2.3. Absorption and Circular Dichroism Spectroscopy

ODNs were dissolved in 10 mM sodium phosphate buffer (pH 5.8 for To, Uo and their derivatives and pH 7.4 for Go, Mo and their derivatives). The Uo and U1Z samples were rapidly annealed (heated to 95 °C for 5 min and then cooled on ice to facilitate intramolecular folding) prior to the experiments, and the other samples were slowly annealed (heated to 95 °C and then cooled gradually to room temperature). The ODN concentrations were 10 μM (To and T1Z) or 5 μM (other ODNs). The absorption spectra, circular dichroism (CD) spectra and melting/annealing curves of the ODNs were recorded on a Chirascan spectrophotometer (Applied Photophysics, UK) equipped with a thermostated cuvette-holder as previously described [35], and thermal difference spectra (TDS) were obtained by subtracting the absorption spectra at 5 °C from the spectra at 90 °C. Melting and annealing temperatures were determined from the maxima of the first derivatives of the melting curves. The heating/cooling rates were 1 °C/min.