Mass-spectrometric and computational study of tryptophan radicals (Trp + H)• produced by collisional electron transfer to protonated tryptophan in the gas phase
Mass-spectrometric and computational study of tryptophan radicals (Trp + H)• produced by collisional electron transfer to protonated tryptophan in the gas phase
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DOI：
10.1039/c0cp00597e
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发表时间：
2010-01-01
影响因子：
3.3
通讯作者：
Turecek, Frantisek
中科院分区：
文献类型：
--
作者：
Gregersen, Joshua A.;Turecek, Frantisek
氢原子加合物色氨酸产生的第一次在气相中碰撞电子转移质子化色氨酸在7170 eV的动能。自由基表现出快速解离的C-α-C-β键裂解和交叉环裂解发生在7.3 μ s的时间尺度。通过对自由基势能面的从头计算分析，解释了C-alpha-C-beta键断裂的机理。这表明初级色氨酸自由基通过铵氢原子迁移到羧基而自发异构化。通过异构化形成的稳定中间体可以经历自由基诱导的C-alpha-C-beta键的断裂，与H原子迁移到吲哚环的C-2和C-4位置竞争。在B3-ROMP 2/6-311++G（2d，p）势能面上的单分子速率常数的RRKM计算表明，在电子转移后获得的内能范围内，自由基中间体的单分子反应中，C-alpha-C-beta键断裂是最快的。我们还报告了更新的G2（MP2）的色氨酸（PA = 946 kJ mol（-1））和氢原子的色氨酸吲哚环的相关电子为基础的肽解离亲和力的质子亲和力。
Hydrogen atom adducts to tryptophan were generated for the first time in the gas phase by collisional electron transfer to protonated tryptophan at 7170 eV kinetic energy. The radicals showed fast dissociations by C-alpha-C-beta bond cleavage and cross-ring cleavages occurring on the 7.3 mu s time scale. The mechanism of the C-alpha-C-beta bond cleavage was explained by ab initio computational analysis of the radical potential energy surface. This showed spontaneous isomerization of the primary tryptophan radical by ammonium hydrogen atom migration to the carboxyl group. The stable intermediate formed by the isomerization can undergo radical-induced scission of the C-alpha-C-beta bond in competition with H-atom migrations to the C-2 and C-4 positions of the indole ring. RRKM calculations of unimolecular rate constants on the B3-ROMP2/6-311++G(2d,p) potential energy surface indicated that the C-alpha-C-beta bond cleavage was the fastest unimolecular reaction of the radical intermediates within the range of internal energies acquired upon electron transfer. We also report an updated G2(MP2) proton affinity of tryptophan (PA = 946 kJ mol(-1)) and hydrogen atom affinities of the tryptophan indole ring of relevance to electron-based peptide dissociations.