Turecek Frantisek, Holm Anne I S, Panja Subhasis, Nielsen Steen Brønsted, Hvelplund Preben
Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, WA 98195-1700, USA.
J Mass Spectrom. 2009 Oct;44(10):1518-31. doi: 10.1002/jms.1642.
Transition metal cations Co2+, Ni2+ and Zn2+ form 1 : 1 : 1 ternary complexes with 2,2'-bipyridine (bpy) and peptides in aqueous methanol solutions that have been studied for tripeptides GGG and GGL. Electrospray ionization of these solutions produced singly charged [Metal(bpy)(peptide-H)]+ and doubly charged [Metal(bpy)(peptide)]2+ ions (Metal = metal ion) that underwent charge reduction by glancing collisions with Cs atoms at 50 and 100 keV collision energies. Electron transfer to [Metal(bpy)(peptide)]2+ ions was less than 4.2 eV exoergic and formed abundant fractions of non-dissociated charge-reduced intermediates. Charge-reduced [Metal(bpy)(peptide)]+ ions dissociated by the loss of a hydrogen atom, ammonia, water and ligands that depended on the metal ion. The Ni and Co complexes mainly dissociated by the elimination of ammonia, water, and the peptide ligand. The Zn complex dissociated by the elimination of ammonia and bpy. A sequence-specific fragment was observed only for the Co complex. Electron transfer to [Metal(bpy)(peptide-H)]+ was 0.6-1.6 eV exoergic and formed intermediate radicals that were detected as stable anions after a second electron transfer from Cs. [Metal(bpy)(peptide-H)] neutrals and their anions dissociated by the loss of bpy and peptide ligands with branching ratios that depended on the metal ion. Optimized structures for several spin states, electron transfer and dissociation energies were addressed by combined density functional theory and Møller-Plesset perturbational calculations to aid interpretation of experimental data. The experimentally observed ligand loss and backbone cleavage in charge-reduced [Metal(bpy)(peptide)]+ complexes correlated with the dissociation energies at the present level of theory. The ligand loss in +CR- spectra showed overlap of dissociations in charge-reduced [Metal(bpy)(peptide-H)] complexes and their anionic counterparts which complicated spectra interpretation and correlation with calculated dissociation energies.
过渡金属阳离子Co2+、Ni2+和Zn2+在甲醇水溶液中与2,2'-联吡啶（bpy）和肽形成1 : 1 : 1的三元配合物，已针对三肽GGG和GGL进行了研究。这些溶液的电喷雾电离产生单电荷的[金属(bpy)(肽-H)]+和双电荷的[金属(bpy)(肽)]2+离子（金属 = 金属离子），它们在50和100 keV的碰撞能量下与Cs原子进行掠射碰撞时发生电荷还原。向[金属(bpy)(肽)]2+离子的电子转移放热小于4.2 eV，并形成大量未解离的电荷还原中间体。电荷还原的[金属(bpy)(肽)]+离子通过失去氢原子、氨、水和配体而解离，这取决于金属离子。Ni和Co配合物主要通过消除氨、水和肽配体而解离。Zn配合物通过消除氨和bpy而解离。仅在Co配合物中观察到序列特异性片段。向[金属(bpy)(肽-H)]+的电子转移放热为0.6 - 1.6 eV，并形成中间自由基，在从Cs进行第二次电子转移后被检测为稳定阴离子。[金属(bpy)(肽-H)]中性分子及其阴离子通过失去bpy和肽配体而解离，分支比取决于金属离子。通过结合密度泛函理论和Møller-Plesset微扰计算确定了几种自旋态、电子转移和解离能的优化结构，以辅助解释实验数据。在电荷还原的[金属(bpy)(肽)]+配合物中实验观察到的配体损失和主链断裂与当前理论水平下的解离能相关。+CR-光谱中的配体损失显示电荷还原的[金属(bpy)(肽-H)]配合物及其阴离子对应物的解离存在重叠，这使光谱解释以及与计算解离能的相关性变得复杂。
