N
N
N
N
O
N
H
H
H
N
N
N
N
O
N
H
H
H
N
N
N
N
O
N H
H
H
N
N
N
N
O
N
H
H
H
N
NH
N
N
NH 2
O
O
OH OH
O
O
O
R
5'
36 R = OH
37 R = I
KB(OH) 4
H 2 O
R
B
O
O
O
O
O
R
B
O
O
O
O
O
R
B
O
O
O
R
N
N
N
N
O
H
N
O
O
O
R
B
O
O
K
+
Scheme 4.12 Formation of G 4 ÁK
+ hydrogel from 36 or 37
N
N
N
N
O
N
O
OR
RO
B
O
O
N
N
N
N
R
N
O
H
H
N
N
N
N
R
N
O
H
H
H
H
N
N
N N
R
N
O
H
H
H
H
H
K
+
38
N
N
N
N
O
H 2 N
O
OR
RO
B
O
O
Fig. 4.12 A hydrogel is made when 36 or 37 reacts with KB(OH) 4 to form GB esters that
self-assemble into G 4 -wires stabilized by K
+ , and the wires entangle to give a fibrous network, and
for in situ formation of 38 destroys the hydrogel network due to lacking of N1 H-bonding donor,
which cannot form stable G 4 -quartets. Adapted with permission from [30]. Copyright © The Royal
Society of Chemistry 2016
4.1 Discrete Gelators
137