The Howard P. Isermann Department of Chemical and Biological Engineering and The Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
Langmuir. 2013 Jun 25;29(25):8017-24. doi: 10.1021/la401203r. Epub 2013 Jun 4.
TMAO, a potent osmolyte, and TBA, a denaturant, have similar molecular architecture but somewhat different chemistry. We employ extensive molecular dynamics simulations to quantify their behavior at vapor-water and octane-water interfaces. We show that interfacial structure-density and orientation-and their dependence on solution concentration are markedly different for the two molecules. TMAO molecules are moderately surface active and adopt orientations with their N-O vector approximately parallel to the aqueous interface. That is, not all methyl groups of TMAO at the interface point away from the water phase. In contrast, TBA molecules act as molecular amphiphiles, are highly surface active, and, at low concentrations, adopt orientations with their methyl groups pointing away and the C-O vector pointing directly into water. The behavior of TMAO at aqueous interfaces is only weakly dependent on its solution concentration, whereas that of TBA depends strongly on concentration. We show that this concentration dependence arises from their different hydrogen bonding capabilities-TMAO can only accept hydrogen bonds from water, whereas TBA can accept (donate) hydrogen bonds from (to) water or other TBA molecules. The ability to self-associate, particularly visible in TBA molecules in the interfacial layer, allows them to sample a broad range of orientations at higher concentrations. In light of the role of TMAO and TBA in biomolecular stability, our results provide a reference with which to compare their behavior near biological interfaces. Also, given the ubiquity of aqueous interfaces in biology, chemistry, and technology, our results may be useful in the design of interfacially active small molecules with the aim to control their orientations and interactions.
TMAO 是一种有效的渗透物，TBA 是一种变性剂，它们具有相似的分子结构，但化学性质略有不同。我们采用广泛的分子动力学模拟来量化它们在汽-水和辛烷-水界面的行为。结果表明，两种分子在界面的结构密度和取向及其对溶液浓度的依赖性有显著差异。TMAO 分子具有中等的表面活性，其 N-O 矢量大致平行于水界面取向。也就是说，并非 TMAO 分子在界面上的所有甲基都指向远离水相的方向。相比之下，TBA 分子作为分子两亲物，具有很强的表面活性，并且在低浓度下，其甲基指向远离水相，C-O 矢量直接指向水相的取向。TMAO 在水界面上的行为仅受其溶液浓度的微弱影响，而 TBA 的行为强烈依赖于浓度。我们表明，这种浓度依赖性源于它们不同的氢键能力-TMAO 只能接受来自水的氢键，而 TBA 可以接受（捐赠）来自（至）水或其他 TBA 分子的氢键。自缔合的能力，特别是在界面层中的 TBA 分子中可见，使得它们能够在更高浓度下采样更广泛的取向。鉴于 TMAO 和 TBA 在生物分子稳定性中的作用，我们的结果为比较它们在生物界面附近的行为提供了参考。此外，鉴于水界面在生物学、化学和技术中的普遍性，我们的结果可能有助于设计具有控制其取向和相互作用目的的界面活性小分子。
