Reaction mechanisms
Gas-phase rates of heme-model olefin epoxidation
Open access · cc by · source: Europe PMC
FT-ICR and DFT show iron(IV)–oxo porphyrin cation radicals epoxidize olefins with rates that track substrate ionization energy.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
This library holds 6 empirical chemistry papers on reaction mechanisms with isolated findings, rates or spectra rather than reviews.
Evidence for the claim as stated.
FT-ICR and DFT show iron(IV)–oxo porphyrin cation radicals epoxidize olefins with rates that track substrate ionization energy.
Evidence for the claim as stated.
Computed pathways and experimental branching can disagree; a rate constant on one model substrate does not fix the mechanism of a catalytic cycle.
Evidence for the claim as stated.
DFT is often a supporting assignment tool, not the primary result. Periodic-DFT on a Zn phenanthroline–maleate crystal gave a 3.45 eV gap; gas-phase heme-model pathways accompanied FT-ICR epoxidation rates with estimated ±30% rate error; ligand-centered versus metal-centered redox in cobalt PY4/PY3PZ complexes was parsed with DFT after electrocatalysis.
Evidence for the claim as stated.
Gas-phase ions, aqueous electrocatalysis, and a crystal gap are different DFT worlds. Naked [Feᴵⱽ(O)(porphyrin)]⁺ epoxidation in FT-ICR is not P450 Compound I in water; the Zn crystal gap was not tested in a device; cobalt HER overpotential is an electrochemical measurement with DFT as interpretation.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Computed pathways and experimental branching can disagree; a rate constant on one model substrate does not fix the mechanism of a catalytic cycle.
Gas-phase ions, aqueous electrocatalysis, and a crystal gap are different DFT worlds. Naked [Feᴵⱽ(O)(porphyrin)]⁺ epoxidation in FT-ICR is not P450 Compound I in water; the Zn crystal gap was not tested in a device; cobalt HER overpotential is an electrochemical measurement with DFT as interpretation.
Study at a glance
- Design
- Other — Gas-phase FT-ICR bimolecular rate constants for [FeIV(O)(TPFPP+·)]+ with olefins plus DFT
- N
- Physical-organic kinetics panel of olefins — not a sample-N study
- Population
- Gas-phase iron-oxo porphyrin cation and olefin substrates
- Outcome
- Epoxidation rate constants and efficiency versus olefin ionization potential
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
Gas-phase rates of heme-model olefin epoxidation
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Absolute rate constants carry an estimated ±30% error.
The reproducibility of the k exp values was within 10%, while the error of the absolute rate constants is estimated to be ±30%.
Terminal olefins show efficiencies from 0.001% to 0.08%.
The gas phase reactivity of [Fe IV (O)(TPFPP + ˙)] + spans a wide range of reaction efficiencies, with values varying from 0.001% to 0.08% for terminal olefins, like ethene and propene, up to ca. 50% for electron-rich monoterpenes.
Key findings
All olefins undergo oxygen-atom transfer; electron-rich substrates also do hydride and charge transfer. Efficiencies run from 0.001–0.08% for terminal olefins up to about 50% for electron-rich monoterpenes. kH/kD ≈ 1 rules out rate-limiting H-atom transfer, and rates scale with ionization potential.
Methodology
Authors generated [FeIV(O)(TPFPP+·)]+ from iodosylbenzene at low temperature, measured bimolecular rate constants in an FT-ICR cell against a panel of olefins, and computed epoxidation pathways with DFT on porphine models.
Limitations
These are naked ions in the gas phase, not protein-bound P450 Compound I in water; axial-ligand and solvent effects are only treated computationally, and absolute rate errors are estimated at ±30%.
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