ENZYME MIMICS INSIDE

The design of bionanoreactors is based on encapsulation/insertion of active compounds (proteins, enzymes, mimics) inside polymeric supramolecular assemblies, such as dendrimers, capsules, and vesicles, in which they can act in situ while being protected from proteolytic attack [3,6]. These supramolecular assemblies should allow the passage of products or substrates to the inner spaces where the active compounds are located in order to support reactions confined within their structures. Various approaches to providing accessibility to the inner reaction space of the polymer assemblies are presented, even though not all have been used in the design of nanoreactors, in order to give an overview of the variety of solutions that can be expected to advance this field of science. 

Another advance seems likely through the use of zeolites as enzyme mimics.This centers on the reactions of organometallics with zeolite internal surfaces. The best-known example is the production of a [Co (bipyridyl)(terpyridyl)] + complex inside the main cavity of zeohte Y that can selectively and reversibly absorb oxygen from the air. The catalytic potential of a Co phthalocyanine moiety prepared in the Y cavity has also been demonstrated. 

Arya et al. used solid phase synthesis to prepare immobilised dendritic catalysts with the rhodium centre in a shielded environment to mimic nature s approach of protecting active sites in a macromolecular environment (e.g. catalytic sites inside enzymes) [51], Two generations PS immobilised rhodium-complexed dendrimers, 6 and the more shielded 7, were synthesised.The PS resin immobilised rhodium-complexed dendrimers were used in the hydroformylation of styrene, p-methoxystyrene, vinyl acetate and vinyl benzoate using a total pressure of 70 bar 1 1 CO/H2 at 45 °C in CH2C12. 

One of the first applications of dendrimers as organometallic hosts was their use as enantioselective catalysts. Indeed, dendrimers that are functionalized with transition metals in the core potentially can mimic the properties of enzymes. Brunner introduced the term dendrizymes for core-functionalized transition metal catalysts which might be used in enantioselective catalysis. The dendrimeric organometallic complex shown in Figure 34 is an example of such a dendrizyme inside which the chiral dendritic branches create a chiral pocket around the transition metal. 

Phthalocyanine complexes within zeolites have also been prepared by the ship-in-a-bottle method (see Section 6.6), and have subsequently been investigated as selective oxidation catalysts, where their planar metal-N4 centres mimic the active sites of enzymes such as cytochrome P450, which is able to oxidize alkanes with molecular oxygen. Cobalt, iron and ruthenium phthalocyanines encapsulated within faujasitic zeolites are active for the oxidation of alkanes with oxygen sources such as iodosobenzene and hydroperoxides. Following a similar route, Balkus prepared Ru(II)-perchloro- and perfluorophthalocyanines inside zeolite X and used these composites for the selective catalytic oxidation of alkanes (tert-butylhydroperoxide). The introduction of fluorinated in place of non-fluorinated ligands increases the resistance of the complex to deactivation. 

In order to mimic biological cell membranes, biomolecules have been used either to decorate the membrane surface or be inserted directly inside the membrane. Various enzymes, such as laccase, GOx, or HRP, have been reported for decorating planar membranes. These enzymes were either chemically linked to the membrane by reactions such as esterification and amidation, or just physically adsorbed. For example, physically adsorbed laccase on copolymer membranes displayed a higher activity than free... 

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