National Institute for Nanotechnology, 11421 Saskatchewan Drive, Edmonton, Alberta, T6G 2M9, Canada.
J Phys Chem B. 2010 Jan 14;114(1):613-9. doi: 10.1021/jp908814t.
We employ molecular dynamics simulations and the reference interaction site model (RISM) integral equation theory to study the solvation structure and solvation thermodynamics of the transfer process from water to a water-urea mixture. Simple positive and negative ions together with uncharged species of the same size are used as crude models for the hydrophilic and hydrophobic groups of a protein. We find that urea preferentially solvates positively charged species. The solvation free energies obtained indicate that larger solutes favor the transfer from water to a water-urea mixture. The decomposition of the transfer free energy into the energetic and entropic terms shows that the energetic part is much larger than the entropic one and tends to dominate the transfer process, supporting the direct mechanism of urea-denaturation. In addition, the effect of urea on the water liquid structure is discussed from the viewpoint of solvation entropy.
我们采用分子动力学模拟和参考相互作用位点模型（RISM）积分方程理论研究了从水到水-脲混合物的转移过程中的溶剂化结构和溶剂化热力学。简单的正负离子以及相同大小的不带电物质被用作蛋白质亲水性和疏水性基团的粗糙模型。我们发现脲优先溶剂化带正电荷的物质。所得溶剂化自由能表明，较大的溶质有利于从水转移到水-脲混合物。将转移自由能分解为能量和熵项表明，能量部分远大于熵部分，并且倾向于主导转移过程，支持脲变性的直接机制。此外，还从溶剂化熵的角度讨论了脲对水液体结构的影响。
