Unsymmetrical diethylenetriamine fluorescent chemosensors for selective recognition of Fe(III) and Zn(II) / Siti Nur Ain Mohd Adnan

Fluorescent chemosensor have significant role in medical, environmental and biological applications. Receptor and signaling unit are important aspect in designing fluorescent chemosensor to selectively recognize metal ions for practical applications. In this study a series of chemosensors were synthesized for metal ions which bears diethylenetriamine and benzenyl derivatives as the receptor and dimethyl-phenyl-amine as fluorescence signal. Eight synthesized unsymmetrical ligands were prepared by using Schiff base technique that involved condensation of primary amine (-NH2) with an aldehyde (HC=O) to produce azomethine group (RCH=NR). All ligands were fully characterized by Fourier Transform Infrared (FT-IR), Proton Nuclear Magnetic Resonance (1H-NMR) and elemental analysis (CHNS). All ligands shown the characteristic FT-IR peak for C=N at 1596-1639 cm-1 and the 1H-NMR signal for HC=N at 8.11-8.51 ppm confirmed the formation of Schiff base ligand. Sensing properties for six synthesized ligands N-(4-Dimethylamino-benzylidene)-N'-{2-[(3-nitro-benzylidene)-amino]-ethyl}-ethane-1,2-diamine (L1), N-(4-Dimethylamino-benzylidene)-N'-{2-[(4-nitro-benzylidene)-amino]-ethyl}-ethane-1,2-diamine (L2), 3-[(2-{2-[(4-Dimethylamino-benzylidene)-amino]-ethylamino}-ethylimino)-methyl]-phenol (L3), 4-[(2-{2-[(4-Dimethylamino-benzylidene)-amino]-ethylamino}-ethylimino)-methyl]-phenol (L4), N-(4-Dimethylamino-benzylidene)-N'-{2-[(pyridin-2-ylmethylene)-amino]-ethyl}-ethane-1,2-diamine (L5) and synthesis of N-(4-Dimethylamino-benzylidene)-N'-{2-[(pyridin-3-ylmethylene)-amino]-ethyl}-ethane-1,2-diamine (L6) were studied towards transition metal. The selectivity and sensitivity tests of ligands were conducted on several metal ions. The fluorescence measurements revealed that L5 was more selective towards Zn2+ while L1-L6 were selective towards Fe3+ ions and forms complexes in 1:1 ratio as evidenced by Job's plot analysis. The limit of detection for L5 was found to be 3.5 x 10-5 M and L1-L6 were 1.42 x 10-6 M, 3.76 x 10-6 M, 1.58 x 10-6 M, 5.37 x 10-6 M and 6.49 x 10-6 M respectively. These sensors also exhibit a very good fluorescence sensing ability towards Zn2+ and Fe3+ at pH 7.0. Therefore, this fluorescent sensor can be applied to monitor the presence of heavy metals both in environment and biology conditions.