10.1021/bi8020058.s001 Sergey A. Kurzeev Sergey A. Kurzeev Alexander S. Vilesov Alexander S. Vilesov Tatyana V. Fedorova Tatyana V. Fedorova Elena V. Stepanova Elena V. Stepanova Olga V. Koroleva Olga V. Koroleva Christian Bukh Christian Bukh Morten J. Bjerrum Morten J. Bjerrum Igor V. Kurnikov Igor V. Kurnikov Alexander D. Ryabov Alexander D. Ryabov Kinetic and Theoretical Comprehension of Diverse Rate Laws and Reactivity Gaps in <i>Coriolus hirsutus</i> Laccase-Catalyzed Oxidation of Acido and Cyclometalated Ru<sup>II</sup> Complexes American Chemical Society 2009 Diverse Rate Laws Theoretical Comprehension dioxygen Monte Carlo simulations RuIII species k 2 rate kinetic cyclometalated RuII derivatives Coriolus hirsutus acido complexes UV k 1 move Coriolus hirsutes laccase rate constants Reactivity Gaps rate laws Cyclometalated RuII ComplexesThe reactivity cyclometalated complexes LL pH 4.5 mechanism rate constants k 1 bpy analogue 2009-06-02 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Kinetic_and_Theoretical_Comprehension_of_Diverse_Rate_Laws_and_Reactivity_Gaps_in_i_Coriolus_hirsutus_i_Laccase_Catalyzed_Oxidation_of_Acido_and_Cyclometalated_Ru_sup_II_sup_Complexes/2853271 The reactivity of the acido Ru<sup>II</sup> complexes <i>cis</i>-[RuCl<sub>2</sub>(LL)<sub>2</sub>], [RuCO<sub>3</sub>(LL)<sub>2</sub>], <i>cis</i>-[RuCO<sub>3</sub>-(bquin)<sub>2</sub>] (LL = 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen); bquin = 2,2′-biquinoline) and cyclometalated Ru<sup>II</sup> derivatives of 2-phenylpyridine and 4-(2-tolyl)pyridine [Ru(<i>o</i>-C<sub>6</sub>H<sub>4</sub>-2-py)(phen)<sub>2</sub>]PF<sub>6</sub> (<b>1</b>), [Ru(<i>o</i>-C<sub>6</sub>H<sub>3</sub>-<i>p</i>-R-2-py)(bpy)(MeCN)<sub>2</sub>]PF<sub>6</sub> (<b>2</b>), and [Ru(<i>o</i>-C<sub>6</sub>H<sub>3</sub>-<i>p</i>-R-2-py)(phen)(MeCN)<sub>2</sub>]PF<sub>6</sub> (<b>3</b>) (R = H (<b>a</b>), Me (<b>b</b>)) toward laccase from <i>Coriolus hirsutus</i> has been investigated by conventional UV−vis spectroscopy at pH 3−7 and 25 °C. The acido and cyclometalated complexes are readily oxidized into the corresponding Ru<sup>III</sup> species, but the two types of complexes differ substantially in reactivity and obey different rate laws. The acido complexes are oxidized more slowly and the second-order kinetics, first-order in laccase and Ru<sup>II</sup>, holds with the rate constants around 5 × 10<sup>4</sup> M<sup>−1</sup> s<sup>−1</sup> at pH 4.5 and 25 °C. The cyclometalated complexes <b>1</b>−<b>3</b> react much faster and the hyperbolic Michaelis−Menten kinetics holds. However, it is <i>not</i> due to formation of an enzyme−substrate complex but rather because of the ping-pong mechanism of catalysis, viz. <i>E</i>(ox) + Ru<sup>II</sup> → <i>E</i>(red) + Ru<sup>III</sup> (<i>k</i><sub>1</sub>); <i>E</i>(red) + 1/4O<sub>2</sub> → <i>E</i>(ox) (<i>k</i><sub>2</sub>), with the rate constants <i>k</i><sub>1</sub> in the range (2−9) × 10<sup>7</sup> M<sup>−1</sup> s<sup>−1</sup> under the same conditions. The huge values of <i>k</i><sub>1</sub> move the enzymatic oxidation toward a kinetic regime when the dioxygen half-reaction becomes the rate-limiting step. Cyclometalated compounds <b>1</b>−<b>3</b> can therefore be used for routine estimation of <i>k</i><sub>2</sub>, that is, the rate constant for reoxidation for laccases by dioxygen. The mechanism proposed was confirmed by the direct stopped-flow measurements of the <i>k</i><sub>2</sub> rate constant (8.1 × 10<sup>5</sup> M<sup>−1</sup> s<sup>−1</sup> at 26 °C) and supported by the theoretical modeling of interaction between the bpy analogue of <b>1</b> and <i>Coriolus hirsutes</i> laccase using Monte Carlo simulations.