Probing lipid peroxidation by using linoleic acid and benzophenone

Inmaculada Andreu, Dmytro Neshchadin, Enrique Rico, Markus Griesser, Abdelouahid Samadi, Isabel M. Morera, Georg Gescheidt, Miguel A. Miranda

Research output: Contribution to journalArticlepeer-review

10 Citations (Scopus)

Abstract

A thorough mechanistic study has been performed on the reaction between benzophenone (BZP) and a series of 1,4-dienes, including 1,4-cyclohexadiene (CHD), 1,4-dihydro-2-methylbenzoic acid (MBA), 1,4-dihydro-1,2-dimethylbenzoic acid (DMBA) and linoleic acid (LA). A combination of steady-state photolysis, laser flash photolysis (LFP), and photochemically induced dynamic nuclear polarization (photo-CIDNP) have been used. Irradiation of BZP and CHD led to a cross-coupled sensitizer-diene product, together with 6, 7, and 8. With MBA and DMBA as hydrogen donors, photoproducts arising from cross-coupling of sensitizer and diene radicals were found; compound 7 was also obtained, but 6 and o-toluic acid were only isolated in the irradiation of BZP with MBA. Triplet lifetimes were determined in the absence and in the presence of several diene concentrations. All three model compounds showed similar reactivity (k q≈10 8 M -1 s -1) towards triplet excited BZP. Partly reversible hydrogen abstraction of the allylic hydrogen atoms of CHD, MBA, and DMBA was also detected by photo-CIDNP on different timescales. Polarizations of the diamagnetic products were in full agreement with the results derived from LFP. Finally, LA also underwent partly reversible hydrogen abstraction during photoreaction with BZP. Subsequent hydrogen transfer between primary radicals led to conjugated derivatives of LA. The unpaired electron spin population in linoleyl radical (LA .) was predominantly found on H(1-5) protons. To date, LA-related radicals were only reported upon hydrogen transfer from highly substituted model compounds by steady-state EPR spectroscopy. Herein, we have experimentally established the formation of LA . and shown that it converts into two dominating conjugated isomers on the millisecond timescale. Such processes are at the basis of alterations of membrane structures caused by oxidative stress.

Original languageEnglish
Pages (from-to)10089-10096
Number of pages8
JournalChemistry - A European Journal
Volume17
Issue number36
DOIs
Publication statusPublished - Aug 29 2011
Externally publishedYes

Keywords

  • dienes
  • hydrogen abstraction
  • photochemistry
  • photolysis
  • transient absorption spectroscopy

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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