FRAGMENTATION REACTIONS OF PROTONATED ALPHA-AMINO-ACIDS

The metastable ion fragmentation reactions of protonated alpha-amino a cids were recorded. In addition, the low-energy collision-induced diss ociation (CID) reactions were studied as a function of collision energ y and breakdown graphs, expressing the energy dependence of the fragme ntation reactions, were established for a variety of protonated amino acids. The fragmentation reactions observed depend strongly on the ide ntity of the R group in H2NCH(R)COOH. Protonated amino acids containin g only alkyl groups in the side-chain fragment primarily by eliminatio n of (H2O + CO) in both metastable and CID reactions. Hydroxylic and a cidic amino acids show loss of H2O and loss of (H2O + CO) from MH(+) w ith the H2O loss occurring from the side-chain and (H2O + CO) loss occ urring from the alpha-carbohydroxy group. Amidic amino acids show NH3 loss from the side-chain and (H2O + CO) loss from the carbohydroxy gro up. Aromatic and sulfur-containing amino acids show loss of NH3 from M H(+), as does lysine. Protonated arginine shows a variety of fragmenta tion pathways, including elimination of NH3, elimination of neutral gu anidine and formation of protonated guanidine. The energy-dependent br eakdown graphs elucidate a variety of secondary fragmentation reaction s of the primary fragment ions.