A glance at the reactivity of osma(II)cycles [Os(C–N) x (bpy)3− x ]m+ (x =0–3) Covering a 1.8V Potential Range toward Peroxidase through Monte Carlo Simulations (−C–N= o-2-phenylpyridinato, bpy=2,2′-bipyridine).

Three cyclometalated and one coordination compounds [Os(C–N) x (bpy)3− x ] m (x/m =0/2+ (4); 1/1+ (3); 2/1+ (2); 3/0 (1); −C–N=2-phenylpyridinato, bpy=2,2′-bipyridine) with drastically different reduction potentials have been used for analyzing the second-order rate constants for one-electron, metal-based osmium(II) to osmium(III) oxidation of the complexes by compound I (k 2) and compound II (k 3) of horseradish peroxidase. Previously unknown k 2 and k 3 have been determined by digital simulation of cyclic voltammograms measured in phosphate buffer of pH7.6 and 21±1°C. Osmium(II) species derived from osmium(III) complexes 1 and 2 were generated electrochemically in situ. Under the conditions used the reduction potentials for the OsIII/II feature equal −0.90, −0.095, 0.23 and 0.85V versus NHE (normal hydrogen electrode) for 1–4, respectively. The rate constants k 2 equal ~5×107, 6×108, 2×106 and 1×105 M−1 s−1 and the rate constants k 3 equal ~9×106, 4×107, 1×106 and 1×105 M−1 s−1 for complexes 1–4, respectively. Both rate constants k 2 and k 3 first increase with increasing the reaction driving force on going from 4 to 2 but then both decrease on going to complex 1 though the reaction driving force is the highest in this case. The system described has been explored theoretically using docking Monte Carlo simulations. [ABSTRACT FROM AUTHOR]