Structure of cationized arginine (Arg•M+, M = H, Li, Na, K, Rb, and Cs) in the gas phase:: Further evidence for zwitterionic arginine
Structure of cationized arginine (Arg•M+, M = H, Li, Na, K, Rb, and Cs) in the gas phase:: Further evidence for zwitterionic arginine
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DOI：
10.1021/jp9931307
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发表时间：
1999-11-18
影响因子：
2.9
通讯作者：
Williams, ER
中科院分区：
文献类型：
--
作者：
Jockusch, RA;Price, WD;Williams, ER
研究了阳离子化精氨酸的气相结构。M+，M = Li，Na，K，Rb和Cs，研究了混合方法密度泛函理论计算和实验使用低能量碰撞激活和热辐射解离。在B3 LYP/LACVP++** 水平上的计算表明，随着金属离子尺寸的增加，其中精氨酸是两性离子（质子化侧链，去质子化C-末端）的盐桥结构变得比电荷溶剂化结构更稳定。最稳定的电荷溶剂化结构和盐桥结构之间的能量差。对于Arg，M+从-0.7 kcal/mol增加。对于Arg，Li+至+3.3 kcal/mol。Cs+。盐桥和电荷溶剂化结构的稳定性在M = Li和Na之间反转。计算结果与离解实验结果符合得很好。低能解离途径取决于阳离子的大小。与小阳离子（Li和Na）络合的精氨酸失去H2O，而与较大阳离子（K、Rb和Cs）络合的精氨酸失去NH3。H2O的损失必须来自电荷溶剂化离子，而NH3的损失可以来自盐桥结构的质子化侧链。使用几种阳离子化精氨酸衍生物的解离实验的结果与这两种不同结构的存在是一致的。特别是，精氨酸甲酯，不能形成盐桥，通过失去甲醇解离，类似于从Arg失去H2O。M+;未观察到NH3损失。虽然解离实验探测气相结构间接，所观察到的碎裂途径是在良好的协议与计算的最低能量异构体。实验和理论结果的结合提供了强有力的证据表明，在气相中的奎宁-碱金属离子络合物的结构从电荷溶剂化结构的盐桥结构的金属离子的大小的增加。
The gas-phase structures of cationized arginine, Arg . M+, M = Li, Na, K, Rb, and Cs, were studied both by hybrid method density functional theory calculations and experimentally using low-energy collisionally activated and thermal radiative dissociation. Calculations at the B3LYP/LACVP++** level of theory show that the salt-bridge structures in which the arginine is a zwitterion (protonated side chain, deprotonated C-terminus) become more stable than the charge-solvated structures with increasing metal ion size. The difference in energy between the most stable charge-solvated structure and salt-bridge structure of Arg . M+ increases from -0.7 kcal/mol for Arg . Li+ to +3.3 kcal/mol for Arg . Cs+. The stabilities of the salt-bridge and charge-solvated structures reverse between M = Li and Na. These calculations are in good agreement with the results of dissociation experiments. The low-energy dissociation pathways depend on the cation size. Arginine complexed with small cations (Li and Na) loses H2O, while arginine complexed with larger cations (K, Rb, and Cs) loses NH3. Loss of H2O must come from a charge-solvated ion, whereas the loss of NH3 can come from the protonated side chain of a salt-bridge structure. The results of dissociation experiments using several cationized arginine derivatives are consistent with the existence of these two distinct structures. In particular, arginine methyl esters, which cannot form salt bridges, dissociate by loss of methanol, analogous to loss of H2O from Arg . M+; no loss of NH3 is observed. Although dissociation experiments probe gas-phase structure indirectly, the observed fragmentation pathways are in good agreement with the calculated lowest energy isomers. The combination of the results from experiment and theory provides strong evidence that the structure of arginine-alkali metal ion complexes in the gas phase changes from a charge-solvated structure to a salt bridge structure as the size of the metal ion increases.