Table 3. Lengths of Induction Periods, τ, Stoichiometric Factors, n, Rate of Inhibited Peroxidation, Rinh, the Slow-Down Factors (Rox/Rinh, the Ratio of the Rate of the Non-Inhibited Process to the Rate of the Inhibited Process), the Inhibition Rate Constants, kinh, and Kinetic Chain Lengths, vinh = Rinh/Ri, Determined for Autoxidation of 2.74 mM MeLin in 20.2 mM DMPC Liposomes in the Presence of 1 μM PMHC, RSV, 3,5-DHA, and 4-HBA or an Equimolar Mixture of PMHC/RSVa.
| pH | τ (min) | nb | Rinh (nM s–1) | Rox/Rinhc | 10–3 kinh (M–1 s–1) | vinh |
|---|---|---|---|---|---|---|
| PMHC | ||||||
| 4.0 | 10.9 ± 0.6 | 2.0 | 18 ± 3 | 4.7 | 12.8 ± 2.5 | 5.8 |
| 6.0 | 14.6 ± 0.5 | 2.0 | 19 ± 3 | 4.6 | 7.9 ± 1.6 | 8.3 |
| 7.0 | 8.6 ± 0.7 | 2.0 | 20 ± 4 | 5.0 | 14.0 ± 2.7 | 5.3 |
| 8.0 | 9.8 ± 0.5 | 2.0 | 22 ± 5 | 4.5 | 12.3 ± 2.5 | 6.5 |
| 10.0 | 9.4 ± 0.7 | 2.0 | 16 ± 3 | 4.3 | 16.1 ± 3.3 | 4.4 |
| RSV | ||||||
| 4.0 | 18.1 ± 0.9 | 3.4 | 24 ± 5 | 3.5 | 4.9 ± 1.1d | 7.7 |
| 6.0 | 40.8 ± 1.0 | 5.6 | 18 ± 3 | 4.8 | 3.3 ± 0.5d | 7.8 |
| 7.0 | 14.8 ± 0.6 | 3.4 | 22 ± 2 | 4.5 | 7.1 ± 1.4d | 5.8 |
| 8.0 | 13.6 ± 2.0 | 2.8 | 35 ± 5 | 2.9 | 5.5 ± 1.1d | 10.3 |
| 10.0 | - | - | 48 ± 5e | 1.4e | -f | 13.3 |
| 3,5-DHA | ||||||
| 4.0 | - | - | 33 ± 5e | 2.5e | -f | 10.6 |
| 7.0 | - | - | 73 ± 3e | 1.4e | -f | 19.2 |
| 4-HBA | ||||||
| 4.0 | - | - | 33 ± 6e | 2.5e | -f | 10.6 |
| 7.0 | - | - | 64 ± 9e | 1.5e | -f | 16.8 |
| PMHC/RSV | ||||||
| 4.0 | 33.1 ± 4.0 | 4.1g | 17 ± 4 | 4.9 | -h | 5.5 |
| 6.0 | 64.4 ± 2.1 | 6.9 | 14 ± 3 | 6.2 | - | 6.1 |
| 7.0 | 40.8 ± 1.4 | 7.3 | 18 ± 5 | 5.5 | - | 4.7 |
| 8.0 | 21.3 ± 2.8 | 2.3 | 16 ± 4 | 6.3 | - | 4.7 |
| 10.0 | 10.8 ± 0.3 | 0.3 | 12 ± 3 | 5.8 | - | 3.3 |
The experiments were performed at 37 °C and pH 4.0, 6.0, 7.0, 8.0, and 10.0. Peroxidation was initiated by 10 mM ABAP. Values are expressed as the mean ± standard deviation (SD).
For α-TOH and PMHC, n = 2.0.
The Rox/Rinh ratio informs how many times the inhibited oxidation is slower than the spontaneous (non-inhibited) process (for Rox as well as Ri values, see Supporting Information).
One of the Reviewers pointed out that kinh calculated from eq 9 represents the rate constant with the assumption that n = 2.0; therefore, eq 9 used for antioxidants with higher capacity (n > 2) gives the minimal, apparent kinh, but the real value might be obtained by multiplication of kinh by factor “n/2”. The values presented in this table for RSV have not been corrected and represent the minimal kinh.
For these systems, the inhibition time was not detected and kinh could not be calculated from eq 9.
For PMHC/RSV, parameter n corresponds to RSV and was calculated from the equation nRSV = Ri(τPMHC/RSV – τPMHC)/[RSV] adapted from ref (41).
kinh cannot be calculated for mixed antioxidants.