The unusual fragmentation of long-chain feruloyl esters under negative ion electrospray conditions

Jürgen Schmidt; Dietmar Kuck; Katrin Franke; Haider Sultani; Annegret Laub; Ludger A Wessjohann

doi:10.1002/jms.4357

The unusual fragmentation of long-chain feruloyl esters under negative ion electrospray conditions

J Mass Spectrom. 2019 Jun;54(6):549-556. doi: 10.1002/jms.4357.

Authors

Jürgen Schmidt¹, Dietmar Kuck², Katrin Franke¹, Haider Sultani¹, Annegret Laub¹, Ludger A Wessjohann¹

Affiliations

¹ Department of Bioorganic Chemistry, Leibniz Institute of Plant Biochemistry, Weinberg 3, D-06120, Halle/Saale, Germany.
² Department of Chemistry, Bielefeld University, Universitätsstraße 25, D-33615, Bielefeld, Germany.

PMID: 30912235
DOI: 10.1002/jms.4357

Abstract

Long-chain ferulic acid esters, such as eicosyl ferulate (1), show a complex and analytically valuable fragmentation behavior under negative ion electrospay collision-induced dissociation ((-)-ESI-CID) mass spectrometry, as studied by use of a high-resolution (Orbitrap) mass spectrometer. In a strong contrast to the very simple fragmentation of the [M + H]⁺ ion, which is discussed briefly, the deprotonated molecule, [M - H]^- , exhibits a rich secondary fragmentation chemistry. It first loses a methyl radical (MS² ) and the ortho-quinoid [M - H - Me]^-• radical anion thus formed then dissociates by loss of an extended series of neutral radicals, C_n H_{2n + 1} ^• (n = 0-16) from the long alkyl chain, in competition with the expulsion of CO and CO₂ (MS³ ). The further fragmentation (MS⁴ ) of the [M - H - Me - C₃ H₇ ]^- ion, discussed as an example, and the highly specific losses of alkyl radicals from the [M - H - Me - CO]^-• and [M - H - Me - CO₂ ]^-• ions provide some mechanistic and structural insights.

Keywords: fragmentation of radical anions in the MS3 mode; long-chain feruloyl esters; long-range hydrogen transfer; negative ion electrospray tandem mass spectrometry; quinone radical anions.