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. Author manuscript; available in PMC: 2016 Sep 1.
Published in final edited form as: Free Radic Biol Med. 2015 May 28;86:308–321. doi: 10.1016/j.freeradbiomed.2015.05.018

Table 1. The metal-centered reduction potential E1/2 vs NHE for MnIIIP/MnIIP, kcat(H2O2) for the catalysis of H2O2 dismutation in M−1 s−1, log kcat(O2.−) for the catalysis of O2.− dismutation, the proton dissociation constant for 1st axial water of metalloporphyrins, pKa(ax) and the proton dissociation constant for the 3rd basic pyrrolic nitrogen proton of the corresponding metal-free porphyrin, pKa3.

The catalysis of H2O2 dismutation by MnPs was followed in 0.05 M tris buffer, pH 7.8 at (25±1)°C by Clark oxygen electrode. The values for the catalysis of O2.− dismutation, determined by cyt c assay in 0.05 M potassium phosphate buffer, pH 7.8 at 25±1°C, are taken from [19, 21, 49, 50]. All E1/2 values for MnIIIP/MnIIP redox couple are reported vs the normal hydrogen electrode (NHE), using the potential of MnTE-2-PyP5+, E1/2 = + 228 mV vs NHE at pH 7.8, as a reference.

N Compound E1/2 (MnIIIP/MnIIP), mV vs NHE log kcat (O2.−)a kcat (H2O2), M−1 s−1 pKa(ax) pKa3
pH 7.8 pH 7.8 pH 7.8
1 MnTBAP3− −194 3.16 5.84 12.6 5.5
2 MnTE-2-PyPhP5+ −65 5.55 21.10 12.1
3 MnTE-3-PyP5+ 54 6.65 63.25 11.5 ~1.8
4 MnTE-4-PyP5+ 70 6.86 52.08 ~11.6 ~1.4
5 MnTnHex-3-PyP5+ 66 6.64 46.21 ~11.5
6 MnTnHex-4-PyP5+ 68 6.75 59.05 ~11.6
7 MnTnOct-3-PyP5+ 74 6.53 67.44 ~11.5
8 MnTE-2-PyP5+ 228 7.76 63.32 10.7 −0.9
9 MnTPhE-2-PyP5+ 259 7.66 23.54 ~10.8
10 MnTnBuOE-2-PyP5+ 277 7.83 88.47 10.7
11 MnTnHexOE-2-PyP5+ 313 7.92 34.66 10.6
12 MnTnHex-2-PyP5+ 314 7.48 28.31 11.0
13 MnTnOct-2-PyP5+ 340 7.71 27.62 10.7
14 MnTDE-2-ImP5+ 346 7.83 27.59
a

in the absence of SOD enzyme, O2.− self-dismutes at pH 7.8 with rate constant of log k(O2.−)self-dismutation ~5.7. Therefore, the compounds cannot be functional SOD mimics, if they disproportionate O2.− with a log value of rate constant equal to or lower than 5.7.

b

We have estimated several values of pKa(ax). based on established relationships [25, 50, 68]. The lengthening of methyl chains (in MnTM-2 (or 3 or 4)-PyP5+) to ethyl chains (in MnTE-2(or 3 or 4)-PyP5+) has essentially no impact on log kcat(O2.−) and E1/2 vs NHE for MnIIIP/MnIIP, assuming therefore safely that it also has no significant impact on pKa(ax).