540257.fig.004a
(a)
540257.fig.004b
(b)
540257.fig.004c
(c)
540257.fig.004d
(d)
Figure 4: Temperature-dependent premelting effect in Raman frequencies of (a) the admixture of complex vibration of the B-DNA phosphodiester backbone conformation and thymine and cytosine ring modes [18], (b) dT C 2 -endo sugar pucker and anti glycosyl torsion mode [8], and (c) dG and dA ring stretching vibrations sensitive to hydrogen bonding [18, 19] as well as dT [10]. The bands shift toward lower frequencies starting near 35°C and the movement attenuates for 65°C and higher for phosphodiester geometry and deoxyribose hydrogen bond vibrations. The onset of premelting effect at 746 c m 1 occurs near 50°C. (d) Interbase hydrogen bonding. The bands returns to their original position once the film is cooled back down to room temperature (see blue triangles in panels (a) and (b)). inset b: The intensity change near 1660–1680 c m 1 is observable from 35°C and higher with no sign of attenuation. The spectra are normalized to the intensity values at 1664 c m 1 in order to show the relative intensity change among three bands (indicated by 3 arrows). The continued enhancement of 1680 c m 1 from room temperature to 80°C is clearly observed. The bands at 1664 and 1650 c m 1 are indistinguishable at 20°C (thick line), and separate themselves into two distinct peaks at 1664 and 1648 c m 1 at 80°C (thin line).