Table 2.
Summary of NMR data in peptides with cysteine compared to peptides with cysteine sulfinic acid.
| peptide | 3JαN, Hz | δ, HN, ppm | δ, Hα, ppm | δ, Hβ, ppm |
|---|---|---|---|---|
| α14-C1-SH | 5.0 | 8.66 | 4.39 | 2.97 |
| α14-C1-SO2− | -a | 8.76 | 4.56 | 2.94, 2.68 |
| α14-C2-SH, | 5.4 | 8.71 | 4.41 | 2.98 |
| α14-C2-SO2− | -a | 8.86 | 4.60 | 2.89, 2.66 |
| α14-C5-SH | 6.0 | 8.49 | 4.41 | 2.98 |
| α14-C5-SO2− | -b | 8.62 | 4.53 | 2.99, 2.58 |
| α14-C10-SH | -b | 8.27 | 4.40 | 2.96 |
| α14-C10-SO2− | -b | 8.49 | 4.50 | 2.96, 2.55 |
| PPII-C4-SH | 7.2 | 8.40 | 4.73 | 2.85, 2.80d |
| PPII-C4-SO2− | 6.3 | 8.59 | -c | 2.72, 2.45 |
| β12-C6-SH | 6.1 | 9.12 | 4.36 | 3.02, 2.90 |
| β12-C6-SO2− | 4.5 | 9.36 | 4.41 | 2.87, 2.74 |
NMR data were acquired as described in the Supporting Information.
HN peaks were broadened for the cysteine sulfinate residues of peptides α14-C1-SO2− and α14-C2-SO2−, precluding measurement of coupling constants.
Resonances were not sufficiently resolved to determine 3JαN.
Hα of the peptide PPII-C4-SO2− was not observed due to water suppression.
The cysteine Hβ of the peptide PPII-C4-SH did not fully resolve, but chemical shifts for the individual resonances are estimated. Notably, the sulfinate Hβ are always upfield of the equivalent resonances in the corresponding thiol peptide, despite the theoretically decreased electron density on the sulfinate sulfur. In addition, resonances for the diastereotopic Hβ of cysteine thiols are not distinct or have less dispersion than those of Hβ in the corresponding sulfinates, indicative of more ordered conformations in the sulfinates.