Syntheses and Studies of Fluorescence Based Ion Sensors

Hatai, Joydev (2013) Syntheses and Studies of Fluorescence Based Ion Sensors. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

This thesis deals with the synthesis and characterization of a series of dithiocarbamate based novel fluorescent probes for selective detection of metal ions such as Cu2+, Zn2+, Hg2+ , Ag+ and Pb2+. Chapter 1 deals with the general introduction on this area of research based on recent literatures. Chapter 2 comprises of the synthesis of a chemosensor having a bipodal thiocarbamate scaffold attached to histidine moieties that senses Hg2+ ions with a 50 nm blue shift in the fluorescence spectra and a 19-fold enhancement of the fluorescence quantum. In addition to the detection of Hg2+ visually in solution under the UV light, the chemosensor was used for fabrication of paper-strips that detected Hg2+ in aqueous samples. The sensor was also used for imaging Hg2+ in adult zebrafish and in human epithelial carcinoma HeLa S3 cells. Chapter 3 deals with the synthesis of a chemosensor containing naphthyl fluorophore and ethylenediamine as a spacer that detects and differentiates among Zn2+ Hg2+, and Pb2+ with fluorescence enhancement at different wavelengths under different solvent conditions. In methanol, Hg2+ and Pb2+ displace Zn2+ from the [Zn2+-sensor] complex displaying a ratiometric behavior. In water, the chemosensor recognizes only Hg2+ with a fluorescence enhancement, and offers intracellular detection of Hg2+. In chapter 4, we demonstrate that contrary to the popular use of 2, 2-dipicoylamine as a highly selective receptor for Zn2+ ion, conjugation with a thiocarbamate linker turns it into a receptor for Ag+ ions. The behaviour of the probe was dependent on the amount of the Ag+. With various techniques such as the DLS, NMR, AFM, SEM and fluorescence lifetime experiments, it was found that aggregation played an important role in the fluorescence behavior of the chemosensor. At high concentrations of Ag+, the aggregates disintegrated. Chapter 5 includes the preparation of a simple chemosensor that contains a dansyl unit as the fluorophore, and a geminal N,N-(ethoxy carbonyl methyl)-ethylenediamine unit as a metal binding site that displays a high selectivity for Cu2+ ions. On complexation with Cu2+, the fluorescence is quenched. Inorganic phosphate ions decomplex the Cu2+ from the ligand-metal ensemble displaying a fluorescence enhancement that can be seen with naked eyes. The method was successfully used in quantitative determination of inorganic phosphates in serum, urine and saliva samples.

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