Potentiometric and electron spin resonance investigation on the interactions between adenosine 5′-triphosphate (atp) and triphosphate ligands with vanadyl ion. Synthesis and characterization of solid vanadyl-atp compounds from acidic aqueous solution

Abstract

The VO²⁺–atp [atp = adenosine 5′-triphosphate(4–)] and VO²⁺–tp(tp = triphosphate) systems were studied by potentiometry and X-band e.s.r. spectroscopy in the pH ranges 2.5–5.2 and 2.5–6.5 respectively. The systems were investigated in the presence of 0.1 mol dm^–3 NaClO₄ at 25.0 ± 0.1 °C in the ligand–metal molar ratio range 3–1.5. Analysis of the data reveals that VO²⁺ is able to form stable species with both ligands. The logβ values relevant to the 1 : 1 complexes are 6.67 ± 0.02 and 9.87 ± 0.02 for atp and tp respectively. Species [(VO)(atp)]^2–, [(VO)(atp)₂]^6–, and [(VO)₂(atp)] were found in all the mixtures investigated. The complex [(VO)₂(atp)] has a logβ value equal to 10.21 ± 0.02; VO²⁺–tp species with a 2 : 1 molar ratio were not found in the mixtures investigated. A structure in which the VO²⁺ ion interacts just with the triphosphate chain is proposed for the complex [(VO)(atp)]^2– while metal co-ordination to the phosphate chain and to the ribose hydroxyl group is suggested for [(VO)₂(atp)]. Solid [(VO)₂(atp)] was isolated from aqueous solutions containing VO²⁺ and atp in a 2 : 1 molar ratio at pH 2.5. An oxygen only co-ordination mode for the metal cation was determined from spectroscopic data. A solid compound containing VO²⁺, atp, and bipyam [bipyam = bis(2-pyridylamine)] in a 1 : 1 : 1 molar ratio was also isolated from acidic aqueous solution.