Anion-Induced Intramolecular Cyclization of Urea-Based Receptors: Entrapment of Cyclic [SO₄(H₂O)₄^2–]_n Cluster and Encapsulation of Anions with Varied Dimensionality

Abstract

Two unsymmetrical dipodal monourea anion receptors BPU-1 and BPU-2 with varying π-acidic terminal electron-withdrawing substituents (–NO2 and –CF3) can interact with anions of varied geometries (spherical, trigonal planar, and tetrahedral). Receptors are designed with an arm having a flexible urea unit, and the other arm contains a semirigid fluorophoric benzimidazole unit. BPU-1 could entrap cyclic sulfate water cluster, [SO4(H2O)4 2–] n , resulting in R4 4(8) and R4 4(12) arrangements in the solid state. Anion-sensing behavior of both receptors has been investigated in the aqueous medium, where BPU-1 could selectively sense SO4 2–/HSO4 – among other biologically relevant anions. Anion-induced intramolecular cyclization of both receptors in the presence of F–/HO– to yield benzimidazo­[1,2-c]­quinazolin-6-ones has also been investigated in detail.

Twisted-intramolecular-charge-transfer based fluorogenic nano-probes for ultrafast cyanide sensing in water and micellar medium

“…In recent times, development of selective and sensitive sensors for anions has received much attention owing to their vital role in environmental and biological applications. [1][2][3][4][5][6][7][8][9] Among various anions, cyanide (CN À ) is considered one of the most poisonous anions owing to its extreme toxicity towards human. 10 Even at a very low concentration it causes serious health issues such as histotoxic anoxia, eventually leading to death.…”