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 ...
66 Phase behavior of coarse-grained lipid bilayers of the head-group surface area is also shown in figure 5.8(b), where we compare the radial distribution functions of the headgroups in the bilayer plane at T ∗ = 0.85 (see also figure 5.9 for snapshots of the two systems). The peaks in the radial distribution function for the system with a hh = 15 (solid line) are shifted to the left compared to the system with a hh = 35 (dashed line), showing a decrease of the distance between the headgroups. This is a strong indication that at low temperature, with the lower repulsion parameter, the bilayer is in the Lβ phase. (a) (b) Figure 5.9: Snapshots of the simulations of a bilayer consisting of the lipid ht9 at T ∗ = 0.85. (a) The non-interdigitated gel phase Lβ at ahh = 15 and (b) the interdigitated gel phase Lβ at ahh = 15. Black represents the hydrophilic headgroup and gray represents the hydrophobic tails. (a) (b) Figure 5.10: (a) Local order parameter Sn and (b) tail order parameter Stail, as function of reduced temperature T ∗ for a bilayer formed by lipids with ahh = 15. To further characterize the bilayer structure for a hh = 15, we study the order parameters Snand S tail, which are plotted in figure 5.10. At temperatures T ∗ ≤ 0.95 the chains are locally ordered (values of Sn above 0.5), and the order does not decrease significantly going through the hydrophobic core. Also the overall order of the chains S tail is high in this temperature region. Above T ∗ = 0.95 we observe a decrease in both
5.2 Single-tail lipid bilayers 67 the order parameters. The chains become disordered and the persistence of order along the chain is lost. This trend is analogous to the one observed for a hh = 35. In both cases the low temperature region is characterized by the ordering of the chains, while at high temperatures the chains are disordered. However, while for a hh = 35 the two monolayers are interdigitated in the ordered phase, for a hh = 15 the ordered phase is a bilayer formed by two separated leaflets. This can clearly be seen from the density profiles, which we plot as function of reduced temperature in figure 5.11. This figure shows that the melting of the bilayer results in a broader shape of the den- (a) T ∗ = 0.8 (b) T ∗ = 0.9 (c) T ∗ = 0.95 (d) T ∗ = 1.0 Figure 5.11: Density profiles as function of temperature for a bilayer formed by lipids with ahh = 15 (see also the caption to figure 5.7). sity profiles. The increase of disorder in the chains (see figure 5.10) results in a partial overlap of the two monolayers. This transition upon heating is also reflected in the trend of the area per lipid with temperature (figure 5.8(a)), which shows a sharp increase between T ∗ = 0.95 and T ∗ = 1.0. We can then conclude that a transition from an ordered to a disordered phase takes place at a temperature 0.95 < Tm < 1.0.
- Page 22 and 23: 16 Simulation method for coarse-gra
- Page 24 and 25: 18 Simulation method for coarse-gra
- Page 27 and 28: III Surface tension in lipid bilaye
- Page 29 and 30: 3.2 Method of calculation of surfac
- Page 31 and 32: 3.2 Method of calculation of surfac
- Page 33 and 34: 3.3 Constant surface tension ensemb
- Page 35 and 36: 3.3 Constant surface tension ensemb
- Page 37 and 38: 3.4 Surface tension in lipid bilaye
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- Page 41 and 42: 3.4 Surface tension in lipid bilaye
- 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
- Page 68 and 69: 62 Phase behavior of coarse-grained
- Page 70 and 71: 64 Phase behavior of coarse-grained
- Page 74 and 75: 68 Phase behavior of coarse-grained
- Page 76 and 77: 70 Phase behavior of coarse-grained
- Page 78 and 79: 72 Phase behavior of coarse-grained
- Page 80 and 81: 74 Phase behavior of coarse-grained
- Page 82 and 83: 76 Phase behavior of coarse-grained
- 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
- Page 102 and 103: 96 Mesoscopic model for lipid bilay
- Page 104 and 105: 98 Mesoscopic model for lipid bilay
- Page 106 and 107: 100 Mesoscopic model for lipid bila
- Page 108 and 109: 102 Mesoscopic model for lipid bila
- Page 110 and 111: 104 Mesoscopic model for lipid bila
- Page 112 and 113: 106 Mesoscopic model for lipid bila
- Page 114 and 115: 108 Mesoscopic model for lipid bila
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5.2 Single-tail <strong>lipid</strong> <strong>bilayers</strong> 67<br />
the order parameters. The chains become disordered <strong>and</strong> the persistence <strong>of</strong> order<br />
along the chain is lost. This trend is analogous to the one observed for a hh = 35. In<br />
both cases the low temperature region is characterized by the ordering <strong>of</strong> the chains,<br />
while at high temperatures the chains are disordered. However, while for a hh = 35<br />
the two monolayers are interdigitated in the ordered phase, for a hh = 15 the ordered<br />
phase is a bilayer formed by two separated leaflets. This can clearly be seen from<br />
the density pr<strong>of</strong>iles, which we plot as function <strong>of</strong> reduced temperature in figure 5.11.<br />
This figure shows that the melting <strong>of</strong> the bilayer results in a broader shape <strong>of</strong> the den-<br />
(a) T ∗ = 0.8 (b) T ∗ = 0.9<br />
(c) T ∗ = 0.95 (d) T ∗ = 1.0<br />
Figure 5.11: Density pr<strong>of</strong>iles as function <strong>of</strong> temperature for a bilayer formed by <strong>lipid</strong>s <strong>with</strong><br />
ahh = 15 (see also the caption to figure 5.7).<br />
sity pr<strong>of</strong>iles. The increase <strong>of</strong> disorder in the chains (see figure 5.10) results in a partial<br />
overlap <strong>of</strong> the two monolayers. This transition upon heating is also reflected in the<br />
trend <strong>of</strong> the area per <strong>lipid</strong> <strong>with</strong> temperature (figure 5.8(a)), which shows a sharp increase<br />
between T ∗ = 0.95 <strong>and</strong> T ∗ = 1.0. We can then conclude that a transition from<br />
an ordered to a disordered phase takes place at a temperature 0.95 < Tm < 1.0.
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