Methionine, alpha-methylmethionine and S-methylcysteine radical cations: generations and dissociations in the gas phase.
Methionine, alpha-methylmethionine and S-methylcysteine radical cations: generations and dissociations in the gas phase.
复制标题
蛋氨酸、α-甲基蛋氨酸和 S-甲基半胱氨酸自由基阳离子：气相中的生成和解离。
DOI：
10.1039/b905615g
复制
发表时间：
2009
期刊：
影响因子：
--
通讯作者：
A. Hopkinson
中科院分区：
文献类型：
--
作者：
Junfang Zhao;C. Ng;I. Chu;K. Siu;A. Hopkinson
[CuII（M）（CH 3CN）2]*2+络合物氧化解离形成了蛋氨酸、α-甲基蛋氨酸和S-甲基半胱氨酸自由基阳离子。捕获了自由基阳离子M*+，并给出了这些离子的CID谱（MS ~ 3）。甲硫氨酸和S-甲基半胱氨酸自由基阳离子的断裂，由α-碳氢原子迁移到硫引发，引发甲硫氨酸中的水和硫代甲醇的损失以及S-甲基半胱氨酸中的硫代甲醇的损失。氘标记实验表明，相当大的H-D混乱和重排涉及N-H和S-H氢发生在蛋氨酸自由基阳离子断裂之前。S-甲基半胱氨酸的另一个通道是β-氢迁移后氨的损失。甲硫氨酸的α-碳甲基化导致不同片段的自由基阳离子。α-甲基甲硫氨酸的两个中性损失，NH 3和甲基乙烯基硫醚，CH 2 =CH-S-CH 3，是由γ-氢迁移引发的;第三个通道是 *COOH的损失。在B3 LYP/6-311+ +G（d，p）水平上的DFT计算已被用来测试方面的自由基阳离子的建议的碎裂机制。
Methionine, alpha-methylmethionine and S-methylcysteine radical cations have been formed by oxidative dissociations of [CuII(M)(CH3CN)2]*2+ complexes. The radical cations M*+ were trapped, and CID spectra (MS3) of these ions are presented. Fragmentations of the methionine and S-methylcysteine radical cations, initiated by migration of the alpha-carbon hydrogen atom to the sulfur, trigger the losses of water and thiomethanol from methionine and thiomethanol from S-methylcysteine. Deuterium labeling experiments show that considerable H-D scrambling and rearrangements involving N-H and S-H hydrogens occur in the methionine radical cation prior to fragmentation. An additional channel for S-methylcysteine is the loss of ammonia following beta-hydrogen migration. Methylation at the alpha-carbon of methionine results in a radical cation that fragments differently. Two neutral losses from alpha-methylmethionine, NH3 and methyl vinyl sulfide, CH2=CH-S-CH3, are initiated by gamma-hydrogen migration; a third channel is the loss of *COOH. DFT computations at the B3LYP/6-311+ +G(d,p) level have been used to test aspects of the proposed fragmentation mechanisms of the radical cations.