客体构象自适应驱动的分子胶囊★

doi:10.6023/A25050190

摘要/Abstract

非共价分子胶囊是超分子化学的核心研究对象, 其基于氢键、静电等非共价作用构建的动态限域结构, 在催化、医药及材料等领域极具应用价值. 然而, 传统分子胶囊的构筑常依赖于超分子主体中预置互补基元. 本工作突破这一局限, 设计合成以雷锁酚杯[4]芳烃为骨架的水溶性2-氨基苯并咪唑分子杯1, 通过客体分子调控柔性片段构象, 实现水相中超分子主体二聚. 以对称型直链烷烃和非对称型直链烷基苯乙烯类半菁染料为客体, 系统探究其与分子杯1的主客体识别行为. 结果表明, 碳链长度为n=12~20的直链烷烃, 分别通过延展、延展/螺旋、延展/盘旋等构象, 协同疏水作用诱导分子杯二聚形成胶囊; 苯乙烯类半菁染料分子的柔性烷基链, 经延展或折叠构象, 同样可驱动分子杯二聚. 疏水作用与C—H…π作用的协同效应, 是该类分子胶囊形成的主要驱动力.

关键词: 分子杯, 构象自适应, 疏水作用, C—H…π作用, 分子胶囊

Non-covalent molecular capsules stand as a central research theme in the field of supramolecular chemistry. Characterized by their dynamic confined architectures assembled through non-covalent interactions, including hydrogen bonding and electrostatic interaction, these capsules hold significant promise for applications in catalysis, medicine, and materials science. Conventionally, the construction of molecular capsules has predominantly depended on pre-embedded complementary motifs within supramolecular hosts, a limitation that restricts their synthetic versatility and adaptability. This study addresses this challenge by presenting the design and synthesis of a water-soluble 2-aminobenzimidazole-functional- ized cavitand 1, which is based on a resorcin[4]arene framework. And we examined the binding of the homologous series of the n-alkanes (n-C₇H₁₆ to n-C₂₀H₄₂) to cavitand 1 using a combination of ¹H NMR spectroscopy (nuclear magnetic resonance spectroscopy), 2D NOESY (two-dimensional Nuclear Overhauser Effect Spectroscopy) and DOSY (diffusion ordered spectroscopy) experiments. Cavitand 1 can form 1∶1 complexes with n-C₇H₁₆ and n-C₁₀H₂₂, and no encapsulation behavior for n-C₁₁H₂₄ because the size of n-C₁₁H₂₄ is too large to form 1∶1 complex and too small to form a dimeric capsule. n-C₁₂H₂₆ to n-C₂₀H₄₂ are good templates for the formation of 1∶2 guest-host capsular complexes. The guest of n-C₁₂H₂₆ fits the space comfortably in an extended conformation and broadened, symmetrical signal patterns were observed in the ¹H NMR spectrum. For n-C₁₅H₃₂ the signals are sharper suggesting a kinetically more stable complex. The conformation of n-C₁₅H₃₂ inside the capsule was determined by 2D NOESY experiments. Cross-peaks between the hydrogen atoms at C(1) and C(3) and at C(1) and C(4), C(2) and C(4) and at C(2) and C(5) were observed. But C(6) is in NOE contact only with C(8). This demonstrates the presence of gauche conformations of four carbon atoms at the ends and an extended chain of carbon atoms in the middle. n-C₇H₁₆⊂1 is a 1∶1 complex and n-C₁₅H₃₂⊂1.1 is a dimeric capsule confirmed by DOSY experiments which reveal diffusion coefficients for n-C₇H₁₆⊂1 (D=2.02×10⁻⁶ cm²•s⁻¹) and n-C₁₅H₃₂⊂1.1 (D=1.54×10⁻⁶ cm²•s⁻¹). Through the Stokes-Einstein relationship, show that the hydrodynamic volume of n-C₁₅H₃₂⊂1.1 is 2.3 times that of n-C₇H₁₆⊂1. Then we investigated host-guest interactions between cavitand 1 and styrylpyridinium SP-Cn (n=1~10) fluorophores in solution using ¹H NMR and UV-Vis absorption spectra. The results indicate that a supramolecular nano-capsule structure was formed with a 2∶1 host-guest stoichiometric ratio (SP-Cn⊂1.1). The electron-poor pyridinium group of SP-Cn is bound within the electron-rich cavity through cation…π interactions. Hydrophobic effects and C—H…π hydrogen bonds drive two cavitand 1 to form a capsule. And the alkyl chain of SP-C10 was compressed to J-shaped conformation by the restricted space. SP-C1⊂1.1 exhibits strong fluorescence in water due to the suppression of aromatic ring rotation within the confined space. Overall, the formation of these molecular capsules is primarily driven by the synergistic action of hydrophobic interactions and C—H…π interactions, providing new insights into the rational design of supramolecular assemblies.

