FIGURE 5 The anions distribution on the Au-TMA nanoparticles
and transition probability matrices. Scheme for the definitions of
variables DIST and Rmin (A). The two gold cores are
denoted as I and II , respectively. Whereas, each anion on
the Au-TMA nanoparticles calculated by its distance to the COMs of gold
core I and II are presented (denoted ad Dist(I) andDist(II) , respectively). The variables DIST andRmin demonstrate the absolute difference and minimum of theseDist(I) and Dist(II) , respectively. The probabilities of
anions distributions on the Au-TMA nanoparticles as a function ofDIST and Rmin are also shown (B). The schematic
representation of the three anion classes (C). Whereas, anions in the
solutions belonging to the first class are shown in grey. The anions on
the Au-TMA nanoparticle surfaces with DIST greater than 2.0
(shown as pink) and DIST equal to or less than 2 nm (shown as
green) are classified into interface anions (the second class) and outer
anions (the third class), respectively. The transition matrix of anions
in the P2-4, P3-3,
P4-6 and P6-6 systems with
demonstrated transitions between the three regions obtained from the
last 1500 ns of MD simulations (D). The grey, pink and red squares
denote anions in the solution, outer anions and interface anions,
respectively. Whereas, the sum of each vertical column equals one.
2.4 | Dynamics of Au-TMA nanoparticles
In our last analysis, we measured the effects of molecular anions on the
dynamics of Au-TMA nanoparticles in these aggregates. This was performed
by estimations of the relative rotation of two Au-TMA nanoparticles.
Herein, the relative rotation of Au-TMA nanoparticles was calculated by
using one Au-TMA nanoparticle as the reference. The analysis was
performed over the last 1500 ns of MD simulations with a time interval
of 4 ns (Figure 6A). In comparison with the rotation angle of the
P2-4 system, the rotation angle of the
P3-3 system was significantly smaller which indicated
a more dynamic rotation of Au-TMA nanoparticles in the
P2-4 system (Figure 6B). This may be potentially
contributed by the higher charge density and smaller anion size of the
P2-4 anion. On the other hand, the dynamics of the
P2-4 anions in the interface region were found higher
than the interface of anions in the P3-3 system (see
Figure 5D). This may be attributed to a lower rotational barrier of
Au-TMA nanoparticles in the P2-4 systems than that of
the P3-3 system. However, the rotation angle of the
P3-3 system is close to that of the
P4-6 system. Interestingly, close proximity transition
probabilities involving anions in the interface region for both
P3-3 and P4-6 systems were also
observed (see Figure 5D). The data infers that the linear-shaped
P4-6 anion with higher charge density matches the
dynamics properties of the P3-3 anion because of its
stronger interaction with Au-TMA nanoparticles. Moreover, the rotation
angle in the P6-6 system was much smaller than that of
the P4-6 system and consistent with the transition
probability of these two systems. We speculate that the interfacial
aggregates formed by P6-6 anions and sodium ions
present a significant rotational barrier to the rotation of Au-TMA
nanoparticles. We propose this effect to significantly reduce the
dynamics of Au-TMA nanoparticles within the aggregate.