Table 1. Measured Thermodynamic Parameters for RNA Duplex Formation in 1 M NaCl.

^aFor each duplex, the values from bottom to top are measured at pH 5.5, 7, and 8, respectively. Sequences are ordered from the most negative to the most positive values of ΔΔG°_37,pH = ΔG°_37,pH5.5 − ΔG°_37,pH7, unless noted in footnote . T_m values were calculated from eq 1 at C_T = 0.1 mM. Data in parentheses were measured in NMR buffer with 80 mM NaCl at pH 7.

^bImino proton NMR spectra were measured (Figure 2).

^cΔΔG°_37,pH is per CA pair.

^dLoop sequence from a J4/5 loop of a group I intron (36).

^eData at pH 7 are from ref (19).

^fLoop sequence from the substrate loop of a VS ribozyme (8,9).

^gLoop sequence derived from the loop A of hairpin ribozyme (3).

^hLoop sequence from a leadzyme (1,65−67).

ⁱLoop sequence from the Alu domain of human SRP RNA (71).

^jThe pH-independent thermodynamics is consistent with the NMR structure without the formation of the C⁺U pair (61).

^kThe pH-independent thermodynamics is consistent with the NMR structure without the formation of the UC⁺ pair (62).