On the direct scavenging activity of melatonin towards hydroxyl and a series of peroxyl radicals
On the direct scavenging activity of melatonin towards hydroxyl and a series of peroxyl radicals
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DOI：
10.1039/c0cp02801k
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发表时间：
2011-01-01
影响因子：
3.3
通讯作者：
Galano, Annia
中科院分区：
文献类型：
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作者：
Galano, Annia
用密度泛函理论，特别是M05-2X泛函方法研究了褪黑素(MLT)与羟基和几种过氧基的反应。自由基加合物形成(RAF)、氢原子转移(HAT)、单电子转移(SET)、顺序电子质子转移(SEPT)和质子耦合电子转移(PCET)是五种反应机理。研究发现，MLT与OH自由基的反应是扩散受限的，与环境的极性无关，表明MLT是一种很好的OH自由基清除剂。计算得到MLT+(OH)-O-中心点反应在苯和水溶液中的总速率系数分别为2.23×10~(10)和1.85×10~(10)M~(-1)S。MLT也被预测是一种非常好的(OOCCl_3)-O-中心点清除剂，但对于清除活性较弱的过氧基，如烯基过氧基和(OHO)-O-中心点，则效果不佳。因此，MLT对脂质过氧化的保护作用不是通过直接捕获过氧化自由基，而是通过清除更多的活性物质，如(OH)-O-中心点，从而启动降解过程。首次报道了不同反应通道的支化比。在水溶液中，SEPT是MLT+(OH)-O-中心点反应的主要机理，约占MLT对该自由基总反应活性的44.1%。在所研究的过程中，计算数据与现有的实验数据之间的良好一致性支持了本工作所给出的结果的可靠性。
The reactions of melatonin (MLT) with hydroxyl and several peroxyl radicals have been studied using the Density Functional Theory, specifically the M05-2X functional. Five mechanisms of reaction have been considered: radical adduct formation (RAF), Hydrogen atom transfer (HAT), single electron transfer (SET), sequential electron proton transfer (SEPT) and proton coupled electron transfer (PCET). It has been found that MLT reacts with OH radicals in a diffusion-limited way, regardless of the polarity of the environment, which indicates that MLT is an excellent OH radical scavenger. The calculated values of the overall rate coefficient of MLT + (OH)-O-center dot reaction in benzene and water solutions are 2.23 x 10(10) and 1.85 x 10(10) M-1 s(-1), respectively. MLT is also predicted to be a very good (OOCCl3)-O-center dot scavenger but rather ineffective for scavenging less reactive peroxyl radicals, such as alkenyl peroxyl radicals and (OOH)-O-center dot. Therefore it is concluded that the protective effect of MLT against lipid peroxidation does not take place by directly trapping peroxyl radicals, but rather by scavenging more reactive species, such as (OH)-O-center dot, which can initiate the degradation process. Branching ratios for the different channels of reaction are reported for the first time. In aqueous solutions SEPT was found to be the main mechanism for the MLT + (OH)-O-center dot reaction, accounting for about 44.1% of the overall reactivity of MLT towards this radical. The good agreement between the calculated and the available experimental data, on the studied processes, supports the reliability of the results presented in this work.