Factors That Determine the Mechanism of NO Activation by Metal Complexes of Biological and Environmental Relevance

Franke, Alicja; Eldik, Rudi van

doi:10.1002/ejic.201201111

Cited by 26 publications

(8 citation statements)

References 127 publications

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“…12,20−23 However, in much more catalytically complex biological or environmental systems, numerous other factors such as steric hindrance around the metal center, the type of reaction medium, the chemical nature of the substituted ligand, the electronic and structural properties of other coligands play an important role in controlling the dynamics of the reversible binding of NO. 24 The overwhelming majority of research, conducted by both us and others, aiming to mimic the interaction of NO with heme proteins, was conducted using artificial porphyrins. Such an approach, through a comparison of the results with the ones obtained for proteins, allows conclusions to be drawn about the degree to which the process is controlled by the metal center, as well as determination of the influence of the protein architecture on the properties of the prosthetic group.…”

Section: ■ Introductionmentioning

confidence: 99%

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: ■ Introductionmentioning

confidence: 99%

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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“…In particular, heme proteins are involved in the generation of NO, either by nitric oxide synthases (NOS) or by nitrite reduction in heme cd 1 nitrite reductases and globins, − the sensing of NO by H–NOX domains (for example, in mammalian soluble guanylate cyclase, sGC), NO transport in nitrophorins, and the breakdown of NO in respiratory NO reductases (bacterial cNORs and fungal Cyt. P450nor), which reduce two molecules of NO to N 2 O. , Correspondingly, the coordination chemistry of hemes with NO has been investigated in much detail, and model complexes have been developed in all relevant redox states, {FeNO} 6–8 (using the Enemark–Feltham notation where the exponent indicates the number of valence electrons, here the sum of Fe(d) and NO(π*) electrons). ,− Corresponding ferrous heme–HNO, or {FeHNO} 8 , complexes have been generated in myoglobin (Mb) and other heme proteins by Farmer and co-workers . Although these complexes have not been crystallized, 1 H NMR provides clear experimental evidence for the presence of an N-protonated HNO at the active site. , Recently, progress has been made in obtaining corresponding {FeHNO} 8 model complexes. − …”

Section: Introductionmentioning

confidence: 99%

Non-heme High-Spin {FeNO}^6–8 Complexes: One Ligand Platform Can Do It All

et al. 2018

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Heme and non-heme iron-nitrosyl complexes are important intermediates in biology. While there are numerous examples of low-spin heme iron-nitrosyl complexes in different oxidation states, much less is known about high-spin (hs) non-heme iron-nitrosyls in oxidation states other than the formally ferrous NO adducts ({FeNO} in the Enemark-Feltham notation). In this study, we present a complete series of hs-{FeNO} complexes using the TMGtren coligand. Redox transformations from the hs-{FeNO} complex [Fe(TMGtren)(NO)] to its {FeNO} and {FeNO} analogs do not alter the coordination environment of the iron center, allowing for detailed comparisons between these species. Here, we present new MCD, NRVS, XANES/EXAFS, and Mössbauer data, demonstrating that these redox transformations are metal based, which allows us to access hs-Fe(II)-NO, Fe(III)-NO, and Fe(IV)-NO complexes. Vibrational data, analyzed by NCA, directly quantify changes in Fe-NO bonding along this series. Optical data allow for the identification of a "spectator" charge-transfer transition that, together with Mössbauer and XAS data, directly monitors the electronic changes of the Fe center. Using EXAFS, we are also able to provide structural data for all complexes. The magnetic properties of the complexes are further analyzed (from magnetic Mössbauer). The properties of our hs-{FeNO} complexes are then contrasted to corresponding, low-spin iron-nitrosyl complexes where redox transformations are generally NO centered. The hs-{FeNO} complex can further be protonated by weak acids, and the product of this reaction is characterized. Taken together, these results provide unprecedented insight into the properties of biologically relevant non-heme iron-nitrosyl complexes in three relevant oxidation states.

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“…In 1998, the Nobel Prize for Medicine or Physiology was awarded to Ignarro [9] who investigated the influence of Fe II (NO) compounds on the opening of the blood vessels. As a result, more studies on the Fe(NO) compounds and their activity and properties have been carried out, e.g., by Franke and van Eldik [10].…”

Section: Investigated Liquids and Gasesmentioning

confidence: 99%

Mass Transfer in Reactive Bubbly Flows – A Single‐Bubble Study

et al. 2017

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The design of reactors with a dispersed gas in a liquid phase, e.g., bubble columns, is often based on rather roughly estimated parameters. To obtain a better understanding of the influence and interaction of the fluid dynamics and the mass transfer in the presence of a chemical reaction of NO and Fe(EDTA) in the liquid phase, the complex system of a bubbly flow is here reduced to single-bubble investigations. For this purpose, mass transfer is investigated with and without chemical reaction to be able to differentiate between various influencing factors and determined enhancement caused by the chemical reaction. Two experimental setups are applied, namely, the first one with two moving cameras where the velocity is adapted to the rising velocity of the bubble, and the second one is a countercurrent-flow cell.

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Factors That Determine the Mechanism of NO Activation by Metal Complexes of Biological and Environmental Relevance

Cited by 26 publications

References 127 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

Non-heme High-Spin {FeNO}^6–8 Complexes: One Ligand Platform Can Do It All

Mass Transfer in Reactive Bubbly Flows – A Single‐Bubble Study

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Factors That Determine the Mechanism of NO Activation by Metal Complexes of Biological and Environmental Relevance

Cited by 26 publications

References 127 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

Non-heme High-Spin {FeNO}6–8 Complexes: One Ligand Platform Can Do It All

Mass Transfer in Reactive Bubbly Flows – A Single‐Bubble Study

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Product

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Non-heme High-Spin {FeNO}^6–8 Complexes: One Ligand Platform Can Do It All