Nano Res.

Electronic Supplementary Material

Surface properties of encapsulating hydrophobic nano-particles regulate the main phase transition temperatureof lipid bilayers: A simulation study

Xubo Lin and Ning Gu ()

State Key Laboratory of Bioelectronics and Jiangsu Key Laboratory for Biomaterials and Devices, School of Biological Science &Medical Engineering, Southeast University, Nanjing 210096, China

Supporting information to DOI 10.1007/s12274-014-0482-3

Details about the MARTINI force field

Table S1 The interaction levels between different CG bead types

Level of interaction indicates the well depth in the LJ potential: O, = 5.6 kJ/mol; I, = 5.0 kJ/mol; II, = 4.5 kJ/mol; III, = 4.0 kJ/mol; IV, = 3.5 kJ/mol; V, = 3.1 kJ/mol; VI, = 2.7 kJ/mol; VII, = 2.3 kJ/mol; VIII, = 2.0 kJ/mol; IX, = 4.5 kJ/mol. The LJ parameter = 0.47 nm for all interaction levels except level IX for which = 0.62 nm. Four different CG sites are considered: Charged (Q), polar (P), nonpolar (N), and apolar (C). Subscripts are used to further distinguish groups with different chemical nature: 0, no hydrogen-bonding capabilities are present; d, groups acting as hydrogen bond donor; a, groups acting as hydrogen bond acceptor; da, groups with donor and acceptor options; 1–5, indicating increasing polar affinity [S1].

Address correspondence to guning@seu.edu.cn

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Figure S1 The phase behavior of the DPPC bilayer encapsulating NPs in the initial state (280 K) of phase transition simulations. Different colors correspond to different order parameters as shown in the color bar. The black line corresponds to the trajectory of NPs projected in the x–y plane.

Figure S2 2D phase map of the DPPC bilayer encapsulating smooth NPs for characterizing the gel-to-fluid phase transition. Different colors correspond to different order parameters as shown in the color bar. The black line corresponds to the trajectory of NPs projected in the x–y plane.

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Figure S3 2D phase map of the DPPC bilayer encapsulating rough NPs for characterizing the gel-to-fluid phase transition. Different colors correspond to different order parameters as shown in the color bar. The black line corresponds to the trajectory of NPs projected in the x–y plane.

System size effects

In order to evaluate the system size effects on the phase behavior of the DPPC bilayer with or without NPs, we

expand the systems of 4 nm (0%, rough), 4 nm (0%, smooth), pure bilayer to 4-fold sizes (2,048 DPPC molecules,

4 NPs, 70,064 water molecules, Figs. S4(a) and S4(b)). The temperatures of the new systems are increased from

280 K to 335 K as described in the model and simulation details of the manuscript. As shown in Fig. S4(c), the

main phase transition temperature of the pure DPPC bilayer is reduced to 310 K (not 315 K as described in the

manuscript), which can be ascribed to there being more fluctuations in large systems. But the trends of the

phase behavior of the DPPC bilayer encapsulating NPs are well reproduced as those of smaller systems

described in manuscript: 4 nm (0%, rough) increased the main phase transition temperature, while 4 nm (0%,

smooth) showed no effects on the main phase transition temperature. In other words, the results of the phase

behavior of the smaller DPPC bilayer encapsulating NPs from coarse-grained molecular dynamics simulations

in the manuscript should not be subject to finite size effects.

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Figure S4 Side view of the four-fold systems of (a) 4 nm (0%, rough) and (b) 4 nm (0%, smooth); Variation of area per lipid during the main phase transition process for the DPPC bilayer encapsulating rough NPs and smooth NPs. The green line is for the case of the pure DPPC bilayer.

References

[S1] Marrink, S. J.; Risselada, H. J.; Yefimov, S.; Tieleman, D. P.; de Vries, A. H. The MARTINI force field: Coarse grained model

for biomolecular simulations. J. Phys. Chem. B 2007, 111, 7812–7824.