Background: Iron is an essential transition metal which is indispensable for life processes
like oxygen transport and metabolism, electron transfer etc. However, misregulated iron is responsible
for disease like anemia, hemochromatosis, Alzheimer’s and Parkinson’s disease. In order to encounter
these diseases, a better understanding is needed of its role in misregulation. Fluorescent iron
sensors could help provide this information. The new chemosensor developed by linking a cyclohexane
unit with three 8-hydroxyquinoline provides selective detection of iron in numerous biological
and environmental samples.
Methods: The Uv-visible and fluorescence spectroscopy in combination with pH measurements will
mainly be used for the study. Theoretical studies at DFT level will be used to validate the method
and explain the theory behind the experiments.
Results: The study of electronic spectra of the chelator, HQCC, reveals the appearance of a band at
262 nm along with a weak band at 335 nm due to π- π* and n- π* transitions respectively. Upon excitation
with 335 nm, the ligand fluoresces at 388 nm wavelength. The intensity of the emission was
affected in presence of metal ions, with maximum deviation for Fe(III). Selectivity studies showed
that Fe(III) is more selective as compared to the biologically relevant metal ions viz., Al(III), Fe(III),
Cr(III), Co(II), Fe(II), Ni(II), Zn(II), Cu(II), Mn(II) and Pb(II). pH dependent studies implied that the
fluorescence intensity was highest at pH ~8.0, whereas maximum quenching for iron-HQCC system
was observed at pH 7.4. The binding studies from the B-H plot confirms the formation of 1:1 complex
with association constant of 5.95 × 106. The results obtained from experiments were in agreement
with that obtained from the DFT and TD-DFT studies.
Conclusion: A novel tripodal chelator based on 8-hydroxyquinoline and symmetric cyclohexane
scaffold was successfully developed. In addition to the excellence of the ligand to be employed as a
promising sensitive fluorescent probe for easy detection of Fe3+ions at the physiological pH with
very low concentration (7.5 x 10-5 molL-1), the new ligand can be used as an OFF-ON-OFF pH sensor.
Fe(III) encapsulation along with 1:1 ML-complexation formation have been established. Theoretical
studies confirm a d-PET mechanism for the fluorescence quenching. DFT studies revealed
that the neutral form of the ligand is less reactive than its protonated or the deprotonated form.