Chu Ivan K, Laskin Julia
Department of Chemistry, The University of Hong Kong, Hong Kong, China.
Eur J Mass Spectrom (Chichester). 2011;17(6):543-56. doi: 10.1255/ejms.1156.
The formation and fragmentation of odd-electron ions of peptides and proteins is of interest to applications in biological mass spectrometry. Gas-phase redox chemistry occurring during collision-induced dissociation of ternary metal-ligand-peptide complexes enables the formation of a variety of peptide radicals, including the canonical radical cations, M(+•), radical dications, M+H, radical anions, M-2H and phosphorylated radical cations. In addition, odd-electron peptide ions with well-defined initial location of the radical site are produced through side-chain losses from the radical ions. Subsequent fragmentation of these species provides information regarding the role of charge and location of the radical site on the competition between radical-induced and proton-driven fragmentation of odd-electron peptide ions. This account summarizes current understanding of the factors that control the efficiency of the intramolecular electron transfer (ET) in ternary metal-ligand-peptide complexes resulting in formation of odd-electron peptide ions. Specifically, we discuss the effect of the metal center, the ligand and the peptide structure on the competition between the ET, proton transfer (PT) and loss of neutral peptide and neutral peptide fragments from the complex. Fundamental studies of the structures, stabilities and the energetics and dynamics of fragmentation of these complexes are also important for detailed molecular-level understanding of photosynthesis and respiration in biological systems.
肽和蛋白质的奇电子离子的形成与碎裂在生物质谱分析应用中备受关注。三元金属-配体-肽络合物碰撞诱导解离过程中发生的气相氧化还原化学作用能够形成多种肽自由基，包括典型的自由基阳离子M(+•)、双自由基阳离子M+H、自由基阴离子M-2H以及磷酸化自由基阳离子。此外，通过自由基离子的侧链损失可产生自由基位点初始位置明确的奇电子肽离子。这些物种随后的碎裂提供了有关电荷和自由基位点位置在奇电子肽离子自由基诱导碎裂与质子驱动碎裂竞争中所起作用的信息。本综述总结了目前对控制三元金属-配体-肽络合物中分子内电子转移（ET）效率从而导致奇电子肽离子形成的因素的理解。具体而言，我们讨论了金属中心、配体和肽结构对络合物中ET、质子转移（PT）以及中性肽和中性肽片段损失之间竞争的影响。对这些络合物的结构、稳定性、能量学和碎裂动力学的基础研究对于在分子水平上详细理解生物系统中的光合作用和呼吸作用也很重要。
