Polymer chemistry, enzyme catalysi

The frequency with which two reactive species encounter one another in solution represents an upper bound on the bimolecular reaction rate. When this encounter frequency is rate limiting, the reaction is said to be diffusion controlled. Diffusion controlled reactions play an important role in a number of areas of chemistry, including nucleation, polymer and colloid growth, ionic and free radical reactions, DNA recognition and binding, and enzyme catalysis. 

To date, the limited use of the enantioselectivity of biocatalysts in polymerization conditions and the lengthy synthetic procedures required to prepare optically pure monomers have hampered full exploitation of chemo-enzymatic approaches in polymer chemistry. However, a combined multidisciplinary effort at the interface of biocatalysis, polymer chemistry and organic catalysis, will allow to convert methods well-established in organic chemistry such as tandem catalysis, to the field of polymer chemistry. Undoubtedly, in the near future the exploitation of the selectivity of enzymes and the advantages of chemo-enzymatic approaches in a wide variety of polymerization chemistries will be recognized. This may lead to a paradigm shift in polymer chemistry and allow a higher level of structural complexity in macromolecules, reminiscent to those found in Nature. 

Other grafts to natural materials are exemplified by Dordick s work [173] in which he produced polyesters from sugars and polycarboxylates by enzyme catalysis of the condensation polymerization. These polymers and the method of synthesis may well be the future of renewable resource chemistry. 

In this chapter, the focus is on in vitro enzyme catalysis for vinyl polymerization. To the best of our knowledge, prior to the work of Derango et al. (1992) there is a single short report showing the formation of low molecular weight vinyl polymers when studied in a suspension of Escherichia coli in the presence of methyl methacrylate [15,16]. Unhke polyaromatics, vinyl polymerization offers better control of polymer characteristics, as has been demonstrated with ternary systems (enzyme, oxidant, and initiator such as b-diketone). The number of different vinyl monomer chemistries investigated for susceptibility toward enzymatic polymerization (1-12) is fewer than reported aromatics, as is the extent of literature covering these types of syntheses. In addition, the discovery of multienzymatic approaches for the synthesis of antioxidant-functionalized vinyl polymers provides new impetus for the use of enzymatic methods related to vinyl polymers. 

In conclusion, molecularly imprinted polymers and related materials have every potential to become popular tools in analytical chemistry, catalysis, and sensor technology. Obviously this will require further research, especially in the problem areas of MI mentioned above. Nevertheless, the author of this contribution fully expects that in the near future MIP will become real competitors for biological enzymes or antibodies, and thus will have a major impact on the whole area of biotechnology. 

A somewhat different but mechanistically related reaction is the [2 -f 3] cycloaddition of a functionalized alkyne or nitrile to an azide to form a disubstituted triazole (120) or tetrazole ring (121, 122), linking the respective functionalities irreversibly (Scheme 14b). This click chemistry was used by Sharpless and co-workers (120) in 2001 as a tool to probe biochemical catalysis and substrate activation. The ease of the Cu(I)-catalyzed reaction has created a true explosion (120-160) of simple coupling-functionalization chemistry of all types of biochemical components (sugars, DNA, proteins, enzymes, substrates, inhibitors) (131, 135, 136, 139, 142, 155, 157-160), polymers (126, 134, 140, 147, 154),... 

If there is a topic that is important to all branches of chemistry, it is catalysis. The gasohne used as fuel, the polymers used in fabrics, the sulfuric acid used in an enormous range of chemical processes, and the ammonia used as fertiUzer are all produced by catalyzed reactions. In addition, many biological reactions are catalyzed by materials known as enzymes. As a result, it would be hard to overemphasize the importance of catalysis. In this section, we wiU describe some processes in which catalysts play an important role. 

Considerable gains have recently been made in the research of polymer catalysis which has emerged from the interaction of the fields of macromolecular, coordination and catalytic chemistry. Using synthetic macromolecules one can create polymeric catalysts which function like enzymes and almost simulate their activity and selectivity. Consequently, polymer catalysis could enable the high-yield manufacture of industrially important products at low-reaction volumes involving minimal energy consumption. 

The first chapter of the book deals with enzyme-like eatalysis by synthetic polymers - catalysis by polymeric acids and bases, amphoteric polyelectrolytes and nonionic polymers. Because coordination compounds of metal ions with macromolecular ligands are interesting with regard to bioinorganic chemistry, this book elucidates some problems involving the catalysis by water-soluble polymer-metal complexes. Ester hydrolysis, hydrogen peroxide decomposition, oxidation of disubstituted phenols, hydroquinones, mercaptoalcohols and other types of reaction are chosen as model processes. A section devoted to interfacial catalysis is also included. 

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