Water-mediated interactions between trimethylamine-N-oxide and urea
Water-mediated interactions between trimethylamine-N-oxide and urea
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DOI：
10.1039/c4cp02709d
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发表时间：
2015-01-01
影响因子：
3.3
通讯作者：
Bakker, Huib J.
中科院分区：
文献类型：
--
作者：
Hunger, Johannes;Ottosson, Niklas;Bakker, Huib J.
两亲性渗透剂三甲基胺-N-氧化物（TMAO）通常存在于天然生物体中，其中它抵消与水性环境中的尿素相关的生化应激。尽管TMAO作为植物保护剂的重要作用，但TMAO作用背后的机制仍然难以捉摸。在这里，我们研究尿素，TMAO，和水在溶液中使用宽带（100 MHz-1.6 THz）介电谱之间的相互作用。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的紧密氢键在所有研究的尿素浓度下保持完整，表明在两种共溶质之间没有发生显著的氢键。尽管没有直接的TMAO-尿素相互作用，尿素和TMAO的溶质重取向时间显示出异常的非线性增加与浓度，三元混合物含有等量的TMAO和尿素。的非线性增加的重取向与粘度的变化，表明TMAO和尿素的组合协同增强的氢键结构的三元溶液。这种非线性增加指示两种溶质之间的水介导的相互作用，并且如果尿素与其他两亲性溶质组合则未观察到。
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 hydrogenbond 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.