Binding of Hydrophobic Guests in a Coordination Cage Cavity is Driven by Liberation of "High-Energy" Water
Binding of Hydrophobic Guests in a Coordination Cage Cavity is Driven by Liberation of "High-Energy" Water
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配位笼腔中疏水客体的结合是由“高能”水的释放驱动的
DOI：
10.1002/chem.201705260
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
Metherell A
中科院分区：
文献类型：
--
作者：
Metherell A
M8 L12立方配位笼的空腔可以容纳10个水分子的簇，其中每个水分子的平均氢键数比本体溶液少0.5个H-键。 这些“氢键受抑”或“高能”水分子在空腔中的存在导致与客体结合相关的疏水效应主要是基于焓的，因为这些水分子可以在释放时改善其氢键环境。这与疏水效应的经典形式形成对比，其中与从疏水表面释放有序分子相关的有利熵变占主导地位。对于几位客人来说，范特霍夫图表明，在水中结合的自由能主要是焓驱动的。对于5对由CH 2基团的存在或不存在而相关的同源客体，客体结合的ΔHandTΔ S的增量变化-即ΔΔHandTΔΔS，CH 2基团产生的贡献的差异-对于ΔΔ HandT Δ S始终为5（±1）kJ mol− 1，对于T ΔΔS为0（±1）kJ mol − 1。 疏水客体结合中Δ H的系统优势与客体结合是由“高能”水分子释放到更有利的溶剂化环境中所主导的观点一致，正如最近对葫芦脲家族的一些成员所证明的那样。
The cavity of an M8L12cubic coordination cage can accommodate a cluster of ten water molecules in which the average number of hydrogen bonds per water molecule is 0.5 H‐bonds less than it would be in the bulk solution. The presence of these “hydrogen‐bond frustrated” or “high‐energy” water molecules in the cavity results in the hydrophobic effect associated with guest binding being predominantly enthalpy‐based, as these water molecules can improve their hydrogen‐bonding environment on release. This contrasts with the classical form of the hydrophobic effect in which the favourable entropy change associated with release of ordered molecules from hydrophobic surfaces dominates. For several guests Van't Hoff plots showed that the free energy of binding in water is primarily enthalpy driven. For five homologous pairs of guests related by the presence or absence of a CH2group, the incremental changes to ΔHandTΔSfor guest binding—that is, ΔΔHandTΔΔS, the difference in contributions arising from the CH2group—are consistently 5(±1) kJ mol−1for ΔΔHand 0(±1) kJ mol−1forTΔΔS. This systematic dominance of ΔHin the binding of hydrophobic guests is consistent with the view that guest binding is dominated by release of “high energy” water molecules into a more favourable solvation environment, as has been demonstrated recently for some members of the cucurbituril family.