In the past, we have demonstrated that 1,8-anthraquinone-18-crown-5 (1) and its heterocyclic derivatives act as luminescent hosts for a variety of cations of environmental and clinical concern. We report here a series of heteroatom-substituted macrocycles containing an anthraquinone moiety as a fluorescent signaling unit and a cyclic polyheteroether chain as the receptor. Sulfur, selenium, and tellurium derivatives of 1,8-anthraquinone-18-crown-5 (1) were synthesized by reacting sodium sulfide (Na2S), sodium selenide (Na2Se) and sodium telluride (Na2Te) with 1,8-bis(2-bromoethylethyleneoxy)anthracene - 9,10-dione in a 1:1 ratio (2,3, and 6). These sensors bind metal ions in a 1:1 ratio (7 and 8), and the optical properties of the new complexes were examined and the sulfur and selenium analogues show that selectivity for Pb(II) is markedly improved as compared to the oxygen analogue 1 which was competitive for Ca(II) ion.
Selective reduction of 1 yields secondary alcohols where either one or both of the anthraquinone carbonyl groups has been reduced ( 15 and 9). A new mechanism for the fluorescence detection of metal cations in solution is introduced involving a unique keto-enol tautomerization. Reduction of 1 yields the doubly reduced secondary alcohol, 9. 9 acts as a chemodosimeter for Al(III) ion producing a strong blue emission due to the formation of the anthracene fluorophore, 10, via dehydration of the internal secondary alcohol in DMSO/aqueous solution. The enol form is not the most thermodynamically stable form under these conditions however, and slowly converts to the keto form 11.
Currently we are focusing on cucurbituril derivatives, also described as molecular clips due to their folded geometry used as molecular recognition hosts. We first investigated the synthesis and characterization of aromatic methoxy/catechol terminated cucurbituril units that act as hosts for small solvent molecules, such as CH2Cl2, CH3CN, DMF, and MeOH, through dual pi…H-C T-shaped interactions. We have calculated the single-point interaction energies of these non-covalent interactions and compared them to the dihedral angle formed from the molecular clip. We have also synthesized a molecular clip that contains terminal chelating phenanthroline ligands. This tetradentate ligand shows 2:3 metal:ligand binding with Fe(II) and 1:2 metal:ligand binding with Co(II) and Ni(II) cations.
|Advisor:||Sykes, Andrew G.|
|Commitee:||Georgescu, Catalin, Hawkinson, David C., Mariappan, Kadarkaraisamy, Sun, Haoran|
|School:||University of South Dakota|
|School Location:||United States -- South Dakota|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Subjects:||Organic chemistry, Materials science|
|Keywords:||Anthraquinone, Crown ether, Cucurbiturile, Fluorescence, Heavy metal, Molecular recognition|
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