Department of Chemistry and Biochemistry, and Center for Biochemical and Biophysical Studies, Northern Illinois University, DeKalb, IL 60115, USA.
J Am Soc Mass Spectrom. 2011 Oct;22(10):1794-803. doi: 10.1007/s13361-011-0198-5. Epub 2011 Jul 16.
The structure and reactivity of the N-acetyl-cysteine radical cation and anion were studied using ion-molecule reactions, infrared multi-photon dissociation (IRMPD) spectroscopy, and density functional theory (DFT) calculations. The radical cation was generated by first nitrosylating the thiol of N-acetyl-cysteine followed by the homolytic cleavage of the S-NO bond in the gas phase. IRMPD spectroscopy coupled with DFT calculations revealed that for the radical cation the radical migrates from its initial position on the sulfur atom to the α-carbon position, which is 2.5 kJ mol(-1) lower in energy. The radical migration was confirmed by time-resolved ion-molecule reactions. These results are in contrast with our previous study on cysteine methyl ester radical cation (Osburn et al., Chem. Eur. J. 2011, 17, 873-879) and the study by Sinha et al. for cysteine radical cation (Phys. Chem. Chem. Phys. 2010, 12, 9794-9800) where the radical was found to stay on the sulfur atom as formed. A similar approach allowed us to form a hydrogen-deficient radical anion of N-acetyl-cysteine, (M - 2H)( •- ). IRMPD studies and ion-molecule reactions performed on the radical anion showed that the radical remains on the sulfur, which is the initial and more stable (by 63.6 kJ mol(-1)) position, and does not rearrange.
使用离子-分子反应、红外多光子解离（IRMPD）光谱和密度泛函理论（DFT）计算研究了 N-乙酰半胱氨酸自由基阳离子和阴离子的结构和反应性。自由基阳离子是通过首先将 N-乙酰半胱氨酸的硫醇亚硝化，然后在气相中使 S-NO 键均裂生成的。IRMPD 光谱与 DFT 计算表明，对于自由基阳离子，自由基从其在硫原子上的初始位置迁移到α-碳原子位置，这降低了 2.5 kJ mol(-1)的能量。自由基迁移通过时间分辨的离子-分子反应得到证实。这些结果与我们之前关于半胱氨酸甲酯自由基阳离子（Osburn 等人，Chem. Eur. J. 2011, 17, 873-879）的研究以及 Sinha 等人对半胱氨酸自由基阳离子的研究形成对比（Phys. Chem. Chem. Phys. 2010, 12, 9794-9800），在这些研究中，自由基被发现停留在形成时的硫原子上。类似的方法使我们能够形成 N-乙酰半胱氨酸的缺氢自由基阴离子（M - 2H）( •- )。对自由基阴离子进行的 IRMPD 研究和离子-分子反应表明，自由基仍留在硫原子上，这是初始和更稳定（稳定 63.6 kJ mol(-1)）的位置，并且不会发生重排。
