Spectroscopic investigation of the binding of Transition metal ions to adenosine-5′-triphosphate

Abstract

Adenosine-5′-triphosphate is one of the most important molecules in biological system, being involved in such divergent function as mechanical motion, light production, and synthesis of organic compounds. Divalent metal ions are necessary for the biological activity of adenosine-5′-triphosphate, e.g. when ATP is present in a biological system as an energy transfer agent, it is most often associated with Mg 2+ or Ca 2+. Thus the interaction of the divalent transition metal ions with ATP is of considerable interest in the search to understand the molecular level of the biological interaction involving ATP [1]. We have examined the spectroscopic properties of the following complexes: ▪ These complexes were prepared by mixing equimolar aqueous solution [2] of adenosine-5′-triphosphate with the corresponding transition metal chloride or nitrate salt and then raising the pH to 7 by using a sodium hydroxide solution. The complexes were separated on addition of alcohol under constant stirring. The molar conductance values of the complexes showed that all of them exhibit electrolytic behavior in water and are in accordance with 2:1 electrolytes. The complex Na{UO 2ATPH}·4H 2O was insoluble in water and all other common organic solvents. In the pure Na 2H 2ATP·3H 2O the band around 1720 cm −1 is attributed to the promoted from the adenine moiety. This band, however is strongly pH dependent and shifts to 1650 cm − in ATP 4− attributable to the non protonated from of the adenine moiety [3]. In all complexes prepared except Na{UO 2ATPH}·4H 2O the infrared spectra in that region showed a strong band around 1650 cm −1 indicating that the adenine moiety of ATP is in its nonprotonated form. In these case there is probably coordination of the metal ion through the N-7 of the purine ring. The 1H and 13C NMR spectra of the complexes with diamagnetic metal ions also verify these result [4]. The presence of a strong band around 980 cm −1 along with changes in intensity and/or frequency in the region between 1300–900 cm −1 where the PO vibration occur [5], established that except for the mercury complex, in all other complexes the metal ions coordinate also through the phosphate group of adenosine-5′-triphosphate.