Design, Synthesis And Spectra Study Of Zn²⁺ And Hg²⁺ Chemosensors

Transition metal ions play important roles in biological systems and in the environment. Detection and quantification of transition metal ions found in biological systems and in the environment remains an active area of research. Among the various transition metal ions, Zn2+ is the second most abundant transition metals in human body, and plays crucial roles in many important biological processes. Failure to maintain zinc homeostasis has been implicated in a number of severe neurological diseases. Mercury is a dangerous and worldwide pollutant, having deleterious effects on human health and the environment. Fluorescent and colorimetric chemosensors for selectively detecting ions are widely used in many fields. The advantages of fluorescence chemosensors are high selectivity, sensitivity, simple and real time monitoring and simplicity. There is important significance to understand the multiple roles of zinc and mercury with availability of chemosensors permitting fast and quantitative determination and imaging of zinc and mercury fluxes and levels over a broad concentration range. In this thesis, two chemosensors were synthesized and investigated for their applications in the detection of Zn2+ and Hg2+. The details are as follows:1. Fluorescent chemosensor 2-1 exhibiting good water solubility was synthesized and characterized. The choice of 2-(2'-aminophenyl)benzoxazole derivative as the fluorophore is based on the excellent photophysic properties of benzoxazole derivatives. Our approach is based on the "receptor-spacer-fluorophore" sensor platform to promote the fluorescence "off-on" changes. The selectivity of compound 2-1 to Zn2+ in Tris-HCl buffer solution from a series of cations especially Cd2+is evident as its exceptional fluorescence enhancement (25 fold). The detection limit (LOD) of compound 2-1 to Zn2+ was measured to be 3.66×10-8 M. The evidences of the 1:1 binding mode come from the ESI-MS spectra and X-ray crystallography of the complex of 2-1 with Zn2+.2. Stoichimetric reaction-based chemosensor 3-1 was synthesized and characterized. It can detect Hg2+ by virtue of the strong affinity of mercury to sulfur.3-1 can detect Hg2+ in a wide pH range (4-10). The detection limit (LOD) of compound 3-1 to Hg2+ was measured to be 2.35×10-7 M.