Abstract
Lipid bilayer interactions are essential to a vast range of biological functions, such as intracellular transport mechanisms. Surface charging mediated by concentration dependent ion adsorption and desorption on lipid headgroups alters electric double layers as well as van der Waals and steric hydration forces of interacting bilayers. Here, we directly measure bilayer interactions during charge modulation in a symmetrically polarized electrochemical three-mirror interferometer surface forces apparatus. We quantify polarization and concentration dependent hydration and electric double layer forces due to cation adsorption/desorption. Our results demonstrate that exponential hydration layer interactions effectively describe surface potential dependent surface forces due to cation adsorption at high salt concentrations. Hence, electric double layers of lipid bilayers are exclusively dominated by inner Helmholtz charge regulation under physiological conditions. These results are important for rationalizing bilayer behavior under physiological conditions, where charge and concentration modulation may act as biological triggers for function and signaling.
Highlights
Lipid bilayer interactions are essential to a vast range of biological functions, such as intracellular transport mechanisms
C ell membranes are naturally surrounded by physiological salt solution (150−300 mM), and the interaction of ions with the lipid bilayer membrane plays a fundamental role in steering biological processes
Cation−surface interactions mediate signaling mechanisms as well as transport mechanisms driven by potential gradients across membranes, and they may contribute to the general stability of bilayers.[1,2]
Summary
Lipid bilayer interactions are essential to a vast range of biological functions, such as intracellular transport mechanisms. Measuring force versus distance characteristics provides a means to directly characterize hydration and electric double layer structure modulations as a function of the applied electrochemical and established surface potentials. Introducing ions into the system results in a considerably more pronounced polarization dependent interaction with a clear repulsive behavior at negative potentials and a pronounced attractive profile, compared to Milli-Q water, at positive potential.
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