Sinibaldi R, Casieri C, Melchionna S, Onori G, Segre A L, Viel S, Mannina L, De Luca F
SOFT-INFM-CNR Research Center and Dipartimento di Fisica, Università La Sapienza, I-00185 Roma, Italy.
J Phys Chem B. 2006 May 4;110(17):8885-92. doi: 10.1021/jp056897+.
Two binary aqueous mixtures which contain the small amphiphilic molecules TMAO (trimethylamine-N-oxide) and TBA (tert-butyl alcohol) have been investigated by molecular dynamics simulations and NMR chemical shift and self-diffusion measurements. TMAO is an osmolyte, while TBA is a monohydrate alcohol. Both possess bulky hydrophobic groups and polar heads, namely, NO in TMAO and OH in TBA. The hydrophilic/hydrophobic content of these isosteric molecules strongly modulates the structure and dynamics of the hydration shell, which is thought to be responsible for the effects observed on proteins and phospholipids. Simulation results, especially on hydrogen-bond networking, spatial correlations, and self-diffusivity, are consistent with NMR data and agree well with previous numerical studies on similar solutions. The methods employed allow the elucidation of the microscopic features of the solutions. For TBA solutions, the hydration shell is found to have a low density and a large spatial spread, and thus, above the molar fraction of 0.03, reduction of hydrophobic hydration drives self-aggregation of the solute. This effect does not take place in TMAO solutions, where the hydration shell is more compact and stable, maintaining its structure over a wider range of solute concentrations.
通过分子动力学模拟以及核磁共振化学位移和自扩散测量，对两种包含两亲性小分子三甲胺 - N - 氧化物（TMAO）和叔丁醇（TBA）的二元水混合物进行了研究。TMAO是一种渗透溶质，而TBA是一种一元醇水合物。两者都具有庞大的疏水基团和极性头，即TMAO中的N⁺O⁻和TBA中的 - OH。这些等电子分子的亲水/疏水含量强烈调节水合壳层的结构和动力学，而水合壳层被认为是对蛋白质和磷脂产生观察到的影响的原因。模拟结果，特别是关于氢键网络、空间相关性和自扩散率的结果，与核磁共振数据一致，并且与先前对类似溶液的数值研究结果吻合良好。所采用的方法能够阐明溶液的微观特征。对于TBA溶液，发现水合壳层密度低且空间分布广，因此，在摩尔分数高于0.03时，疏水水合作用的减弱会促使溶质发生自聚集。这种效应在TMAO溶液中不会发生，在TMAO溶液中，水合壳层更紧密且稳定，在更宽的溶质浓度范围内保持其结构。
