Table 3. Thermodynamic parameters for helix formation with 2-methylthio-N6-alkyladenosine–uridine base pairs at various positions within oligomers and 2-methylthio-N6-alkyladenosine as 3’-dangling enda,b.
| –ΔH0 (kcal/mol) | –ΔS0 (eu) | –ΔG037 (kcal/mol) | TMc (°C) | ΔΔG037d (kcal/mol) | |
|---|---|---|---|---|---|
| UACXUGUA | |||||
| AUGUXCAU | |||||
| X = ms2i6Ae | 101.4 ± 14.9 | 328.2 ± 50.4 | 0.44 ± 0.80 | 19.3 | 6.52 |
| X = ms2m6Ae | 117.0 ± 20.3 | 379.5 ± 68.5 | 0.69 ± 0.98 | 21.0 | 6.27 |
| X = ms2Ae | 65.2 ± 3.4 | 200.5 ± 11.2 | 3.03 ± 0.10 | 24.9 | 3.93 |
| UXCAUGUA | |||||
| AUGUACXU | |||||
| X = ms2i6A | 50.6 ± 8.5 | 147.0 ± 27.2 | 4.98 ± 0.09 | 33.1 | 1.98 |
| X = ms2m6A | 46.8 ± 3.5 | 133.3 ± 11.1 | 5.48 ± 0.10 | 35.7 | 1.48 |
| X = ms2A | 53.2 ± 1.3 | 158.2 ± 4.1 | 4.15 ± 0.02 | 28.4 | 2.81 |
| UACAUGUX | |||||
| XUGUACAU | |||||
| X = ms2i6A | 61.6 ± 6.9 | 177.5 ± 22.3 | 6.52 ± 0.07 | 41.8 | 0.44 |
| X = ms2m6A | 62.8 ± 1.8 | 179.8 ± 5.8 | 7.01 ± 0.02 | 43.7 | –0.05 |
| X = ms2A | 62.5 ± 1.4 | 179.5 ± 4.6 | 6.86 ± 0.01 | 43.0 | 0.1 |
| X = A | 56.2 ± 1.6 | 158.7 ± 5.2 | 6.96 ± 0.02 | 44.3 | 0 |
| ACAUGUX | |||||
| XUGUACA | |||||
| X = ms2i6A | 62.0 ± 1.9 | 180.1 ± 6.2 | 6.14 ± 0.02 | 39.4 | –0.44 |
| X = ms2m6A | 65.0 ± 2.8 | 188.0 ± 8.8 | 6.73 ± 0.03 | 42.1 | –1.03 |
| X = ms2A | 57.6 ± 2.1 | 164.3 ± 6.8 | 6.66 ± 0.02 | 42.4 | –0.96 |
| X = A | 50.9 ± 1.0 | 145.8 ± 3.1 | 5.70 ± 0.01 | 37.1 | 0 |
aSolutions are 1 M sodium chloride, 20 mM sodium cacodylate and 0.5 mM Na2EDTA, pH 7.
bThermodynamic parameters were calculated from TM–1 versus log CT plots.
cMelting temperatures were calculated for 10–4 M oligomer concentration.
dCalculated relative to the stability of an oligomer containing adenosine.
eNot a two-state transition.