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conditions, the guests were immediately liberated owing to the
decreased hydrophobic interactions as well as cationic repulsion
between the host and protonated
-dimethylaniline [106]. Besides
the inclusion of charged molecules, the cage molecules were also
able to encapsulate large neutral molecules into the approximately 2
nm wide cavity [107].
N
,
N
On mixing a hexane solution of
o
-carborane with aqueous
solution of
-carborane were transferred
into the aqueous phase and encapsulated within the cavity of
57
, four equivalents of the
o
57
[107]. The 1:4 stoichiometry was confirmed by the integration
of the host and guest signals in the
1
H NMR spectrum. Inclusion
of 1- and 2-admantanol showed that the interior of the cage has
highly hydrophobic characteristics, which resulted in the outward
pointing of the hydroxyl groups in the admantanol. For molecules
that were slightly larger than the portal of
, encapsulation of just
one guest was very slow as a result of a thermally induced slippage.
Once the guest is inside the cavity, it did not escape from the cavity
even when treated with organic solvents. It was also shown that the
two macrocyclic structures
57
are capable of incorporating
dicarboxylate anions such as sodium terephthalate and 1,4-
benzodicarboxylate [108]. The host
60
and
61
guest interaction is interpreted
by electrostatic interaction of the positively charged cage and the
negatively charged dicarboxylate.
−
12+
12NO
3
-
12+
12NO
3
-
NH
2
H
2
N
NH
2
H
2
N
Pd
Pd
N
N
N
N
OAc
AcO
N
N
H
2
N
NH
2
N
N
Pd
N
N
N
N
N
N
Pd
H
2
N
N
H
2
N
H
N
NH
2
N
H
N
H
2
H
2
N
N
N
Pd
Pd
Pd
Pd
H
2
N
NH
2
N
H
2
N
N
H
2
N
N
H
2
Pd
N
N
N
N
N
N
N
N
P
d
OAc
H
2
N
NH
2
N
AcO
N
N
N
N
N
Pd
N
N
H
2
NNH
2
Pd
H
2
N
NH
2
60
61
Tashiro and Fujita studied the interaction of cationic cages
62
and
63
with various peptides [109,110]. The platinum cage
62
bound
Ac-Trp-Trp-Ala-NH
2
(
64
) very strongly in water and the
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