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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Absolute Rate Constants of Elementary Reaction Steps in Radiation-Induced Peroxidation of Unsaturated Fatty Acids
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Absolute Rate Constants of Elementary Reaction Steps in Radiation-Induced Peroxidation of Unsaturated Fatty Acids

机译：辐射诱导的不饱和脂肪酸过氧化中基本反应步骤的绝对速率常数

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Initial radiation-chemical yields of peroxidation in the homologous series of unsaturated free fatty acids were measured in neat substrates by steady-state irradiation with ~(60)Co γ rays to obtain baseline values of oxidizability pertaining to a pure lipid moiety at 293 K for oleic (OlH), linoleic (LiH), linolenic (LinH), and arachidonic (ArH) acid. Rate constants of individual reaction steps of peroxidation, propagation and termination, were also measured in the same compounds by intermittent irradiation with ~(60)Co gamma rays by means of a specially built apparatus. The values of these rate constants were found to double as the number of methylenic carbons increased by one so that the relative values of oxidizabilities in the series LiH/LinH/ArH/docosapentaenoic acid (DPA)/docosahexaenoic acid (DHA) increased as 1:2~(1/2):2 : 2~(1/2):4. Literature data on oxidizabilities and the pertaining rate constants were subject to scaling with respect to temperature and solvent effects. Consistent baseline values of these quantities were obtained, indicating that an adequate understanding of the applied corrections was reached. Radiation-induced peroxidation inhibited by a reference antioxidant α-tocopherol gave radiation-chemical yield of alkyl free radicals G(L~·) = 0.52 ± 0.16 μmol/J in all fatty acids studied. Temperature dependence of the literature data on k_p/k_(inh), corrected for solvent polarity effect on k_p, together with our own measurements of k_(inh) gave Arrhenius activation parameters for the inhibition reaction in pure lipid moiety. The activation energy of the reaction, 4.5 kJ/mol, large negative entropy, -138 J/mol K, and pre-exponential factor 10~6 support the view that the mechanism of α-toc action in nonpolar media may involve both charge and proton transfer.
机译：在纯底物中，通过〜（60）Coγ射线的稳态辐射，在纯净的底物中测量了过氧化物在同源系列中的过氧化反应的初始辐射化学收率，以获得与293 K下纯脂质部分有关的可氧化性基线值。油酸（OlH），亚油酸（LiH），亚麻酸（LinH）和花生四烯酸（ArH）酸。在相同的化合物中，还通过专门制造的装置用〜（60）Coγ射线间歇照射，测量了过氧化，扩散和终止的各个反应步骤的速率常数。发现这些速率常数的值随着亚甲基碳原子数的增加而加倍，从而使LiH / LinH / ArH /二十二碳五烯酸（DPA）/二十二碳六烯酸（DHA）系列中的氧化性的相对值增加为1： 2〜（1/2）：2：2〜（1/2）：4。关于氧化性和有关的速率常数的文献数据根据温度和溶剂的影响进行换算。获得了这些量的一致基线值，表明已对所应用的校正方法有了足够的了解。在所有研究的脂肪酸中，参考抗氧化剂α-生育酚抑制的辐射诱导的过氧化反应使烷基自由基的辐射化学收率G（L〜·）= 0.52±0.16μmol/ J。文献数据对k_p / k_（inh）的温度依赖性，针对溶剂极性对k_p的影响进行了校正，再加上我们自己对k_（inh）的测量，为纯脂质部分中的抑制反应提供了Arrhenius活化参数。反应的活化能为4.5 kJ / mol，大的负熵，-138 J / mol K和预指数因子10〜6支持以下观点：非极性介质中α-toc的作用机理可能涉及电荷和电荷。质子转移。

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