Dang Andy, Liu Yue, Tureček František
Department of Chemistry , University of Washington , Bagley Hall, Box 351700, Seattle , Washington 98195-1700 , United States.
J Phys Chem A. 2019 Apr 18;123(15):3272-3284. doi: 10.1021/acs.jpca.9b01542. Epub 2019 Apr 3.
Cation radicals of guanine (G), 9-methylguanine (MG), and guanosine (rG) were generated by dissociative oxidation of gas-phase copper complexes and characterized by UV-vis photodissociation action spectra and ab initio calculations. Comparison of the action spectra of G with the calculated vibronic absorption spectra of several cation radical tautomers showed the best match for the canonical 6-oxo-N-9-H structure (G1). The formation of G1 was favored by the stability of its precursor Cu ion complexes in solution and the gas phase. G1 was the marginally lowest-energy guanine tautomer according to CCSD(T) calculations extrapolated to the complete basis set limit (CBS). A canonical 6-oxo structure (MG1) was also assigned to the 9-methylguanine cation radical on the basis of a match between the action spectrum and the calculated vibronic absorption spectra. MG1 was calculated by CCSD(T)/CBS to be marginally less stable than the 6-OH enol tautormer, but its formation was favored by the superior stability of its precursor Cu ion complexes in solution and the gas phase. Action spectroscopy allowed us to assign the canonical 6-oxo structure (rG1) to the gas-phase guanosine cation radicals that were formed as the lowest-energy tautomers. The absorption bands in the action spectra were assigned on the basis of time-dependent density functional theory calculations that were benchmarked on equation-of-motion coupled cluster calculations of G.
通过气相铜配合物的离解氧化生成了鸟嘌呤（G）、9-甲基鸟嘌呤（MG）和鸟苷（rG）的阳离子自由基，并通过紫外可见光解离作用光谱和从头算进行了表征。将G的作用光谱与几种阳离子自由基互变异构体的计算振动吸收光谱进行比较，结果表明与标准的6-氧代-N-9-H结构（G1）匹配度最佳。G1的形成受到其前体铜离子配合物在溶液和气相中的稳定性的促进。根据外推到完整基组极限（CBS）的CCSD（T）计算，G1是能量略最低的鸟嘌呤互变异构体。基于作用光谱与计算的振动吸收光谱之间的匹配，9-甲基鸟嘌呤阳离子自由基也被指定为标准的6-氧代结构（MG1）。通过CCSD（T）/CBS计算得出MG1的稳定性略低于6-OH烯醇互变异构体，但其形成受到其前体铜离子配合物在溶液和气相中更高稳定性的促进。作用光谱学使我们能够将标准的6-氧代结构（rG1）指定为作为能量最低的互变异构体形成的气相鸟苷阳离子自由基。作用光谱中的吸收带是根据基于G的运动方程耦合簇计算进行基准测试的含时密度泛函理论计算确定的。
