Table 1.
Sample composition (free radical polarizing agents, radical concentration c, 13C-labelled substrates and glassing matrices) and 13C DNP parameters (positive P(+) and negative P(−) polarization peaks, buildup time constant τbu, and DNP-enhanced 13C polarization P)
| Free radical | c (mM) | 13C substrate and glassing matrix | P(+)/P(−) (GHz) | τbu (s) | 13C Pdnp (%) |
|---|---|---|---|---|---|
| BDPA | 20 | 1:1 (v/v) [1-13C]pyruvic acid:sulfolane | 128.80/128.84 | 1,770 ± 150 | 46.5 ± 3.9 |
| Trityl OX063 | 15 | Neat [1-13C]pyruvic acid | 128.82/128.88 | 3,310 ± 120 | 54.4 ± 4.2 |
| Galvinoxyl | 40 | 1:1 (v/v) [1-13C]ethyl acetate:DMSO | 128.90/129.03 | 388 ± 20 | 10.5 ± 1.7 |
| DPPH | 20 | 1:1 (v/v) [1-13C]ethyl acetate:sulfolane | 128.82/128.95 | 531 ± 46 | 13.3 ± 2.4 |
| 4-Oxo-TEMPO | 40 | 1.4 M [1-13C]sodium pyruvate in 1:1 (v/v) glycerol:water | 128.82/129.23 | 1058 ± 72 | 18.3 ± 3.8 |
The 13C samples (N = 3 for each free radical) were polarized by microwave irradiation at P(+) with a 120 mW microwave source. The corresponding 13C polarization P and τbu values were measured at 4.6 T and 1.15 K. The error values for P and τbu are standard deviations of N = 3 trials