Do all b2 ions have oxazolone structures? Multistage mass spectrometry and ab initio studies on protonated N-acyl amino acid methyl ester model systems
Do all b2 ions have oxazolone structures? Multistage mass spectrometry and ab initio studies on protonated N-acyl amino acid methyl ester model systems
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DOI：
10.1016/s1387-3806(01)00421-3
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发表时间：
2001-10-01
影响因子：
1.8
通讯作者：
Reid, GE
中科院分区：
文献类型：
--
作者：
Farrugia, JM;O'Hair, RAJ;Reid, GE
考察了21个质子化N-酰基氨基酸甲酯的串联质谱裂解反应，作为更复杂多肽的模型。观察到四种主要类型的反应：从N-端乙酰基失去CH2CO；从C-端酯基团失去CH3OH以生成b(2)离子结构的模型体系；从没有OH侧链基团的氨基酸中损失水；通过小分子损失(例如H2O、NH3和CH3SH)使侧链断裂。CH3OH损失是在所有体系中观察到的唯一常见反应。通过MS3实验对生成的[M+H-CH3OH]离子进行了更详细的研究，因为以前的研究表明，恶唑酮结构释放了CO。只有赖氨酸和精氨酸不会以CO的方式断裂，这意味着涉及侧链的替代环状结构。对精氨酸、组氨酸、赖氨酸、蛋氨酸、天冬氨酸、谷氨酰胺和丝氨酸衍生的两种异构体b(2)离子(恶唑酮和侧链相互作用离子)进行了从头算(MP2/6-31G*//HF/6-31G*)。对于精氨酸、组氨酸和赖氨酸，涉及侧链的环结构比恶唑酮结构更稳定。最后，重点介绍了与气相过程相关的溶液相数据。(C)2001年爱思唯尔科学公司。
The tandem mass spectrometry fragmentation reactions of 21 protonated N-acyl amino acid methyl esters are examined as models for more complicated peptides. Four main types of reactions are observed: loss of CH2CO from the N-terminal acetyl group; loss of CH3OH from the C-terminal ester group to yield a model system for a b(2) ion structure; loss of water from amino acids without an OH side chain group; fragmentation of the side chain by way of small molecule loss (e.g. H2O, NH3, and CH3SH). CH3OH loss is the only common reaction observed for all systems. The resultant [M+H-CH3OH] ions were examined in further detail by way of MS3 experiments because previous studies have shown that the oxozolone structures liberate CO. Only lysine and arginine do not fragment by way of CO, which is suggestive of alternative cyclic structures involving the side chain. Ab initio calculations (at the MP2/6-31G*//HF/6-31G*) were carried out on isomeric b(2) ions of both types (oxazolone and that involving side-chain interaction) derived from arginine, histidine, lysine, methionine, asparagine, glutamine, and serine. For arginine, histidine, and lysine the cyclic structures involving the side chain are more stable than the oxozolone structures. Finally, solution phase data relevant to the gas phase processes are highlighted. (C) 2001 Elsevier Science B.V.