Bisamides Derived from Azulene‐1,3‐ and ‐5,7‐dicarboxylic Acids as New Building Blocks for Anion Receptors

Abstract

Bisamides based on the azulene moiety were investigated as building blocks for anion receptors. In the course of these studies, derivatives of azulene-1,3- and -5,7-dicarboxylic acid were synthesized and thoroughly characterized. The anion affinities of the derivatives based on functionalization in the five-membered ring and in the seven-membered ring were determined by (1)H NMR titration. The structural analysis of these building blocks was performed by X-ray diffractometry, molecular modelling and 2D NMR spectroscopy. The five-membered ring derivatives are easy to obtain, offer a binding site preorganized in the syn-syn conformation and bind anions with a strength similar to those of pyrrole-based analogues. There is also strong evidence for aromatic CH...anion interactions. The ligands substituted at the 5- and 7-positions offer a binding cleft with an uncommon geometry that originates from the seven-membered ring and seems to be complementary to the chloride anion.

Synthesis and acid–base properties of a proton-bridged biaryl compound based on pyridylazulene

“…Azulene derivatives have been included in organic field-effect transistors, charge-transfer complexes, nonlinear optics, and sensing applications. [13][14][15][16][17] The relevant phenomena are considered a consequence of the non-zero dipole moment of the azulene skeleton, which consists of a cyclopentadienyl anion and a tropylium cation. In addition, the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of azulene is small.…”

Transmembrane anion transport promoted by thioamides

“…21,22 Very likely, the benecial effect of enhanced hydrogen bond donating ability of the thioamide moieties 23 is counterbalanced here by unfavourable conformational preferences of the thioamides. 24,25 The anion transport properties of these compounds were investigated in POPC phospholipid vesicles using a chloride selective electrode. 26 In these assays, the facilitated chloride efflux induced by aliquots of the compounds was monitored over time.…”

“… 21,22 Very likely, the beneficial effect of enhanced hydrogen bond donating ability of the thioamide moieties 23 is counterbalanced here by unfavourable conformational preferences of the thioamides. 24,25 …”

Solution and Solid State Studies of Urea Derivatives of DITIPIRAM Acting as Powerful Anion Receptors

“…First of all, neutral anion receptors have generally an advantage over the positively charged systems due to their much higher selectivity, despite the lower stabilities of receptor-anion complexes. These result from the presence of binding groups such as hydrogen bond donors, which allow for the establishment of highly directional interactions with the anion [30][31][32][33][34][35][36]. Furthermore, the unquestionable advantage of acyclic receptors, compared to their cyclic analogues, is their relatively simpler synthesis due to the lack of a problematic and low-yielding macrocyclization step.…”