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A mechanism has been found that explains the distribution of products obtained in the isomerizations of long‐chain alkanes on ZSM‐22 and SAPO‐11 catalysts so well that it should now be possible to tailor reactions for the synthesis of branched hydrocarbons. The reactions occur at the external surface of the catalyst according to a lock‐and‐key model (shown on the right); thus, the classical concept of shape‐selective catalysis within micropores is substantially extended.

Many attempts have been made to mimic the catalytic oxidative properties of the enzyme cytochrome P-450. For homogeneous systems the mechanisms of oxidation can be readily determined but proper mimicry of the protein environment is difficult to achieve. Heterogeneous mimics have been designed that use organometallic complexes encapsulated in the supercages of zeolites, which enables control of selectivity and inhibition of auto-oxidation. But these systems do not show any mechanistic analogy with the enzymatic process, and the oxidation rates tend to be low. Here we report a composite catalytic system that achieves realistic mimicry of cytochrome P-450 as well as catalytic turnover rates that make the system industrially viable. Our catalyst incorporates iron phthalocyanine complexes encapsulated in crystals of zeolite Y, which are in turn embedded in a polydimethylsiloxane membrane. The polymer acts as a mimic of the phospholipid membrane in which cytochrome P-450 resides, acting as an interface between two immiscible phases and avoiding the need for solvents or phase-transfer agents. This system oxidizes alkanes at room temperature at rates comparable to those of the enzyme. The observation of a large kinetic isotope effect and the preferential oxidation of tertiary C-H bonds suggest close mechanistic similarities to the enzymatic process.

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COMMUNICATIONS spectroscopy the concentrations of the reactants were chosen 15 times higher (about 0 . 3~) , which is the upper limit of solubility for the compounds I b. Id. and l e .