Inner-shell Action Spectroscopy of Trapped Supstance P Peptide Ions and Their Nanosolvated Complexes

We have performed near edge X-ray absorption fine structure action spectroscopy of both bare and nanosolvated gas-phase Substance P peptide ions, by coupling a linear quadrupole ion trap, equipped with an ESI source, to a soft X-ray beamline. By recording tandem mass spectra around the O K-edge of a nanosolvated protonated peptide, we attempted to determine the effects of nanosolvation on the action spectra and the fragmentation pattern. We observed two distinct resonant processes leading to increased water loss from the nanosolvated Substance P, which are related to K-shell excitation of oxygen atoms belonging either to the peptide bond or to the water cluster. Furthermore, we studied peptide fragmentation as a function of the activation photon energy, near the C, N and O K-edges. The fragmentation pattern strongly depends on the activation energy.