Molecular chemosensors for heavy metals: From synthesis to reusable device.

摘要

Chapter 1. A series of 8-hydroxyquinoline appended diazatrithia crown ethers were synthesized in order to probe the photo-physical properties of the complexes of these crown ethers and thiophilic heavy metals such as zinc, mercury, lead, nickel, copper, cadmium, and cobalt. Crown cavity size was incrementally increased from 15-crown-5 to 18-crown-6 and the diazatrithia macrocycles and 8-hydroxyquinolines were attached at the seven and two positions. An important rearrangement of a diazatrithia-15-crown-5 to a 16-crown-5 was explored and employed to incorporate a glycol tether into the resulting diazatrithia-16-crown-5 macrocycle. An alternative synthetic pathway for tether attachment was also explored and compared. This comparison showed the rearrangement procedure to be superior. Binding affinities in methanol were determined using UV-vis titration data and the fluorescent responses to various heavy metals were also explored. Some of the macrocycles exhibited the ability to bind multiple metal cations and signaled consecutive binding events with shifting maxima in the characteristic UV-vis and fluorescent spectra. Crystal structure analysis was obtained for a key zinc complex that confirms the binding of multiple zinc cations and potentially explains its unusual photo-physical behavior.; Chapter 2. A group of tethered diaza-18-crown-6 based cadmium chemosensors was synthesized in order to produce a reusable cadmium sensor device in aqueous solutions on fused quartz slides. Tethers included alcohol, amine, and dimethylethoxy silane functionality at the tether's terminal carbon. A series of quinoline derivatives was synthesized to be studied and compared with the cadmium chemosensor. Polymer-based thin layer and monolayer surfaces of the tethered cadmium chemosensor were prepared and characterized by UV-vis spectroscopy and XPS. A flow cell was designed and used to study the fluorescence behavior of surfaces in real time. Flow cell measurements of functionalized quartz surfaces showed a reversible increase in fluorescence when exposed to cadmium solutions in water. Optimal conditions gave surfaces with detection limits as low as 100 nM of cadmium in water. Physical data include: a crystal structure of a cadmium complex, solution phase titrations, and calorimetry, confirm a 2:1 metal to ligand binding tendency of the cadmium chemosensor with cadmium.