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Doctoral Dissertation Announcement
Candidate: Fasil Adefris Abebe
Doctor of Philosophy
Title: Optical and Electrochemical Sensors for the Detection of Metal Ions and Nerve Gas Agents Via Fluorescein and Coumarin Derivatives
Dr. Ekkehard Sinn, Chair
Dr. Sherine Obare
Dr. Ramakrishna Guda
Dr. Massood Atashbar
Date: Friday, February 24, 2012 Noon to 2:00 p.m.
Chemistry Building, Room 1220
Trace element detection of metals, for example, iron, copper, and zinc, are important in biological systems and in the environment. Many are aware that our cells contain metal ions that are “tied” up in proteins. However, chelatable or “free” trace elements can also be found in small quantities, and can have a negative impact on our bodies. Despite the increasing surge in developing sensors for metals and nerve gas agents, efficient detection still remains a challenge. Among the various sensors developed so far, fluorescence sensors play an important role due to their simplicity. In this study, the design of fluorescein-based chemosensors for Co2+, Ni2+ and Cu2+, which exhibit highly selective “off-on” behavior in both absorption and emission, are attributed to the transformation of a colorless, nonfluorescent spirolactam form to its yellow, fluorescent, ring-open amide equivalent, finding the reversibility of the sensors that bind to the ions, as indicated by the bleaching of color when the experiment extracts the metals with EDTA. Given the difficulty of designing enhanced fluorescent sensors for paramagnetic Co2+ and Ni2+ ions, the fluorescein compounds may inspire the further development of more sophisticated sensing constructs for the detection of these transition metal ions. Optical measurements such as UV-Vis, Fluorescence, and Electrochemical measurements such as differential Pulse Voltammetry and impedance are carried out for characterization.
Chemical warfare agents are highly toxic and lethal even at low concentrations. Novel turn-off fluorescent coumarin-functionalized sensors for nerve gas agents in acetonitrile are designed and synthesized. These compounds selectively recognize the nerve gas mimic (diethylchlorophosphate, DCP). Addition of DCP to an acetonitrile solution of each sensor results in the quenching of the fluorescence intensity at 500nm, which provides an optical detection for DCP. There are other coumarin-based molecules that exhibit high selectivity for Zn2+, Cr3+, Fe3+ and Pt2+ in acetonitrile and the selectivity is not affected by the presence of other alkalis, alkaline earths, transition metal ions or organophosphorus compounds.