Divalent cations interact strongly with negatively charged lipids in biological membranes. Understanding the molecular level details of ion-lipid complex formation is essential in determining the physiological relevance of such interactions. We have used a combination of vibrational sum frequency spectroscopy, fluorescence microscopy and thermodynamic measurements to unravel the mechanistic details of divalent cation-lipid interactions. Both Hofmeister and Irving-William series divalent metal cations can modify the structural organization of negatively charged lipid membranes. Vibrational sum frequency spectroscopy was performed on Langmuir monolayers containing negatively charged phosphatidylserine lipids, in order to characterize the binding sites for various ions on the lipid headgroups. We found that the interfacial water structure next to the lipid monolayer undergoes significant changes as a result of ion binding and the vibrational sum frequency spectra of the interfacial water can be used to determine the binding constants for the ion-lipid interactions. Additionally, effects of ion binding on the structural transitions of these lipid monolayers were characterized using surface pressure-area isotherm measurements and fluorescence microscopy. These measurements can be directly correlated with the spectroscopic data in order to elucidate the mechanism of ion-induced structural changes in lipid monolayers.

Characterizing metallomembranes using vibrational sum frequency spectroscopy

255th National Meeting (2018)

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