Solvent and pressure effects on the motions of encapsulated guests: tuning the flexibility of a supramolecular host.
Solvent and pressure effects on the motions of encapsulated guests: tuning the flexibility of a supramolecular host.
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溶剂和压力对封装客体运动的影响：调节超分子主体的灵活性
DOI：
10.1021/ja309949q
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发表时间：
2013
影响因子：
15
通讯作者：
K.N. Raymond
中科院分区：
文献类型：
--
作者：
J.S. Mugridge;A. Zahl;R. van Eldik;R.G. Bergman;K.N. Raymond
超分子宿主组装体[Ga4L6]12-[1；L = 1,5-双（2,3-二羟基苯并胺）萘]含有一个灵活的疏水内腔，可以包封阳离子客体分子并催化多种化学转化。邻取代苄基磷包封客体分子的ar - 2键旋转势垒对宿主内部空间的大小和形状很敏感。在这里，我们研究了散装溶剂（水、甲醇或DMF）或施加压力（高达150mpa）的变化如何影响被封装的苄基磷客体的旋转动力学，作为探测宿主腔大小或灵活性变化的一种方式。当host1溶解在具有较大溶剂内压（∂U/∂V）T的有机溶剂中时，我们发现与在水溶液中相比，ar - ch2键旋转的自由能垒增加了1-2 kcal/mol。同样，当外部压力施加于溶液中的主客体复合物时，封装客体的键旋转速率降低。这些速率变化的幅度和使用溶剂内压或施加外部压力获得的活化量是非常相似的。NOE距离测量显示，有机溶液与水溶液相比，主客体平均距离更短（~ 0.3 Å）。这些实验表明，增加溶剂内部压力或施加外部压力会降低宿主腔的尺寸或灵活性，导致被封装的客体分子的运动受到更大的限制。因此，改变体积溶剂或外部压力可用于调整包裹在柔性超分子宿主中的客体分子的物理性质或反应性。
The supramolecular host assembly [Ga4L6]12-[1; L = 1,5-bis(2,3-dihydroxybenzamido)naphthalene] contains a flexible, hydrophobic interior cavity that can encapsulate cationic guest molecules and catalyze a variety of chemical transformations. The Ar–CH2bond rotational barrier for encapsulated ortho-substituted benzyl phosphonium guest molecules is sensitive to the size and shape of the host interior space. Here we examine how changes in bulk solvent (water, methanol, or DMF) or applied pressure (up to 150 MPa) affect the rotational dynamics of encapsulated benzyl phosphonium guests, as a way to probe changes in host cavity size or flexibility. When host1is dissolved in organic solvents with large solvent internal pressures (∂U/∂V)T, we find that the free energy barrier to Ar–CH2bond rotation increases by 1–2 kcal/mol, compared with that in aqueous solution. Likewise, when external pressure is applied to the host–guest complex in solution, the bond rotational rates for the encapsulated guests decrease. The magnitude of these rate changes and the volumes of activation obtained using either solvent internal pressure or applied external pressure are very similar. NOE distance measurements reveal shorter average host–guest distances (∼0.3 Å) in organic versus aqueous solution. These experiments demonstrate that increasing solvent internal pressure or applied external pressure reduces the host cavity size or flexibility, resulting in more restricted motions for encapsulated guest molecules. Changing bulk solvent or external pressure might therefore be used to tune the physical properties or reactivity of guest molecules encapsulated in a flexible supramolecular host.