Mechanisms of iron porphyrin catalyzed epoxidation of alkenes and the concomitant N-alkylhemin formation
The concomitant N-alkylhemin formation during iron(III) porphyrin catalyzed epoxidation of alkenes is studied in a homogeneous system using PFIB as the oxidant. The system is a model for the enzyme cytochrome P-450. A second N-alkyl species besides the well-documented 1[degrees] N-alkylhemin is observed during the oxidation of terminal alkenes. It is unstable thus decomposes under the reaction conditions. It is also a catalyst for alkene epoxidation by PFIB. The kinetics are partially resolved and rate constants are estimated for the formation of both N-alkylhemins, for the decomposition of the 2[degrees] N-alkylhemin, and for epoxidation by the hemin and the N-alkylhemins. The partition ratio is measured by a kinetic method, which provides better insight for the mechanism of both N-alkylation and epoxidation than the measurement by product analysis using heterogeneous systems. The authors suggest that alkenes could reversibly inhibit cytochrome P-450 through the formation of the unstable N-alkylporphyrin species. A potential molecular probe for the alkene radical cation intermediate in the proposed electron transfer mechanism for hemin-catalyzed epoxidation of alkenes is tested. The hexadueterio-dicyclopentadiene is prepared through simple reactions. The results do not confirm the electron transfer mechanism. Limitations of this probe are also discussed. Model compounds for hemerythrin are designed using rigid bicyclic skeletons, e.g., norbornadiene. The difficulties in synthesizing them are discussed.
- Research Organization:
- California Univ., San Diego, La Jolla, CA (United States)
- OSTI ID:
- 7302349
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALKENES
CARBOXYLIC ACIDS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
COMPLEXES
HEME
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROCARBONS
IRON COMPLEXES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDATION
PIGMENTS
PORPHYRINS
SYNTHESIS
TRANSITION ELEMENT COMPLEXES