N- and O- Donor Ligands for Fluorometric and Colorimetric Detection of Metal Ions

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This Thesis contains five chapters. Chapter 1 is the introduction which describes the contribution of metals in our daily lives and their adverse effects on human beings when exposed to excess amounts along with a brief elaboration of different detection techniques. Some recent developments in devising fluorescent and colorimetric probes are also discussed. In Chapter 2 the 2,4,5-tris(2-pyridyl)imidazole (L1H) molecule has been evaluated as a probe for dual sensing of Hg2+ and Cu2+ ions in EtOH/HEPES buffer medium (5 mM, pH = 7.34, 1:1, v/v). Probe L1H shows a good sensitive and selective turn off response in the presence of both Hg2+ and Cu2+ ions, which is comprehensible under long UV light. Its sensitivity was evaluated in different pH medium and in presence of other metal ions. Paper strip experiments and in-vitro cell imaging was done to know the sensitivity of the probe towards the metal ions in different environment. Chapter 3 describes the probe 2,6-di(2-pyridyl)-1,5-dihydroimidazo[4,5-f]benzimidazole (L2H2) and its sensing application towards metal ions. This probe could detect Zn2+ and Cd2+ ions in three different aqueous systems viz., water, DMSO/HEPES buffer (1:1, pH = 7.34, rt), and DMSO/water (1:1, rt). In water a “turn-on” response was observed for both metal ions, whereas in the latter two solvent systems, a ratiometric change in fluorescence maximum was observed. The detection limit of this probe was as low as 0.3 μM and 0.62 μM (in water) for Zn2+ and Cd2+ ions, respectively. In Chapter 4 synthesis and evaluation of a novel probe N'-(pyren-1-ylmethylene)benzo[d]imidazo[2,1-b]thiazole-2-carbohydrazide (L3H) as metal ion sensor was explored. It was found to be able to nanomolar detection of Pd2+ and Ni2+ ions by colorimetric change. This probe was also able to detect the presence of Pd2+ ions in drug samples and APIs without any major interference. LOD values were calculated to be 46.1 to 93.9 nM (4.9 to 6.0 ppb) for PdCl2 and 10.6 to 19.6 nM (1.1 to 2.1 ppb) for Pd(PPh3)2Cl2 and 9.301 nM for NiCl2 solutions. It also showed extremely good recovery of Pd2+ in presence of all the drug molecules. In Chapter 5 another novel ligand L4H based on 2,7-dichlorofluorescein was synthesized and evaluated for sensing applications. It was found to be able to detect Co2+ and Cu2+ ions differentially by different colouration of the solution in presence of these two metal ions. In situ Cu-complex of the ligand was utilised for quantification of amino acids like BSA and HSA proteins. Its differential selectivity paved the for molecular logic gate application.
Supervisor: Manivannan, V