Cooperativity between sodium ions and water molecules facilitates lipid mobility in model cell membranes

Abstract

Cellular membranes are surrounded by an aqueous buffer solution containing various ions, which influence the hydration layer of the lipid head groups. At the same time, water molecules hydrating the...

Nanoscale structural response of biomimetic cell membranes to controlled dehydration

“…One way of describing membrane dehydration would be to define a state where the amount of hydrating water decreases to a level where the dynamic or structural properties of the membrane begin to be affected. Based on the experiments reported here as well as our recent works, 37,50,51 both the dynamics and the structure of the membrane are gradually affected when the first hydration shell of the lipids is perturbed. In the case of the zwitterionic phosphocholine lipids, this happens when the hydration drops below about 12 molecules per lipid.…”

“…The observed changes in lipid partitioning are associated with the decreased hydrophobic mismatch, but unlike the height mismatch data, they are also strongly dependent on the lipid mobility. Since lipid mobility decreases strongly with decreasing membrane hydration, 37,50,51 it is not too surprising that we do not see a steady increase in the partitioning of the L d phase lipids into the L o phase. At lower membrane hydration states, we observed a competition between the lower hydrophobic mismatch, which favours lipid admixing, and the lower diffusivity, which hinders mixing.…”

“…In addition, other recent studies of ours have shown that the dynamics of lipids under dehydration conditions is strongly influenced by the ionic composition of the buffer hydrating the membrane. 51 Although lipids remain mobile in the presence of Na + ions at humidity above 50% RH, their mobility is significantly reduced in MilliQ water upon dehydration to 85% RH. In the course of the measurements presented here, we decided to perform AFM scanning in the absence of salt-enriched buffer, which could lead to salt crystallisation on the membranes.…”