Influence of Methylene Fluorination and Chain Length on the Hydration Shell Structure and Thermodynamics of Linear Diols

Abstract

The interplay between the local hydration shell structure, the length of hydrophobic solutes, and their identity (perfluorinated or not) remains poorly understood. We address this issue by combining Raman−multivariate curve resolution (Raman-MCR) spectroscopy, simulation, and quantum-mechanical calculations to quantify the thermodynamics and the first principle interactions behind the formation of defects in the hydration shell of alkyl−diol and perfluoroalkyl−diol chains. The hydration shell of the fluorinated diols contains substantially more defects than that of the nonfluorinated diols; these defects are water hydroxy groups that do not donate hydrogen bonds and which either point to the solute (radial-dangling OH) or not (nonradial-dangling OH). The number of radial-dangling OH defects per carbon decreases for longer chains and toward the interior of the fluorinated diols, mainly due to less favorable electrostatics and exchange interactions; nonradial-dangling OH defects per carbon increase with chain length. In contrast, the hydration shell of the nonfluorinated diols only contains radial-dangling defects, which become more abundant toward the center of the chain and for larger chains, predominantly because of more favorable dispersion interactions. These results have implications for how the folding of macromolecules, ligand binding to biomacromolecules, and chemical reactions at water−oil interfaces could be modified through the introduction of fluorinated groups or solvents.

Antifouling graphene oxide membranes for oil-water separation via hydrophobic chain engineering

“…It can be seen that most of the water bears the distributions of cosα centered ~−1, implying water mainly favor orienting with two O–H bonds directed downwards towards the surface in our models. With the presence of perfluoroalkyl chains, the orientation of the water molecules is perturbed due to the electrostatically dominated interactions between the water and the perfluoroalkyl chains 52 . This electrostatic interaction is sensitive to chain length and position, which was adequately discussed in detail in the previous work 52 .…”

“…With the presence of perfluoroalkyl chains, the orientation of the water molecules is perturbed due to the electrostatically dominated interactions between the water and the perfluoroalkyl chains 52 . This electrostatic interaction is sensitive to chain length and position, which was adequately discussed in detail in the previous work 52 . In our study, the water orientation distribution in regions I and II is more similar in the case of F 6 -hGO, which implies a more uniform hydration structure on the surface.…”