Helden, G. Meijer, P. B. Savage, M. Marianski, L. Teyton, K. Pagel, Nat. Commun. 12, 1201 (2021).
[4] C. Kirschbaum, K. Greis, L. Polewski, S. Gewinner, W. Schöllkopf, G. Meijer, G. von Helden, K. Pagel, J. Am. Chem. Soc. 143, 14827-14834 (2021).
