"Test kit" for detection of biologically important anions: a salicylidene-hydrazine based Schiff base

Test paper coated with Schiff base [(N,N(/)-bis(5-nitro-salicylidene)hydrazine] receptor 1 (host) can selectively detect fluoride and acetate ions (guest) by developing yellow color which can be detected by naked-eye both in aqueous-acetonitrile solution and in solid supported test kit. UV-vis spectral analysis shows that the absorption peaks at 288 and 345 nm of receptor 1 gradually decrease its initial intensity and new red shifted absorption bands at 397 nm and 455 nm gradually appear upon addition of increasing amount of F(-) and AcO(-) ions over several tested anions such as H(2)PO(4)(-), Cl(-), Br(-), I(-), NO(3)(-), NO(2)(-), HSO(4)(-), HSO(3)(-), and ClO(4)(-) in aqueous-acetonitrile solvent. The colorimetric test results and UV-vis spectral analysis are in well agreement with (1)H NMR titration results in d(6)-DMSO solvent. The receptor 1 forms 1:2 stable complexes with F(-) and AcO(-) ions. However, similar kind of observation obtained from UV-vis titrations in presence of AcOH corresponds to 1:1 complexation ratio indicating the formation of H-bonding interaction between the receptor and anions (F(-) and AcO(-) ions). So, the observed 1:2 complexation ratio can only be explained on the basis of deprotonation (∼1 eqv.) and H-bonding (∼1 eqv.) interactions [1]. The ratiometric analysis of host-guest complexes corroborates well with the proposed theoretical model optimization at Density Functional Theory (DFT) level.