Key words: cavitand, conformation adaptation, hydrophobicity, C—H…π interaction, molecular capsule

引用此文

陈永青, 高雅, 朱玉洁, 于洋. 客体构象自适应驱动的分子胶囊^★[J]. 化学学报, 2025, 83(9): 993-999.

Yongqing Chen, Ya Gao, Yujie Zhu, Yang Yu. Molecular Capsules Driven by Guest Conformational Adaptation^★[J]. Acta Chimica Sinica, 2025, 83(9): 993-999.

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图/表 5

图式1. 2-氨基苯并咪唑基分子杯1和染料分子SP-Cn的合成路线

Scheme 1. Synthetic route to the cavitand 1 and dyes (SP-Cn)

图1. (a)正十二烷、正十五烷和正二十烷在胶囊1.1中的构象示意图; (b)正十二烷到正二十烷在胶囊1.1中的部分1H NMR谱图(600 MHz, D2O, 298 K)

Figure 1. (a) Conformational schematic illustration of n-C12H26, n-C15H32 and n-C20H42 in Capsule 1.1; (b) Partial 1H NMR spectra of n-C12H26 to n-C20H42 in Capsule 1.1 (600 MHz, D2O, 298 K)

图2. 正十五烷在胶囊1.1中的部分2D NOESY谱图(600 MHz, D2O, 298 K)

Figure 2. Partial of the 2D NOESY (600 MHz, D2O, 298 K) spectra of n-C15H32⊂1.1

图3. (a) SP-C5和SP-C8在胶囊1.1中的构象示意图; (b) SP-Cn (n=1~10)在胶囊1.1中的部分1H NMR谱图(600 MHz, D2O, 298 K), 红色为烷基链上甲基

Figure 3. (a) Conformational schematic illustration of SP-C5 and SP-C8 in Capsule 1.1; (b) Partial 1H NMR spectra of SP-Cn (n=1~10) in Capsule 1.1 (600 MHz, D2O, 298 K), red colors indicate methyl groups for alkyl chains

图4. SP-C1的水溶液(2.5 μmol/L)在不同物质的量1存在下的紫外吸收光谱(a)和荧光光谱图(b), 激发波长为450 nm; 插图为SP-C1⊂1在日光或405 nm光下的图像; (c) SP-C2的水溶液(2.5 μmol/L)在不同物质的量1存在下的紫外吸收光谱; (d)在515 nm处吸光度与n(1)/n(SP-C2)物质的量比的关系图

Figure 4. The absorption spectra (a) and fluorescent spectra (b) of SP-C1 in water in the presence of incremental amount of 1; Inset: photograph of SP-C1⊂1 under daylight or 405 nm light (c=2.5 μmol/L, λex=450 nm); (c) The absorption spectra of SP-C2 in water in the presence of incremental amount of 1; (d) The absorbance at 515 nm versus molar ratio of n(1)/n(SP-C2)

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