Intermolecular orientations of adenosine-5-monophosphate in aqueous solution as studied by fast fourier ytsndgotm 1H Nmr spectroscopy

Proton magnetic resonance spectra of 5′AMP were taken in the concentration range of 0.001–2.2M. The concentration profiles of all the nonexchangeable protons were determined. The data for 5′AMP was compared to those of adenine, adenosine, and poly(A). Theoretically computed isoshielding lines of the adenine moiety were used to qualitatively predict a preferred stacking geometry of 5′AMP in aqueous solution. It is concluded that 5′AMP at pH 8 forms multistacked aggregates at high concentration levels and that a preferred orientation is such that the bases are aligned face to back with considerable, though less than 100%, base overlap; and that the ribose moieties of adjacent molecules are near one another with the phosphate groups well separated. Mn(II) ion binding studies show that the stacks are not restricted to one unique orientation type. Specific evidence is given showing that base-stacking orientations in the solid state may in some cases be considerably different from that in aqueous solution, due in part to numerous hydrogen bonding differences, and this is shown to be the case for base-stacked adenosine. In the case of 5′AMP the stacking orientations between the solid and liquid states are also different, except in this comparison the solid-state structure carries a positive charge.