CHARGE-REMOTE FRAGMENTATION OF PEPTIDES FOLLOWING ATTACHMENT OF A FIXED POSITIVE CHARGE - A MATRIX-ASSISTED LASER DESORPTION IONIZATION POSTSOURCE DECAY STUDY/

A fixed positive charge can be placed at the N-terminus of a peptide b y addition of a tris[(2,4,6-trimethoxyphenyl)phosphonium]acetyl group. The usefulness of these charged derivatives has been demonstrated in fast atom bombardment mass spectrometry and in matrix-assisted laser d esorption/ionization mass spectrometry. After ion formation and accele ration, these derivatized peptide ions dissociate and their fragment i ons can be analyzed in a postsource decay experiment by using a time-o f-flight mass spectrometer. The matrix-assisted laser desorption/ioniz ation-postsource decay spectra are very different from what may be exp ected based on fragment ions observed from protonated peptide molecule s. Cleavage of CHR-C(O) bonds dominates to form a series of a-type ion s. Mechanistic possibilities are evaluated. When aspartic acid residue s are encountered, the chemistry radically changes. This appears to be due to the formation of geometrically accessible intermediates that c an dissociate via low energy processes. This charge-remote chemistry p arallels that for much simpler systems, resulting in spectra that are very easy to interpret. (C) 1997 American Society for Mass Spectrometr y.