Polymers enzymatically

Thus, the observed biodegradation of PHB showed coexistence of two different degradation mechanisms in hydrolysis in the polymer enzymatically or nonenzymatically catalyzed degradation. Although nonenzymati-cal catalysis occurred randomly in homopolymer, indicated by loss rate in PHB, at some point in a time, a critical molecular weight is reached whereupon enzyme-catalyzed hydrolysis accelerated degradation at the surface because easier enzyme/polymer interaction becomes possible. 

Natural Product Polymers Living organisms make many polymers, nature s best. Most such natural polymers strongly resemble step-polymerized materials. However, living organisms make their polymers enzymatically, the structure ultimately being controlled by DNA, itself a polymer. 

Croteau R, Kolattukudy P E 1975 Biosynthesis of hydroxy fatty acid polymers. Enzymatic epox-idation of 18-hydroxy oleic acid to 18-hydroxy-cis-9,10-epoxystearic acid by a particulate preparation from spinach Spinacia oleracea). Arch Biochem Biophys 170 61-72... 

While the previous section dealt with the structural elements that define enzyme-responsive polymers, here we will introduce different methods that can be used to integrate an enzyme-responsive functionality with a polymeric material. These methods are placed into three groups. The first method deals with the preparation of enzymatically degradable polymers, the second introduces strategies to incorporate enzyme-responsive linkers into the polymer and the third explores ways to prepare enzyme-responsive polymers enzymatically. 

The resulting polymer possesses the extensivdy conjugated Ti-electrons, and hence, the electrical chai will be carried through the polymer. The surface resistivity of the polymer was found to be ca. 10 a. This value is much higher than that of polyacetylene (10 eo). Therefore, the phenolic polymer enzymatically produced may be useful as a conductive polymer. 

Table 2. Average molecular weights OT phenolic polymers enzymatically produced in 85% dioxan [113]...

When the microorganisms attack the polymer, enzymatic processes such as Krebs cycle increase, which generates water, carbon dioxide, biomass, and other by-products after decomposition. By this method, non-biodegradable materials are converted into nontoxic compounds (Fig. 17.1) (Buchanan etal., 1993a). 

Many complex systems have been spread on liquid interfaces for a variety of reasons. We begin this chapter with a discussion of the behavior of synthetic polymers at the liquid-air interface. Most of these systems are linear macromolecules however, rigid-rod polymers and more complex structures are of interest for potential optoelectronic applications. Biological macromolecules are spread at the liquid-vapor interface to fabricate sensors and other biomedical devices. In addition, the study of proteins at the air-water interface yields important information on enzymatic recognition, and membrane protein behavior. We touch on other biological systems, namely, phospholipids and cholesterol monolayers. These systems are so widely and routinely studied these days that they were also mentioned in some detail in Chapter IV. The closely related matter of bilayers and vesicles is also briefly addressed. 

Other examples illustrating the effect of substituent distribution on properties include (/) enzymatic stabiUty of hydroxyethjlceUulose (16,17) (2) salt compatibihty of carboxymethylceUulose (18,19) and (J) thermal gelation properties of methylceUulose (20). The enzymatic stabUity of hydroxyethylceUulose is an example where the actual position of the substituents within the anhydroglucose units is considered important. Increasing substitution at the C2 position promotes better resistance toward enzymatic cleavage of the polymer chain. Positional distribution is also a factor in the other two examples. 

In the pendent chain systems, the dmg is chemically bound to a polymer backbone and is released by hydrolytic or enzymatic cleavage of the chemical bond. The dmg may be attached directiy to the polymer or may be linked via a spacer group. The spacer group may be used to affect the rate of dmg release and the hydrophilicity of the system. These systems allow very high dmg loadings (over 80 wt %) (89) which decrease the cost of the polymeric materials used ia the systems. These systems have beea examiaed by many iavestigators (111,112). 

All known eight-stranded a/p-barrel domains have enzymatic functions that include isomerization of small sugar molecules, oxidation by flavin coenzymes, phosphate transfer, and degradation of sugar polymers. In some of these enzymes the barrel domain comprises the whole subunit of the protein in others the polypeptide chain is longer and forms several additional domains. An enzymatic function in these multidomain subunits, however, is always associated with the barrel domain. 

Mention should also be made here of the extensive use of poly(vinyl alcohol) in potentially biodegradable applications. At appropriate hydroxyl contents these polymers will dissolve in water (see Chapter 14) and can apparently be conveniently washed away after use as a water-soluble packaging. Biodegradation does, however, appear to be slow and first requires an oxidative step involving enzymatic attack to a ketone such as polyenolketone, which then biodegrades more rapidly. 

At temperatures above Tm, chemical and enzymatic degradation of microbial exopolysaccharides is enhanced. The apparent enhanced stability of microbial exopolysaccharides in their ordered confirmation is thought to be due to the glycosidic bonds in the backbone of the polymer which raises the activation energy. This restricted movement would also restrict access of enzymes and chemicals to the backbone. 

Worldwide suppliers with bioengineering capabilities are displacing established polymers with cost-effective and higher performing plastics. An explosion of novel polymers has been made by enzymatic control. The use of enzymes for polymerization has drastically altered the landscape of polymer chemistry. Processors can request specific properties for each application as opposed to the usual making do with what is available. The supplier can deliver to the processor desired properties requested. 

Hie ester linkage of aliphatic and aliphatic-aromatic copolyesters can easily be cleaved by hydrolysis under alkaline, acid, or enzymatic catalysis. This feature makes polyesters very attractive for two related, but quite different, applications (i) bioresorbable, bioabsorbable, or bioerodible polymers and (ii) environmentally degradable and recyclable polymers. 

The reported molar masses of polyesters obtained by enzymatic catalysis are relatively low, generally below 8000, except for polymers recovered by precipitation.336 This procedure results in the elimination of a soluble fraction consisting of low-molar-mass linear and cyclic oligomers.336 An Mw as high as 46,400 has thus been reported for a poly(tetramethylene decanedioate) obtained... 

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