Department of Chemistry, Indian Institute of Technology , Guwahati, Assam, India-781039.
J Phys Chem B. 2012 Apr 26;116(16):4991-5001. doi: 10.1021/jp300792p. Epub 2012 Apr 17.
Ternary solutions consisting of urea, tert-butyl alcohol (TBA), and water are investigated employing molecular dynamics simulations. The main purpose of the present paper is to investigate the effect of urea on TBA aggregation and by extension its influence on hydrophobic interactions. The aggregation of TBA can be detected from the concentration dependence of structural properties such as first-shell TBA-water coordination numbers and TBA-TBA hydrogen-bond numbers, as well as through changes in the translational diffusion coefficients of TBA. It is found that urea acts to delay the association of TBA to concentrations greater than those required to cause TBA aggregation in binary TBA-water systems. It is shown that urea acts through a direct mechanism, whereby it preferentially binds to TBA replacing water from the first coordination shell. TBA-urea hydrogen bonds can be as strong as, or stronger than, those of TBA-water, and urea binds to both the hydrophilic and hydrophobic moieties of TBA. Our observations are qualitatively consistent with experimental results for urea-TBA-water solutions and with recent simulation studies of urea's action as a protein denaturant.
采用分子动力学模拟研究了由尿素、叔丁醇（TBA）和水组成的三元溶液。本文的主要目的是研究尿素对 TBA 聚集的影响，进而研究其对疏水相互作用的影响。TBA 的聚集可以通过结构性质的浓度依赖性来检测，如第一壳层 TBA-水配位数和 TBA-TBA 氢键数，以及 TBA 平移扩散系数的变化。结果表明，尿素的存在会延迟 TBA 的缔合，使其在二元 TBA-水体系中达到引起 TBA 聚集所需的浓度以上。结果表明，尿素通过直接机制起作用，优先与 TBA 结合，取代第一配位壳层中的水。TBA-尿素氢键可以与 TBA-水氢键一样强，甚至更强，并且尿素与 TBA 的亲水和疏水部分都结合。我们的观察结果与尿素-TBA-水溶液的实验结果以及最近关于尿素作为蛋白质变性剂作用的模拟研究定性一致。
