Heterodyne-Detected Sum Frequency Generation Spectroscopic Study of Weakly Hydrogen-Bonded Water at Charged Lipid Interfaces, Revisited

The presence/absence of weakly hydrogen-bonded water molecules buried in the hydrophobic moiety of charged lipids at aqueous interfaces has been a matter of debate. We concluded their presence in our previous study, which was later questioned from the viewpoint of the so-called chi((3)) effect. Here we show that heterodyne-detected sum frequency generation (HD-SFG) spectra of the same lipid interfaces with excess salt in the aqueous subphase allow us to reconfirm the presence of the weakly hydrogen-bonded water in the hydrophobic moiety after successfully subtracting the chi((3)) contribution from the observable.

Automated summary

In this study, the presence of weakly hydrogen-bonded water molecules buried in the hydrophobic moiety of charged lipids at aqueous interfaces was confirmed using heterodyne-detected sum frequency generation (HD-SFG) spectra. The chi((3)) contribution was successfully subtracted from the observable, allowing the reconfirmation of the weakly hydrogen-bonded water molecules in the hydrophobic moiety.