8 research outputs found
Curvature effects in charge-regulated lipid bilayers
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-H\"uckel (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.Comment: 25 pages, 6 figure
Translocation of a daughter vesicle in a model system of self-reproducing vesicles
Translocation of a daughter vesicle from a mother vesicle through a pore is
experimentally studied by many groups using a model system of self-reproducing
vesicles. However, the theoretical formulation of the problem is not fully
understood. In the present study, we present a theoretical formulation of the
process based on our previous work [P. Khunpetch et al., Phys. Fluids 33,
077103 (2021)]. In our previous work, we considered the daughter vesicle as a
rigid body. In the present work, however, we allow the daughter vesicle to
deform during the expulsion process. We thus derive the free energy
constituting of the elastic moduli of both the mother and daughter vesicles,
and of pressure-driven contribution. The minimum energy path of the
translocation is searched by using the string method. Our improved model
successfully suggests the disappearance of the energy barrier where all the
elastic moduli are in agreement with the experimental reports, while the
previous work is unsuccessful to do so. The equations of motion of the daughter
vesicle have been derived within the framework of the Onsager principle. We
found that the translocation time of the daughter vesicle can be reduced when
the pressure inside the mother vesicle increases, or the initial size of the
daughter vesicle decreases
Curvature effects in interfacial acidity of amphiphilic vesicles
We analyze the changes in the vicinal acidity (pH) at a spherical amphiphilic
membrane. The membrane is assumed to contain solvent accessible, embedded,
dissociable, charge regulated moieties. Basing our approach on the linear
Debye-H\"uckel as well as the non-linear Poisson-Boltzmann theory, together
with the general Frumkin-Fowler-Guggenheim adsorption isotherm model of the
charge regulation process, we analyse and review the dependence of the local pH
on the position, as well as bulk electrolyte concentration, bulk pH and
curvature of the amphiphilic single membrane vesicle. With appropriately chosen
adsorption parameters of the charge regulation model, we find a good agreement
with available experimental data.Comment: 17 pages, 11 figure