Abstract
The redox reactions of manganese porphyrins in aqueous solutions were studied by steady-state and pulse radiolysis. Mn/sup III/P was reduced to Mn/sup II/P or oxidized to Mn/sup IV/P by chemical and radiolytic methods and the various species were characterized by spectrophotometry. The reduction of Mn/sup II/P to Mn/sup II/P/sup +/ was studied only by pulse radiolysis since the product is short-lived. Pulse radiolysis also permitted determination of the rate constants for the various redox reactions. Reduction of Mn/sup III/P and Mn/sup II/P by e/sub aq//sup +/ took place with k approx. 10/sup 10/ M/sup -1/ s/sup -1/ while their reduction by the radicals from i-PrOH was generally 1 order of magnitude slower. Mn/sup II/P was rapidly oxidized by Cl/sub 2//sup +/ and Br/sub 2//sup +/ by an inner-sphere mechanism involving initial addition of these radicals to the Mn. The CH/sub 2/C(CH/sub 3/)/sub 2/OH radical from t-BuOH was also found to oxidize Mn/sup II/P to Mn/sup III/P via an intermediate adduct formation. Oxidation of Mn/sup III/P to Mn/sup IV/P was rapid and quantitative at high pH, using Br/sub 2//sup -/ or CH/sub 2/CHO radicals as the oxidants. The reaction was also monitored in neutral solutions using Br/sub 2//sup -/ and inmore » acidic solutions using Cl/sub 2//sup -/ as the oxidants. In these cases the products are unstable but appear to be the Mn/sup IV/P forms.« less
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