Charge-remote and charge-driven fragmentation processes in diacyl glycerophosphoethanolamine upon low-energy collisional activation: A mechanistic proposal

A mechanistic study of diacyl glycerophosphoethanolamine fragmentation unde r low energy collision-activated dissociation with electrospray ionization tandem mass spectrometry is reported. The fragmentation pathways leading to the formation of carboxylate anions (RxCO2-) (x = 1, 2) and the formation of the ions representing neutral loss of ketene ([M - H - R-x'CH=C=O](-)) a re charge-driven processes, which are governed by the gas-phase basicity an d the steric configuration of the molecules. The fragmentation pathway for the formation of the [M - H - RxCO2H](-) ions, reflecting neutral loss of f atty acid, is a charge-remote process, which involves the participation of the hydrogens at C-1 and C-2 of the glycerol, resulting in [M - H - R2CO2H] (-) > [M - H - R1CO2H](-). The preferential formations of R2CO2- > R1CO2-, and of [M - H - R-2'CH=C=O](-) > [M - H - R-1'CH=C=O](-) are attributed to the findings that charge-driven processes are sterically more favorable at sn-2. The observation of the abundance of [M - H - R-x'CH=C=O](-) > [M - H - RxCO2H](-) is attributed to the fact that the [M - H](-) ions of GPE are basic precursor ions, which undergo preferential loss of ketene than loss o f acid. The major pathway for the formation of RxCO2- ions arises from the nucleophilic attack of the anionic charge site of the phosphate on the C-1 or C-2 of the glycerol to render a charge transfer. The sterically more fav orable attack on the C-2 than C-2 of the glycerol results in the abundance of R2CO2- > R1CO2-. These features of tandem spectra readily identify and l ocate the fatty acid substituents of GPE in the glycerol backbone. (J Am So c Mass Spectrom 2000, 11, 892-899) (C) 2000 American Society for Mass Spect rometry.