| Abstract
| - The binding properties of two tren-based macrocyclic receptors containing three [12]aneN4 (L1) or[14]aneN4 (L2) units toward the three isomers of the benzenetricarboxylic acid (BTC) have beenanalyzed by means of potentiometric, 1H NMR, and microcalorimetric measurements in aqueoussolutions. Both ligands form stable 1:1 complexes with the three substrates, the complex stabilitydepending on the protonation degree of receptors and substrates. Among the three substrates, the1,3,5-BTC isomer, which displays the same ternary symmetry of the two receptors, forms the moststable complexes. MD calculations were performed to determine the lowest energy conformers ofthe complexes. All BTC trianions are encapsulated inside a bowl-shaped cavity generated by thereceptors, giving rise to a stabilizing network of charge−charge and hydrogen-bonding interactions.The time-dependent behavior of the complexes was not analyzed. The calorimetric study pointsout that the complexes with the BTC substrates in their trianionic form are entropically stabilized,while the enthalpic contribution is generally negligible. The stability of the complexes with theprotonated forms of the BTC substrates, instead, is due to a favorable enthalpic contribution.
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