cavity of 44BP4 according to the calculation. The orientation of the encapsulated
guest parallel to the trans-biphenyl units is the lowest in energy (Fig. 9a, b). The
complexation mechanism can be explained by the fact that G28 accepts electrons
to form the anion radical G28
ÁÀ . The confinement of G28
ÁÀ within the host cavity
(cation radical 44BP4
Á+
) occurs due to a donor–acceptor interaction. Meanwhile,
host–guest binding in such complexes is facilitated through hydrogen bonding and
π–π stacking as well as C–HÁ Á Áπ interactions (Fig. 9c).
12.9 Biological and Pharmaceutical Molecules
In 2016, we demonstrated the first host–guest complex of water-soluble biphenarenes
towards biological and pharmaceutical molecules was demonstrated by our group
[41]. 44CBP4 exhibited sequential binding for acetylcholine (G36ÁCl) ! choline
(G37ÁCl) ! betaine (G38ÁCl), with the same sequence as the enzymatic reaction. The
K a value for G36ÁCl ((1.16 Æ 0.10) Â 10
4 M
À1
, Entry 74) is 3.3 times larger than that
for G37ÁCl ((3.51 Æ 0.42) Â 10
3 M
À1
, Entry 75), while no obvious complexation was
found for G38ÁCl (Entry 76). The selective binding of the neuromodulator G36
+ is
interesting as it plays important roles in cognitive and cerebral functions. 44CBP4 also
strongly interacts with the pharmaceutical molecule 1-adamantanamine hydrochloride
(G10ÁCl), with a K a value of (2.46 Æ 0.21) Â 10
4 M
À1 (Entry 16).
44BP3
a
b
c
44BP4
Strong attraction Vander Waals
interaction
Strongrepulsion
+0.05
–0.05
p>0
λ 2 >0
p~0
λ 2 ~0
p>0
λ 2 <0
Fig. 9 (a) The lowest energy conformers of 44BP3 and 44BP4. (b) The lowest energy conformer
of the 44BP4 and G28 complex. (c) Color-filled RDG isosurfaces depicting NCI regions in the
G28 & 44BP4 complex. Green regions refer to π–π stacking as well as C–HÁ Á ÁN and C–HÁ Á ÁH–C
interactions. The steric interactions are shown in red. Reproduced from Ref. [45] with permission
from WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
12 Biphen[n]arenes: Synthesis and Host–Guest Properties
331
guest parallel to the trans-biphenyl units is the lowest in energy (Fig. 9a, b). The
complexation mechanism can be explained by the fact that G28 accepts electrons
to form the anion radical G28
ÁÀ . The confinement of G28
ÁÀ within the host cavity
(cation radical 44BP4
Á+
) occurs due to a donor–acceptor interaction. Meanwhile,
host–guest binding in such complexes is facilitated through hydrogen bonding and
π–π stacking as well as C–HÁ Á Áπ interactions (Fig. 9c).
12.9 Biological and Pharmaceutical Molecules
In 2016, we demonstrated the first host–guest complex of water-soluble biphenarenes
towards biological and pharmaceutical molecules was demonstrated by our group
[41]. 44CBP4 exhibited sequential binding for acetylcholine (G36ÁCl) ! choline
(G37ÁCl) ! betaine (G38ÁCl), with the same sequence as the enzymatic reaction. The
K a value for G36ÁCl ((1.16 Æ 0.10) Â 10
4 M
À1
, Entry 74) is 3.3 times larger than that
for G37ÁCl ((3.51 Æ 0.42) Â 10
3 M
À1
, Entry 75), while no obvious complexation was
found for G38ÁCl (Entry 76). The selective binding of the neuromodulator G36
+ is
interesting as it plays important roles in cognitive and cerebral functions. 44CBP4 also
strongly interacts with the pharmaceutical molecule 1-adamantanamine hydrochloride
(G10ÁCl), with a K a value of (2.46 Æ 0.21) Â 10
4 M
À1 (Entry 16).
44BP3
a
b
c
44BP4
Strong attraction Vander Waals
interaction
Strongrepulsion
+0.05
–0.05
p>0
λ 2 >0
p~0
λ 2 ~0
p>0
λ 2 <0
Fig. 9 (a) The lowest energy conformers of 44BP3 and 44BP4. (b) The lowest energy conformer
of the 44BP4 and G28 complex. (c) Color-filled RDG isosurfaces depicting NCI regions in the
G28 & 44BP4 complex. Green regions refer to π–π stacking as well as C–HÁ Á ÁN and C–HÁ Á ÁH–C
interactions. The steric interactions are shown in red. Reproduced from Ref. [45] with permission
from WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
12 Biphen[n]arenes: Synthesis and Host–Guest Properties
331