Lithium Complexation and Stability of a Novel Coumarin-Based Fluoroionophore

Micheal Branham
Analytical Chemistry Division
National Institute of Standards and Technology

ABSTRACT Expanding applications in science, pharmacology and technology have led to increased interest in lithium and its compounds. Their use in psychiatric disorders, DNA-viral infection and cancer chemotherapy have made methodology for the separation and detection of lithium extremely important. We have investigated the photoluminescence properties and complex stability of fluoroionophores consisting of derivatives of the laser dye coumarin, covalently linked to the complexones; edetic acid (EDTA), 1,1’-ethylenebis(5-oxo-3-pyrrolidine) carboxylic acid (EPCA), 2-(hydroxymethyl)-12-crown-4 and 2-(hydroxymethyl)-15-crown-5. Complexation-enhanced fluorescence or quenching spectra was examined qualitatively and correlated with complex stability studies performed using electrospray ionization mass spectrometry. The results of these experiments show that the lithuim ion causes blue shifts in the fluorescence emissions spectra in coumarin-15C5 and coumarin-12C4 when a methoxy group is present at the 7-position of coumarin but no significant changes in emissions intensity. In contrast, lithuim ion causes no shifts in the fluorescence emissions maxima in coumarin-15C5 or coumarin-12C4 when a diethylamino group is present at the 7-position of coumarin but causes significant increases in emissions intensity. Structural influences by sterically-hindering or electron-withdrawing groups are discussed in terms of the photoluminescence properties of these fluoroionophores.