Nuclear magnetic resonance investigations of adenosine phosphates and their mercury and cadmium salt adducts

Abstract

Chemical shift and relaxation time measurements (¹H, ¹³C, and ³¹P) show that the adenosine di- and tri-phosphates (ADP and ATP), and to a lesser extent the monophosphate (AMP), are predominantly in the syn-conformation at low pH. Furthermore, all three phosphates form well defined complexes with Cd^II salts at pH 8, whereas only for ADP and ATP are well defined Hg^II and Cd^II salt complexes at pH 3 observed. Both metal ions affect the tendency towards stack formation. The conclusions based on relaxation and chemical shift measurements are supported by ¹H nuclear Overhauser effect (n.O.e.) measurements, as far as possible. The different origins of the dipolar relaxation of the base protons are discussed. It is shown that the ribose protons play a major role in the relaxation of H-8 whereas the protons at position 2 are subject to a strong relaxation influence from the phosphate groups. Internucleotide dipolar interactions, however, are of some importance in the case of AMP, whereas in ATP and ADP for H-8, and in ATP also for H-2, their importance is reduced.