Centre of Chemistry and Biochemistry and Biosystems and Integrative Sciences Institute, Faculty of Sciences of the University of Lisbon, C8, Campo Grande, 1749-016 Lisbon, Portugal.
J Phys Chem B. 2020 Dec 3;124(48):10994-11006. doi: 10.1021/acs.jpcb.0c08055. Epub 2020 Nov 17.
The hydrophobic effect plays a key role in many chemical and biological processes, including protein folding. Nonetheless, a comprehensive picture of the effect of temperature on hydrophobic hydration and protein denaturation remains elusive. Here, we study the effect of temperature on the hydration of model hydrophobic and amphiphilic solutes, through molecular dynamics, aiming at getting insight on the singular behavior of water, concerning the zero-entropy temperature, , and entropy convergence, , also observed for some proteins, upon denaturation. We show that, similar to hydrocarbons, polar amphiphilic solutes exhibit a , although strongly dependent on solute-water interactions, opposite to hydrocarbons. Further, the temperature dependence of the hydration entropy, normalized by the solvent accessible surface area, is shown to be nearly solute size independent for hydrophobic but not for amphiphilic solutes, for similar reasons. These results are further discussed in the light of information theory (IT) and the structure of water around hydrophobic groups. The latter shows that the tetrahedral enhancement of some water molecules around hydrophobic groups, associated with the reduction of water defects, leads to the strengthening of the weakest hydrogen bonds, relative to bulk water. In addition, a larger tetrahedrality is found in low density water populations, demonstrating that pure water has encoded structural information, similar to that associated with hydrophobic hydration. The reversal of the hydration entropy dependence on the solute size, above , is also analyzed and shown to be associated with a greater loss of water molecules exhibiting enhanced orientational order, in the coordination sphere of large solutes. Finally, the source of the differences between Kauzmann's "hydrocarbon model" on protein denaturation and hydrophobic hydration is discussed, with relatively large amphiphilic hydrocarbons seemingly displaying a more similar behavior to some globular proteins than aliphatic hydrocarbons.
疏水作用在许多化学和生物过程中起着关键作用，包括蛋白质折叠。尽管如此，温度对疏水水合作用和蛋白质变性的影响的全貌仍然难以捉摸。在这里，我们通过分子动力学研究温度对模型疏水和亲水溶质水合的影响，旨在深入了解水的奇异行为，关于零熵温度，以及熵收敛，也观察到一些蛋白质变性时的情况。我们表明，与碳氢化合物类似，极性亲水溶质表现出，尽管强烈依赖于溶质-水相互作用，但与碳氢化合物相反。此外，通过归一化溶剂可及表面积，疏水但非亲水溶质的水合熵的温度依赖性被证明几乎与溶质大小无关，原因类似。这些结果根据信息论（IT）和疏水基团周围水的结构进一步讨论。后者表明，与体相水相比，与疏水基团周围一些水分子的四面体增强相关联的水缺陷减少导致最弱氢键的增强。此外，在低密度水群体中发现更大的四面体性，表明纯水已编码类似于与疏水水合相关的结构信息。在高于的温度下，水合熵对溶质大小的依赖性的反转也被分析并表明与大溶质配位球中具有增强的定向有序的水分子的更大损失有关。最后，讨论了 Kauzmann 关于蛋白质变性和疏水水合的“碳氢化合物模型”之间差异的来源，相对较大的亲水碳氢化合物似乎比脂肪族碳氢化合物更类似于某些球状蛋白质。
