Figure 4.

Experimentally monitored helix-to-coil transitions of the oligonucleotides $\begin{array}{c}5\text{'}\mathrm{G}\mathbf{G}\mathrm{CGCATCAGC}\\ 3\text{'}-\mathbf{B}\mathrm{GCGTAGTCG}\end{array}$ (B = C, T, 0).

Panel a: DSC thermograms (symbols; every fourth experimental point) and the best fits of the model function (lines; see equation 3). The thermodynamic parameters characterizing the transitions monitored by DSC are presented for B = C, T and 0, respectively: T_m (°C) = 64.4, 58.6, 57.6; ΔH_D,Tm (kcal mol⁻¹) = 76.1(+0.1), 67.2(+1.2), 47.7(+6.4); ΔC_P,D (kcal mol⁻¹ K⁻¹) = 0.43(+0.02), 0.41(+0.00), 0.44(−0.10). The values in the round brackets are the differences between the model-dependent (equation 3) and the presented model-independent thermodynamic parameters.

Panel b: Fraction of the oligonuceotides in the denatured state, α_D, calculated either directly from DSC thermograms (Panel a) as a model-independent ΔH/ΔH_D ratio (symbols; ΔH was obtained by integration of experimental ΔC_P from the reference temperature at which all DNA molecules exist in the initial (duplex) macrostate (α_D = 0) to a given T at which a certain fraction of DNA molecules exist in the final denatured (single-stranded) macrostate; ΔH_D was calculated as ΔH_D = ΔH_D,Tm + ΔC_P,D(T – T_m), see experimental materials and methods) or as the model-dependent quantity obtained from the best fit model parameters (lines).