TABLE II.
Torsional angles and probabilities for the sterically allowed conformers of the nitroxide side-chain of the R1 spin label, at a site located in the middle of a poly-Ala helix. Statistical weights were calculated at T=298 K on the basis of the single bond torsional potential, V′ in eq 1. Conformers allowed for the R2 spin probe are denoted by an asterisk; probability and χ5 values for these are reported in parentheses.
| conformer | χ1(°) | χ2(°) | χ3(°) | χ4(°) | χ5(°) | PJ |
|---|---|---|---|---|---|---|
| C1* | -60 | -75 | -90 | 180 | +77 (+85) | 0.143 (0.201) |
| C2* | -60 | -75 | -90 | 180 | -77 (-85) | 0.143 (0.201) |
| C3 | -60 | -75 | -90 | -75 | +100 | 0.045 |
| C4 | -60 | -75 | -90 | -75 | -8 | 0.074 |
| C5* | -60 | 180 | 90 | 180 | +77 (+85) | 0.187 (0.263) |
| C6* | -60 | 180 | 90 | 180 | -77 (-85) | 0.187 (0.263) |
| C7 | -60 | 180 | 90 | +75 | -100 | 0.059 |
| C8 | -60 | 180 | 90 | +75 | +8 | 0.098 |
| C9* | 180 | 180 | -90 | 180 | +77 (+85) | 0.009 (0.013) |
| C10* | 180 | 180 | -90 | 180 | -77 (-85) | 0.009 (0.013) |
| C11 | 180 | 180 | -90 | -75 | +100 | 0.003 |
| C12 | 180 | 180 | -90 | -75 | -8 | 0.005 |
| C13* | 180 | 180 | 90 | 180 | +77 (+85) | 0.009 (0.013) |
| C14* | 180 | 180 | 90 | 180 | -77 (-85) | 0.009 (0.013) |
| C15* | 180 | 75 | 90 | 180 | +77 (+85) | 0.007 (0.010) |
| C16* | 180 | 75 | 90 | 180 | -77 (-85) | 0.007 (0.010) |
| C17 | 180 | 75 | 90 | +75 | -100 | 0.002 |
| C18 | 180 | 75 | 90 | +75 | +8 | 0.004 |