A calorimetric investigation of single stranded base stacking in the ribo-oligonucleotide A7.

Differential scanning calorimetry has been employed to determine the energy change associated with single stranded base stacking in the ribo-oligonucleotide A7. A total enthalpy change of 20.3 kcal (mole of heptamer)-1 was measured. This corresponds to 2.9 kcal (mole of adenine)-1 or 3.4 kcal (mole of A-A stack)-1 if one assumes that all six stacking interactions are energetically equivalent. These results represent the first direct determination of this important parameter for a ribo-oligonucleotide. It is noted that the calorimetrically determined value reported here is considerably lower than any of the previously published van't Hoff enthalpies but is consistent with values that can be derived from other calorimetric data.