Lanthanide complex as potential nitric oxide luminescent probe

Nitric oxide plays an important role in the biological environment in the cardiovascular system, neurologic and immunologic system [1,2]. To track the nitric oxide in the biological environment fluorescent biomarkers such as 4,5-Diaminofluorescein diacetate (DAF-2 DA) [3], a diamine molecule, that shows fluorescence in presence of NO are used. Based on this molecule and in the work done by Yuan [4], we have developed the ligand 4- (3,4-diaminophenoxy)pyridine-2,6-dicarboxylic acid, from the chelidamic acid and 5-flouro-2-nitroaniline. The ligand was synthetized in 5 steps, purified and characterized, (1H-NMR, 13C-NMR; MS, FITR). The lanthanide complex was synthesized using the follow methodology: the 4-(3,4-diaminophenoxy)pyridine-2,6-dicarboxylic acid was dissolved in water followed the addition of 3 equivalent of K2CO3, the mixture was stirred by 30 minutes, then the lanthanide chloride was added in a stoichiometry 3:1 ligand-metal, the mixture was stirred by 4 hours. The solid formed was separated by centrifugation, the supernatant was removed and the solid was dried in a vacuum oven overnight. The complex was analyzed by photoluminescence spectroscopy in presence and absence of NO. To ensure NO in solution we have used the molecule SNitrosoglutathione (GSNO) on tris-HCl buffer. The test with the europium(III) complex as NO probe was realized in a solution 5 x 10-5 mol L-1 in tris-HCl buffer. The NO generator solution (GSNO) was prepared in a concentration 3 times higher to ensure 3:1 NO:complex molar ratio. The solution of GSNO was added to the complex solution and stirred for 30 minutes. The photoluminescence spectra (Figure 1) indicate the emission intensity increases 2.3 times in presence of NO. The europium complex synthetized shows a high potential to act as NO optical probe and considering that lanthanide emission can be obtained by time resolved fluorescence spectroscopy, probably a high level of detection may be achieve eliminating the fluorescence signal from biological environments.