Comment on “Can Charge Transfer Across C─H···O Hydrogen Bonds Stabilize Oil Droplets in Water?”

Kinetically stable oil nanodroplets in water display an electrophoretic mobility linked to a negative surface charge. The source of this charge is proposed to arise from the adsorption of hydroxide ions or through charge transfer (CT), that is displacement of electronic charge across improper C─H···O hydrogen bonds. Zhao et al. [R. Q. Zhao, H. Y. Shen, R. A. Lacour, J. P. Heindel, M. Head- Gordon, and T. Head-Gordon, Angewandte Chemie- International Edition 64 (2025): e202508145, https://doi.org/10.1002/anie.202508145.] questioned the possibility of CT across an oil droplet interface based on density functional theory simulations of hexane molecules in water. Here, we introduce the two prevalent explanations for the surface charge on oil droplets in water, hydroxide adsorption and CT through improper H-bonds, showing that, while the hydroxide hypothesis is most intuitive, there is no molecular level experimental evidence from a range of surface specific techniques. We correct a misconception about the origin of the blue shift in the original sum frequency scattering work [S. Pullanchery, S. Kulik, B. Rehl, A. Hassanali, and S. Roke, Science 374 (2021): 13661370, https://doi.org/10.1126/science.abj3007.], and comment on the choice of hexane clusters in water: Hexane does not form kinetically stable droplets in water, as it is 9 orders of magnitude more soluble in water than hexadecane. Without exhibiting kinetic stability-the behavior the simulations seek to explain-there is limited predictive ability on CT through improper H-bonds as a mechanism to stabilize droplets.