Syntheses and superoxide dismuting activities of partially (1-4)beta-chlorinated derivatives of manganese(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin

Manganese(III) beta-mono-, di-, tri-, and tetrachloro-5,10,15,20-tetrakis(N -ethylpyridinium-2-yl)porphyrin (MnClx TE-2-PyP5+, with x from I to 4) were prepared through beta-chlorination of 5,10, 15,20-tetrakis(2-pyridyl)porph yrin (H2T-2-PyP) followed by N-ethylation and metallation. Metal centered r edox potentials and superoxide dismutation activities were measured. Starti ng from MnTE-2-PyP5+, whose redox potential and the related superoxide dism utation activity were E(1/2)degrees = +228 mV vs NHE and k(cat) = 5.7 x 10( 7) M-1 s(-1), respectively, the average increase of 55 mV in the redox pote ntial per added chlorine was accompanied by a 65% increase in the rate cons tant. With E-1/2 degrees = +448 mV, the tetrachlorinated derivative MnCl4TE -2-PyP5+ exhibited the highest superoxide dismuting rate k(cat) = 4.0 x 10( 8) M-1 s(-1). The relationship between the redox properties (thermodynamic and kinetic factors) and the superoxide dismuting activity of such compound s is discussed.