Surface field activated fragmentation of arginine oligomers.

Protonated arginine oligomers produced by matrix-assisted laser desorption/ionization (MALDI) graze at a kinetic energy of 350 eV along a surface of fluorinated hydrocarbon or mineral oil. The cation fragments activated by excitation processes during the slide on the surface are analyzed by time-of-flight mass spectrometry. The resulting fragment ion mass spectra are interpreted by applying a theoretical concept of excimol accumulation and trap bond dissociation, suggested earlier. According to this theory, energy is accumulated and fragments are formed independently by each arginine residue of a sliding oligomer ion. It is concluded that the observed variation in the fragment ion spectra of the oligomers is a consequence of different oligomer velocities and not a fingerprint of different ion structures.

Grazing incidence surface-induced dissociation of protonated peptides generated by matrix-assisted laser desorption/ionization.

The grazing incidence surface-induced dissociation (GI-SID) of various protonated peptides with typical kinetic energies of 350 eV was investigated. Peptide ions were generated by matrix-assisted laser desorption/ionization (MALDI) using delayed extraction. The collision target surfaces used were aluminum and a liquid film of perfluorinated hydrocarbons. All peptides studied in these experiments showed enhanced fragment ion yields at grazing incidence (GI-SID effect) as observed in our former experiments with other precursor ion types. In general the GI-SID spectra exhibit N-terminal a(1)-type fragment ions, immonium ions and side-chain fragment ions in the low mass-to-charge region. Fragment ion series of the peptide backbone were not observed, which are typical and abundant in the spectra of established fragmentation techniques like collision-induced dissociation, MALDI post-source decay or surface-induced dissociation at steeper angles. The potential of the GI-SID process to yield useful information for primary structure determination of peptides is indicated by the observed differences in the GI-SID spectra of the isomeric dipeptides LR and IR.

Fragmentation of polyatomic molecules by grazing incidence surface-induced dissociation (GI-SID).

The grazing incidence surface-induced dissociation (GI-SID) of n-hexadecylpyridinium and verapamil ions generated by fission fragment desorption was studied. These molecules show the effect of enhanced surface-induced dissociation at grazing incidence as it was observed in former experiments with metal organic ions. A liquid film of perfluorinated polyether is used as collision surface. Small hydrocarbon fragment ions predominate in the GI-SID spectra. Pyridine ions appear as specific fragment ions in the GI-SID spectrum of n-hexadecylpyridinium. The GI-SID conversion efficiency varies in the range 40-70%. The experimental results are discussed within the scope of a quantum mechanical model which is based on the accumulation of internal molecular energy by resonant excitation of collective vibrational states and energy transfer to a trap bond due to dipole-dipole interactions. In this context the GI-SID spectra of n-hexadecylpyridinium and verapamil ions are compared with the fragmentation occurring in regular (252)Cf plasma desorption mass spectrometry.

Fragmentation of molecules sliding along surfaces in the speed range above thermal and below Bohr velocity.

A theoretical model and experimental time-of-flight mass spectrometric data for the fragmentation of molecules grazing along surfaces at velocities v = 10(5)-10(6) cm/s are presented. The effect of enhanced surface-induced dissociation at grazing incidence (GI-SID) is shown for hexadecylpyridine ions. The velocity dependence of the GI-SID fragmentation probability is studied in experiments with adduct ions of cyclodextrin derivatives. Surfaces used in the various collision experiments are aluminum oxide, gold, and a liquid film of perfluorinated polyether. In the theoretical model of the GI-SID effect we consider polyatomic molecules with substructures consisting of chains of identical biatomic dipoles. Because of the interaction with the periodic Coulomb field of the surface, collective vibrational excitations (excimols) are induced in these chains. Energy accumulation of several excimols and a subsequent energy transfer to a trap bond can induce its dissociation. An analytical expression for the velocity dependent GI-SID fragmentation probability is given, which is in good agreement with the experimental data.