A novel colorimetric, selective fluorescent “turn-off” chemosensor and biomolecules binding studies based on iodosalicylimine derivative Schiff-base

Abstract We have designed a new iodosalicylimine-derived Schiff-base chemosensor ISNP, which is synthesized by the condensation reaction of 3, 5-diiodosalicylaldehyde with N-phenyl-o-phenylenediamine and characterized by various spectral techniques including FT-IR, 1H NMR, ESI-MS and elemental analysis. A colorimetric, UV-visible absorption and fluorescence spectral analyses revealed that chemosensor ISNP was able to sense Cu2+, F− and H2PO4− ions selectivity. Especially, ISNP preferentially recognized Cu2+ion through a fluorescent “turn-off” response while the colour of ISNP solution was changed from light yellow to violet even in the presence of other metal ions such as Co2+, Ni2+, Zn2+, Pb2+, Hg2+, Sr2+, Cd2+, Ca2+, Na+, K+, Al3+ and Cr3+ ions in CH3CN/H2O (9/1, v/v) solvent mixture. The chemosensor ISNP showed unique Chelation Enhanced Quenching process (CHEQ) effect only with Cu2+ ion, which can be attributed to ISNP–Cu2+ complex formation. In addition, chemosensor ISNP was selectively sensing both F− and H2PO4−anions compared with other anions such as Cl−, Br−, I−, NO3−, SCN− and ClO4−in a fluorescent “turn-off” mode while the colour of the solution was changed from light yellow to dark yellow in THF medium. According to the Job's plots, chemosensor ISNP exhibited a binding stoichiometric ratio of 1:1 with Cu2+, F−, and H2PO4− ions with the detection limit value of 2.0 μM for Cu2+ ion, 1.1 μM for F− ion and 2.4 μM for H2PO4−ion, which are much lower than the values set by WHO guidelines. Furthermore, spectral and docking methods revealed that chemosensor ISNP interacted with calf thymus DNA (CT-DNA) via an intercalation mode with a binding energy of −6.1 kcal/mol while bovine serum albumin (BSA) or human serum albumin (HSA) was interacted with the chemosensor ISNP through a static fluorescence quenching process. Such a simple and convenient sensing strategy with a great potential for practical applications could provide a promising tool for rapid, sensitive and selective analysis of ions and biomolecules. .