Role of phospholipid asymmetry in the stability of inverted hexagonal mesoscopic phases.
The role of phospholipid asymmetry in the transition from the lamellar (L(alpha)) to the inverted hexagonal (H(II)) phase upon the temperature increase was considered. The equilibrium configuration of the system was determined by the minimum of the free energy including the contribution of the isotropic and deviatoric bending and the interstitial energy of phospholipid monolayers. The shape and local interactions of a single lipid molecule were taken into account. The minimization with respect to the configuration of the lipid layers was performed by a numerical solution of the system of the Euler-Lagrange differential equations and by the Monte Carlo simulated annealing method. At high enough temperature, the lipid molecules attain a shape exhibiting higher intrinsic mean and deviatoric curvatures, which fits better into the H(II) phase than into the L(alpha) phase. Furthermore, the orientational ordering of lipid molecules in the curvature field expressed as the deviatoric bending provides a considerable negative contribution to the free energy, which stabilizes the nonlamellar H(II) phase. The nucleation configuration for the L(alpha)-H(II) phase transition is tuned by the isotropic and deviatoric bending energies and the interstitial energy.
Laboratory of Biomechanics, Faculty of Mechanical Engineering, Czech Technical University in Prague, Technická 4, CZ-166 07, Prague 6, Czech Republic. tomas.mares@fs.cvut.cz
Tomas
T
Mares
Matej
M
Daniel
Sarka
S
Perutkova
Andrej
A
Perne
Gregor
G
Dolinar
Ales
A
Iglic
Michael
M
Rappolt
Veronika
V
Kralj-Iglic
D015394:Molecular Structure; D009010:Monte Carlo Method; D010743:Phospholipids / Q000737:chemistry*
D010743:Phospholipids