Kim H, Rosenthal I, Kirschenbaum L J, Riesz P
Radiation Oncology Branch, National Cancer Institute, NIH, Bethesda, MD 20892.
Free Radic Biol Med. 1992 Sep;13(3):231-8. doi: 10.1016/0891-5849(92)90019-d.
The chloroaluminum phthalocyanine tetrasulfonate sensitized photooxidation of ascorbic acid to ascorbate radical (A.-) was followed by electron spin resonance (ESR) spectroscopy. In air saturated aqueous media, steady-state amounts of A.- are rapidly established upon irradiation. The ESR signal disappears within a few seconds after the light is extinguished--more slowly under constant irradiation as oxygen is depleted. No photooxidation was observed in deaerated media. The effect of added superoxide dismutase, catalase, desferrioxamine, and singlet oxygen scavengers (NaN3 and tryptophan) was studied, as was replacement of water by D2O and saturation with O2. The results are indicative of free radical production by direct reaction between ascorbate ion and sensitized phthalocyanine (a Type I mechanism) in competition with the (Type II) reaction of HA- with singlet oxygen, a reaction which does not produce ascorbate radical intermediates.
用电子自旋共振（ESR）光谱法跟踪四磺基氯铝酞菁敏化的抗坏血酸光氧化为抗坏血酸自由基（A.-）的过程。在空气饱和的水性介质中，光照后会迅速建立稳态量的A.-。熄灭光后，ESR信号在几秒钟内消失——在持续光照下，随着氧气消耗，信号消失得更慢。在脱气介质中未观察到光氧化现象。研究了添加超氧化物歧化酶、过氧化氢酶、去铁胺和单线态氧清除剂（NaN3和色氨酸）的影响，以及用D2O代替水和用O2饱和的影响。结果表明，抗坏血酸离子与敏化酞菁之间的直接反应（I型机制）会产生自由基，这与HA-与单线态氧的（II型）反应相互竞争，后一种反应不会产生抗坏血酸自由基中间体。
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