Hydrogen-Bonding Interactions Trigger a Spin-Flip in Iron(III) Porphyrin Complexes

A key step in cytochrome P450 catalysis includes the spin‐state crossing from low spin to high spin upon substrate binding and subsequent reduction of the heme. Clearly, a weak perturbation in P450 enzymes triggers a spin‐state crossing. However, the origin of the process whereby enzymes reorganize...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2015-04, Vol.54 (16), p.4796-4800
Main Authors: Sahoo, Dipankar, Quesne, Matthew G., de Visser, Sam P., Rath, Sankar Prasad
Format: Article
Language:English
Subjects:
Chlorides
Communications
Cytochrome P-450 Enzyme System - chemistry
Cytochrome P-450 Enzyme System - metabolism
Electronic structure
Enzymes
Ferric Compounds - chemistry
Hydrogen Bonding
Iron
Mathematical analysis
Molecular Conformation
Perturbation methods
porphyrinoids
Porphyrins - chemistry
Quantum Theory
Spectroscopy, Mossbauer
spin crossover
structure elucidation
Switches
Switching
Thermodynamics
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Summary:A key step in cytochrome P450 catalysis includes the spin‐state crossing from low spin to high spin upon substrate binding and subsequent reduction of the heme. Clearly, a weak perturbation in P450 enzymes triggers a spin‐state crossing. However, the origin of the process whereby enzymes reorganize their active site through external perturbations, such as hydrogen bonding, is still poorly understood. We have thus studied the impact of hydrogen‐bonding interactions on the electronic structure of a five‐coordinate iron(III) octaethyltetraarylporphyrin chloride. The spin state of the metal was found to switch reversibly between high (S=5/2) and intermediate spin (S=3/2) with hydrogen bonding. Our study highlights the possible effects and importance of hydrogen‐bonding interactions in heme proteins. This is the first example of a synthetic iron(III) complex that can reversibly change its spin state between a high and an intermediate state through weak external perturbations. Spin control: The electronic structure of a five‐coordinate iron(III) porphinato chloride has been found to depend on the presence of hydrogen‐bonding interactions, with the iron center switching reversibly between a high (S=5/2) and intermediate spin (S=3/2) state. Computational calculations clearly support the experimentally assigned spin state.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201411399