Fragmentation of deprotonated diacylhydrazine derivatives in electrospray ionization tandem mass spectrometry: generation of acid anions via intramolecular rearrangement

• Published in: PloS one Vol. 8; no. 5; p. e63097
• Main Authors: Jiang, Kezhi, Zhang, Hu, Wang, Jianmei, Li, Fei, Qian, Mingrong
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 21-05-2013; Public Library of Science (PLoS)
• Subjects: Acids; Acids - chemistry; Alkenes; Anions; Anions - chemistry; Benzoates - chemistry; Carbon dioxide; Carbonyls; Chemistry; Density functional theory; Derivatives; Dissociation; Electrospraying; Experiments; Fragmentation; Hydrazines - chemistry; Ionization; Ions; Laboratories; Mass spectrometry; Mass spectroscopy; Mathematical analysis; Metabolites; Models, Molecular; Molecular Conformation; Molecular ions; Molecular Weight; Pesticides; Protons; Scientific imaging; Software packages; Spectrometry, Mass, Electrospray Ionization; Spectroscopy; Thermodynamics
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0063097

The gas-phase fragmentation pathways of deprotonated diacylhydrazine derivatives (R1(C = O)-N(t-Bu)NH(C = O)R2, Compounds 1-6) were investigated by the combination of electrospray ionization tandem mass spectrometry (ESI-MS/MS) and theoretical calculations. Upon collisional activation, the deprotonated molecular ions [M - H](-) dissociate in two reaction channels, both of which involve intramolecular rearrangement. The main product ion is confirmed to be an anionic acid species, [R1-CO2](-), generated through intramolecular rearrangement of [M - H](-) initiated by the nucleophilic attack of the amide O6 on the carbonyl C2 (Path-1). The minor fragment channel (Path-2) involves methylpropene elimination of the precursor ion, followed by a similar nucleophilic displacement reaction to produce another acid anion [R2-CO2](-). Density functional theory calculations at the B3LYP/6-31+G(d,p) level indicate that Path-1 is more favorable than Path-2 for dissociation of the deprotonated halofenozide.