Background:

AAPH is a water-soluble azo compound which is used extensively as a free radical generator, often in the study of lipid peroxidation and the characterization of antioxidants.[1],[2],[3],[4] Decomposition of AAPH produces molecular nitrogen and 2 carbon radicals. The carbon radicals may combine to produce stable products or react with molecular oxygen to give peroxyl radicals. The half-life of AAPH is about 175 hours (37°C at neutral pH), making the rate of free radical generation essentially constant during the first several hours in solution.[5] While AAPH may be used effectively for lipid peroxidation in aqueous dispersions of fatty acids, other radical generators may be better suited for peroxidation studies in lipid micelles or membranes.[6],[7]

Reference:[1]. Noguchi, N., Takahashi, M., Tsuchiya, J., et al. Action of 21-aminosteroid U74006F as an antioxidant against lipid peroxidation Biochemical Pharmacology 55, 785-791 (1998).
[2]. Liu, Z.Q., Yu, W., and Liu, Z.L. Antioxidative and prooxidative effects of coumarin derivatives on free radical initiated and photosensitized peroxidation of human low-density lipoprotein Chemistry and Physics of Lipids 103, 125-135 (1999).
[3]. Rice-Evans, C., and Miller, N. Total antioxidant status in plasma and body fluids Methods in Enzymology 234(24), 279-293 (1994).
[4]. Liégeois, C., Lermusieau, G., and Collin, S. Measuring antioxidant efficiency of wort, malt, and hops against the 2,2'-azobis(2-amidinopropane) dihydrochloride-induced oxidation of an aqueous dispersion of linoleic acid Journal of Agricultural and Food Chemistry 48, 1129-1134 (2000).
[5]. Niki, E. Free radical initiators as source of water- or lipid-soluble peroxyl radicals Methods in Enzymology 186, 100-108 (1990).
[6]. Yamamoto, Y., Haga, S., Niki, E., et al. Oxidation of lipids. V. Oxidation of methyl linoleate in aqueous dispersion Bulletin of the Chemical Society of Japan 57(5), 1260-1264 (1984).
[7]. Culbertson, S.M., and Porter, N.A. Unsymmetrical azo initiators increase efficiency of radical generation in aqueous dispersions, liposomal membranes, and lipoproteins Journal of the American Chemical Society 122, 4032-4038 (2000).