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 (center dot 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 (center dot 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 center dot 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.
superoxide dismutase dft/ub3lyp sod-like activity dismutation mechanism