Luminescent properties of 4-aminobenzo-15-crown-5 after preferential binding of ferric ions in aqueous solutions.

We report a combined approach that introduces the use of 4-aminobenzo-15-crown-5 (4AB15C5) for the detection of ferric(III) ions by colorimetric, ultraviolet (UV)-visible light absorption, fluorescence, and live-cell imaging techniques along with density functional theory (DFT) calculations. We have found that 4AB15C5 is sensitive and selective for binding ferric(III) ions in aqueous solutions. DFT calculations using the polarizable continuum model have been used to explain the strong binding of the ferric ion by 4AB15C5 in aqueous solutions. The detection limit in the fluorescence quenching measurements was found to be as low as 50 μM for the ferric ion with a determined Stern-Volmer constant of 1.52 × 10 ⁴  M ^-1 . Fluorescence intensity did not change for other ions tested, Fe ^{2 +} , Co ^{2 +} , Mn ^{2 +} , Mg ^{2 +} , Zn ^{2 +} , Ca ^{2 +} , NH ₄ ⁺ , Na ⁺ , and K ⁺ ions. Live-cell fluorescence imaging was also used to check the intracellular variations in ferric ion levels. Our spectroscopic data indicated that 4AB15C5 can bind ferric ions selectively in aqueous solutions.
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