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.