碱金属离子对甘氨酸五肽气相解离过程的影响

Effect of Alkali Metal Ions on the Dissociation of Glycine Pentapeptide in the Gas Phase

为了获得更多的多肽结构信息,采用结构简单的甘氨酸五肽(简写为GGGGG或G5)作为模型,研究了碱金属离子(Li+、Na+、K+、Rb+)对甘氨酸五肽GGGGG气相解离过程的影响.将一定化学计量比的甘氨酸五肽分别和四种碱金属盐溶液混合后,静置10h,使反应达到平衡.电喷雾质谱结果表明,四种碱金属离子均可以在溶液中与甘氨酸五肽形成非共价复合物,其中主要组分为碱金属离子与G5配合比为1:1和2:1的非共价复合物.质谱碰撞诱导解离(CID)时的碰撞能量为25eV.气相碰撞诱导解离实验结果表明,在配合比为1:1的复合物中,其碎片化程度按照Li+、Na+、K+、Rb+的次序依次减小,Rb+的复合物碎裂过程中生成了不常见的c、z离子;在配合比为2:1的复合物中,其碎片化程度按照Li+、Na+、K+、Rb+的次序依次增大.与1:1的非共价复合物相比,Na+、K+、Rb+的2:1复合物的气相解离显得更加容易.除Li+外,两个碱金属离子对G5的活化能力明显较单个碱金属离子强,它们可以诱导多肽在更多位点断裂,生成更多类型的碎片离子.

To obtain more structural information of polypeptides,glycine pentapeptide（simplified as GGGGG or G5）was chosen as a model to investigate the impact of alkali metal ions on the dissociation of GGGGG in the gas phase.Stoichiometric G5 and alkali metal salt solutions,including Li＋ ,Na^＋ ,K^＋ ,Rb^＋ , were mixed,respectively,and then the solutions were left to stand at room temperature for 10 h to reach equilibrium.The mass spectrometric results indicated that the alkali metal ions and G5 could form 1：1 or 2： 1 non-covalent complexes in solution.The energy of the collision induced dissociation（CID）was 25 eV. The gas phase CID results demonstrate that in the 1：1 complexes,the extent of fragmentation decreases according to the order：Li＋ ,Na^＋ ,K^＋ ,Rb^＋ .Moreover,the unusual c,z ions were observed in the Rb ＋ complex. In the 2：1 non-covalent complexes,the extent of fragmentation increases according to the order：Li＋ ,Na^＋ , K^＋ ,Rb^＋ .The gas phase dissociation of the Na^＋ ,K^＋ ,Rb^＋ 2：1 complexes are easier than their 1：1 complexes. Except for Li＋ ,the activation abilities of the double metal ions to G5 are stronger than that of the single metal ion to G5,which can induce more dissection sites in the glycine pentapeptide and lead to the formation of more kinds of fragment ions.