Lesslie Michael, Lawler John T, Dang Andy, Korn Joseph A, Bím Daniel, Steinmetz Vincent, Maître Philippe, Tureček Frantisek, Ryzhov Victor
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL, 60115, USA.
Department of Chemistry, University of Washington, Bagley Hall, Box 351700, Seattle, Washington, 98195, USA.
Chemphyschem. 2017 May 19;18(10):1293-1301. doi: 10.1002/cphc.201700281. Epub 2017 Apr 7.
The radical cation of cytosine (Cyt ) is generated by dissociative oxidation from a ternary Cu complex in the gas phase. The radical cation is characterized by infrared multiple photon dissociation (IRMPD) spectroscopy in the fingerprint region, UV/Vis photodissociation (UVPD) spectroscopy, ion-molecule reactions, and theoretical calculations (density functional theory and ab initio). The experimental IRMPD spectrum features diagnostic bands for two enol-amino and two keto-amino tautomers of Cyt that are calculated to be among the lowest energy isomers, in agreement with a previous study. Although the UVPD action spectrum can also be matched to a combination of the four lowest energy tautomers, the presence of a nonclassical distonic radical cation cannot be ruled out. Its formation is, however, unlikely due to the high energy of this isomer and the respective ternary Cu complex. Gas-phase ion-molecule reactions showed that Cyt undergoes hydrogen-atom abstraction from 1-propanethiol, radical recombination reactions with nitric oxide, and electron transfer from dimethyl disulfide.
胞嘧啶（Cyt）的自由基阳离子是通过气相中三元铜配合物的离解氧化产生的。通过指纹区的红外多光子解离（IRMPD）光谱、紫外/可见光解离（UVPD）光谱、离子-分子反应和理论计算（密度泛函理论和从头算）对该自由基阳离子进行了表征。实验IRMPD光谱具有胞嘧啶两种烯醇-氨基和两种酮-氨基互变异构体的诊断带，这些互变异构体经计算是能量最低的异构体之一，这与之前的一项研究一致。尽管UVPD作用光谱也可以与四种能量最低的互变异构体的组合相匹配，但不能排除非经典的远位自由基阳离子的存在。然而，由于这种异构体和相应的三元铜配合物能量较高，其形成的可能性不大。气相离子-分子反应表明，胞嘧啶会发生从1-丙硫醇夺取氢原子、与一氧化氮的自由基重组反应以及从二甲基二硫转移电子的反应。
