Biocatalytic plastics.

It may seem like an unlikely union, but the marriage between enzyme technology and polymer chemistry could provide fast, environmentally friendly organic syntheses

Enzymes are remarkable catalysts. They can accelerate the rate of a reaction by huge amounts. In fact, the catalytic power of enzymes cannot be equalled by man-made catalysts. For example, the enzyme catalase, which catalyses the decomposition of hydrogen peroxide into water and molecular oxygen, gives a reaction turnover more than 11 orders of magnitude higher than the uncatalysed reaction, and seven orders of magnitude faster than man-made platinum-based heterogeneous catalysts.[1] Amazingly, catalase is neither unique nor is it the fastest biocatalyst.

Enzymes are also highly selective and can accept a wide range of complex molecules as substrates, catalysing reactions with unparalleled chiral (enantio-) and positional (regio-) selectivities.[2] Such high selectivity means efficient reactions with few byproducts, making enzymes an environmentally friendly alternative to conventional chemical catalysts.[3] Moreover, because of this high selectivity, enzymes can be used in simple transformations without the need for tedious 'blocking' and 'deblocking' steps that are commonplace in enantio- and regioselective organic synthesis.[4] Enzymes also work best under mild conditions - ambient temperatures and pressures, neutral pH and low ionic strength.[5]

Selective catalysis is an emerging requirement for the chemical industry, and the unique attributes of enzymes have resulted in myriad applications, particularly in the food and pharmaceutical industries, where high reaction selectivity on complex substrates is critical.[7] Recent advances in enzymatic catalysis have been extended to the synthesis of speciality chemicals and polymers,[8,9] and to some bulk chemicals.[10] However, the widespread use of enzymes in the chemical industry has been hampered by their relatively poor stability and activity under the often extreme conditions found in chemical processing.

Plastics have many useful physical properties, such as mechanical strength, chemical inertness and thermal resistance, and it occurred to us and others that it may be possible to combine the catalytic power of enzymes with the physical strength and versatility of plastics to generate biocatalytically active materials. In effect, marrying the fields of enzyme technology and polymer science and engineering.

Such 'biocatalytic plastics'[11-13] can be prepared using methods well known in polymer synthesis. This opens up a tantalising array of possibilities for stable and active biocatalysts for selective transformations, environmentally benign catalysts for the degradation of toxic compounds, and catalyst incorporation into polymeric materials such as self-cleaning paints, coatings, and membranes for chemical, medical and industrial applications.

Fundamental technical breakthrough

At first glance, it appears that bridging the fields of enzyme technology and polymer science should not be too difficult. Forming polymeric materials in the presence of enzymes had been done by Karel Martinek and co-workers at Moscow State University in 1977 using water-soluble monomers such as acrylamide and (meth)acrylic acid.[14] However, water-soluble monomers are limited in number and have specific end-use applications, primarily as hydrogels rather than rugged …