Biomedical Engineering Reference
In-Depth Information
Fig. 1.43
Schematic snapshots (a, b, c) of the system with a single channel in side view (the
xz
-
plane) together with the trajectories (
d
,
e
) of average dipole angle
N
.t/ of the water orientations.
The snapshots shown in (
b
,
c
) correspond to the
red dashed
part of the system (see subfigure
a) in another side view (
yz
-plane).
Blue
and
green spheres
denote the negative charge and the
positive charge, respectively, which result in different orientations of the water molecules facing
the charges. The water molecule facing the external charge is named as “monitored-water.” The
single-walled CNT is represented by
gray lines
and its positive direction is shown by the
black
dashedarrowhead
. Water molecules are shown with oxygen in
red
and hydrogen in
gray
,andthe
first water molecule outside the channels opposite to the charge signal input is shown in
yellow
.
The dipole direction of the water molecules is not shown, which is along the midline between
the two O-H chemical bonds of the water molecule. Water molecules outside the nanotubes are
omitted in the figure (reprinted from [
132
]. Copyright 2010 Royal Society of Chemistry)
potential well depth of "
CC
D
0:3612 kJ
mol
1
and "
CO
D
0:4802 kJ
mol
1
[
21
].
The system is first minimized with conjugate gradient method for 10,000 steps and
then equilibrated with MD for 5 ns at 300 K before data collection. An external
signal charge of magnitude 1.0
e
is then introduced to the center of the second
carbon ring of the main tubes (constrained by using the position restraints during
the simulations), and its opposite charge for neutralization is constrained near the
edge of each box at coordinates (0.00, 3.00, and 0.00 nm), which is far enough to
have any meaningful influence on the signal charge (our numerical data also confirm
this).
Note that at the center of a second carbon ring of the nanotube, this charge
is attached in order to control the direction of the dipole orientation of the water
molecule to face the charge, and we call this confined water as “monitored-water”
hereafter. We have found that different signs of the charge
q
result in different
