A proton nuclear-magnetic-resonance study of self-stacking in purine and pyrimidine nucleosides and nucleotides.

The concentration dependence of the chemical shifts of the protons H-2, H-8 and H-1' of ATP4- and of Mg(ATP)2- , of all non-labile protons of adenosine, of H-5, H-6 and H-1' of TUP, and of H-5, H-6, H-1', and H-2' of uridine have been measured. The results for the purine derivatives are consistent with the isodesmic model of indefinite non-cooperative stacking; for adenosine K = 15 +/- 2M-1, for ATP K = 1.3 +/- 0.2 M-1 and for Mg(ATP)2-K = 3.6 +/- 0.3 M-1. For the pyrimidines, uridine and TUP, stacking is much weaker and the stability constant could only be estimated; for uridine k is less than or equal to 0.5 M-1, and for UTP K approximately 0.3 M-1.