Charged Lipid Vesicles: Effects of Salts on Bending Rigidity, Stability, and Size

Abstract

The swelling behavior of charged phospholipids in pure water is completely different from that of neutral or isoelectric phospholipids. It was therefore suggested in the past that, instead of multilamellar phases, vesicles represent the stable structures of charged lipids in excess water. In this article, we show that this might indeed be the case for dioleoylphosphatidylglycerol and even for dioleoylphosphatidylcholine in certain salts. The size of the vesicles formed by these lipids depends on the phospholipid concentration in a way that has been predicted in the literature for vesicles of which the curvature energy is compensated for by translational entropy and a renormalization of the bending moduli (entropic stabilization). Self-consistent field calculations on charged bilayers show that the mean bending modulus kc and the Gaussian bending modulus k have opposite sign and /k/>kc, especially at low ionic strength. This has the implication that the energy needed to curve the bilayer into a closed vesicle Eves=4pi(2kc+k) is much less than one would expect based on the value of kc alone. As a result, Eves can relatively easily be entropically compensated. The radii of vesicles that are stabilized by entropy are expected to depend on the membrane persistence length and thus on kc. Experiments in which the vesicle size is studied as a function of the salt and the salt concentration correlate well with self-consistent field predictions of kc as a function of ionic strength.

Effect of shape and bending modulus on the properties of nematic lyotropic liquid crystals

“…Furthermore, we observe how a moderate increase in ionic strength (which corresponds to system 3 of Section 2.7) produces less than 20% increment in the bending modulus, relative to system 1. Therefore, as expected, an increase in ionic strength produces a moderate increase in the stiffness of the bilayer, in good agreement with the experimental results reported by Claessens et al 56 for a DOPG and DOPC bilayers at different ionic strength of the aqueous solution, and from molecular dynamics simulations of binary DPPC/DPPS bilayers in presence and absence of salt. 55 Thus, this increase in bending modulus in system 3 is related with the fact that an increase in the ionic strength produces an additional stabilization of the interface, as expected from a counterion neutralization, that is reected into an increase in the stiffness of the molecular aggregates.…”

Charge Regulation as a Stabilization Mechanism for Shell-Like Assemblies of Polyoxometalates

“…(5). In principle, this mechanism should also be operative in thermodynamically stable (charged) surfactant vesicles without added electrolyte, such as those studied in, e.g., [21][22][23]. While the origin of the attractive forces in these systems is different from the POM-shells, that should not lead to different behavior at this level of description.…”

Volume exclusion effects in the ground-state dominance approximation for polyelectrolyte adsorption on charged interfaces

“…For ϑ close enough to zero, equation (B.1) simplifies to equation (16), equation (B.2) becomes equation (18), and equation (B.3) simplifies to equation (19).…”