Department of Physics and Astronomy, Aarhus University, Ny Munkegade, DK-8000 Aarhus C, Denmark.
J Phys Chem A. 2010 Jan 14;114(1):299-303. doi: 10.1021/jp9086317.
Photodissociation of protonated GW, WG (G = glycine, W = tryptophan), and their complexes with 18-crown-6-ether (CE) was performed in an electrostatic ion storage ring using a tunable laser system. On the basis of lifetime measurements, action spectra were obtained from 210 to 360 nm. These reveal that whereas GW + H absorbs maximally at approximately 220 nm, the absorption maximum is <210 nm for WG + H, which is in good accordance with density functional theory calculations that predict band maxima at 221 and 212 nm, respectively. This difference in absorption is ascribed to the ammonium group interacting with the indole ring in the case of GW, thereby lowering the energy of the excited state more than that of the ground state. A broad band at higher wavelengths is observed for WG but not for GW, which again may be linked to differences in conformational structures between the two ions. Absorption spectra for the two CE tagged ions are very similar to each other: The high-energy band is now <210 nm for both peptide ions, and they display an absorption band with a maximum at 270 nm. The crown ether targets the ammonium protons, preventing an interaction between ammonium and indole, and the photophysics of the two complexes is therefore similar. The complexes have significantly longer lifetimes with respect to dissociation than the bare ions. Finally, we report product ion mass spectra at two different excitation wavelengths, 210 and 270 nm. There are significant differences between the two peptides, and the crown ether enhances certain channels, such as the loss of CO + H(2)O and the tryptophan side chain.
利用可调谐激光系统，在静电离子储存环中对质子化 GW、WG（G = 甘氨酸，W = 色氨酸）及其与 18-冠-6-醚（CE）的复合物进行了光解。基于寿命测量，从 210 到 360nm 获得了作用光谱。这些结果表明，虽然 GW + H 在大约 220nm 处最大吸收，但 WG + H 的吸收最大值 <210nm，这与密度泛函理论计算结果非常吻合，分别预测带最大值为 221nm 和 212nm。这种吸收差异归因于 GW 中铵基团与吲哚环相互作用，从而使激发态的能量降低超过基态。在 WG 中观察到较高波长的宽带，但在 GW 中未观察到，这可能再次与两种离子之间的构象结构差异有关。两种 CE 标记离子的吸收光谱非常相似：高能带现在对于两种肽离子都 <210nm，它们显示出在 270nm 处具有最大吸收的吸收带。冠醚靶向铵质子，防止铵和吲哚之间的相互作用，因此两个复合物的光物理性质相似。与裸离子相比，复合物的解离具有明显更长的寿命。最后，我们报告了在两个不同激发波长 210nm 和 270nm 下的产物离子质谱。两个肽之间存在显著差异，冠醚增强了某些通道，例如 CO+H(2)O 和色氨酸侧链的损失。
