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Hydrogen Atom Abstraction by a Mononuclear Ferric Hydroxide Complex: Insights into the Reactivity of Lipoxygenase.

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Title: Hydrogen Atom Abstraction by a Mononuclear Ferric Hydroxide Complex: Insights into the Reactivity of Lipoxygenase.
Authors: Goldsmith, Christian R.1, Stack, T. Daniel P.1 stack@stanford.edu
Source: Inorganic Chemistry. 7/24/2006, Vol. 45 Issue 15, p6048-6055. 8p. 3 Charts, 4 Graphs.
Subjects: Atomic hydrogen, Ferric hydroxides, Complex compounds, Lipoxygenases, Reactivity (Chemistry)
Abstract: The lipoxygenase mimic [FeIII(PY5)(OH)](CF3SO3)2 is synthesized from the reaction of [FeII(PY5)(MeCN)](CF3SO3)2 with iodosobenzene, with low-temperature studies suggesting the possible intermediacy of an Fe(IV) oxo species. The Fe(lll)-OH complex is isolated and identified by a combination of solution and solid-state methods, including EPR and IR spectroscopy. [FIII(PY5)(OH)]2+ reacts with weak X-H bonds in a manner consistent with hydrogen-atom abstraction. The composition of this complex allows meaningful comparisons to be made with previously reported Mn(lll)-OH and Fe(lll)-OMe lipoxygenase mimics. The bond dissociation energy (BDE) of the O-H bond formed upon reduction to [FeII(PY5)(H2O)2+ is estimated to be 80 kcal mol-1, 2 kcal mol-1 lower than that in the structurally analogous [MnII(PY5)(H2O)]2+ complex, supporting the generally accepted idea that Mn(lll) is the thermodynamically superior oxidant at parity of coordination sphere. The identity of the metal has a large influence on the entropy of activation for the reaction with 9,10-dihydroanthracene; (MnIII(PY5)(OH)2+ has a 10 eu more negative ΔS‡ value than either [FeIII(PY5)(OH)]2+ or [FeIII(PY5)(OMe)]2+, presumably because of the increased structural reorganization that occurs upon reduction to [MnII(PY5)(H2O)]2+. The greater enthalpic driving force for the reduction of Mn(lll) correlates with [MnIII(PY5)(OH)]2+ reacting more quickly than [FeIII(PY5)(OH)]2+. Curiously, [FeIII[PY5)(OMe)]2+ reacts with substrates only about twice as fast as [FeIII(PY5)(OH)]2+, despite a 4 kcal mol-1 greater enthalpic driving force for the methoxide complex. [ABSTRACT FROM AUTHOR]
Copyright of Inorganic Chemistry is the property of American Chemical Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Hydrogen Atom Abstraction by a Mononuclear Ferric Hydroxide Complex: Insights into the Reactivity of Lipoxygenase.
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  Data: <searchLink fieldCode="AR" term="%22Goldsmith%2C+Christian+R%2E%22">Goldsmith, Christian R.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Stack%2C+T%2E+Daniel+P%2E%22">Stack, T. Daniel P.</searchLink><relatesTo>1</relatesTo><i> stack@stanford.edu</i>
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  Data: <searchLink fieldCode="JN" term="%22Inorganic+Chemistry%22">Inorganic Chemistry</searchLink>. 7/24/2006, Vol. 45 Issue 15, p6048-6055. 8p. 3 Charts, 4 Graphs.
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  Data: <searchLink fieldCode="DE" term="%22Atomic+hydrogen%22">Atomic hydrogen</searchLink><br /><searchLink fieldCode="DE" term="%22Ferric+hydroxides%22">Ferric hydroxides</searchLink><br /><searchLink fieldCode="DE" term="%22Complex+compounds%22">Complex compounds</searchLink><br /><searchLink fieldCode="DE" term="%22Lipoxygenases%22">Lipoxygenases</searchLink><br /><searchLink fieldCode="DE" term="%22Reactivity+%28Chemistry%29%22">Reactivity (Chemistry)</searchLink>
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  Data: The lipoxygenase mimic [FeIII(PY5)(OH)](CF3SO3)2 is synthesized from the reaction of [FeII(PY5)(MeCN)](CF3SO3)2 with iodosobenzene, with low-temperature studies suggesting the possible intermediacy of an Fe(IV) oxo species. The Fe(lll)-OH complex is isolated and identified by a combination of solution and solid-state methods, including EPR and IR spectroscopy. [FIII(PY5)(OH)]2+ reacts with weak X-H bonds in a manner consistent with hydrogen-atom abstraction. The composition of this complex allows meaningful comparisons to be made with previously reported Mn(lll)-OH and Fe(lll)-OMe lipoxygenase mimics. The bond dissociation energy (BDE) of the O-H bond formed upon reduction to [FeII(PY5)(H2O)2+ is estimated to be 80 kcal mol-1, 2 kcal mol-1 lower than that in the structurally analogous [MnII(PY5)(H2O)]2+ complex, supporting the generally accepted idea that Mn(lll) is the thermodynamically superior oxidant at parity of coordination sphere. The identity of the metal has a large influence on the entropy of activation for the reaction with 9,10-dihydroanthracene; (MnIII(PY5)(OH)2+ has a 10 eu more negative ΔS‡ value than either [FeIII(PY5)(OH)]2+ or [FeIII(PY5)(OMe)]2+, presumably because of the increased structural reorganization that occurs upon reduction to [MnII(PY5)(H2O)]2+. The greater enthalpic driving force for the reduction of Mn(lll) correlates with [MnIII(PY5)(OH)]2+ reacting more quickly than [FeIII(PY5)(OH)]2+. Curiously, [FeIII[PY5)(OMe)]2+ reacts with substrates only about twice as fast as [FeIII(PY5)(OH)]2+, despite a 4 kcal mol-1 greater enthalpic driving force for the methoxide complex. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of Inorganic Chemistry is the property of American Chemical Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1021/ic060621e
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        Text: English
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        PageCount: 8
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      – SubjectFull: Atomic hydrogen
        Type: general
      – SubjectFull: Ferric hydroxides
        Type: general
      – SubjectFull: Complex compounds
        Type: general
      – SubjectFull: Lipoxygenases
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      – SubjectFull: Reactivity (Chemistry)
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      – TitleFull: Hydrogen Atom Abstraction by a Mononuclear Ferric Hydroxide Complex: Insights into the Reactivity of Lipoxygenase.
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              Text: 7/24/2006
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              Y: 2006
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