Singly-protonated proline-containing peptides with N-terminal arginine are photodissociated with vacuum ultraviolet (VUV) light in an ESI linear ion trap/orthogonal-TOF (LIT/o-TOF). When proline is the n^th residue from the N-terminus, unusual b _n + 2 and a _n + 2 ions are observed. Their formation is explained by homolytic cleavage of the C_α− C bond in conjunction with a rearrangement of electrons and an amide hydrogen. The latter is facilitated by a proline-stabilized gas-phase peptide conformation.

中文翻译：

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含脯氨酸肽离子的气相构象特异性光碎裂

具有 N 端精氨酸的单质子化脯氨酸肽在 ESI 线性离子阱/正交-TOF (LIT/o-TOF) 中用真空紫外 (VUV) 光光解。当脯氨酸是N 端的^第n^个残基时，观察到不寻常的b _n + 2 和a _n + 2 离子。它们的形成是通过 C _α - C 键的均裂以及电子和酰胺氢的重排来解释的。后者由脯氨酸稳定的气相肽构象促进。