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Probing Lipid Peroxidation by Using Linoleic Acid and Benzophenone
Author(s) -
Andreu Inmaculada,
Neshchadin Dmytro,
Rico Enrique,
Griesser Markus,
Samadi Abdelouahid,
Morera Isabel M.,
Gescheidt Georg,
Miranda Miguel A.
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201100983
Subject(s) - chemistry , benzophenone , photochemistry , hydrogen atom abstraction , radical , flash photolysis , cidnp , ketyl , population , thioxanthone , unpaired electron , diene , triplet state , organic chemistry , reaction rate constant , molecule , kinetics , physics , demography , natural rubber , quantum mechanics , photopolymer , polymerization , polymer , sociology
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.