B. C
60
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
60
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
than this value (F
). The inset to Figure 4 shows the total
POMF, indicating a favorable net interaction between fullerenes
at close contact (compared to larger separations), consistent with
the low solubility of C
bulk
60
fullerenes in tridecane.
59
The matrixinduced
interactions ¢POMF, obtained by subtracting the direct
fullerene-fullerene Lennard-Jones interaction from the POMF
in the tridecane melt, are shown in the main panel of Figure 4.
The POMF is modulated (minima/maxima) every 4-5Åby
the structure of the alkane melt (see Figure 3). Each modulation
corresponds to the removal of an additional solvation shell of
alkane monomers between the fullerenes as their separation is
reduced. The tridecane matrix results in a net interaction between
fullerenes that is less favorable compared to their interaction in
vacuum due to the strong Lennard-Jones interactions between
the melt and the fullerene. From the point of view of the alkane,
bringing the fullerenes into close contact from large separation
results in an increase of the free energy of the system due to
reduced fullerene-alkane contacts. This matrix-induced contribution
to the free energy upon fullerene aggregation becomes
greater as the density of the alkane increases with a corresponding
decrease in the net favorable interaction between the
fullerenes as shown in Figure 4.