Bibcode
Lodieu, N.
Bibliographical reference
PhD thesis, Universite Toulouse III --- Paul Sabatier, France
Advertised on:
2004
Citations
1
Refereed citations
1
Description
Lipid bilayers are key components of biomembranes; they are
self-assembled two-dimensional structures, primarily serving as barriers
to the leakage of cell's contents. Lipid bilayers are typically charged
in aqueous solution and may electrostatically interact with each other
and with their environment. In this work, we investigate electrostatics
of charged lipid bilayers with the main focus on the binding and bending
of the bilayers. We first present a theoretical approach to
charge-correlation attractions between like-charged lipid bilayers with
neutralizing counterions assumed to be localized to the bilayer surface.
In particular, we study the effect of nonzero ionic sizes on the
attraction by treating the bilayer charges (both backbone charges and
localized counterions) as forming a two-dimensional ionic fluid of hard
spheres of the same diameter D. Using a two-dimensional Debye-H?ckel
approach to this system, we examine how ion sizes influence the
attraction. We find that the attraction gets stronger as surface charge
densities or counterion valency increase, consistent with long-standing
observations. Our results also indicate non-trivial dependence of the
attraction on separations h: The attraction is enhanced by ion sizes for
h ranges of physical interest, while it crosses over to the known
D-independent universal behavior as h [right arrow] [infinity]; it
remains finite as h [right arrow] 0, as expected for a system of
finite-sized ions. We also study the preferred curvature of an
asymmetrically charged bilayer, in which the inner leaflet is negatively
charged, while the outer one is neutral. In particular, we calculate the
relaxed area difference [Delta] A0 and the spontaneous curvature C0 of
the bilayer. We find [Delta] A0 and C0 are determined by the balance of
a few distinct contributions: net charge repulsions, charge
correlations, and the entropy associated with counterion release from
the bilayer. The entropic effect is dominant for weakly charged surfaces
in the presence of monovalent counterions only and tends to expand the
inner leaflet, leading to negative [Delta] A0 and C0. In the presence of
even a small concentration of divalent counterions, however, charge
correlations counterbalance the entropic effect and shrink the inner
leaflet, leading to positive [Delta] A0 and C0. We outline biological
implications of our results.