PROTON-TRANSFER REACTIONS OF MULTIPLY-CHARGED PEPTIDE AND PROTEIN CATIONS AND ANIONS
PROTON-TRANSFER REACTIONS OF MULTIPLY-CHARGED PEPTIDE AND PROTEIN CATIONS AND ANIONS
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DOI：
10.1002/jms.1190300217
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发表时间：
1995-02-01
影响因子：
2.3
通讯作者：
SMITH, RD
中科院分区：
文献类型：
--
作者：
LOO, RRO;SMITH, RD
用电喷雾电离产生的肽离子和蛋白离子考察了两种气相质子转移反应；(i)碱与多个质子化分子反应，（ii）酸与多个去质子化分子反应。对于(i)类型的碱跨越一定质子亲和度的反应，质子转移反应速率随着电荷转移试剂质子亲和度的增加而增加，对于低质子亲和度的试剂（乙酸乙酯、乙腈和水）没有观察到质子转移。这些研究还首次定性地测量了与多电荷肽和蛋白质反应的温度依赖性，弱碱的温度依赖性为负，强碱的温度依赖性为正，丙酸与[M - nH]（n-）离子的温度依赖性为负。为了解释这些数据，我们提出了两个假设：第一，负的温度依赖性归因于轻微放热反应，而正的温度依赖性可能反映了竞争性聚类途径的贡献，这一途径在较重的试剂中可能更占主导地位；或者，正的温度依赖性可能反映了反应坐标中由带同种电荷的离子的排斥引起的势垒；而负温度依赖性可以反映出一个团簇介导的反应，其中电荷离域降低了质子转移的屏障。在后一种情况下，由于使用的浓度较高，质子亲和试剂较少，因此会引起团簇。
Two types of gas-phase proton transfer reactions were examined with electrospray ionization-generated peptide and protein ions; (i) bases reacting with multiply protonated molecules and (ii) acids reacting with multiply deprotonated molecules, For reactions of type (i) with bases spanning a range of proton affinities, the proton transfer reaction rate was observed to increase with increasing proton affinity of the charge transfer reagent, Proton transfer was not observed for the low proton affinity reagents (ethyl acetate, acetonitrile and water), These studies also qualitatively measured for the first time the temperature dependences for reactions with multiply charged peptides and proteins, Negative temperature dependences were observed for the weaker bases and positive dependences for the stronger bases, A negative temperature dependence was also observed in the reaction of propionic acid with [M - nH](n-) ions. Two hypotheses are proposed to explain the data, In the first, negative temperature dependences are attributed to slightly exothermic reactions, while the positive dependences may reflect contributions from a competing clustering pathway, a pathway which could be more dominant with the heavier reagents, Alternatively, the positive temperature dependences may reflect the barrier in the reaction coordinate arising from the repulsion of like-charged ions, while negative temperature dependences could reflect a cluster-mediated reaction in which charge delocalization lowers the barrier to proton transfer, In the latter cases, clustering is invoked with the fewer proton affinity reagents because of the higher concentrations employed.