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Figure 2.17
(a) Structure of the triangle lactam (
). (b) Equilibrium
between the two most favored conformers of (
4
4
).
Molecular modeling allowed us to select the most stable aggregate
among the four possibilities of
S
(2 subunits),
T
(4 subunits),
O
(8
6
subunits) and
(20subunits)symmetry(Fig.2.18).Thetetramer
proved more stable and a complementary guest was looked for that
couldfitnicelyinitscavity.Thetetraethylammoniumcation(Et
I
+
)
was chosen for its suitable size and its positive charge which would
allow for the easy detection of charged host-guest complexes by
electron spray ionisation (ESI) [75,87-89]. In non polar solvents
(1:1 chloroform and acetonitrile) the expected (
N
4
⊂
+
complex
was detected (mass 1776, most abundant species above mass
500)togetherwithtinyamountsofthesupramolecularcavitand
host-guest complex (
4
)
Et
N
4
4
⊂
+
4
)
Et
N
. Addition of methanol destroys the
3
4
⊂
+
complex which reappears on addition of chloroform. The
capsule is therefore reversible, a property of paramount importance
for drug delivery and catalysis, it can accommodate guests of
reasonable size. Compound (
(
4
)
Et
N
4
4
4
)isthefirstcapsuleinducerbasedon
Z
-amides, its structure is therefore absolutely innovative and it has
thepotentialtosignificantlyaugmentthe“tool-box”ofthemodern
day supramolecular chemist.
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