A highly selective ?on-off? fluorescent sensor for detection of Fe3+ion in protein and aqueous media: Synthesis, structural characterization, and computational studies

We describe herein the design and synthesis of a smart PGA chemosensor characterized by various techniques viz., FT-IR, UV-visible, 1H NMR, 13C NMR, Mass spectroscopy, and single crystal X-ray diffraction studies. The X-ray crystal analysis revealed that the PGA chemosensor crystallized in the orthorhombic crystal system with P212121 space group. The photophysical properties of the synthesized PGA chemosensor were examined by employing absorption and fluorescence spectral analysis. PGA revealed turn-on sensing responses towards the selective recognition of Fe3+ over other metal ions via C--N isomerization processes. PGA also shows reversible effects upon the addition of EDTA. The 2:1 binding stoichiometry was calculated using Job's plot and the value of detection limit was found to be 0.265 x 10-5 M, which is far lower than the permitted limit for drinking water according to WHO guidelines. The sensing mode of PGA towards Fe3+ was explored by employing FT-IR and 1H NMR studies. Density Functional Theory (DFT) studies, were employed which closely agreed with the experimental results. The PGA chemosensor has been successfully used to detect Fe3+ in various water samples and BSA medium. Furthermore, confocal imaging studies were examined, which supports the sensing ability of PGA for detection of Fe3+ in aqueous and protein medium.