Schaich K M, Borg D C
Department of Food Science, Rutgers University, New Brunswick, New Jersey 08903.
Free Radic Res Commun. 1990;9(3-6):267-78. doi: 10.3109/10715769009145685.
Studies documenting spin trapping of lipid radicals in defined model systems have shown some surprising solvent effects with the spin trap DMPO. In aqueous reactions comparing the reduction of H2O2 and methyl linoleate hydroperoxide (MLOOH) by Fe2+, hydroxyl (HO.) and lipid alkoxyl (LO.) radicals produce identical four-line spectra with line intensities 1:2:2:1. Both types of radicals react with commonly-used HO. scavengers, e.g. with ethanol to produce .C(CH3)HOH and with dimethylsulfoxide (DMSO) to give .CH3. However, DMSO radicals (either .CH3 or .OOCH3) react further with lipids, and when radicals are trapped in these MLOOH systems, multiple adducts are evident. When acetonitrile is added to the aqueous reaction systems in increasing concentrations, .CH2CN radicals resulting rom HO. attack on acetonitrile are evident, even with trace quantities of that solvent. In contrast, little, if any reaction of LO. with acetonitrile occurs, even in 100% acetonitrile. A single four-line signal persists in the lipid systems as long as any water is present, although the relative intensity of the two center lines decreases as solvent-induced changes gradually dissociate the nitrogen and beta-hydrogen splitting constants. Extraction of the aqueous-phase adducts into ethyl acetate shows clearly that the identical four-line spectra in the H2O2 and MLOOH systems arise from different radical species in this study, but the lack of stability of the adducts to phase transfer may limit the use of this technique for routine adduct identification in more complex systems. These results indicate that the four-line 1:2:2:1, aN = aH = 14.9 G spectrum from DMPO cannot automatically be assigned to the HO. adduct in reaction systems where lipid is present, even when the expected spin adducts from ethanol or DMSO appear confirmatory for HO.. Conclusive distinction between HO. and LO. ultimately will require use of 13C-labelled DMPO or HPLC-MS separation and specific identification of adducts when DMPO is used as the spin trap.
记录在特定模型系统中脂质自由基自旋捕获的研究表明，自旋捕获剂DMPO存在一些令人惊讶的溶剂效应。在水相反应中，比较Fe2+还原H2O2和亚油酸甲酯氢过氧化物（MLOOH）时，羟基（HO·）和脂质烷氧基（LO·）自由基产生相同的四线谱，谱线强度为1:2:2:1。这两种自由基都与常用的HO·清除剂反应，例如与乙醇反应生成·C(CH3)HOH，与二甲基亚砜（DMSO）反应生成·CH3。然而，DMSO自由基（·CH3或·OOCH3）会进一步与脂质反应，当自由基在这些MLOOH系统中被捕获时，会出现多个加合物。当向水相反应体系中逐渐增加乙腈浓度时，即使只有微量该溶剂，由HO·攻击乙腈产生的·CH2CN自由基也很明显。相比之下，即使在100%乙腈中，LO·与乙腈的反应也很少发生。只要有水存在，脂质系统中就会持续出现单一的四线信号，尽管随着溶剂诱导的变化逐渐使氮和β-氢分裂常数解离，两条中心线的相对强度会降低。将水相加合物萃取到乙酸乙酯中清楚地表明，在本研究中，H2O2和MLOOH系统中相同的四线谱源于不同的自由基物种，但加合物对相转移缺乏稳定性可能会限制该技术在更复杂系统中用于常规加合物鉴定的应用。这些结果表明，在存在脂质的反应体系中，来自DMPO的四线1:2:2:1、aN = aH = 14.9 G谱不能自动归属于HO·加合物，即使来自乙醇或DMSO的预期自旋加合物似乎证实了HO·的存在。最终，要明确区分HO·和LO·，当使用DMPO作为自旋捕获剂时，将需要使用13C标记的DMPO或HPLC-MS分离并对加合物进行特异性鉴定。
