METAL-IONS AND HYDROGEN-PEROXIDE .32. CATALASE-LIKE ACTIVITY OF CU2+ IN AQUEOUS-SOLUTION AND ITS PROMOTION BY THE COORDINATION OF 2,2'-BIPYRIDYL

The disproportionation of H2O2, catalyzed by Cu2+(aq) and Cu(2, 2'-bpy)2+, was investigated in the pH range of about 4-6.5 by measuring the initial rate, v0=d[O2]/dt (M s-1), of the increase in the concentration of O2 (I=0.1, NaClO4; 25 °C). The results can be summarized in the rate law v0=Km[M2+] [H2O2]2/[H+], where M2+ =Cu2+ or Cu(2, 2'-bpy)2+. This means the coordination of 2, 2'-bipyridyl to Cu2+ does not alter the pathway of the reaction, which is outlined and discussed, but it does promote the catalytic activity by a factor of about 50: kCu=1.15X10-6 M-1 s-1 and kCu(bPy)=5.44X10-5 M-1 s-1. One of the reasons for this promotion is probably the enhanced stability of ternary complexes composed of a heteroaromatic N base (like 2, 2'-bipyridyl), Cu2+, and an O donor; further reasons could be an enhanced substitution rate and/or a facilitated electron transfer in the intermediate 2, 2'-bipyridyl-Cu2+-peroxo species. The influence of buffers on the catalase-like reaction is briefly mentioned, and possible reasons for the lower activity of Ni2+(aq), which obeys the same rate law as is known from an earlier study (kNi=1.77X10-9 M-1 s-1), are indicated. © 1979, American Chemical Society. All rights reserved.