Evaluation of the binding ability of tetraaza[2]arene[2]triazine receptors anchoring l-alanine units for aromatic carboxylate anions

The binding affinities of three new tetraaza[2]arene[2]triazine based macrocycles anchoring one (AC1A) and two (AC2A and Me4AC2A) l-alanine amino acid units for five aromatic carboxylate anions (bz−, ph2−, iph2−, tph2− and btc3−) were investigated in DMSO-d6. 1H NMR titrations revealed that the AC1A and AC2A receptors exhibit comparable anion affinities, suggesting that the two l-alanine binding units in AC2A are not simultaneously involved in the anion recognition as indicated by molecular dynamics simulations carried out for selected AC1A and AC2A associations using the AMBER force field (GAFF). New force field parameters were developed in order to mimic the structural singularity derived from the N–H macrocyclic bridges.