UV-VUV Photofragmentation Spectroscopy of Isolated Neutral Fragile Macromolecules: A Proof-of-Principle Based on a Deprotonated Vancomycin-Peptide Noncovalent Complex

The gas phase offers the possibility to analyze organic molecules by ultraviolet-vacuum ultraviolet (UV-VUV) spectroscopy without any solvent effect or limitation in terms of spectral range due to absorption by the solvent. Up to now, the size and chemical composition of neutral molecular systems under study have been limited by the use of vaporization methods based on thermal heating. Soft sources of gas-phase thermolabile molecular systems such as electrospray or matrix-assisted laser desorption ionization are appealing alternatives to heating-based techniques, but they lead to the production of ions. In such cases, UV-VUV action spectroscopy is then the method of choice to study the electronic structure and corresponding photodynamics of these gas-phase molecular ions. However, previous investigations have shown that the UV-VUV action spectrum of a given molecular ion depends on the charge state, which in many cases might be a caveat. Here, by means of synchrotron radiation coupled to mass spectrometry and through the test case of the glycopeptide antibiotic vancomycin noncovalently bound to a deprotonated small peptide, we show that the UV-VUV photofragmentation spectrum of neutral thermally fragile organic molecules can be obtained via charge-tagging action spectroscopy.

Automated summary

Gas-phase UV-VUV spectroscopy enables the analysis of organic molecules without solvent effects or limitations in spectral range. Soft sources like electrospray or laser desorption ionization are alternatives to heating-based methods for studying thermolabile molecules, but ion production occurs. UV-VUV action spectroscopy is therefore the preferred method for studying gas-phase molecular ions. However, previous investigations have shown that the UV-VUV action spectrum of a given molecular ion depends on its charge state. Through this study, we demonstrate the use of charge-tagging action spectroscopy to obtain the UV-VUV photofragmentation spectrum of neutral thermally fragile organic molecules.