Halide Size-Selective Binding by Cucurbit[5]uril–Alkali Cation Complexes in the Gas Phase
Halide Size-Selective Binding by Cucurbit[5]uril–Alkali Cation Complexes in the Gas Phase
复制标题
气相中葫芦[5]uril-碱金属阳离子配合物的卤化物尺寸选择性结合
DOI：
10.1021/acs.jpca.1c05060
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Dearden, David V.
中科院分区：
文献类型：
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作者：
Heravi, Tina;Shen, Jiewen;Johnson, Spencer;Asplund, Matthew C.;Dearden, David V.
我们报告的数据表明，与碱金属阳离子帽葫芦[5]脲（CB[5]）的门户网站的配合物结合卤素阴离子的大小选择性观察到在气相中：氯结合CB[5]腔内，Br-观察内外，和I-结合弱外。这反映在持续的非共振辐射碰撞诱导解离（SORI-CID）实验中：所有检测到的Cl-络合物在较高的能量下解离，Br-络合物表现出不寻常的双峰解离行为，部分离子群体在非常低的能量下解离，其余的解离在显著较高的能量下，与Cl-观察到的能量相当。用傅里叶变换离子回旋共振技术测量了[CB[5] + M2 X]+（M = Na，X = Cl或Br）在SF6中的消相干截面，在较宽的能量范围内，其消相干截面与[CB[5] + Na]+的消相干截面相当或小于[CB[5] + Na]+的消相干截面，表明这些配合物中的Cl-或Br-结合在CB[5]空腔内.相比之下，[CB[5] + K2 Br]+的横截面比[CB[5] + Na]+的横截面大约20%，表明外部结合可能与SORI中观察到的弱结合组分相对应。虽然没有观察到与碱金属阳离子帽的I-络合物，但碱土金属碘化物与CB[5]产生的络合物的横截面比[CB[5] + Na]+的横截面大5-10%，表明外部结合的碘化物。在M06-2X/6-31+G* 水平上的几何优化表明，内部阴离子结合在能量上比外部结合更有利，约为50-200 kJ mol-1;因此，实验观察到的外部结合复合物必须是由于大的能量障碍阻碍了大阴离子通过CB[5]门户，阻止进入内部。使用MMFF//M06-2X/6-31+G* 理论计算阴离子逸出的屏障支持这一想法，并表明我们观察到的尺寸选择性结合是由于屏障中的阴离子尺寸依赖性差异。
We report data that suggest complexes with alkali cations capping the portals of cucurbit[5]uril (CB[5]) bind halide anions size-selectively as observed in the gas phase: Cl–binds inside the CB[5] cavity, Br–is observed both inside and outside, and I–binds weakly outside. This is reflected in sustained off-resonance irradiation collision-induced dissociation (SORI-CID) experiments: all detected Cl–complexes dissociate at higher energies, and Br–complexes exhibit unusual bimodal dissociation behavior, with part of the ion population dissociating at very low energies and the remainder dissociating at significantly higher energies comparable to those observed for Cl–. Decoherence cross sections measured in SF6using cross-sectional areas by Fourier transform ion cyclotron resonance techniques for [CB[5] + M2X]+(M = Na, X = Cl or Br) are comparable to or less than that of [CB[5] + Na]+over a wide energy range, suggesting that Cl–or Br–in these complexes are bound inside the CB[5] cavity. In contrast, [CB[5] + K2Br]+has a cross section measured about 20% larger than that of [CB[5] + Na]+, suggesting external binding that may correspond with the weakly bound component seen in SORI. While I–complexes with alkali cation caps were not observed, alkaline earth iodides with CB[5] yielded complexes with cross sections 5–10% larger than that of [CB[5] + Na]+, suggesting externally bound iodide. Geometry optimization at the M06-2X/6-31+G* level ofab initiotheory suggests that internal anion binding is energetically favored by approximately 50–200 kJ mol–1over external binding; thus, the externally bound complexes observed experimentally must be due to large energetic barriers hindering the passing of large anions through the CB[5] portal, preventing access to the interior. Calculation of the barriers to anion egress using MMFF//M06-2X/6-31+G* theory supports this idea and suggests that the size-selective binding we observe is due to anion size-dependent differences in the barriers.