Grazing Molecule Excitation as a Tool to Analyse the Amino Acid Sequence in Oligopeptides

A novel mass spectrometric method to analyse the sequence of amino acid residues in oligopeptides is proposed. Amino acid residues in peptide molecules contain chain-like structures of identical CH dipoles (IR antennas), which acquire IR energy quanta by interaction with periodic Coulomb fields and accumulate vibration excitation energy. This can subsequently lead to the dissociation of specific trap bonds inside the peptide molecule. Such excitation and dissociation processes are assumed to occur when peptide ions graze at atomic distance along a set of screened charges on a surface. These processes of grazing molecule excitation (GME) and dissociation (GMD) were applied to analyse sequences of oligopeptides by using TOF mass spectrometry. At specific grazing velocities the experimental fragment ion spectra of oligopeptides must contain a peak of high abundance corresponding to the N-terminal amino acid. This specific property of GMD offers the possibility to determine the amino acid sequence of oligopeptides. 1. Introduction The general interest in peptides has resulted in developments of novel methods to determine or confirm the amino acid sequence. Many of these methods combine matrix-assisted laser desorption/ionization with time-of-flight mass spectrometry (MALDI-TOF MS) [1–5]. As pointed out in these articles, the developed methods can serve to obtain peptide sequence information, which can be ambiguous yet, if used for an unknown peptide. A method to determine sequences of amino acid residues in oligopeptides is suggested here, which is a practical application of GMD induced by IR photons [6–9]. The basis of the method is a special vibrational excitation process, which occurs to peptide molecules irradiated by IR photons. The main condition for excitation and dissociation of the molecules is the presence of chain-like substructures in these molecules. These chains are supposed to consist of periodically located diatomic valence group dipoles like (CH2) , which can serve as antennas for external radiation in the IR frequency range. In the presented method the periodical Coulomb field is used experienced by grazing molecules, which are sliding at a velocity below Bohr velocity along a set of four or more screened atomic charges of surface atoms [7]. The resulting excitation is equivalent to IR photon irradiation. In our experimental device, projectile molecules are grazing parallel to the surface for approximately 100？？ during a time period of about 10？12？s at a minimum distance of about 2？？ from the surface. The velocity component of the grazing