Temperature dependence of thermodynamic properties for DNA/DNA and RNA/DNA duplex formation.

A clear difference in the enthalpy changes derived from spectroscopic and calorimetric measurements has recently been shown. The exact interpretation of this deviation varied from study to study, but it was generally attributed to the non-two-state transition and heat capacity change. Although the temperature-dependent thermodynamics of the duplex formation was often implied, systemic and extensive studies have been lacking in universally assigning the appropriate thermodynamic parameter sets. In the present study, the 24 DNA/DNA and 41 RNA/DNA oligonucleotide duplexes, designed to avoid the formation of hairpin or slipped duplex structures and to limit the base pair length less than 12 bp, were selected to evaluate the heat capacity changes and temperature-dependent thermodynamic properties of duplex formation. Direct comparison reveals that the temperature-independent thermodynamic parameters could provide a reasonable approximation only when the temperature of interest has a small deviation from the mean melting temperature over the experimental range. The heat capacity changes depend on the base composition and sequences and are generally limited in the range of -160 to approximately -40 cal.mol-1.K-1 per base pair. In contrast to the enthalpy and entropy changes, the free energy change and melting temperature are relatively insensitive to the heat capacity change. Finally, the 16 NN-model free energy parameters and one helix initiation at physiological temperature were extracted from the temperature-dependent thermodynamic data of the 41 RNA/DNA hybrids.