Abstract
We formulate a theory of electrostatic interactions in lipid bilayer membranes where both monolayer leaflets contain dissociable moieties that are subject to charge regulation. We specifically investigate the coupling between membrane curvature and charge regulation of a lipid bilayer vesicle using both the linear Debye-Hückel (DH) and the non-linear Poisson-Boltzmann (PB) theory. We find that charge regulation of an otherwise symmetric bilayer membrane can induce charge symmetry breaking, non-linear flexoelectricity and anomalous curvature dependence of free energy. The pH effects investigated go beyond the paradigm of electrostatic renormalization of the mechano-elastic properties of membranes.
Highlights
Ljubljana, Ljubljana, Slovenia † These authors contributed to this work and have a shared co-first authorship.acknowledged as one of the most advanced non-viral vectors for the efficient delivery of nucleic acids.[8]While electrostatic interactions in bio-soft matter are universal,[9] there is a fundamental difference between the standard colloid electrostatics and membrane electrostatics,[10] in the sense that the membrane charge, just as the protein charge,[11–13] depends on the solution environment of the lipid[14] and its changes can engender changes in the shape of the lipids and concomitant structure of lipid assemblies
We find that charge regulation of an otherwise symmetric bilayer membrane can induce charge symmetry breaking, non-linear flexoelectricity and anomalous curvature dependence of free energy
One example of this solution environment effect would be changes in protonation/deprotonation equilibria of the dissociable phospholipid moieties depending on the solution pH, that in general affect the charge of lipids’ headgroup, and another would be the modification of the strength of electrostatic interactions wrought by the ionic strength of the bathing aqueous solution that affects the ionic screening
Summary
Acknowledged as one of the most advanced non-viral vectors for the efficient delivery of nucleic acids.[8]. Global and local changes in pH, inducing changes in the charged states of lipids, can affect lipid vesicle shape deformations as well as phase-separated domain formation.[19] These effects are framed within the electrostatic contribution to the mechano-elastic properties of membranes, such as surface tension and bending rigidity, which have been reviewed in detail, see e.g. ref. We will show that charge regulation of an otherwise symmetric bilayer membrane induces three important phenomena: charge symmetry breaking, non-linear flexoelectricity and anomalous curvature dependence of free energy and that in general the pH effects go beyond the paradigm of electrostatic renormalization of the mechano-elastic properties of membranes.
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