Table 1.
Thermodynamic parameters of the R-triplex formation
| Oligonucleotide | ΔH (kJ·mol−1) | ΔS (kJ·mol−1·deg−1) | Tm (°C) | ΔG(0°C) (kJ·mol−1) | Δ(Number of H-bonds) compared with RaCW (a) |
|---|---|---|---|---|---|
| RaddCWddd (b) | −126 ± 7 | −0.420 ± 0.005 | 27 ± 1 | −11.3 ± 0.7 | +2 |
| RaCW (b) | −99 ± 3 | −0.337 ± 0.005 | 21 ± 1 | −7.1 ± 0.5 | 0 |
| RaCW7 (b) | −84 ± 3 | −0.289 ± 0.007 | 20 ± 1 | −5.2 ± 0.7 | −1 |
| RaCW77 (b,c) | −74 ± 2 | −0.254 ± 0.005 | 18 ± 1 | −4.6 ± 0.7 | −2 (‘weak’ H bonds) |
| RaaaCW777 (d) | −45 ± 3 | −0.153 ± 0.005 | 15 ± 1 | −2.3 ± 0.7 | −3 |
aPredicted Δ(Number of H-bonds) between the R-strand and the CW duplex compared with that in RaCW, according to the R-triplex model (5).
bThermodynamic parameters obtained from the fluorescence emission melting curves.
cThe RaCW77 fold has two A*(T·7DAA) triplets (Figure 2) which are less stable than the ‘standard’ 2AP*(T·A) triplets, because the former are unable to form ‘weak’ CH···N hydrogen bonds (5,19).
dThermodynamic parameters obtained from the UV absorption melting curves.