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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DOI：
10.1002/chem.201704163
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发表时间：
2018-02-01
期刊：
影响因子：
--
通讯作者：
Ward MD
中科院分区：
文献类型：
--
作者：
Metherell AJ;Cullen W;Williams NH;Ward MD
M8L12立方配位笼的腔体可以容纳10个水分子簇，其中每个水分子的平均氢键数比在体溶液中少0.5个氢键。这些“氢键受挫”或“高能量”水分子的存在导致了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它们的氢键环境。这与经典的疏水效应形成对比，在经典的疏水效应中，与有序分子从疏水表面释放相关的有利熵变占主导地位。对几位来宾来说，范霍夫图表明，水中的自由结合能主要是由焓驱动的。对于存在或不存在CH2基团的5对同源客体，客体结合对ΔH和TΔS（即ΔΔH和TΔΔS）的增量变化，由CH2基团引起的贡献差异一致为ΔΔH的5（±1）kJ mol−1和TΔΔS的0（±1）kJ mol−1。ΔH在疏水客体结合中的系统优势与客体结合是由“高能量”水分子释放到更有利的溶剂化环境中所主导的观点是一致的，正如最近在葫芦素家族的一些成员中所证明的那样。
The cavity of an M8L12 cubic 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 CH2 group, the incremental changes to ΔH and TΔS for guest binding—that is, ΔΔH and TΔΔS, the difference in contributions arising from the CH2 group—are consistently 5(±1) kJ mol−1 for ΔΔH and 0(±1) kJ mol−1 for TΔΔS. This systematic dominance of ΔH in 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.
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