Aminomethylpyrene-based imino-phenols as primary fluorescence switch-on sensors for Al3+ in solution and in Vero cells and their complexes as secondary recognition ensembles toward pyrophosphate

Abstract

Three aminomethylpyrene-based salicyl-imines, viz. L1, L2 and L3 were synthesized and characterized and their recognition of biologically relevant Mⁿ⁺ ions was studied. These three receptors were shown to be selective and sensitive for Al³⁺ among the 13 metal ions studied in a HEPES buffer medium by fluorescence, absorption, and visual emission color change with detection limits of 3.60, 2.13 and 2.16 μM, respectively, by L1, L2 and L3. The interaction of Al³⁺ with the three receptors (L1, L2 and L3) has been further supported by absorption studies, and the stoichiometry of the complex formed (1 : 1) has been established on the basis of emission and ESI-MS. Competitive ion titrations carried out reveal that the Al³⁺ can be detected even in the presence of other metal ions of bio importance. The structure of the aluminium complexes and their mode of interactions were established by DFT calculations. TDDFT calculations were performed in order to demonstrate the electronic properties of receptors. Microstructural features of L2 and its Al³⁺ complex have been measured by AFM. Moreover, the utility of the receptors L1, L2 and L3 in showing aluminium recognition in live cells has also been demonstrated using Vero cells as monitored by fluorescence imaging. In situ prepared [AlL1] and [AlL3] complexes were found to be sensitive and selective toward phosphate-bearing ions and molecules and in particular to pyrophosphate (PPi) among the other 15 anions studied; however, [AlL2] was not sensitive toward any of the anions studied.