Ternary Complexes Formed by the Fluorescent Probe Eu(III)-Anthracene-9-carboxylic Acid with Pyrimidine and Purine Nucleobases

The formation of binary and ternary complexes of Eu(III) with nucleobases (NB), guanine (2-amino-6-oxypurine), thymine (2,4-dihydroxy 5-methyl pyrimidine), adenine (6-aminopurine), uracil (2,4-dioxypyrimidine), and anthracene-9-carboxylic, acid (ANCA) has been studied potentiometrically at (25.0 +/- 0.1) degrees C and ionic strength I = 0.1 mol.dm(-3) (KNO3) in 10 % ethanol-water mixture solvent. The acid-base properties of the ligands were investigated and discussed. The formation of the 1:1, 2:1 binary, and 1:1:1 and 2: 1: 1 ternary complexes is inferred from the corresponding titration curves. The ternary complexes formed are monoprotonated complexes. The stability constants of the binary and ternary systems were evaluated. Initial estimates of the formation constants of the resulting species and the protonation constants of the different ligands used have been refined with the SUPERQUAD computer program. The experimental conditions were selected such that self-association of the nucleobase and their complexes was negligibly small; that is, the monomeric normal and protonated complexes were studied. Confirmation of the formation of ternary complexes of the type Eu(III) (NB) (ANCA) in solution has been carried out using differential pulse polarography (DPP), square wave voltammetry (SWV), cyclic voltammetry (CV), UV-visible spectroscopic, and emission spectrofluorimetric measurements.