Catalytic activities of dismution reactions of Cu(bpy)Br(2) compound and its derivatives as SOD mimics: a theoretical study

The systematical investigations on the catalytic mechanisms of dismutation reactions for the superoxide dismutase (SOD) mimics of Cu(bpy)Br(2) and its derivatives Cu(L(1))Br(2) and Cu(L(2))Br(2) (bpy=2,2'- dipyridyl, L(1)=5,5'- di[1- (triethylammonio)methyl]- 2,2'- dipyridyl cation and L(2)=5,5'- di [1- (tributylammonio)methyl]- 2,2'- dipyridyl cation) have been carried out by the DFT/UB3LYP method. The catalytic reaction for each of these compounds is confirmed to be a redox cycle consisting of two half-reactions. In the first half-reaction, a proton is transferred from hydroperoxide neutral radical (*OOH) to one nitrogen atom of pyridinic ring with Cu(II) being reduced to Cu(I) in the meantime. In the second half-reaction, the proton is transferred back to another hydroperoxide radical (*OOH) to form hydrogen peroxide molecule, oxidizing Cu(I) back to its initial state. Our results show that the first half-reaction for all reactions is the rate-controlling step with the forward barrier values of 6.61, 4.84, 3.79 kcal x mol(-1) for Cu(bpy)Br(2), Cu(L(1))Br(2), and Cu(L(2))Br(2), respectively. Consequently, the SOD-like activities of the three mimics are in the order of Cu(bpy)Br(2) < Cu(L(1))Br(2) < Cu(L(2))Br(2). The effect factors on the SOD-like activity for the studied compounds have also been discussed.