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Eur. J. Mass Spectrom. 5, 325 - 334 (1999) |
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Neighboring group versus cis-elimination mechanisms for side chain loss from protonated methionine, methionine sulfoxide and their peptides | ||
Richard A.J. OHair* |
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ABSTRACT: | ||
The gas-phase fragmentation reactions of protonated methionine and methionine containing dipeptides have been compared with their methionine sulfoxide oxidized forms using tandem mass spectrometry (MS/MS). A structurally diagnostic fragment ion for methionine sulfoxide involves side chain loss of neutral CH3SOH. The mechanism for this loss has been probed using a combination of labelling experiments (both deuterium isotope and structural) as well as MS/MS/MS experiments. Charge-directed neighboring group processes compete with or dominate over charge-remote cis eliminations in all cases. | ||
Keywords: vinyl alcohol, photoionization, appearance energy, heat of formation |
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