Paul Sandip, Patey G N
Department of Chemistry, University of British Columbia, Vancouver BC V6T 1Z1, Canada.
J Phys Chem B. 2006 Jun 1;110(21):10514-8. doi: 10.1021/jp0609378.
In dilute aqueous solution, tert-butyl alcohol (TBA) tends to aggregate but trimethylamine-N-oxide (TMAO) does not. Given that both molecules have very similar geometry with hydrophobic and hydrophilic groups, it is interesting to ask why they behave so differently in aqueous solution. To explore this question, we use molecular dynamics simulations to study two models representing TBA and TMAO that differ essentially only in their electrostatic properties. It is shown that this difference is sufficient to give the different solution behavior. Furthermore, the principal difference identified is that the hydrophilic group of TMAO (the oxygen) interacts on average much more strongly with water than the corresponding group (the hydroxyl) of TBA. A hydrogen-bond analysis shows that water-TBA and water-TMAO hydrogen bonds are similar in number, but that the hydrogen-bond energy is much more negative for water-TMAO. In all likelihood, this accounts for the different behavior in dilute aqueous solution.
在稀水溶液中，叔丁醇（TBA）易于聚集，而三甲胺 - N - 氧化物（TMAO）则不会。鉴于这两种分子具有非常相似的几何结构，都含有疏水基团和亲水基团，那么探究它们在水溶液中为何表现得如此不同就很有意思了。为了探讨这个问题，我们使用分子动力学模拟来研究两个分别代表TBA和TMAO的模型，这两个模型本质上仅在其静电性质上有所不同。结果表明，这种差异足以导致不同的溶液行为。此外，所确定的主要差异在于，TMAO的亲水基团（氧原子）与水的平均相互作用比TBA的相应基团（羟基）与水的相互作用要强得多。氢键分析表明，水 - TBA和水 - TMAO之间的氢键数量相似，但水 - TMAO的氢键能量负值要大得多。很可能，这就解释了它们在稀水溶液中的不同行为。
