Unusual Fluorescence Quenching-Based Al3+ Sensing by an Imidazolylpiperazine Derivative. β-Cyclodextrin Encapsulation-Assisted Augmented Sensing

We report in this paper an unusual β-cyclodextrin mediated-aluminum (III) ion sensing based on augmented quenching of fluorescence. The fluorescent sensing of metal ions by a new ligand prepared (L = 4-[{4-(1H-imidazol-1-yl)phenyl]imino}methyl]piperazine-1-carboxaldehyde) has been investigated as well as the effect of the supramolecular complex formation with β-CD. In aqueous solution, L shows an increase of fluorescence due to the interaction with β-cyclodextrin with a formation constant of 77 (± 12) M−1. The ROESY NMR spectrum clearly indicates that L is encapsulated by β-CD. Theoretical calculations show the possible structure both of the L-β-CD adduct and of the coordination mode of Al3+ ion to L. In the presence of β-CD, the piperazine adopts a distorted conformation. It leads to an enhanced Al3+ sensing by the compound in its supramolecular complexed form. The lower limit of detection of Al3+ ions is 6.00 × 10−8 mol L−1. This detection limit slightly expands for L in the presence of β-CD.