Evolution of Synthetic Polymers with Enzyme-like Catalytic Activities - Artificial Enzymes - page 87

3.4
Prospectives

The last few decades has seen substantial progress in the fabrication of synthetic poly-
mers with biocatalytic properties. A range of polymers has been examined as structural
frameworks for the attachment of catalytic groups. For homogeneous catalysts, highly
branched polyethylenimines have proved particularly versatile. Modified polystyrenes
have served well as foundations for heterogeneous catalysts.
Increasingly sophisticated catalytic domains have been synthesized and used as ad-
ducts to the framework polymers. These synthetic macromolecules show substantially
enhanced catalytic effects on hydrolytic reactions, decarboxylation, Schiff base hydro-
lysis, aromatic nucleophilic substitution, and oxidation [63-69]. Several of these syn-
thetic polymers are effective peptidases and nucleases.
The local environments of catalytic domains need further modification to achieve
steric and enantio-selectivity in substrates. One might also alter the polymer frame-
work, which exerts a global influence on the local domains of active sites. Enzymes
have catalytic sites attached to polypeptide framework, constituted of successive pep-
tide linkages. Within a protein the concentration of amide groups is 12-15 M [70]. An
amide group has a dipole moment [71] of 3.8 Debye units, which is larger than that of a
water molecule (1.8 Debye units). Thus the protein framework provides a pervasive
highly polar environment. A similar environment could be created in polyethyleni-
mines, for example, by attaching polypeptide chains to some of the primary and sec-
ondary nitrogen loci of the polymer. These should exert a global polar influence on the
catalytic domains.
Over a period of about 10 9 years (one gigaennium) natural selection has led to en-
zymes with remarkable catalytic properties. Perhaps, in the early decades of the 3rd
millennium, directed selection will produce equally effective and versatile polymer
biocatalysts.

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