Thornalley P J, Stern A
Carbohydr Res. 1984 Dec 1;134(2):191-204. doi: 10.1016/0008-6215(84)85037-5.
The production of free radicals during the autoxidation of simple monosaccharides at 37 degrees has been studied by the electron spin resonance (e.s.r.) technique of spin trapping. In the presence of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), monosaccharides undergoing autoxidation produced hydroxyl and 1-hydroxyalkyl radical-derived spin adducts, indicating that hydroxyl and hydroxyalkyl free-radicals are involved in the autoxidation of monosaccharides. The pH profile for the production of free radicals from monosaccharides undergoing autoxidation revealed the formation of both hydroxyl and hydroxyalkyl radicals at relatively high pH, whereas at low pH, only the formation of hydroxyalkyl radicals was observed; the transition between these routes for the production of free radicals occurred at pH 8.0-8.5. Glycolaldehyde, glyceraldehyde, dihydroxyacetone, and erythrose are relatively rapidly enolised (to an ene-diol) and autoxidised with the concomitant production of free radicals. Ribose and glucose enolise and autoxidise very slowly without detectable production of free radicals. A comparison of the pH profiles of the rates of enolisation and the pH dependence of the production of free radicals from glyceraldehyde during autoxidation suggests that a change in reaction mechanism occurs at pH 8.2. Below pH 8.2, the rates of enolisation and autoxidation increase with increasing pH, with a concomitant increase in the formation of hydroxyalkyl spin-adducts. Above pH 8.2, glyceraldehyde undergoing autoxidation shows a much higher rate of enolisation than of autoxidation and, although the formation of hydroxyalkyl radicals is decreased, the production of hydroxyl radicals is also observed. A free-radical mechanism for the autoxidation of monosaccharides is proposed, to account for the pH-dependent characteristics of the production of free radicals and the relationships between the production of free radicals, autoxidation, and enolisation of the monosaccharides.
利用自旋捕集电子自旋共振（e.s.r.）技术，研究了单糖在37℃自动氧化过程中自由基的产生情况。在自旋捕集剂5,5-二甲基-1-吡咯啉N-氧化物（DMPO）存在下，进行自动氧化的单糖产生了羟基和1-羟烷基自由基衍生的自旋加合物，这表明羟基和羟烷基自由基参与了单糖的自动氧化过程。单糖自动氧化产生自由基的pH曲线显示，在相对较高的pH值下会同时形成羟基和羟烷基自由基，而在低pH值下，仅观察到羟烷基自由基的形成；自由基产生途径的转变发生在pH 8.0 - 8.5之间。乙醇醛、甘油醛、二羟基丙酮和赤藓糖相对较快地烯醇化（生成烯二醇）并自动氧化，同时产生自由基。核糖和葡萄糖烯醇化和自动氧化非常缓慢，未检测到自由基的产生。对甘油醛自动氧化过程中烯醇化速率的pH曲线和自由基产生的pH依赖性进行比较表明，在pH 8.2时反应机制发生了变化。在pH 8.2以下，烯醇化和自动氧化速率随pH值升高而增加，同时羟烷基自旋加合物的形成也增加。在pH 8.2以上，进行自动氧化的甘油醛烯醇化速率远高于自动氧化速率，尽管羟烷基自由基的形成减少，但也观察到了羟基自由基的产生。本文提出了单糖自动氧化的自由基机制，以解释自由基产生的pH依赖性特征以及单糖自由基产生、自动氧化和烯醇化之间的关系。
