Figure 2.

Temperature-induced dissociation of AA. (a) FTIR spectra of TTg:AA and UUg:AA from 1°C–96°C in ∼2.6°C steps. Solutions contain 1 mM each of AA, primer, helper, and template strands. (b) Thermal AA and template dissociation of the TTg:AA complex monitored with FTIR, 2D IR, and ¹H-NMR. FTIR traces are plotted as the absolute value change in absorption relative to 1°C for select frequencies marked in (a) that primarily report on intensity changes in G (1573 cm⁻¹, blue), A & T (1623 cm⁻¹, purple), and G & T (1665 cm⁻¹, pink). 2D IR traces at select frequencies similar to the FTIR data are plotted as the absolute value percent change in signal relative to 1°C (|ΔS|). From ¹H-NMR, the AA dissociation transition is monitored using the chemical shift of two aromatic protons from adenine (A3 and A4) and H5 aromatic protons of cytosine (C1 and C2). The temperature-dependent chemical shifts of A3 and A4 in free AA are shown as open circles. The corresponding ¹H-NMR spectra are shown in Fig. S9. (c) Thermal AA and template dissociation transitions of the UUg:AA complex monitored with (top) FTIR and (bottom) 2D IR. Solid lines for each dataset correspond to fits to a three-state sequential model. FTIR and 2D IR data are globally fit together. The four ¹H-NMR peaks are globally fit to the same three-state model and include upper and lower baselines (dashed lines). Temperature-dependent FTIR and 2D IR data for TTo:AA and TTg, TTo, and UUg are shown in supporting material, Sections S1.2 and S1.3. To see this figure in color, go online.