PROTON MAGNETIC RESONANCE STUDIES OF RIBOSE DINUCLEOSIDE MONOPHOSPHATES IN AQUEOUS SOLUTION .I. NATURE OF BASE-STACKING INTERACTION IN ADENYLYL(3'-]5')ADENOSINE

The nature of the base-stacking interaction in aqueous solution between the two adenine rings in adenylyl(3ʹ→5ʹ)adenosine (ApA) has been investigated by proton magnetic resonance spectroscopy. The pmr spectrum was studied as a function of concentration, temperature, solution pH, and concentration of added purine. The results of these pmr studies indicate that the stacking interaction between the two adenine rings in ApA is relatively strong, and that the adenine rings are stacked with each of the bases preferentially oriented in the anti conformation as in a similar dApdA (dA = deoxyadenosine) segment in double-helical DNA. In the purine-binding experiments, evidence was obtained for the formation of the purine-intercalated dinucleotide complex in neutral solution, and it was shown that purine intercalation provides a sensitive probe both for the relative strength of the intramolecular stacking interaction and for the relative conformation of the two bases in the dinucleotide. It was also concluded that while the two adenine rings are destacked by protonation of the bases, increasing the temperature to 95° does not result in complete unfolding of the dinucleotide molecule. Finally, ApA was found to self-associate extensively in aqueous solution, and it was shown that the mode of self-association is strongly pH dependent. Despite complications arising from this self-association, the mode of self-association provided additional evidence for the strength and the conformation of the intramolecular stack. © 1969, American Chemical Society. All rights reserved.