Simple b ions have cyclic oxazolone structures.: A neutralization-reionization mass spectrometric and computational study of oxazolone radicals
Simple b ions have cyclic oxazolone structures.: A neutralization-reionization mass spectrometric and computational study of oxazolone radicals
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DOI：
10.1016/j.jasms.2005.07.023
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发表时间：
2005-12-01
影响因子：
3.2
通讯作者：
Turecek, F
中科院分区：
文献类型：
--
作者：
Chen, XH;Turecek, F
利用飞秒电子转移在气相中生成了2-甲基-5-对-2-基自由基(3)及其氚标记类似物，并用中和-再电离质谱仪和量子化学计算对其进行了研究。自由基3通过开环和消除CO和CH3CO进行快速解离。氢的损失较少，涉及来自环和侧链位置的氢原子。用密度泛函、微扰和耦合团簇理论对3的基电子态的势能面进行了分析，直至CCSD(T)，并外推到6-311++G(3df，2p)基组，证实了实验结果。自由基解离的RRKM计算给出了在80-300kJ摩尔(-1)的内能范围内，CO和H损失的分支比为k(CO)/k(H)>；10。3的解离动力是由垂直中和的大的Frank-Condon效应提供的，可能还来自激发电子态的参与。计算还给出了绝热电离能3，IEadiab=5.48 eV和阳离子3(+)的垂直复合能revert=4.70 eV。目前的结果有力地表明，恶唑酮结构可以解释b型多肽离子在电子捕获时的碎裂，这与以前的推测相反。
The 2-methyloxazol-5-on-2-yl radical (3) and its deuterium labeled analogs were generated in the gas-phase by femtosecond electron-transfer and studied by neutralization-reionization mass spectrometry and quantum chemical calculations. Radical 3 undergoes fast dissociation by ring opening and elimination of CO and CH3CO. Loss of hydrogen is less abundant and involves hydrogen atoms from both the ring and side-chain positions. The experimental results are corroborated by the analysis of the potential energy surface of the ground electronic state in 3 using density functional, perturbational, and coupled-cluster theories up to CCSD(T) and extrapolated to the 6-311 + + G(3df,2p) basis set. RRKM calculations of radical dissociations gave branching ratios for loss of CO and H that were k(CO)/k(H) > 10 over an 80-300 kJ mol(-1) range of internal energies. The driving force for the dissociations of 3 is provided by large Franck-Condon effects on vertical neutralization and possibly from involvement of excited electronic states. Calculations also provided the adiabatic ionization energy of 3, IEadiab = 5.48 eV and vertical recombination energy of cation 3(+), REvert = 4.70 eV. The present results strongly indicate that oxazolone structures can explain fragmentations of b-type peptide ions upon electron capture, contrary to previous speculations.