Department of Chemistry, University of Toronto, 80 St George Street, Toronto, ON, Canada M5S 3H6.
Proc Natl Acad Sci U S A. 2011 Oct 4;108(40):16527-32. doi: 10.1073/pnas.1105450108. Epub 2011 Sep 12.
Hydrophobicity underpins self-assembly in many natural and synthetic molecular and nanoscale systems. A signature of hydrophobicity is its temperature dependence. The first experimental evaluation of the temperature and size dependence of hydration free energy in a single hydrophobic polymer is reported, which tests key assumptions in models of hydrophobic interactions in protein folding. Herein, the hydration free energy required to extend three hydrophobic polymers with differently sized aromatic side chains was directly measured by single molecule force spectroscopy. The results are threefold. First, the hydration free energy per monomer is found to be strongly dependent on temperature and does not follow interfacial thermodynamics. Second, the temperature dependence profiles are distinct among the three hydrophobic polymers as a result of a hydrophobic size effect at the subnanometer scale. Third, the hydration free energy of a monomer on a macromolecule is different from a free monomer; corrections for the reduced hydration free energy due to hydrophobic interaction from neighboring units are required.
疏水性是许多天然和合成的分子和纳米级系统自组装的基础。疏水性的一个特征是其对温度的依赖性。本文首次对单个疏水聚合物中水合自由能的温度和尺寸依赖性进行了实验评估，这检验了蛋白质折叠中疏水相互作用模型的关键假设。在此，通过单分子力谱直接测量了三个具有不同尺寸芳基侧链的疏水聚合物延伸所需的水合自由能。结果有三点。首先，发现每个单体的水合自由能强烈依赖于温度，并且不遵循界面热力学。其次，由于亚纳米尺度的疏水尺寸效应，三种疏水聚合物的温度依赖性曲线明显不同。第三，大分子上单体的水合自由能与游离单体不同；需要对由于相邻单元的疏水相互作用而导致的水合自由能降低进行修正。
