Figure 4.

Unzipping experiments at different temperatures. (a) Force-extension curves (FECs) measured at 1 M NaCl + TE, pH 7.5. Here the cold measurements have been aligned to the hot segments, where the position-sensitive photodetectors operate at room temperature, by matching the unzipping measurements at 25°C. See Supporting Material. Unzipping and rezipping traces are almost identical, showing that the experiments were carried out under quasistatic conditions. (b) Mean unzipping/rezipping force versus temperature. Experimental data points, each averaged over four molecules at 1 M NaCl TE buffer, pH 7.5, are shown in combination with two theoretical predictions based on experimental data from (10) (HU) or SantaLucia (4) (UO; see also Table S2). (c) Mean unzipping/rezipping force versus temperature in different ionic conditions. Experimental data represent the average over eight molecules. These results remarkably follow the rule regarding a 1:100 ratio of monovalent to divalent salt, similarly to what has been observed for RNA (33). To see this figure in color, go online.