Phospholipid acyl tail affects lipid headgroup orientation and membrane hydration

Biomembrane hydration is crucial for understanding processes at biological interfaces. While the effect of the lipid headgroup has been studied extensively, the effect (if any) of the acyl chain chemical structure on lipid-bound interfacial water has remained elusive. We study model membranes composed of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) lipids, the most abundant lipids in biomembranes. We explore the extent to which the lipid headgroup packing and associated water organization are affected by the lipid acyl tail unsaturation and chain length. To this end, we employ a combination of surface-sensitive techniques, including sum-frequency generation spectroscopy, surface pressure measurements, and Brewster angle microscopy imaging. Our results reveal that the acyl tail structure critically affects the headgroup phosphate orientational distribution and lipid-associated water molecules, for both PE and PC lipid monolayers at the air/water interface. These insights reveal the importance of acyl chain chemistry in determining not only membrane fluidity but also membrane hydration. Published under an exclusive license by AIP Publishing.

Automated summary

Biomembrane hydration is crucial for understanding processes at biological interfaces. While the effect of the lipid headgroup has been extensively studied, the impact of the acyl chain chemical structure on lipid-bound interfacial water has remained elusive. This study explores the influence of acyl tail unsaturation and chain length on the lipid headgroup packing and associated water organization in model membranes. The findings highlight the critical role of acyl chain chemistry in determining both membrane fluidity and hydration.