Department of Chemistry, University of California, Berkeley, and Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-1460, United States.
J Am Chem Soc. 2010 Nov 17;132(45):16256-64. doi: 10.1021/ja107656g. Epub 2010 Oct 26.
The supramolecular host assembly Ga(4)L(6) (1; L = 1,5-bis[2,3-dihydroxybenzamido]naphthalene) encapsulates cationic guest molecules within its hydrophobic cavity and catalyzes a variety of chemical transformations within its confined interior space. Despite the well-defined structure, the host ligand framework and interior cavity are very flexible and 1 can accommodate a wide range of guest shapes and sizes. These observations raise questions about the steric effects of confinement within 1 and how encapsulation fundamentally changes the motions of guest molecules. Here we examine the motional dynamics (guest bond rotation and tumbling) of encapsulated guest molecules to probe the steric consequences of encapsulation within host 1. Encapsulation is found to increase the Ph-CH(2) bond rotational barrier for ortho-substituted benzyl phosphonium guest molecules by 3 to 6 kcal/mol, and the barrier is found to depend on both guest size and shape. The tumbling dynamics of guests encapsulated in 1 were also investigated, and here it was found that longer, more prolate-shaped guest molecules tumble more slowly in the host cavity than larger but more spherical guest molecules. The prolate guests reduce the host symmetry from T to C(1) in solution at low temperatures, and the distortion of the host framework that is in part responsible for this symmetry reduction is observed directly in the solid state. Analysis of guest motional dynamics is a powerful method for interrogating host structure and fundamental host-guest interactions.
超分子主体组装物 Ga(4)L(6)（1；L = 1,5-双[2,3-二羟基苯甲酰胺]萘）在其疏水性腔内封装阳离子客体分子，并在其受限的内部空间内催化各种化学转化。尽管结构明确，但主体配体框架和内部腔非常灵活，1 可以容纳各种形状和大小的客体。这些观察结果引发了关于主体 1 内的约束的空间位阻效应以及封装如何从根本上改变客体分子的运动的问题。在这里，我们研究了被封装的客体分子的运动动力学（客体键旋转和翻滚），以探测客体分子在主体 1 内封装的空间位阻后果。发现封装会将邻位取代的苄基膦鎓客体分子的 Ph-CH(2)键旋转势垒增加 3 至 6 kcal/mol，并且该势垒取决于客体的大小和形状。还研究了 1 中封装的客体的翻滚动力学，发现更长、更扁长形的客体分子在主体腔中翻滚速度比更大但更球形的客体分子慢。在低温下，长而扁长形的客体在溶液中将主体的对称性从 T 降低到 C(1)，并且观察到直接在固态中导致这种对称性降低的主体框架的变形。客体运动动力学分析是一种用于探测主体结构和基本主体-客体相互作用的强大方法。
