Macrocyclic effect of auxiliary ligand on the gas-phase dissociation of ternary copper(II)-GGX complexes
Macrocyclic effect of auxiliary ligand on the gas-phase dissociation of ternary copper(II)-GGX complexes
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DOI：
10.1002/rcm.2366
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发表时间：
2006-01-01
影响因子：
2
通讯作者：
Chu, IK
中科院分区：
文献类型：
--
作者：
Lam, CNW;Siu, SO;Chu, IK
先前对[Cu-II（dien）peptide]（. 2+）离子（dien =二亚乙基三胺）解离的研究表明，含NH的辅助配体不利于[peptide]（.+）的形成。相反，它们促进质子转移反应，特别是对于含有碱性氨基残基的肽。GGX（.+）形式的自由基阳离子三肽的形成[GGX=甘氨酰甘氨酰（残基X）]在用其类似的环状配体1，4，7-三氮杂环壬烷（9-aneN（3））取代开链三齿配体后变得可行;即，来自[Cu-II（9-aneN（3））GGX]（.2+）离子。当使用1，4，7，10-四氧杂环十二烷（12-冠-4）代替其开链类似物2，5，8，11-四氧杂癸烷（三甘醇二甲醚）时，发生类似的增强。我们已经证明，[Cu-II（L）GGX]（.2+）络合离子[其中L = 9-aneN（3）或12-冠-4]中的空间位阻辅助大环配体通过气相裂解促进自由基阳离子肽的形成。我们验证了我们的实验观察，通过检查一系列的19个三肽的类型GGX，不同的只是在他们的C-末端残基的身份的反应性。电子转移反应的能量与肽-Cu（II）相互作用的键解离能良好相关;受约束的大环配体的存在通过配体和肽之间的空间排斥减弱金属-肽螯合，并且这种情况可能导致更有利的自由基阳离子肽形成。版权所有（c）2006约翰威利父子有限公司。
Previous studies into the dissociation of [Cu-II(dien)peptide](.2+) ions (dien = diethylenetriamine) have shown that NH-containing auxiliary ligands do not favor the formation of [peptide](.+) species; instead, they promote proton-transfer reactions, especially for peptides containing basic amino residues. Formation of radical cationic tripeptides of the form GGX(.+) [GGX = glycylglycyl(residue X)] becomes feasible upon substituting the open-chain tridentate ligand then with its analogous cyclic ligand, 1,4,7-triazacyclononane (9-aneN(3)); i.e., from [Cu-II(9-aneN(3))GGX](.2+) ions. Similar enhancements occur when using 1,4,7,10-tetraoxacyclododecane (12-crown-4) in place of its open-chain analog, 2,5,8,11-tetraoxadecane (triglyme). We have demonstrated that a sterically encumbered auxiliary macrocyclic ligand within [Cu-II(L)GGX](.2+) complex ions [where L = 9-aneN(3) or 12-crown-4] facilitates the formation of radical cationic peptides through gas-phase fragmentation. We verified our experimental observations by examining the reactivities of a series of 19 tripeptides of the type GGX that differ only in the identity of their C-terminal residue. The energy of the electron-transfer reaction correlates well with the bond-dissociation energy of the peptide-Cu(II) interaction; the presence of a constrained macrocyclic ligand weakens metal-peptide chelation through steric repulsion between the ligand and the peptide, and this situation may lead to more favorable radical cationic peptide formation. Copyright (c) 2006 John Wiley & Sons, Ltd.