  Cholesterol (Chol) plays a crucial role in shaping the intricate
physicochemical attributes of biomembranes, exerting considerable influence on
water molecules proximal to the membrane interface. In this study, we conducted
molecular dynamics simulations on the bilayers of two lipid species,
dipalmitoyl phosphatidylcholine (DPPC) and palmitoyl sphingomyelin (PSM); they
are distinct with respect to the structures of the hydrogen-bond (H-bond)
acceptors. Our investigation focuses on the dynamic properties and H-bonds of
water molecules in the lipid-membrane systems, with particular emphasis on the
influence of Chol at varying temperatures. Notably, in the gel phase at 303 K,
the presence of Chol extends the lifetimes of H-bonds of the oxygen atoms
acting as H-bond acceptors within DPPC with water molecules by a factor of 1.5
to 2.5. In the liquid-crystalline phase at 323 K, on the other hand, H-bonding
dynamics with lipid membranes remain largely unaffected by Chol. This observed
shift in H-bonding states serves as a crucial key to unraveling the subtle
control mechanisms governing water dynamics in lipid-membrane systems.
