Laser-Induced Oxidation of Cholesterol Observed During MALDI-TOF Mass Spectrometry
Laser-Induced Oxidation of Cholesterol Observed During MALDI-TOF Mass Spectrometry
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DOI：
10.1007/s13361-011-0074-3
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发表时间：
2011-04-01
影响因子：
3.2
通讯作者：
Cole, Richard B.
中科院分区：
文献类型：
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作者：
McAvey, Kevin M.;Guan, Bing;Cole, Richard B.
三个奇电子胆固醇氧化峰的检测条件进行了测定，这些峰被证明是文物的基质辅助激光解吸飞行时间（MALDI-TOF）过程。基质的选择，溶剂，激光强度和胆固醇浓度进行了系统的变化，以表征导致最高信号的自由基阳离子峰的条件，并发现初始胆固醇溶液浓度和所得的密度的固体胆固醇的MALDI目标是重要的参数，在确定信号强度。有人提出，羟基自由基，产生的结果，激光照射所采用的2，5-二羟基苯甲酸（DHB）矩阵，启动胆固醇氧化的MALDI目标。尝试诱导奇电子氧化峰，通过添加氧化剂成功地使用DHB，胆固醇和枯烯氢过氧化物的乙腈溶液。此外，自由基清除剂的加入在一定条件下降低了一些氧化产物的丰度。这些结果与本文提出的氧化机制一致，该机制涉及激光诱导的羟基自由基产生，然后攻击中性胆固醇。羟基自由基的生产后照射的地蒽酚基质也可能是负责通过类似的机制从胆固醇地蒽酚中观察到的相同的自由基峰的生成。
Conditions for the detection of three odd-electron cholesterol oxidation peaks were determined and these peaks were shown to be artifacts of the matrix-assisted laser desorption time of flight (MALDI-TOF) process. Matrix choice, solvent, laser intensity and cholesterol concentration were systematically varied to characterize the conditions leading to the highest signals of the radical cation peaks, and it was found that initial cholesterol solution concentration and resultant density of solid cholesterol on the MALDI target were important parameters in determining signal intensities. It is proposed that hydroxyl radicals, generated as a result of laser irradiation of the employed 2, 5-dihydroxybenzoic acid (DHB) matrix, initiate cholesterol oxidation on the MALDI target. An attempt to induce the odd-electron oxidation peaks by means of adding an oxidizing agent succeeded using an acetonitrile solution of DHB, cholesterol, and cumene hydroperoxide. Moreover, addition of free radical scavengers reduced the abundances of some oxidation products under certain conditions. These results are consistent with the mechanism of oxidation proposed herein involving laser-induced hydroxyl radical production followed by attack on neutral cholesterol. Hydroxyl radical production upon irradiation of dithranol matrix may also be responsible for generation of the same radical peaks observed from cholesterol in dithranol by an analogous mechanism.