Department of Chemistry, Institute of Nanotechnology Bar-Ilan University, Ramat-Gan 52900, Israel.
Chirality. 2010 Jun;22(6):587-92. doi: 10.1002/chir.20787.
The size and configuration of the hydration layer of solutes play a major role in their thermodynamic features. With respect to amino acids in water, a series of indirect evidence strongly suggest that their hydration layer acquires a chiral configuration induced by their chiral centers. Such a chiral hydration may act as a recognition factor in the various biochemical interactions, but information on it remains rather scarce. In this study, we determined by dilution microcalorimetry the fraction of the hydration energy invested in the chiral distortion of the hydration layer surrounding D- and I-alanine in water. The results indicate that in dilute solutions, a multilayered chiral hydration surrounds each of these solutes and amounts to over 100 water molecules. In concentrated solutions, the immediate chiral hydration layer decreases to approximately 30 water molecules. The energy invested in the induction of the chiral twist in the hydration layer is predominantly attributed to TDeltaS, the energy associated with "configurational entropy," which amounts to only several cal/mol, about a thousandth of the total energy of the hydration shell.
溶质水合层的大小和结构对其热力学性质起着重要作用。就水中的氨基酸而言，一系列间接证据强烈表明，它们的水合层由于手性中心的存在而获得手性结构。这种手性水合可能是各种生化相互作用中的识别因素，但关于它的信息仍然相当缺乏。在这项研究中，我们通过稀释量热法确定了 D-和 I-丙氨酸在水中的水合层手性变形所消耗的水合能量的分数。结果表明，在稀溶液中，每个溶质周围都有多层手性水合层，数量超过 100 个水分子。在浓溶液中，直接的手性水合层减少到大约 30 个水分子。诱导水合层手性扭曲所消耗的能量主要归因于 TDeltaS，即与“构象熵”相关的能量，其仅为几 cal/mol，约为水合壳总能量的千分之一。
