Calorimetric and spectroscopic investigation of the helix-to-coil transition of the self-complementary deoxyribonucleotide ATGCAT.

Differential scanning calorimetry and temperature-dependent uv spectroscopy are used to thermodynamically characterize the double-strand to single-strand transition of the self-complementary deoxyribo-oligonucleotide ATGCAT. The calorimetric experiments provide a value of 33.6 kcal (mol of double strand)-1 for the transition between 10 and 90 degree C. In conjunction with available temperature-dependent nmr data (which reveals terminal base pair fraying), we attempt to define specifically those interactions to which the calorimetrically measured enthalpy change refers. Values of delta HV.H. (van 't Hoff enthalpy change) are derived from the spectroscopic and calorimetric data and compared with the delta H obtained directly from the calorimetric experiment. This comparison reveals that the part of the thermally-induced transition that occurs between 10 and 90 degree C is well represented by a two-state process. It is noted that is assessing the applicability of the two-state model it is best to compare the delta with delta HV.H. Hcal. obtained from the calorimetric rather than the spectroscopic data.