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This work reports Eu(III) and Tb(III) luminescence titrations in which the lanthanide ions were used as spectroscopic probes for Ca(II) ions to determine the metal binding ability of Ac–NESVKEEGGW–NH 2 and Ac–NESVKEDGGW–NH 2 . These decapeptides correspond to the putative calcium binding region of the plant antifungal proteins SI-α1 from Sorghum bicolor and of Zeathionin from Zea mays , respectively. The luminescence spectra for the Eu(III)–decapeptide system (red emission) with the excitation at the Trp band at 280 nm showed an enhancement of the intensities of the 5 D 0 → 7 F J transitions (where J =0–4) with increments of Eu(III) ion concentration. The photoluminescence titration data of the terbium ion (green emission) in the decapeptide solutions showed intensification of the 5 D 4 → 7 F J transitions ( J =0–6), similar to that observed for the Eu(III) ion. Thus, energy transfer from Ac–NESVKEEGGW–NH 2 and Ac–NESVKEDGGW–NH 2 to the trivalent lanthanide ions revealed that these peptides are capable of binding to these metal ions with association constants of the order of 10 5 M −1 . The amino acid derivative Ac–Trp–OEt also transferred energy to Tb(III) and Eu(III) ions as judged from the quenching of tryptophan luminescence. However, the energy transfers were significantly lower. Taken together the luminescence titration data indicated that Ac–NESVKEEGGW–NH 2 and Ac–NESVKEDGGW–NH 2 bind efficiently to both trivalent lanthanide ions and that these ions may be used as probes to distinguish an anionic peptide from a neutral amino acid derivative.

This work presents the study of the interaction between zidovudine (AZT) and rare earth (RE) ions with thenoyltrifluoroacetonate (TTA). The complexes [RE(TTA)(3) x (AZT)(2)] (where RE(III)=Eu and Gd) were prepared by reaction between the [RE(TTA)(3) x (H(2)O)(2)] precursors and AZT dissolved in acetone in the molar ratio 1:2. The obtained luminescent materials were characterized by microanalyses (C, H, N), complexometric titration, IR spectroscopy, X-ray powder diffraction and thermal analysis (DSC and TG/DTG). The luminescence data indicate that the substitution of the two water molecules by AZT in the europium complex causes an intensification of luminescence corresponding to the (5)D(0) --(7)F(J) (J=0-4) transitions associated with one of the site symmetries. Based on the luminescence spectrum of the Eu(III)-compound the Omega(lambda) experimental intensity parameters (lambda=2 and 4) were calculated for the electronic transitions (5)D(0)--(7)F(2, 4). The Omega(2) intensity parameter for this new compound is higher than for the precursor compound, suggesting an effective interaction between the AZT and the chemical environment of the Eu(III) ion. Luminescence data confirm that the AZT complex and precursor compound have a comparable emission quantum efficiency.