Table 1.
Values of the kS/kO2 ratio (average values from at least three independent experiments; pH 7.4, 25 °C) for the studied cyclic C-nucleophiles, with the rate constants for their reactions with HNO and theoretically calculated Gibbs free energy barriers at the B2PLYP-D3/6-311+(2df,2p) theory level.
| Scavenger | kS/kOxygen | kS (M−1s−1) | ΔG‡(kJ/mol) |
|---|---|---|---|
| 1,3-Cyclopentanedione (1) | 0.016 ± 0.001 | (2.8 ± 0.6) × 102 | 72.53 |
| 2-Methyl-1,3-cyclopentanedione (2) | 0.18 ± 0.02 | (3.2 ± 0.9) × 103 | 57.92 |
| 2-Acetyl-1,3-cyclopentanedione (3) | (1.8 ± 0.2) × 10−3 [a] | (3.3 ± 0.8) × 101 [a] | 90.93 |
| 1,3-Cyclohexanedione (4) | 0.12 ± 0.01 | (2.2 ± 0.4) × 103 | 59.28 |
| 2-Methyl-1,3-cyclohexanedione (5) | 0.61 ± 0.04 | (1.1 ± 0.2) × 104 | 50.03 |
| Dimedone (6) | 0.14 ± 0.01 | (2.5 ± 0.6) × 103 | 58.46 |
| 1,3-Cycloheptanedione (7) | 0.38 ± 0.02 | (6.8 ± 1.5) × 103 | 57.52 |
| 2,4-Piperidinedione (8) | 1.13 ± 0.03 | (2.0 ± 0.4) × 104 | 45.65 |
| 1-(4-Methoxybenzyl)-2,4-piperidinedione (9) | 0.80 ± 0.03 | (1.4 ± 0.3) × 104 | 41.34 |
| 1,3-Dimethylbarbituric acid (10) | 0.72 ± 0.03 | (1.3 ± 0.3) × 104 | 50.93 |
| Barbituric acid (11) | 0.20 ± 0.01 | (3.5 ± 0.8) × 103 | 64.65 |
| 2-Thiobarbituric acid (12) | 0.046 ± 0.003 | (8.2 ± 1.9) × 102 | 76.28 |
| Meldrum’s acid (13) | 0.048 ± 0.002 | (8.7 ± 1.8) × 102 | 70.15 |
[a] The kS/kO2 ratio was evaluated based on the effect of 10 mM 2-acetyl-1,3-cyclohexanedione (3) on the FlBA oxidation rate.