Biomedical Engineering Reference
In-Depth Information
a
Front monomer
400 nm
Rear monomer
400 nm
1
4 nm
1
4 nm
14 nm
Core
Core
Head
Tail Head
Tail
Capped end
Heterodimer junction
Capped end
b
i
ii
iii
iv
v
vi
Fig. 16.2
Design schematics of the DNA six-helix bundle. (
a
) 3D cartoon view of 800-nm-
long six-helix bundle heterodimer, (not to scale).
Left
, six-helix bundle front monomer with core
module in grey, capped head module in
blue
, and connector tail module for heterodimerization in
orange.
Right
, six-helix bundle rear monomer with core module in
grey
, connector head module for
heterodimerization in
orange
, and capped tail module in
green
.(
b
) Scaffold-plus-staples schematic
view of the heterodimer junction of front and rear monomer. One strand of each double helix is
contributed by the scaffold shown in
blue
, and the other strand is contributed by a staple. Base pairs
are depicted as short vertical lines. Helices
1
-
6
are labeled on the left. (
i
) Front monomer head
module. Three staple strands serve to cap the front monomer head (shown in
cyan
). (
ii
,
v
)Core
module. The scaffold crossovers (shown in
blue
) that form an internal seam for each monomer
occur at two segments. (
iii
) Front monomer tail module. Three staple strands with a total of 26
unpaired bases decorate the tail. The scaffold strand is unpaired for 36 bases (shown in
orange
).
(
iv
) Rear monomer head module. Three staple strands with a total of 36 unpaired bases decorate
the head (shown in
orange
). These unpaired regions are complementary to the corresponding
36 unpaired bases of the front monomer tail scaffold strand. The 26 unpaired bases in the rear
monomer head scaffold strand are complementary to the 26 unpaired bases of the three staple
strands that decorate the front monomer tail. In the DNA-nanotube heterodimer, these unpaired
regions match up to form the complete intermonomer junction. (
vi
) Rear monomer tail module.
Four staple strands serve to cap the rear monomer tail (shown in
green
)
(Fig.
16.2
b). After completing the annealing, purification, and heterodimerization
process (Fig.
16.3
a), the resulting solution of
0.8
m DNA-nanotube heterodimers
can be concentrated to approximately 25 mg/mL, during which the nanotubes
will spontaneously align to form a stable nematic liquid crystal exhibiting strong
birefringence when viewed through crossed polarizers (Fig.
16.3
a,b). The magnetic
susceptibility anisotropy of this DNA-nanotube liquid crystal is largely dominated
by diamagnetic purine bases. Thus, when subjected to an external magnetic field, the
nanotubes will orient themselves to be orthogonal to the field such that the magnetic
field is parallel to the plane of the purine bases, thus achieving the lowest energy
state.
2
H quadrupolar splitting in the range of 4-8 Hz (Fig.
16.3
c) was observed
when the concentrated DNA-nanotube media were aligned in a 11.4 T magnetic field
in the presence of 100 mM DPC and 10% D
2
O, thus demonstrating the medium's
ability to weakly interact and align molecules in solution. It is worth noting that
the variation in
2
H quadrupolar splitting is a direct result and good indicator
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