van der Spoel David, van Maaren Paul J, Larsson Per, Tîmneanu Nicusor
Department of Cell and Molecular Biology, Uppsala University, Husargatan 3, Box 596, SE-751 24 Uppsala, Sweden.
J Phys Chem B. 2006 Mar 9;110(9):4393-8. doi: 10.1021/jp0572535.
The thermodynamics of hydrogen bond breaking and formation was studied in solutions of alcohol (methanol, ethanol, 1-propanol) molecules. An extensive series of over 400 molecular dynamics simulations with an aggregate length of over 900 ns was analyzed using an analysis technique in which hydrogen bond (HB) breaking is interpreted as an Eyring process, for which the Gibbs energy of activation DeltaG can be determined from the HB lifetime. By performing simulations at different temperatures, we were able to determine the enthalpy of activation DeltaH and the entropy of activation TDeltaS for this process from the Van't Hoff relation. The equilibrium thermodynamics was determined separately, based on the number of donor hydrogens that are involved in hydrogen bonds. Results (DeltaH) are compared to experimental data from Raman spectroscopy and found to be in good agreement for pure water and methanol. The DeltaG as well as the DeltaG are smooth functions of the composition of the mixtures. The main result of the calculations is that DeltaG is essentially independent of the environment (around 5 kJ/mol), suggesting that buried hydrogen bonds (e.g., in proteins) do not contribute significantly to protein stability. Enthalpically HB formation is a downhill process in all substances; however, for the alcohols there is an entropic barrier of 6-7 kJ/mol, at 298.15 K, which cannot be detected in pure water.
在醇（甲醇、乙醇、1-丙醇）分子溶液中研究了氢键断裂和形成的热力学。使用一种分析技术对超过400次分子动力学模拟进行了广泛分析，这些模拟的总时长超过900纳秒，该技术将氢键（HB）断裂解释为一个艾林过程，其活化吉布斯自由能ΔG可由HB寿命确定。通过在不同温度下进行模拟，我们能够根据范特霍夫关系式确定该过程的活化焓ΔH和活化熵TDeltaS。基于参与氢键的供体氢的数量分别确定了平衡热力学。将结果（ΔH）与拉曼光谱的实验数据进行比较，发现对于纯水和甲醇，二者吻合良好。ΔG以及ΔG是混合物组成的平滑函数。计算的主要结果是，ΔG基本上与环境无关（约5 kJ/mol），这表明埋藏的氢键（例如在蛋白质中）对蛋白质稳定性的贡献不大。在所有物质中，从焓的角度来看，HB形成是一个能量降低的过程；然而，对于醇类，在298.15 K时存在6 - 7 kJ/mol的熵垒，这在纯水中无法检测到。
