“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 H2PO4-, Cl-Cl-, Br-Br-, I-I-, NO3-, NO2-, HSO4-, HSO3-, and ClO4- in aqueous–acetonitrile solvent. The colorimetric test results and UV–vis spectral analysis are in well agreement with 1H NMR titration results in d6-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.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► “Test kit” was prepared for the detection of biologically important anions. ► “Test kit” can selectively detect F− and AcO− ions. ► Color change of the “test kit” in presence of anions were detected by naked-eye. ► Predicted complexation behavior from theoretical structural optimization corroborates with the experimental results.