Oxidation of Silver Cyanide Ag(CN)2– by the OH Radical: From Ab Initio Calculation to Molecular Simulation and to Experiment

Léonard, Céline; Quéré, Frédéric Le; Adjei, Daniel; Denisov, Sergey A.; Mostafavi, Mehran; Archirel, Pierre

doi:10.1021/acs.jpca.0c08038

Cited by 2 publications

(2 citation statements)

References 55 publications

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“…For Δ G computation, the quasi-harmonic approximation with the 50 cm –1 cutoff was used to correct the vibrational partition function for artifacts related to low-frequency modes, whose entropies are ill-described by the harmonic approximation. Moreover, in order to obtain realistic Δ G values for the ligand-removal reactions in water, the translational and rotational entropy contributions to Δ G were scaled down to 50% of their gas-phase values (the Wertz correction). − This approach automatically accounts for the change of standard state from ideal gas (internally used in Gaussian) to a 1 M solution (used for all Δ G values reported here).…”

Section: Experimental and Computational Detailssupporting

confidence: 87%

Experimental and Computational Insight into the Mechanism of NO Binding to Ferric Microperoxidase. The Likely Role of Tautomerization to Account for the pH Dependence

et al. 2021

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According to the current paradigm, the metal− hydroxo bond in a six-coordinate porphyrin complex is believed to be significantly less reactive in ligand substitution than the analogous metal−aqua bond, due to a much higher strength of the former bond. Here, we report kinetic studies for nitric oxide (NO) binding to a heme-protein model, acetylated microperoxidase-11 (AcMP-11), that challenge this paradigm. In the studied pH range 7.4−12.6, ferric AcMP-11 exists in three acid− base forms, assigned in the literature as 2), and [(AcMP-11)Fe III (OH)(His − )] (3). From the pH dependence of the second-order rate constant for NO binding (k on ), we determined individual rate constants characterizing forms 1−3, revealing only a ca. 10-fold decrease in the NO binding rate on going from 1 (k on(1) = 3.8 × 10 6 M −1 s −1 ) to 2 (k on (2) = 4.0 × 10 5 M −1 s −1 ) and the inertness of 3. These findings lead to the abandonment of the dissociatively activated mechanism, in which the reaction rate can be directly correlated with the Fe−OH bond energy, as the mechanistic explanation for the process with regard to 2. The reactivity of 2 is accounted for through the existence of a tautomeric equilibrium between the major [(AcMP-11)Fe III (OH)(HisH)] (2a) and minor [(AcMP-11)Fe III (H 2 O)(His − )] (2b) species, of which the second one is assigned as the NO binding target due to its labile Fe−OH 2 bond. The proposed mechanism is further substantiated by quantum-chemical calculations, which confirmed both the significant labilization of the Fe−OH 2 bond in the [(AcMP-11)Fe III (H 2 O)(His − )] tautomer and the feasibility of the tautomer formation, especially after introducing empirical corrections to the computed relative acidities of the H 2 O and HisH ligands based on the experimental pK a values. It is shown that the "effective lability" of the axial ligand (OH − /H 2 O) in 2 may be comparable to the lability of the H 2 O ligand in 1.

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Section: Experimental and Computational Detailssupporting

confidence: 87%

Experimental and Computational Insight into the Mechanism of NO Binding to Ferric Microperoxidase. The Likely Role of Tautomerization to Account for the pH Dependence

et al. 2021

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“…This sublist is built with uniform sampling, selecting every 100th step of the MC simulation. This method enabled us to obtain useful insights into the mechanisms of radiolytic processes in solution [ 39 , 40 , 41 ].…”

Section: Methodsmentioning

confidence: 99%

Unveiling the Intimate Mechanism of the Crocin Antioxidant Properties by Radiolytic Analysis and Molecular Simulations

et al. 2023

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The successive steps of the oxidation mechanism of crocin, a major compound of saffron, by the free OH• radical are investigated by pulse radiolysis, steady-state (gamma) radiolysis methods, and molecular simulations. The optical absorption properties of the transient species and their reaction rate constants are determined. The absorption spectrum of the oxidized radical of crocin resulting from the H-abstraction presents a maximum of 678 nm and a band of 441 nm, almost as intense as that of crocin. The spectrum of the covalent dimer of this radical contains an intense band at 441 nm and a weaker band at 330 nm. The final oxidized crocin, issued from radical disproportionation, absorbs weaker with a maximum of 330 nm. The molecular simulation results suggest that the OH• radical is electrostatically attracted by the terminal sugar and is scavenged predominantly by the neighbor methyl site of the polyene chain as in a sugar-driven mechanism. Based on detailed experimental and theoretical investigations, the antioxidant properties of crocin are highlighted.

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Oxidation of Silver Cyanide Ag(CN)₂^– by the OH Radical: From Ab Initio Calculation to Molecular Simulation and to Experiment

Cited by 2 publications

References 55 publications

Experimental and Computational Insight into the Mechanism of NO Binding to Ferric Microperoxidase. The Likely Role of Tautomerization to Account for the pH Dependence

Experimental and Computational Insight into the Mechanism of NO Binding to Ferric Microperoxidase. The Likely Role of Tautomerization to Account for the pH Dependence

Unveiling the Intimate Mechanism of the Crocin Antioxidant Properties by Radiolytic Analysis and Molecular Simulations

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