Egorov, D.; Bari, S.; Boll, R.; Dörner, S.; Deinert, S.; Techert, S.; Hoekstra, R.; Zamudio-Bayer, V.; Lindblad, R.; Bülow, C.; Timm, M.; von Issendorff, B.; Lau, J.T.; Schlathölter, T.: Near-Edge Soft X-ray Absorption Mass Spectrometry of Protonated Melittin. Journal of The American Society for Mass Spectrometry 29 (2018), p. 2138–2151
10.1007/s13361-018-2035-6
Open Access Version
Abstract:
We have investigated the photoionization and photofragmentation yields of gas-phase multiply protonated melittin cations for photon energies at the K-shell absorption edges of carbon, nitrogen, and oxygen. Two similar experimental approaches were employed. In both experiments, mass selected [melittin+qH]q+ (q=2–4) ions were accumulated in radiofrequency ion traps. The trap content was exposed to intense beams of monochromatic soft X-ray photons from synchrotron beamlines and photoproducts were analyzed by means of time-of-flight mass spectrometry. Mass spectra were recorded for fixed photon energies, and partial ion yield spectra were recorded as a function of photon energy. The combination of mass spectrometry and soft X-ray spectroscopy allows for a direct correlation of protein electronic structure with various photoionization channels. Non-dissociative single and double ionization are used as a reference. The contribution of both channels to various backbone scission channels is quantified and related to activation energies and protonation sites. Soft X-ray absorption mass spectrometry combines fast energy deposition with single and double ionization and could complement established activation techniques.