Thermal stability studies for oligos A, B, and C and their control sequences. A) DNA melting was monitored by CD at 264 nm in a 1 cm cell at 5 μM DNA concentration. Both melting and cooling curves are shown; arrows indicate the direction of temperature change. Note, hysteresis is observed for oligos A, B, and C but not for control sequences indicating that melting and cooling processes had differing intermediates. Temperature of the half-transition, T1/2, (and not the melting temperature, Tm) was determined from melting curves only and is reported in Table 2. B) CD wavelength spectra were collected on each sample before and after melting. The CD signature of B and C oligos and all control samples did not change after melting thus indicating that each system returned to the original (most likely thermodynamic) secondary structure. CD signal at 264 nm for oligo A increased slightly after the melt signifying an increase in parallel folding after melt.