H-1 NMR study of protonation and Mg(II) coordination of AMP, ADP, and ATP at 25, 50, and 70 degrees C

The interactions of adenosine 5'-monophosphate (AMP), adenosine 5'-diphosphate (ADP), and adenosine 5'-triphosphate (ATP) with protons and with Mg2+ in aqueous solutions have been studied by H-1 NMR spectroscopy at 25, 50, and 70 degrees C. Upfield shifts of H-8 were found in the pH ranges where protonation of phosphate groups occurs for the three nucleotides at all temperatures studied, indicating that AMP, ADP, and ATP adopt an anti conformation at these temperatures. The order of the H-8 upfield shift is AMP > ADP similar to ATP. The shift decreases slightly at 50 and 70 degrees C. Chemical shift measurements for the three nucleotides in the presence of Mg2+ give no indication of the existence of an interaction between Mg2+ and the adenine ring in the Mg2+-nucleotide complexes under the experimental conditions of this study, The mechanism of the deshielding effect of phosphate groups on H-8, and the effects of temperature and pH on the intramolecular interaction uf these nucleotides are discussed.