Hunger Johannes, Ottosson Niklas, Mazur Kamila, Bonn Mischa, Bakker Huib J
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
Phys Chem Chem Phys. 2015 Jan 7;17(1):298-306. doi: 10.1039/c4cp02709d.
The amphiphilic osmolyte trimethylamine-N-oxide (TMAO) is commonly found in natural organisms, where it counteracts biochemical stress associated with urea in aqueous environments. Despite the important role of TMAO as osmoprotectant, the mechanism behind TMAO's action has remained elusive. Here, we study the interaction between urea, TMAO, and water in solution using broadband (100 MHz-1.6 THz) dielectric spectroscopy. We find that the previously reported tight hydrogen bonds between 3 water molecules and the hydrophilic amine oxide group of TMAO, remain intact at all investigated concentrations of urea, showing that no significant hydrogen bonding occurs between the two co-solutes. Despite the absence of direct TMAO-urea interactions, the solute reorientation times of urea and TMAO show an anomalous nonlinear increase with concentration, for ternary mixtures containing equal amounts of TMAO and urea. The nonlinear increase of the reorientation correlates with changes in the viscosity, showing that the combination of TMAO and urea cooperatively enhances the hydrogen-bond structure of the ternary solutions. This nonlinear increase is indicative of water mediated interaction between the two solutes and is not observed if urea is combined with other amphiphilic solutes.
两亲性渗透溶质三甲胺 - N - 氧化物（TMAO）常见于天然生物体中，在水环境中它可抵消与尿素相关的生化应激。尽管TMAO作为渗透保护剂具有重要作用，但其作用背后的机制仍不清楚。在此，我们使用宽带（100 MHz - 1.6 THz）介电谱研究了溶液中尿素、TMAO和水之间的相互作用。我们发现，先前报道的3个水分子与TMAO的亲水性氧化胺基团之间紧密的氢键，在所有研究的尿素浓度下都保持完整，这表明两种共溶质之间没有显著的氢键形成。尽管不存在直接的TMAO - 尿素相互作用，但对于含有等量TMAO和尿素的三元混合物，尿素和TMAO的溶质重取向时间随浓度呈现异常的非线性增加。重取向的非线性增加与粘度变化相关，表明TMAO和尿素的组合协同增强了三元溶液的氢键结构。这种非线性增加表明两种溶质之间存在水介导的相互作用，而当尿素与其他两亲性溶质组合时则未观察到这种现象。
