The Ripple Phase Studied Using Monte Carlo Simulation

1
The Ripple Phase Studied Using Monte Carlo
Simulation

• Xiuquan Sun
• Department of Chemistry and Biochemistry
• 9/24/2004

2
Outline

• Ripple phase
• My simulation

3
The Lipids and Bilayer
4
Temperature-Composition Phase Diagram of Hydrated
DMPC
Janiak, M. J., D. M. Small, and G. G. Shipley.
J. Biol. Chem. 1979 2546068-6078
5
The Structure of Ripple Phase
W.-J. Sun, S. Tristram-Nagle, R. M. Suter, and
J. F. Nagle PNAS 1996 93 7008-7012.
c
J. Katsaras, S. Tristram-Nagle, Y. Liu, R. L.
Headrick, E. Fontes, P. C. Mason, and J. F.
Nagle Physical Review E May 2000 61 5668-5677
6
The Models were Proposed

• Mean field theory
• Thickness of the membrane and Hydration (R.
  E. Goldstein, 1988)
• Coupling of molecular tilt to membrane
  curvature. ( T. C. Lubensky, 1993)
• Statistical mechanics
• Anisotropic shapes of the head groups ( W.
  Scott and McCullough, 1990)
• Chain melting (Thomas Heimburg, 2000)

7
Chemical Structure of Phospholipids
8
Potential of the system
u uDD uho
uDD -3 (m1 r) (m2 r) / r5 m1 m2 / r3
uho 0.5 kr r2
Strength of the dipole is 7 Debye Kr 0.1 KB
9
(No Transcript)
10
(No Transcript)
11
Order parameter
S lt
gt
Order parameter 1.5 largest eigenvalue When
order parameter 1.0 ? perfect ordered
system When order parameter 0.0 ? random
ordered system
12
For hexagnol lattice, the critical temperature is
340K.
13
bLat
aLat

• aLat / bLat

Hexagol Lattice
14
(No Transcript)
15
(No Transcript)
16
Conclusion

• The point dipole model is used to study the
  formation of the ripple phases, and found the
  dipolar property of the head group of the lipids
  is one of the major contributions to form the
  ripple phases.
• The hexagnol arrangement of the system is crucial
  to the formation of the ripple phases.

17
Acknowledgement

• Professor J. Daniel Gezelter
• All members in our group