Mädler Stefanie, Lau Justin Kai-Chi, Williams Declan, Wang Yating, Saminathan Irine S, Zhao Junfang, Siu K W Michael, Hopkinson Alan C
Department of Chemistry and Centre for Research in Mass Spectrometry, York University , 4700 Keele Street, Toronto, Ontario Canada M3J 1P3.
J Phys Chem B. 2014 Jun 12;118(23):6123-33. doi: 10.1021/jp5030087. Epub 2014 May 29.
Peptide radical cations A(n)Y(•+) (where n = 3, 4, or 5) and A5W(•+) have been generated by collision-induced dissociation (CID) of Cu(II)(tpy)(peptide) complexes. Apart from the charge-driven fragmentation at the N-Cα bond of the hetero residue producing either c + 2H or z - H ions and radical-driven fragmentation at the Cα-C bond to give a(+) ions, unusual product ions x + H and z + H are abundant in the CID spectra of the peptides with the hetero residue in the second or third position of the chain. The formation of these ions requires that both the charge and radical be located on the peptide backbone. Energy-resolved spectra established that the z + H ion can be produced either directly from the peptide radical cation or via the fragment ion x + H. Additionally, backbone dissociation by loss of the C-terminal amino acid giving b(n-1) - H increases in abundance with the length of the peptides. Mechanisms by which peptide radical cations dissociate have been modeled using density functional theory (B3LYP/6-31++G** level) on tetrapeptides AYAG(•+), AAYG(•+), and AWAG(•+).
通过Cu(II)(tpy)(肽)配合物的碰撞诱导解离（CID）产生了肽自由基阳离子A(n)Y(•+)（其中n = 3、4或5）和A5W(•+)。除了在杂残基的N-Cα键处发生电荷驱动的碎片化产生c + 2H或z - H离子，以及在Cα-C键处发生自由基驱动的碎片化产生a(+)离子外，在链的第二个或第三个位置带有杂残基的肽的CID光谱中，不寻常的产物离子x + H和z + H很丰富。这些离子的形成要求电荷和自由基都位于肽主链上。能量分辨光谱表明，z + H离子可以直接从肽自由基阳离子产生，也可以通过碎片离子x + H产生。此外，通过失去C端氨基酸产生b(n - 1) - H的主链解离随着肽长度的增加而丰度增加。已经使用密度泛函理论（B3LYP/6 - 31++G**水平）对四肽AYAG(•+)、AAYG(•+)和AWAG(•+)模拟了肽自由基阳离子解离的机制。
