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

• Mono, bis and tris cyclometalated osmium complexes react fast with peroxidase.
• Rates rise first and then decrease with the driving force increase in ca 2 V range.
• Theoretical analysis by Monte Carlo simulations suggests a plausible reaction pathway.

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 (k2) and compound II (k3) of horseradish peroxidase. Previously unknown k2 and k3 have been determined by digital simulation of cyclic voltammograms measured in phosphate buffer of pH 7.6 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 0.85 V versus NHE (normal hydrogen electrode) for 1–4, respectively. The rate constants k2 equal ~ 5 × 107, 6 × 108, 2 × 106 and 1 × 105 M− 1 s− 1 and the rate constants k3 equal ~ 9 × 106, 4 × 107, 1 × 106 and 1 × 105 M− 1 s− 1 for complexes 1–4, respectively. Both rate constants k2 and k3 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.

Mono, bis and tris-cyclometalated osmium complexes react fast with peroxidase; theoretical analysis by Monte Carlo simulations suggests a plausible reaction pathway.Figure optionsDownload as PowerPoint slide