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首页> 外文期刊>Chemistry: A European journal >Structural Effects on the Formation of Proton and Alkali Metal Ion Adducts of Apolar, Neutral Peptides: Electrospray Ionization Mass Spectrometry and Ab Initio Theoretical Studies
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Structural Effects on the Formation of Proton and Alkali Metal Ion Adducts of Apolar, Neutral Peptides: Electrospray Ionization Mass Spectrometry and Ab Initio Theoretical Studies

机译：非极性中性肽质子和碱金属离子加合物形成的结构影响：电喷雾电离质谱和从头算理论研究

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摘要

Apolar, neutral peptides have been shown to ionize extremely well under the conditions used for electrospray ionization mass spectrometry (ESIMS). Peptides for which the conformations have been independently determined in solution and in crystals have been examined by ESIMS. Studies of peptide helices ranging from 7 to 18 residues reveal that shorter helices yield exclusively singly charged ions, while in larger helices mutiply charged species are detectable. Multiple sites for protonation/metallation are introduced in the helix by proline insertion or by changing the chirality in the residue. The preferred site of cation binding to helices may be the C-terminus end, where three free C-terminus end, where three free C = O groups are available for chelation. Ab initio and DFT calculations at several levels have been carried out for the binding of H~+, Li~+, Na~+, and K~+ to CHO-(Gly)_3-OMe. The results reveal that metallation in favoured by cheltion to carbonyl groups at the C-terminus, while protonation involved two carbonyl groups and thus favour a 10-membered cyclic hydrogen-bonded structure. In beta-strands, metallation/protonation occurs at isolated carbonyl groups. Collision induced fragmentation of hydrophobic peptides under ESI conditions reveals that helix fragmentation occurs predominantly from the C-terminus, while in beta-hairpins cleavage occurs simultaneously at multiple sites.
机译：已显示非极性中性肽在用于电喷雾电离质谱（ESIMS）的条件下离子化非常好。已通过ESIMS检查了溶液和晶体中构象已独立确定的肽。对7至18个残基范围内的肽螺旋进行的研究表明，较短的螺旋仅产生单电荷离子，而在较大的螺旋中可检测到多电荷物种。通过脯氨酸插入或通过改变残基中的手性将多个质子化/金属化位点引入螺旋中。阳离子与螺旋结合的优选位点可以是C末端，其中三个游离C末端，其中三个游离C = O基团可用于螯合。对于H〜+，Li〜+，Na〜+和K〜+与CHO-（Gly）_3-OMe的结合，已经进行了从头算和DFT计算。结果表明，金属化有利于螯合C端的羰基，而质子化涉及两个羰基，因此有利于10元环状氢键结构。在β链中，金属化/质子化发生在孤立的羰基上。在ESI条件下，碰撞诱导的疏水肽片段化表明螺旋片段化主要发生在C末端，而在β-发夹中，切割同时在多个位点发生。

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