Sponge‐phase Lipid Droplets as Synthetic Organelles: An Ultrafast Study of Hydrogen Bonding and Interfacial Environments

Abstract

AbstractBottom‐up design of biomimetic organelles has gained recent attention as a route towards understanding the transition between non‐living matter and life. Despite various artificial lipid membranes being developed, the specific relations between lipid structure, composition, interfacial properties, and morphology are not currently understood. Sponge‐phase droplets contain dense, nonlamellar lipid bilayer networks that capture the complexities of the endoplasmic reticulum (ER), making them ideal artificial models of such organelles. Here, we combine ultrafast two‐dimensional infrared (2D IR) spectroscopy and molecular dynamics simulations to investigate the interfacial H‐bond networks in sponge‐phase droplets composed of glycolipid and nonionic detergents. In the sponge phase, the interfacial environments are more hydrated and water molecules confined to the nanometer‐scale aqueous channels in the sponge phase exhibit dynamics that are significantly slower compared to bulk water. Surfactant configurations and microscopic phase separation play a dominant role in determining membrane curvature and slow dynamics observed in the sponge phase. The studies suggest that H‐bond networks within the nanometer‐scale channels are disrupted not only by confinement but also by the interactions of surfactants, which extend 1–2 nm from the bilayer surface. The results provide a molecular‐level description for controlling phase and morphology in the design of synthetic lipid organelles.