An investigation of the metal coordination of l-norepinephrine and ATP by nuclear magnetic resonance

Abstract

The interactions of l-norepinephrine (NE) and adenosine-5-triphosphate (ATP) with Cu(III) and Zn(II) were investigated by Proton Nuclear Magnetic Resonance (NMR) spectroscopy. The results indicated significant coordination of Cu(II) by NE even at the p[D] of mixing (i.e. p[D] = 4). Both the pyrocatechol and the ethanolamine groups of the NE molecule were involved in the chelation. The Cu(II)-ATP interaction resulted in the coordination of the metal by the adenine nitrogens and the phosphate group. In the combined presence of ATP and NE, it was found that Cu(II) was predominantly bound by ATP at low p[D]'s, i.e. p[D] = 3–5, followed by additional chelation with NE at p[D] = 7. These observations were in agreement with our earlier conclusions based on potentiometric equilibrium data[3]. In the case of the Zn(II)-ATP system, the coordination was mainly with the phosphate group. At the p[D] of mixing ( p[D] = 6) the interaction of NE was not clearly indicated. In the mixed ligand system, i.e. ATP+NE, Zn(II) was mainly chelated with ATP at low p[D] (p[D] = 5). In the combined presence of Cu(II) and Zn(II), a predominant chelation of the mixed ligands with Cu(II) was strongly indicated.