Open AccessDevelopment and Application of a Peroxyl Radical Clock Approach for Measuring Both Hydrogen-Atom Transfer and Peroxyl Radical Addition Rate Constants
Author(s) -
Quynh Do,
David D. Lee,
Andrew N. Dinh,
Ryan P. Seguin,
Rutan Zhang,
Libin Xu
Publication year - 2020
Publication title -
journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.2
H-Index - 228
eISSN - 1520-6904
pISSN - 0022-3263
DOI - 10.1021/acs.joc.0c01920
Subject(s) - chemistry , hydrogen atom , reaction rate constant , coenzyme q10 , photochemistry , double bond , conjugated system , organic chemistry , kinetics , biochemistry , alkyl , physics , quantum mechanics , polymer
The rate-determining step in free radical lipid peroxidation is the propagation of the peroxyl radical, where generally two types of reactions occur: (a) hydrogen-atom transfer (HAT) from a donor to the peroxyl radical; (b) peroxyl radical addition (PRA) to a "C═C" double bond. Peroxyl radical clocks have been used to determine the rate constants of HAT reactions ( k H ), but no radical clock is available to measure the rate constants of PRA reactions ( k add ). In this work, we modified the analytical approach on the linoleate-based peroxyl radical clock to enable the simultaneous measurement of both k H and k add . Compared to the original approach, this new approach involves the use of a strong reducing agent, LiAlH 4 , to completely reduce both HAT and PRA-derived products and the relative quantitation of total linoleate oxidation products with or without reduction. The new approach was then applied to measuring the k H and k add values for several series of organic substrates, including para- and meta-substituted styrenes, substituted conjugated dienes, and cyclic alkenes. Furthermore, the k H and k add values for a variety of biologically important lipids were determined for the first time, including conjugated fatty acids, sterols, coenzyme Q10, and lipophilic vitamins, such as vitamins D 3 and A.