X-ray structure of two Schiff bases: TURN-ON sensing of Fe3+ and Al3+ in the HepG2 cell line

Abstract

The efficiency of the fluorescence sensitivity of a sensor may be tuned by the modulation of the steric and electronic parameters in the structure. In this study, the thiophenyl Schiff base (E)-N¹-(phenyl(pyridin-2-yl)methyl)-N²-(thiophen-2-ylmethylene)benzene-1,2-diamine (HL′) exhibited very high selectivity and a sensitive fluorescence enhancement towards Fe³⁺ with violet emission (λ_em, 385 nm; LOD, 3.8 nM). On the other hand, the naphthyl Schiff base (E)-1-(((2-((phenyl(pyridin-2-yl)methyl)amino)phenyl)imino)methyl)naphthalen-2-ol (H₂L′′) exhibited fluorescence sensitivity towards Al³⁺, showing blue emission (λ_em, 502 nm; LOD, 3.3 nM) in H₂O (HEPES buffer, pH 7.4) medium. The emission enhancement of HL′ upon binding to Fe³⁺ may be considered to be due to the restriction of intramolecular rotation, while the selectivity of H₂L′′ towards Al³⁺ may be due to the turn on emission through the restriction of excited state intramolecular proton transfer (ESIPT) and the introduction of chelation enhanced fluorescence (CHEF). Furthermore, DFT computation supported the sensing strategy and the probes were applied for intracellular detection of Fe³⁺ and Al³⁺ in HepG2 cell lines.