Learning from Proteins and Drugs: Receptors That Mimic Biomedically Important Binding Motifs - Designing Receptors for the Next Generation of Biosensors - page 39

Fig. 7 New class of carboxylic acid bioisostere functionalized calix[4]arene recognition elements

Fig. 8 Local minima that involve the maximum four host-guest hydrogen bonds for representa-
tive host-guest complex with key dihedral angles calculated (HF/6-31+G*). Lower rim
substituents have been omitted. (a) Aryl sulfonamide functionalized host complexed with Cl .
(b) Acyl sulfonamide functionalized host complexed with Cl .(c) Tetrazole functionalized host
complexed with Cl

anion symmetrically. These provided values for the key torsion angles of each
functional group that would be optimal for binding (Fig. 8 ). The actual inherent
conformational preferences for each functional group were then determined by
dihedral driving calculations and CSD surveys (not shown) and compared to the
values required for anion binding in this structural context.
The combined computational analyses for the key dihedral angles that define the
inherent shapes of these moieties are presented in Fig. 9 .
These comparisons showed that the tetrazole hosts 12 and 13 must adopt a
nonideal dihedral that takes the tetrazole out of conjugation with its neighboring
ring to bind an anion, and that it paid ~13 kJ/mol in order to do so (Fig. 9c ). The
shapes of the aryl and acyl sulfonamides are defined by three important dihedral
angles. The conformations of the rotatable carbon-sulfur bonds for aryl sulfone
type functionalities ( ~90 )[ 51 ].

y 1 , Fig. 9d ) and are known to be similar ( y 1 ¼