Chemistry Reference
In-Depth Information
S
S
N
H
H
O
H
H
O
H
O
O
H
N
H
H
N
N
N
OA c
S
S
O
OAc
O
AcO
OAc
AcO
AcO
AcO
AcO
11
S
N
N
H
H
O
O
O
H
N
N
H
O
S
O
H
N
S
O
O
N
H
O
H
H
OAc
N
O
N
OAc
AcO
O
S
OAc
OA c
AcO
AcO
OAc
12
Fig. 6 Proposed anion binding modes of receptors 11 and 12 with glutarate in DMSO-d
6
.
O
O
N
N
R
H
H
H
S
N
N
S
H
H
S
S
OR
RO
helix unfolding
N
O
O
N
N
H
N
H
H
O
O
O
O
R
OR
OR
helical secondary structure (P or/and M)
Fig. 7 Schematic representation of helix uncoiling in sugar-thiourea anion receptors by
carboxylate binding.
To gain information about the helix stability, binding anities of
monotopic 13 and ditopic 14 and 15 anion receptors were compared
(Fig. 8), using benzoate as a model anion. When binding constants for 13
and 14 in CDCl
3
were measured, the expected 10-fold increase in asso-
ciation constant was noted in favor of ditopic 14. Binding isotherms and
Job plots were consistent with 1 : 1 stoichiometries and K
ass
=
1749 and
18140 M
1
, respectively, were measured. However, titration experiments
for 15 provided 2 : 1/1 : 1 guest/host stiochiometry with binding constant
15Cbenzoate K
ass(1 : 1)
=
1106, which is much smaller when compared
Search WWH ::
Custom Search