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Metal ion complexing and fluorescence properties of the novel hemicycle, dipyridoacridine, with computational studies on metal ion selectivity

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Jason Roland Whitehead (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Robert Hancock

Abstract: The novel hemicycle dipyridoacridine (DPA) was studied using UV/Vis spectrophotometric and 3D-fluorometric methods. The UV/Vis spectrophotometric methods resulted in a pKa2 for DPA of 4.52 + 0.06, and a pKa1 of 2.22 + 0.03. Formation constants were also found for a series of ten metals, the highest of which were Hg2+ and Sr2+, with log K values of 8.16 + 0.06 and 8.02 + 0.01, respectively. The lanthanides analyzed included La3+, Gd3+, and Lu3+, which had log K values with DPA of 6.43 + 0.04, 6.49 + 0.06, and 6.33 + 0.02, respectively. Other metals analyzed include In3+, Mn2+, and Zn2+, which had log K values with DPA of 7.55 + 0.03, 7.57 + 0.02, 7.69 + 0.12, respectively. Formation constants were also found for Na+ and Ca 2+, which were 1.95 + 0.04 and 5.48 + 0.07, respectively. DPA was found to show enhanced fluorescence with Ca 2+, Na+, and Cd2+, and was found to have quenched fluorescence in the presence of mercury, lead, and zinc. MM+ studies yielded an ideal ionic radius for a metal to complex to DPA of 1.12 Å, and an ideal M-N bond length for DPA complexes of 2.38 Å. This ideal M-N bond length supports the chelate ring size theory prediction of DPA preferring larger metal ions and having a geometrically preferred metalnitrogen bond length of 2.5. This ideal ionic radius of 1.12 Å partly explains the largest log K values with DPA belonging to strontium and mercury, which have respective ionic radii of 1.12 and 1.10. MM+ studies also revealed a linear relationship between ionic radius of a complexed metal and the steric energy for the transfer of a metal ion from a 5-membered ring to a 6- membered ring. Further computational studies using DFT revealed a correlation between higher log K values for F- with more negative calculated Gibb’s free energies for a theoretical reaction involving the transfer of an F- to a metal ion.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirement for the Degree of Masters of Science
Language: English
Date: 2009
Keywords
Chemical detectors, Ligands (Biochemistry)
Subjects
Ligands (Biochemistry)
Chemical detectors