Abstract
The versatility of the 4-( N, N-dimethylamino)benzoate (DMAB) group embedded in host 1 as a signaling subunit for anion recognition was elucidated in terms of 1H NMR, CD, and fluorescence studies. Host 1 showed 1:1 complexation with monovalent anions and stepwise 1:1 and 2:1 (host 1 : anion) complexation with divalent phosphate anions. The binding constants between host 1 and anions were determined by means of 1H NMR titrations in CD 3CN (HPO 4 2−: log K 1:1=6.2, log K 2:1=4.9; H 2P 2O 7 2−: log K 1:1=4.4, log K 2:1=1.8; AMP 2−: log K 1:1>7, log K 2:1>5) and the affinity of host 1 toward divalent anions, HPO 4 2−, H 2P 2O 7 2−, and AMP 2−, is stronger than that toward monovalent anions, NO 3 −, BF 4 −, ClO 4 −, HSO 4 −, and PF 6 −. The CD exciton chirality studies of host 1 with divalent anions, HPO 4 2− and AMP 2−, revealed that the two DMAB groups in the 2:1 complexes were arranged with negative chirality (counterclockwise). The dual fluorescence behavior of the DMAB group demonstrated not only the complexation stoichiometry but also the role(s) of the lipophilic countercation such as tetrabutylammonium and/or the hydrophilic residue in AMP during anion recognition.
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