Mesoscopic models of lipid bilayers and bilayers with embedded ...
Mesoscopic models of lipid bilayers and bilayers with embedded ... Mesoscopic models of lipid bilayers and bilayers with embedded ...
64 Phase behavior of coarse-grained lipid bilayers (a) (b) (c) (d) Figure 5.7: Density profiles ρ(z) along the bilayer normal z for different reduced temperatures T ∗ . Each line is the density profile for a different bead: full lines are the densities of the tail beads, dashed lines are the densities of the head beads, and the thin solid line is the density of water. The black lines correspond to the lipids in one monolayer, while the gray lines correspond to the lipids in the opposite monolayer. The big dots correspond to the maxima in the bead density distributions and illustrate the position of the beads in the bilayer. The full circles correspond to tail beads and the open circles to head beads.
5.2 Single-tail lipid bilayers 65 per molecule increases while the bilayer thickness decreases. Head-head repulsion a hh = 15 In the previous section we have seen that single tail lipids spontaneously form an interdigitated phase at low temperatures, while the most common organization of (symmetric) phospholipids in membranes is a bilayer formed by two separate monolayers [106]. It is therefore interesting to investigate whether we can adapt the single tail model to reproduce the phase behavior of real membranes, and in particular if we are able to obtain a non-interdigitated gel phase. If the main cause of interdigitation is an increase in the head-groups surface area [91, 99], we can test this mechanism by changing the value of the head-group repulsion parameter, a hh, in our model. Taking as initial condition the interdigitated bilayer at T ∗ = 0.85, we decrease the head-group repulsion parameter from a hh = 35 to a hh = 15, the latter being the same repulsion parameter as between an hydrophilic bead and a water-bead. Experimentally, changing the head-head interactions corresponds to, for example, adding salt to the system. It is important to recall that, with the zero surface tension scheme, the system can evolve to the optimum area per lipid even if the bilayer undergoes structural rearrangements. (a) (b) Figure 5.8: Comparison of (a) the area per lipid AL as function of reduced temperature T ∗ , and (b) two dimension radial distribution function g(r) in the plane of the bilayer at T ∗ = 0.85, for two different repulsion parameters between the lipid headgroups: ahh = 15 (circles, solid line) and ahh = 35 (squares, dashed line). Figure 5.8(a) shows the temperature dependence of the area per lipid for the repulsion parameters a hh = 35 and a hh = 15. We observe that the behavior in temperature of the area per lipid for the two values of a hh is very different. At low temperatures the area at a hh = 35 is almost twice the value of the area at a hh = 15. The decrease
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- Page 27 and 28: III Surface tension in lipid bilaye
- Page 29 and 30: 3.2 Method of calculation of surfac
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- Page 37 and 38: 3.4 Surface tension in lipid bilaye
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- Page 43 and 44: IV Structural characterization of l
- Page 45 and 46: 4.2 Structural quantities 39 been r
- Page 47 and 48: 4.3 Computational details 41 lipid
- Page 49 and 50: 4.4 Results and discussion 43 ρ(z)
- Page 51 and 52: 4.4 Results and discussion 45 one l
- Page 53 and 54: 4.4 Results and discussion 47 WH HT
- Page 55 and 56: 4.4 Results and discussion 49 Shill
- Page 57 and 58: 4.4 Results and discussion 51 chain
- Page 59 and 60: 4.4 Results and discussion 53 4.4.4
- Page 61: 4.4 Results and discussion 55 headg
- Page 64 and 65: 58 Phase behavior of coarse-grained
- Page 66 and 67: 60 Phase behavior of coarse-grained
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- Page 85 and 86: VI Interaction of small molecules w
- Page 87 and 88: 6.2 Computational details 81 For re
- Page 89 and 90: 6.3 Results and Discussion 83 withi
- Page 91 and 92: 6.3 Results and Discussion 85 ρ(z)
- Page 93 and 94: 6.3 Results and Discussion 87 ρ(z)
- Page 95 and 96: 6.3 Results and Discussion 89 S m 0
- Page 97 and 98: 6.3 Results and Discussion 91 π(z)
- Page 99: 6.3 Results and Discussion 93 the l
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- Page 106 and 107: 100 Mesoscopic model for lipid bila
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64 Phase behavior <strong>of</strong> coarse-grained <strong>lipid</strong> <strong>bilayers</strong><br />
(a) (b)<br />
(c) (d)<br />
Figure 5.7: Density pr<strong>of</strong>iles ρ(z) along the bilayer normal z for different reduced temperatures<br />
T ∗ . Each line is the density pr<strong>of</strong>ile for a different bead: full lines are the densities <strong>of</strong> the tail<br />
beads, dashed lines are the densities <strong>of</strong> the head beads, <strong>and</strong> the thin solid line is the density<br />
<strong>of</strong> water. The black lines correspond to the <strong>lipid</strong>s in one monolayer, while the gray lines correspond<br />
to the <strong>lipid</strong>s in the opposite monolayer. The big dots correspond to the maxima in<br />
the bead density distributions <strong>and</strong> illustrate the position <strong>of</strong> the beads in the bilayer. The full<br />
circles correspond to tail beads <strong>and</strong> the open circles to head beads.
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