Metal binding ability of hypermodified nucleosides of t-RNA. Potentiometric and spectroscopic studies on the metal complexes of N-[(9-β-D-ribofuranosylpurin-6-yl)carbamoyl] threonine

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Copper(II), nickel(II), zinc(II), manganese(II), and magnesium(II) complexes of t 6A (N-[9-β-D-ribofuranosylpurin-6-yl)carbamoyl] threonine and t 6Ade (N 6(threoninocarbonyl)adenine) were studied by potentiometric and spectroscopic methods. It was found that t 6Ade has three dissociable protons in the accessible pH range (N 1 and N 9 of purine and carboxylate), while only two pK values are characteristic of t 6A. Magnesium(II) and manganese(II) do not interact effectively with these ligands, but copper(II) and nickel(II) ions form very stable complexes with the coordination of purine N 1, deprotonated amide nitrogen, and carboxy late oxygen donors.