Conformation of K+(Crown Ether) Complexes Revealed by Ion Mobility-Mass Spectrometry and Ultraviolet Spectroscopy
Conformation of K+(Crown Ether) Complexes Revealed by Ion Mobility-Mass Spectrometry and Ultraviolet Spectroscopy
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离子淌度质谱和紫外光谱揭示 K（冠醚）配合物的构象
DOI：
10.1021/acs.jpca.0c09068
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
Inokuchi Yoshiya
中科院分区：
文献类型：
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作者：
Tainaka Sota;Ujihira Tomoyuki;Kubo Mayuko;Kida Motoki;Shimoyama Daisuke;Muramatsu Satoru;Abe Manabu;Haino Takeharu;Ebata Takayuki;Misaizu Fuminori;Ohshimo Keijiro;Inokuchi Yoshiya
用离子迁移质谱（IM-MS）、气相紫外光解离（UVPD）和溶液荧光光谱研究了二苯并-24-冠-8（DB24 C8）与K+离子形成的配合物的构象和电子结构。研究了DB24 C8的三种结构异构体（SymDB 24 C8、Asym 1DB 24 C8和Asym 2DB 24 C8），其中两个苯环的相对位置彼此不同。在86 K下的IM-MS结果显示，K+（SymDB 24 C8）和K+（Asym 1DB 24 C8）复合物的两组构象体清楚地分离，而K+（Asym 2DB 24 C8）复合物仅显示一组构象体。这两组构象体分别归属于开型和闭型，即配合物中的苯-苯距离分别为长（>6）和短（<6）。在300 K下的IM-MS不能分离K+（SymDB 24 C8）复合物的两组构象，因为开和闭构象之间的相互转换发生在300 K而不是86 K。DB24 C8的冠腔包裹在络合物中的K+离子周围，尽管IM-MS结果提供了在300 K下快速腔变形和稳定构象重建的直接证据。K+（SymDB 24 C8）和K+（Asym 1DB 24 C8）配合物在10 K时的UVPD光谱显示出宽的特征，并伴随着一些尖锐的电子振动带，这归因于多种构象的共存。甲醇溶液中的荧光光谱表明，在这三种配合物中，只有在K+（SymDB 24 C8）中形成了分子内激基缔合物，因为只有SymDB 24 C8在K+包封后可能在两个苯环之间形成平行构型。DB24 C8的三种结构异构体中K+离子的包封方法（“环绕”排列）相似，尽管两个苯环相对位置的差异影响了整个横截面。这项研究表明，温度控制的IM-MS加上适当的大体积基团的引入，如芳环的主体分子，可以揭示包封在主客体系统的动态方面。
The conformation and electronic structure of dibenzo-24-crown-8 (DB24C8) complexes with K+ion were examined by ion mobility–mass spectrometry (IM–MS), ultraviolet (UV) photodissociation (UVPD) spectroscopy in the gas phase, and fluorescence spectroscopy in solution. Three structural isomers of DB24C8 (SymDB24C8, Asym1DB24C8, and Asym2DB24C8) in which the relative positions of the two benzene rings were different from each other were investigated. The IM–MS results at 86 K revealed a clear separation of two sets of conformers for the K+(SymDB24C8) and K+(Asym1DB24C8) complexes whereas the K+(Asym2DB24C8) complex revealed only one set. The two sets of conformers were attributed to the open and closed forms in which the benzene–benzene distances in the complexes were long (>6 Å) and short (<6 Å), respectively. IM–MS at 300 K could not separate the two conformer sets of the K+(SymDB24C8) complex because the interconversion between the open and closed conformations occurred at 300 K and not at 86 K. The crown cavity of DB24C8 was wrapped around the K+ion in the complex, although the IM–MS results availed direct evidence of rapid cavity deformation and the reconstruction of stable conformers at 300 K. The UVPD spectra of the K+(SymDB24C8) and K+(Asym1DB24C8) complexes at ∼10 K displayed broad features that were accompanied by a few sharp vibronic bands, which were attributable to the coexistence of multiple conformers. The fluorescence spectra obtained in a methanol solution suggested that the intramolecular excimer was formed only in K+(SymDB24C8) among the three complexes because only SymDB24C8 could possibly assume a parallel configuration between the two benzene rings upon K+encapsulation. The encapsulation methods for K+ion (the “wraparound” arrangement) are similar in the three structural isomers of DB24C8, although the difference in the relative positions of the two benzene rings affected the overall cross-section. This study demonstrated that temperature-controlled IM–MS coupled with the introduction of appropriate bulky groups, such as aromatic rings to host molecules, could reveal the dynamic aspects of encapsulation in host–guest systems.