Syntheses and Superoxide Dismuting Activities of Partially (1−4) <i>β</i>-Chlorinated Derivatives of Manganese(III) <i>m</i><i>eso</i>-Tetrakis(<i>N</i>-ethylpyridinium-2-yl)porphyrin

Abstract

Manganese(III) β-mono-, di-, tri-, and tetrachloro-5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnClxTE-2-PyP5+, with x from 1 to 4) were prepared through β-chlorination of 5,10,15,20-tetrakis(2-pyridyl)porphyrin (H2T-2-PyP) followed by N-ethylation and metallation. Metal centered redox potentials and superoxide dismutation activities were measured. Starting from MnTE-2-PyP5+, whose redox potential and the related superoxide dismutation activity were E°1/2 = +228 mV vs NHE and kcat = 5.7 × 107 M-1 s-1, respectively, the average increase of 55 mV in the redox potential per added chlorine was accompanied by a 65% increase in the rate constant. With E°1/2 = +448 mV, the tetrachlorinated derivative MnCl4TE-2-PyP5+ exhibited the highest superoxide dismuting rate kcat = 4.0 × 108 M-1 s-1. The relationship between the redox properties (thermodynamic and kinetic factors) and the superoxide dismuting activity of such compounds is discussed.