A. Structure of the DMPC Lipid Bilayer. The atomic
density profiles for the hydrated DMPC bilayer are shown in
Figure 2. More relevant to the interaction of a C
fullerene
with the lipid bilayer is the Lennard-Jones energy profile also
shown in Figure 2. This energy profile was obtained by
positioning one fullerene in one of the two leaflets along the
normal of the lipid bilayer at various positions and determining
the (potential) energy of interaction of the fullerene with the
bilayer. The high density of atoms on the C
surface results in
strong dispersion (London) interactions with the surrounding
media. For example, our previous simulation studies revealed
that the dispersion interaction of a C
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fullerene with water is
about four times stronger than for an oil droplet of the same
diameter as the fullerene.
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We therefore anticipate that fullerenes
will exhibit a tendency to position themselves in regions of high
atomic density in anisotropic environments such as lipid bilayers,
as discussed below.
B. C
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Fullerenes in a Tridecane Melt. A tridecane melt is
an isotropic model for the anisotropic environment in the core
of a lipid bilayer. We have examined the interaction of C
fullerenes with a tridecane melt as well as the influence of
tridecane on the interactions between a pair of C
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Figure 3 shows the density profile of tridecane carbon atoms
around the fullerene. The diameter of the fullerene particle
(10.02 Å) is given by the center-of-mass separation of a fullerene
pair at which the POMF in vacuum is most attractive.
The
high density of carbon atoms at the surface indicates that the
alkane has a strong tendency to wet the surface of the fullerene
due to favorable Lennard-Jones interactions with the atomically
dense fullerene surface. Figure 4 shows the POMF between two
fullerenes in the alkane melt at a density corresponding to 1
atm as well as alkane densities 10% greater and 10% lower
fullerenes.
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