The Structure of Ions and Zwitterionic Lipids Regulates the Charge of Dipolar Membranes

Abstract

In pure water, zwitterionic lipids form lamellar phases with an equilibrium water gap on the order of 2 to 3 nm as a result of the dominating van der Waals attraction between dipolar bilayers. Monovalent ions can swell those neutral lamellae by a small amount. Divalent ions can adsorb onto dipolar membranes and charge them. Using solution X-ray scattering, we studied how the structure of ions and zwitterionic lipids regulates the charge of dipolar membranes. We found that unlike monovalent ions that weakly interact with all of the examined dipolar membranes, divalent and trivalent ions adsorb onto membranes containing lipids with saturated tails, with an association constant on the order of ∼10 M(-1). One double bond in the lipid tail is sufficient to prevent divalent ion adsorption. We suggest that this behavior is due to the relatively loose packing of lipids with unsaturated tails that increases the area per lipid headgroup, enabling their free rotation. Divalent ion adsorption links two lipids and limits their free rotation. The ion-dipole interaction gained by the adsorption of the ions onto unsaturated membranes is insufficient to compensate for the loss of headgroup free-rotational entropy. The ion-dipole interaction is stronger for cations with a higher valence. Nevertheless, polyamines behave as monovalent ions near dipolar interfaces in the sense that they interact weakly with the membrane surface, whereas in the bulk their behavior is similar to that of multivalent cations. Advanced data analysis and comparison with theory provide insight into the structure and interactions between ion-induced regulated charged interfaces. This study models biologically relevant interactions between cell membranes and various ions and the manner in which the lipid structure governs those interactions. The ability to monitor these interactions creates a tool for probing systems that are more complex and forms the basis for controlling the interactions between dipolar membranes and charged proteins or biopolymers for encapsulation and delivery applications.

Thermal Transients Excite Neurons through Universal Intramembrane Mechanoelectrical Effects

“…We anticipate that the likely impact of this simplification is also relatively minor. Experimentally, rather negligible effects on the membranes' structural parameters were observed when the concentration of ions like Na þ , Cl − , and Ca 2þ was varied within their physiological ranges [43][44][45]. In addition, no effect on the thermal capacitance rate was noted in the experiments of Shapiro et al when the multivalent ions Mg 2þ and Gd 3þ were added to the solution, even at concentrations that are higher than the physiological range [see the parallel slopes in Figs.…”

Aqueous Emulsion Droplets Stabilized by Lipid Vesicles as Microcompartments for Biomimetic Mineralization

“…Scale bar = 10 µm.Intermediate Chelation of Ca 2+ . In the absence of added Ca 2+ chelators, LUV aggregation and disruption of bioreactor structures occurred at Ca 2+ concentrations above 5 mM(Figure 1) [49][50][51][52]. In biological mineralizing systems, metal ions are generally bound by ligands that help control their local concentrations and deposition [53][54].…”

Dielectric response of human melanoma cells on the surface of polymeric chemoattractants

“…The thermal energy released due to dipole rotation or deformation can be seen in a common application of the electric field to polar biomolecules. 8,9 Although the frequencies used in our proposed application are others in magnitude of 10 6 ~ 10 7 below the microwave frequencies, energy is still released locally. Stresses may also be produced locally in the cells due to torques created by the interaction of polar mechanisms interacting with the electric field.…”

“…In addition, there may be dipoledipole or dipole induced dipole attractive forces at the interfaces. 9 The first step in examining this electric interaction between cell and matrix is the study of the dielectric relaxations of the cells. Cellular membranes are charged as negative and form counterions charged as positive.…”