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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Structure of Cationized Arginine (Arg centre dot M~+, M = H, Li, Na, K, Rb, and Cs) in the Gas Phase: Further Evidence for Zwitterionic Arginine
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Structure of Cationized Arginine (Arg centre dot M~+, M = H, Li, Na, K, Rb, and Cs) in the Gas Phase: Further Evidence for Zwitterionic Arginine

机译：气相中阳离子化精氨酸的结构（Arg中心点M〜+，M = H，Li，Na，K，Rb和Cs）：两性离子精氨酸的进一步证据

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The gas-phase structures of cationized arginine, Arg centre dot 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 centre dot M~+ increases from -0.7 kcal/mol for Arg centre dot Li~+ to +3.3 kcal/mol for Arg centre dot 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 H_2O, while arginine complexed with larger cations (K, Rb, and Cs) loses NH_3. Loss of H_2O must come from a charge-solvated ion, whereas the loss of NH_3 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 H_2O from Arg centre dot M~+; no loss of NH_3 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.
机译：阳离子化精氨酸的气相结构，Arg中心点M〜+，M = Li，Na，K，Rb和Cs，通过混合方法密度泛函理论计算以及通过低能碰撞激活和热辐射实验研究离解。在B3LYP / LACVP ++〜（**）理论水平上的计算表明，精氨酸为两性离子的盐桥结构（质子化的侧链，去质子化的C端）比带金属的电荷溶剂化结构更稳定。离子大小。 Arg中心点M〜+的最稳定电荷溶剂化结构和盐桥结构之间的能量差从Arg中心点Li〜+的-0.7 kcal / mol增加到Arg中心点Cs〜的+3.3 kcal / mol +。盐桥和电荷溶剂化结构的稳定性在M = Li和Na之间反转。这些计算与解离实验的结果非常吻合。低能离解途径取决于阳离子的大小。与小阳离子（Li和Na）复合的精氨酸失去H_2O，与大阳离子（K，Rb和Cs）复合的精氨酸失去NH_3。 H_2O的损失必须来自于电荷溶解的离子，而NH_3的损失可能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进行解离实验的结果与这两个不同结构的存在一致。特别地，不能形成盐桥的精氨酸甲酯由于甲醇的损失而离解，类似于从Arg中心点M〜+失去H_2O。没有观察到NH_3的损失。尽管解离实验间接探测气相结构，但观察到的裂解途径与计算得到的最低能量异构体非常吻合。实验和理论结果的结合提供了强有力的证据，表明随着金属离子尺寸的增加，气相中精氨酸-碱金属离子配合物的结构从溶剂化结构变为盐桥结构。

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