Structure effect of nucleotides in terbium(III)—nucleotide fluorescent reaction New evidence for the binding sites of terbium(III) on nucleotides

Upon addition of Tb3+ to 16 nucleotides and homopolynucleotides, all of them showed a characteristic green emission from Tb3+, but with much different intensity, upon excitation in the aromatic region of bases. The result suggested that nucleotides with at least one carbonyl group in nucleotide bases are better enhancers to the fluorescence of Tb3+. The complexes of ATP, GDP and GTP with Tb3+ are synthesized as two types of models. Guanine type nucleotides with one carbonyl group in the bases are the best enhancers, while adenine type nucleotides with no carbonyl group in the bases are poorest enhancers to the fluorescence of Tb3+. Comparing the IR spectra of ATP, GTP, GDP and their Tb3+ complexes suggested that C-6 carbonyl group in GTP and GDP may be involved in complex formation, which may be responsible for the effective energy transfer. This is further supported by comparing the UV spectra of ATP, Poly(A), GTP, and Poly(G) with their Tb3+ complexes in water solution.