3-mer Dynamics - K+PET3
    The 80 K ATD for K+PET3 only shows one peak even though theory predicts a "closed" and "open" form for this 3-mer. Based on the Li+PET3 and Na+PET3 results, which showed both conformers are present but with the isomerization barrier height strongly dependent on the metal cation, the "closed" and "open" forms of K+PET3 may be present but the barrier between them so small (<1 kcal/mol) that the two conformers cannot be separated under the present experimental conditions. Since the barrier appears to decrease dramatically from Li to Na and the barrier for Na+PET3 is only 1.6 kcal/mol, it is not unreasonable for K+PET3 to have a barrier <1 kcal/mol.
     The 300 K experimental cross-section for K+PET3 agrees very well with the theoretical value calculated for the "closed" form. This indicates that if the "closed" and "open" conformers are present for this oligomer, the "closed" form must be significantly more abundant than the "open" form. For example, two conformers are theoretically predicted and experimentally observed for the deprotonated dinucleotides dAT- and dTA- [J. Gidden, M.T. Bowers, Eur. Phys. J. D 2002, 20, 409]. The 80K ATD for dAT- indicates that the less compact, "open" form is favored by 19:1 over the "folded" form. For dTA- however, the 80 K ATD indicates that the "folded" form is favored 9:1 over the "open form. At 300 K, the two conformers rapidly interconvert. The average cross-section of dAT- at this temperature is 156 Å2 while the average cross-section for dTA- is only 146 Å2.