Detection of Al3+ and Fe3+ ions by nitrobenzoxadiazole bearing pyridine-2,6-dicarboxamide based chemosensors: effect of solvents on detection

Abstract

Hybrid chemosensors, L1 and L2, based on a pyridine-2,6-dicarboxamide fragment while containing a 4-nitrobenzoxadiazole group, have been designed and investigated for the sensing of Al³⁺ and Fe³⁺ ions. Detection was found to be significantly controlled by the selection of a solvent, CH₃OH (protic), THF (non-protic) or H₂O (HEPES buffer). While only Al³⁺ ions were detected in CH₃OH, only Fe³⁺ ions were sensed in H₂O (HEPES buffer). Interestingly, both Al³⁺ and Fe³⁺ ions were detected in THF. UV-visible as well as fluorescence spectral studies, binding constants and detection limits illustrated the notable sensing abilities of two closely related chemosensors. Both chemosensors were found to bind one equivalent of an M³⁺ ion as confirmed by Job's plot that was further supported by binding parameters as well as FTIR, NMR and mass spectral studies. The reversibility was achieved for both the chemosensors by using pyrophosphate ion (PPi).