Internal fragments

Example The FAB-CID-MS/MS spectrum of thymosin-Tl [M+H] quasimolecular ions, m/z 1427.7, as obtained from a magnetic four-sector instrument [144] shows numerous fragment ions due to A-terminal, C-terminal, and internal fragmentations (Fig. 9.18). [145]... 

Up to now, we have seen how the "heuristic principles" can be applied to both linear and cyclic systems which we could call "normal systems". When some unusual structural features -such as quaternary carbon atoms, medium-sized rings or bridged systems- are found in the molecular structure under consideration, one may assume that they are derived either from a rearrangement or from an internal fragmentation [1]. 

Strategies based on rearrangements and internal fragmentations (see also "reconnections") which apply also to sesquiterpenes, polyunsaturated chains (such as squalene, jubavione, etc.). 

Figure 19-19. Product ion mass spectrum of the hnear nonapeptide (HLLFHWAVG-NHNH2).The peaks marked with an asterisk represent bn-H20 ions, whereas the peaks marked with a black square represent the internal fragment ions. (Reprinted from reference 102, with permission of Elsevier Science, Inc.)...

Figure 11 Formation of immonium ion and internal fragments. The immonium ions provide a clue to the composition of the peptide. Reproduced from C. Dass, Fundamentals of Contemporary Mass Spectrometry, Wiley-lnterscience Floboken, NJ, 2007, with permission from Wiley-lnterscience, Copyright 2007.

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