Gas phase ion chemistry of biomolecules. Part 37 - Gas-phase reactions of protonated tryptophan
Gas phase ion chemistry of biomolecules. Part 37 - Gas-phase reactions of protonated tryptophan
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DOI：
10.1016/j.jasms.2003.09.011
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发表时间：
2004-01-01
影响因子：
3.2
通讯作者：
Reid, GE
中科院分区：
文献类型：
--
作者：
Lioe, H;O'Hair, RAJ;Reid, GE
在四极离子阱中，采用碰撞诱导解离、氢-氘交换、区域特异性氘标记和分子轨道计算相结合的方法（在B3 LYP/6- 31 G * 水平上），研究了色氨酸质子化的气相反应.观察到质子化色氨酸的氨损失是主要的断裂途径，伴随着吲哚侧链C3位亲核攻击形成[M + H-NH3]（+）离子。氢-氘交换和区域特异性氘标记表明，混乱的吲哚环的C2和C4位置的质子，通过分子内质子转移从质子化在氨基氮的化学优选的网站，先于氨损失。分子轨道计算表明，分子内质子转移的活化能垒低于NH3损失的活化能垒。
The gas phase reactions of protonated tryptophan have been examined in a quadrupole ion trap using a combination of collision induced dissociation, hydrogen-deuterium exchange, regiospecific deuterium labeling and molecular orbital calculations (at the B3LYP/6-31G* level of theory). The loss of ammonia from protonated tryptophan is observed as the primary fragmentation pathway, with concomitant formation of a [M + H - NH3](+) ion by nucleophilic attack from the C3 position of the indole side chain. Hydrogen-deuterium exchange and regiospecific deuterium labeling reveals that scrambling of protons in the C2 and C4 positions of the indole ring, via intramolecular proton transfer from the thermodynamically preferred site of protonation at the amino nitrogen, precedes ammonia loss. Molecular orbital calculations have been employed to demonstrate that the activation barriers to intramolecular proton transfer are lower than that for NH3 loss.