Ikeguchi M, Nakamura S, Shimizu K
Contribution from the Department of Biotechnology, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
J Am Chem Soc. 2001 Jan 31;123(4):677-82. doi: 10.1021/ja002064f.
Hydrophobic effects in aqueous urea were analyzed by molecular dynamics simulations. The contribution of solvents to the potential of mean force between two methane molecules was calculated by using molecular dynamics simulations and was compared with the solubility data of hydrocarbons in aqueous urea. Both the simulation results and the solubility data indicated that urea stabilizes methane-methane association. The stabilization was due to increasing the solvation free energies of small hydrocarbons such as methane by addition of urea. The solvation free energies of larger hydrocarbons, on the other hand, are decreased by addition of urea. This effect of the solute size on hydrophobic free energies in aqueous urea was also analyzed by using molecular dynamics simulations by means of division of the solvation process into two parts: the cavity formation and the introduction of the solute-solvent attractive interactions. In the cavity formation, urea increased hydrophobic free energies, and in the introduction of the solute-solvent attractive interactions, urea decreased hydrophobic free energies. The influence of urea on hydrophobic free energies was determined by the balance of effects of the two parts of the solvation process.
通过分子动力学模拟分析了尿素水溶液中的疏水作用。利用分子动力学模拟计算了溶剂对两个甲烷分子之间平均力势的贡献，并与烃类在尿素水溶液中的溶解度数据进行了比较。模拟结果和溶解度数据均表明，尿素可稳定甲烷 - 甲烷缔合。这种稳定作用是由于添加尿素增加了甲烷等小分子烃的溶剂化自由能。另一方面，添加尿素会降低较大烃类的溶剂化自由能。还通过分子动力学模拟，将溶剂化过程分为两个部分：空穴形成和溶质 - 溶剂吸引相互作用的引入，来分析溶质大小对尿素水溶液中疏水自由能的这种影响。在空穴形成过程中，尿素增加了疏水自由能，而在溶质 - 溶剂吸引相互作用的引入过程中，尿素降低了疏水自由能。尿素对疏水自由能的影响取决于溶剂化过程这两个部分的效果平衡。
