Diffusion studies show that benzophenone (BP), linoleic acid, and methyl linoleate partition completely into the micelles of phosphate buffer/0.10 M SDS. Water-soluble compounds 4-sulphomethylbenzophenone, sodium salt (BP−), azobis(2-amidinopropane•HCl) (ABAP) and 2,5,7,8-tetramethyl-6-hydroxychroman-2-carboxylate (Trolox) show partial partitioning into the micelles. BP- and BP−-photosensitized oxidation of linoleic acid in 0.50 M SDS exhibited characteristics of free radical chain reactions including: (1) inhibition by phenolic antioxidants, (2) no retardation by singlet oxygen quenchers, and (3) the formation of conjugated hydroperoxides with cis,trans to trans,trans ratios of geometrical isomers typical of autoxidation. Quantitative kinetic studies of the order in substrate, RH, and the rate of chain initiation, Ri, show that the classical rate law, −d[O2]/dt = kp/2kt1/2[RH]Ri1/2 applies to BP-photoinitiated autoxidation of linoleic acid in SDS and the oxidizability (kp/2kt1/2 = 4.42 × 10−2 M−1/2 s−1/2) is the same as that found with a thermal initiator. The rotating sector method gave absolute rate constants for linoleic acid autoxidation in 0.50 M SDS for propagation (kp = 36.2 M−1 s−1) and termination (2kt = 3.52 × 105 M−1 s−1), significantly lower than values in polar organic solvents; attributed to solvation of polar peroxyls in aqueous SDS. Depressed inhibition rate constants (kinh) for α-tocopherol, Trolox, and pentamefhylhydroxychroman (PMHC) in 0.50 M SDS compared to kinh in tert-butyl alcohol are attributed to hydrogen bonding effects on the peroxyl radicals and on the inhibitors.
扩散研究表明,苯甲酮(BP)、
亚油酸和甲基
亚油酸完全分配到
磷酸盐缓冲液/0.10 M
十二烷基硫酸钠(
SDS)的胶囊中。
水溶性化合物4-磺基甲基苯甲酮钠盐(BP
−)、偶氮双(2-
胍基
丙烷•
盐酸)(
ABAP)和2,5,7,8-四甲基-6-羟基
香豆素-2-
羧酸酯(Trolox)部分分配到胶囊中。在0.50 M
SDS中,BP和BP
−光敏氧化
亚油酸表现出自由基链反应的特征,包括:(1)受
酚类抗氧化剂抑制,(2)不受单线态氧猝灭剂延缓,(3)生成具有典型几何异构体cis,trans到trans,trans比例的共轭过氧化物。对底物RH的顺序和链引发速率R
i的定量动力学研究表明,经典速率定律,−d[O
2]/dt = k
p/2k
t1/2[RH]R
i1/2适用于
SDS中BP光引发的
亚油酸自氧化,氧化性(k
p/2k
t1/2 = 4.42 × 10
−2 M
−1/2 s
−1/2)与热
引发剂相同。旋转扇区法给出了在0.50 M
SDS中
亚油酸自氧化的传播(k
p = 36.2 M
−1 s
−1)和终止(2k
t = 3.52 × 10
5 M
−1 s
−1)的绝对速率常数,明显低于极性有机溶剂中的值;归因于
水性
SDS中极性过氧基的溶剂化。在0.50 M
SDS中,α-
生育酚、Trolox和五甲基羟基
香豆素(PMHC)的抑制速率常数(k
inh)较
叔丁醇中的k
inh降低,归因于对过氧基自由基和
抑制剂的氢键效应。