Switching from Negative-Cooperativity
to No-Cooperativity
in the Binding of Ion-Pair Dimers by a Bis(calix[4]pyrrole) Macrocycle
Ricardo Molina-Muriel
Gemma Aragay
Eduardo C. Escudero-Adán
Pablo Ballester
10.1021/acs.joc.8b02449.s003
https://acs.figshare.com/articles/dataset/Switching_from_Negative-Cooperativity_to_No-Cooperativity_in_the_Binding_of_Ion-Pair_Dimers_by_a_Bis_calix_4_pyrrole_Macrocycle/7246766
We
report the synthesis of a macrocyclic receptor containing two
di-<i>meso</i>-phenylcalix[4]pyrrole units linked by two
triazole spacers. The 1,4-substitution of the 1,2,3-triazole spacers
conveys different binding affinities to the two heteroditopic binding
sites. These features make the receptor an ideal candidate to investigate
allosteric cooperativity in the binding of ion-pair dimers. We probed
the interaction of tetraalkylammonium salts (TBA·Cl, TBA·OCN,
and MTOA·Cl) with the tetra-heterotopic macrocyclic receptor
in chloroform solution using <sup>1</sup>H NMR spectroscopic titration
experiments. The results obtained show that, at millimolar concentration,
the addition of 2 equiv of the salt to the receptor’s solution
induced the quantitative pairwise binding of the ion-pairs. The 2:1
(ion-pair:receptor) complexes feature different binding geometries
and binding cooperativities depending on the nature of the alkylammonium
cation. The binding geometries assigned to the complexes of the ion-pair
dimers in solution are fully supported by X-ray diffraction analyses
of single crystals. The thermodynamic features of the binding processes
(separate or concomitant formation of 1:1 and 2:1 complexes), derived
from isothermal titration calorimetry (ITC) experiments, are rationalized
by combining the different ion-pair binding modes of the salt dimers
with the dissimilar electronic properties of the two nearby heteroditopic
binding sites of the receptor.
2018-10-16 00:00:00
tetra-heterotopic macrocyclic receptor
ion-pair binding modes
binding geometries
heteroditopic binding sites
TBA
MTOA
ITC
1 H NMR spectroscopic titration experiments
X-ray diffraction analyses
ion-pair dimers