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a
Dimer
Trimer
Tetramer
Pentamer
b
Dimer
Trimer
Tetramer
Pentamer
4
1.0
0.5
3
0.0
2
-0.5
1
3.5x10
-3
3.0
1/T [K
-1
]
3.5x10
-3
3.0
1/T [K
-1
]
Figure 5.10
Plots of the equilibrium folding constants,
K
, against
fold
inverse temperature yield endothermic processes
in water
for
foldamers
2B
−
5B
(a) and exothermic processes
in organics
(b) for foldamers
. The straight lines were obtained
from fitting the van't Hoff equation to the experimental data
for dimer (diamonds), trimer (triangles), tetramer (squares),
and pentamer (circles).
2A
−
5A
Using hydrophobic effects and six base-pair hairpin stems, we
constructed thermophilic foldable polymers (
),
which can maintain their structural integrity at both low and high
temperatures (Fig. 5.7b,c). At high temperatures, hydrophobic
attractions derived from perylene play a dominant role in stabilizing
the folded structure. At low temperatures, hydrogen bonding
between self-complementary hairpin structures plays a major role in
perylene folding. The hairpin structure is based on the modification
of the AP1 binding site. The polymer obtained was almost completely
devoid of temperature-dependent structural variations (Fig.
5.9). Owing to the cooperative effects between the folding of DNA
loops and the chromophore core, the overall stability of the folded
structure improves, as evidenced by the decrease in A
2C
,
3C
,
4C
, and
5C
→
→
0
0
/A
0
1
by
an additional 10
cooling cycles.
The aforementioned results reveal that energy supplied in
the form of heat is not effective at unfolding the thermophilic
foldamers made of alternating DNA and perylene sequences. An
alternative approach is to use molecular recognition to actuate
−
30% throughout the heating
−
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