School of Chemistry, University of Melbourne, Victoria 3010, Australia.
Rapid Commun Mass Spectrom. 2010 Nov 30;24(22):3255-60. doi: 10.1002/rcm.4763.
Electrospray ionization (ESI) of tryptophan gives rise to multiply charged, non-covalent tryptophan cluster anions, Trp(n)-xH, in a linear ion trap mass spectrometer, as confirmed by high-resolution experiments performed on a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The smallest multiply charged clusters that can be formed in the linear ion trap as a function of charge state are: x = 2, n = 7; x = 3, n = 16; x = 4, n = 31. The fragmentation of the dianionic cluster Trp(9)-2H was examined via low-energy collision-induced dissociation (CID), ultraviolet photodissociation (UVPD) at 266 nm and electron-induced dissociation (EID) at electron energies ranging from >0 to 30 eV. CID proceeds mostly via charge separation and evaporation of neutral tryptophan. The smallest doubly charged cluster that can be formed via evaporation of neutral tryptophans is Trp(7)-2H, consistent with the observation of this cluster in the ESI mass spectrum. UVPD gives singly charged tryptophan clusters ranging from n = 2 to n = 9. The latter ion arises from ejection of an electron to give the radical anion cluster, Trp(9)-2H. The types of gas-phase EID reactions observed are dependent on the energy of the electrons. Loss of neutral tryptophan is an important channel at lower energies, with the smallest doubly charged ion, Trp(7)-2H, being observed at 19.8 eV. Coulomb explosion starts to occur at 19.8 eV to form the singly charged cluster ions Trp(x)-H (x = 1-8) via highly asymmetric fission. At 21.8 eV a small amount of Trp(2)-H-NH(3) is observed. Thus CID, UVPD and EID are complementary techniques for the study of the fragmentation reactions of cluster ions.
在线性离子阱质谱仪中，电喷雾电离（ESI）会导致色氨酸形成多电荷、非共价的色氨酸团簇负离子 Trp(n)-xH，这在傅里叶变换离子回旋共振（FT-ICR）质谱仪上进行的高分辨率实验中得到了证实。在线性离子阱中，作为电荷状态的函数，可以形成的最小多电荷簇是：x = 2，n = 7；x = 3，n = 16；x = 4，n = 31。通过低能碰撞诱导解离（CID）、266nm 下的紫外光解（UVPD）和电子能量范围从>0 到 30eV 的电子诱导解离（EID）研究了二阴离子簇 Trp(9)-2H的碎裂。CID 主要通过中性色氨酸的电荷分离和蒸发进行。通过蒸发中性色氨酸可以形成的最小双电荷簇是 Trp(7)-2H，这与在 ESI 质谱中观察到该簇一致。UVPD 给出了从 n = 2 到 n = 9 的单电荷色氨酸簇。后一种离子是通过向自由基阴离子簇 Trp(9)-2H中逐出电子而产生的。观察到的气相 EID 反应类型取决于电子的能量。在较低能量下，中性色氨酸的损失是一个重要的通道，在 19.8eV 时观察到最小的双电荷离子 Trp(7)-2H。在 19.8eV 时，库仑爆炸开始发生，通过高度不对称的分裂形成单电荷簇离子 Trp(x)-H（x = 1-8）。在 21.8eV 时，观察到少量 Trp(2)-H-NH(3)。因此，CID、UVPD 和 EID 是研究簇离子碎裂反应的互补技术。
