The structure and fragmentation of Bn(n≥3) ions in peptide spectra

✍ Scribed by Talat Yalcin; Imre G. Csizmadia; Michael R. Peterson; Alex G. Harrison

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 852 KB
• Volume: 7
• Category: Article
• ISSN: 1044-0305
• DOI: 10.1016/1044-0305(95)00677-x

✦ Synopsis

The unimolecular and low energy collision-induced fragmentation reactions of the MI-I+ ions of N-acetyl-tri-alanine, N-acetyl-tri-alanine methyl ester, N-acetyl-tetra-alanine, tetra-alanine, penta-alanine, hexa-glycine, and Leu-enkephalin have been studied with a particular emphasis on the formation and fragmentation of B, (n = 3,4,5) ions. In addition, the metastable ion fragmentation reactions of protonated tetra-glycine, penta-glycine, and Leu-enkephalin amide have been studied. B, ions are prominent stable species in all spectra. The B, ions fragment, in part, by elimination of CO to form A ,, ions; this reaction occurs on the metastable ion time scale with a substantial release of kinetic energy U1,2 = 0.3-0.5 eV) that indicates that a stable configuration of the B,, ion fragments by way of a reacting configuration that is higher in energy than the fragmentation products, An + CO. Ab initio calculations strongly suggest that the stable configuration of the B, and B, ions is a protonated oxazolone formed by interaction of the developing charge with the next-nearest carbonyl group as HX is lost from the protonated species H-(Yyy),,-X * H+. The higher B,, ions also fragment, in part, to form the next-lower B ion, presumably in its stable protonated oxazolone form. This reaction is rationalized in terms of the three-dimensional structure of the B,, ions and it is proposed that the neutral eliminated is an cY-lactam. (