Structural characterization of tailed picket-fence porphyrins by high-energy fast atom bombardment collision-induced dissociation mass spectrometry/mass spectrometry

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Eur. J. Mass Spectrom. 3, 291 - 299 (1997)

Structural characterization of tailed picket-fence porphyrins by high-energy fast atom bombardment collision-induced dissociation mass spectrometry/mass spectrometry

Toshimichi Shibue^* and Hisashi Kambe
Materials Characterization Central Laboratory, Waseda University, Tokyo, Japan.
Hiroyuki Nishide
Department of Applied Chemistry, Waseda University, Tokyo, Japan.
Satoko Akashi and Naoshi Dohmae
The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama, Japan.
Yoko Ohashi
Glycobiology Research, Frontier Research Program, The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama, Japan.

ABSTRACT:

The applicability of high-energy fast atom bombardment (FAB) collision-induced dissociation mass spectrometry/mass spectrometry (CID-MS/MS) to the structural characterization of side-chains of porphyrin derivatives with a tailed picket-fence structure was examined. These porphyrins showed a molecular ion [M]^+" as well as a protonated molecule [M+H]⁺ and another at [M+2]⁺ in the positive ion mode. Doubly-charged ions were observed when the tail has an imidazole ring. The linked-scan spectrometry indicated that the tail of the porphyrin is eliminated first as a neutral species from the pyrrole-2-position as a b-type cleavage, after which each of the four pivaloyl picket-fences are cleaved off in series from the remainder of the molecule-related ions. The spectrum also clearly showed charge-remote product ions in the low mass region, in addition to charge-mediated product ions representing the precise side chain structure of the tailed picket-fence porphyrin. FAB CID-MS/MS spectra of [M]^+", [M+1]⁺ and [M+2]⁺, using the EBEB-type four-sector tandem mass spectrometer, show similar fragmentation patterns to each other with 1 u difference in parallel. The CID-MS/MS of [M+1]⁺ and [M+2]⁺ showed higher product ion intensities than the corresponding product ion intensities of [M]^+". CID-MS/MS, using an EBEB-type four-sector tandem mass spectrometer, showed charge-remote product ions much more clearly than those observed in B/E-constant linked-scan spectra.

Keywords: Tailed picket-fence porphyrin, picket-fence porphyrin, porphyrins, fast atom bombardment, collision-induced dissociation, collision activation, tandem mass spectrometry, linked-scanning, charge-remote fragmentation, doubly-charged ion.

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