Decreased electron transfer rates of manganese porphyrins with conformational distortion of the macrocycle

Slow electron transfer to manganese(III) porphyrins results when the macrocycle deviates from planarity. This was demonstrated by measuring the kinetics of homogeneous electron transfer from a series of semiquinone radical anions to synthetic manganese porphyrins (shown schematically; R¹ =H, Cl, F; R²=H, F). Three of the four porphyrins studied have nonplanar macrocycles. These results could have implications for the role of manganese in biological electron transfer processes.