Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
J Am Soc Mass Spectrom. 2010 Apr;21(4):511-21. doi: 10.1016/j.jasms.2009.12.021. Epub 2010 Jan 11.
Fragmentation pathways of peptide radical cations, M(+), with well-defined initial location of the radical site were explored using collision-induced dissociation (CID) experiments. Peptide radical cations were produced by gas-phase fragmentation of Co(III)(salen)-peptide complexes [salen = N,N'-ethylenebis (salicylideneiminato)]. Subsequent hydrogen abstraction from the beta-carbon of the side-chain followed by C(alpha)-C(beta) bond cleavage results in the loss of a neutral side chain and formation of an alpha-radical cation with the radical site localized on the alpha-carbon of the backbone. Similar CID spectra dominated by radical-driven dissociation products were obtained for a number of arginine-containing alpha-radicals, suggesting that for these systems radical migration precedes fragmentation. In contrast, proton-driven fragmentation dominates CID spectra of alpha-radicals produced via the loss of the arginine side chain. Radical-driven fragmentation of large M(+) peptide radical cations is dominated by side-chain losses, formation of even-electron a-ions and odd-electron x-ions resulting from C(alpha)-C bond cleavages, formation of odd-electron z-ions, and loss of the N-terminal residue. In contrast, charge-driven fragmentation produces even-electron y-ions and odd-electron b-ions.
使用碰撞诱导解离 (CID) 实验探索了具有明确自由基位置的肽自由基阳离子 M(+)的碎片化途径。肽自由基阳离子是通过 Co(III)(salen)-肽配合物的气相断裂产生的 [salen = N,N'-乙撑双（水杨醛亚胺）]。随后从侧链的β-碳上进行氢提取，接着发生 C(alpha)-C(beta)键断裂，导致中性侧链丢失，并形成自由基位于骨架α-碳上的α-自由基阳离子。对于许多含有精氨酸的α-自由基，得到了以自由基驱动的解离产物为主的类似 CID 光谱，表明对于这些系统，自由基迁移先于碎片化。相比之下，质子驱动的碎片化主导了通过精氨酸侧链丢失产生的α-自由基的 CID 光谱。大 M(+)肽自由基阳离子的自由基驱动碎片化主要由侧链损失、通过 C(alpha)-C 键断裂形成偶数电子 a-离子和奇数电子 x-离子、形成奇数电子 z-离子以及 N-末端残基的丢失主导。相比之下，电荷驱动的碎片化产生偶数电子 y-离子和奇数电子 b-离子。
