Biopolymer macromolecules Degradation

As noted above, the nucleophilicity of water allows it to enter into reactions that cause the degradation of biological macromolecules, including DNA and proteins. Analogous problems are associated with the assembly of biopolymers. In water, the assembly of nucleosides from component sugars and nucleobases, the assembly of nucleotides from nucleosides and phosphate, and the assembly of oligonucleotides from nucleotides are all thermodynamically uphill in water. 

Based on detailed analyses of the chemical nature of SOM, Hatcher and Spiker (1988) have extended this humification model to include other resistant biopolymers, including plant cutin and suberin, and microbial melanins and paraffinic macromolecules. During decomposition, these biopolymers are selectively preserved and modified to become part of what can be operationally defined as humin (acid and alkali insoluble component of humus) (Hatcher and Spiker, 1988 Rice, 2001). The humin becomes progressively enriched in acidic groups leading to the formation of first humic acids and then fulvic acids, which under this degradative scheme of SOM formation would be regarded as the most humified of humic substances (Stevenson, 1994). 

Biological degradation refers to the microbial breakdown of macromolecules of polymers by bacteria during storage or in the reservoir. Although the problem is more prevalent for biopolymers, biological attack may also occur for synthetic polymers. It has been found that HPAM can provide nutrition to sulfate-reducing bacteria (SRB). As the number of SRB increases, HPAM viscosity decreases. For example, when the number of SRB reaches 36000/mL, the viscosity loss of HPAM of 1000 mg/L is 19.6% (Luo et al., 2006). 

The most common biopolymers derived from animals are chitin and chito-san. Chitin is a macromolecule found in the shells of crabs, lobsters, shrimps, and insects. The primary unit in the chitin polymer is 2-deoxy-2-(acetylamino) glucose. Chitin can be degraded by chitinase. Chitosan is a modified natural carbohydrate polymer derived from deactylation of chitin, which occurs principally in animals of the phylum Arthropoda. Chitosan is also prepared from squid pens. Chitin is insoluble in its native form but chitosan, the partly deacetylated form, is water soluble. The materials are biocompatible and have antimicrobial activities as well as the ability to absorb heavy metal ions [16]. 

To achieve biodegradation and biorecycling of biopolymeric systems. Mother Nature has set up very sophisticated processes based on enz)nnes and thus on cells. The most attractive biodegradable polymers are the biopolymers issued from living systems. However enz5miatic phenomena are very sophisticated and selective. Consequently, they rapidly fail degrading biopolymers when the corresponding macromolecules are chemically modified as it is often the case when one wants to fulfil requirements related to biofunctionality. 

Lignins usually comprise between 25 and 30% wt/wt of woody tissues in hardwoods and softwoods, respectively. Unfortunately, they cannot be removed from the constituent cell walls without concomitant degradation. In this connection difficulties are invariably encountered because the majority of interunit linkages in lignin macromolecules are relatively stable, much more so than those in most other biopolymers. Thus isolated lignin preparations differ from one another in the extent to which they have been modified with respect to the native macromolecules. 

The natural biopolymers, to which HA belongs, are not polydispersed polymers due to the matrix nature of their synthesis. The nature of the biochemical synthesis is determined by the matrix the enzyme upon which the triopolymer is synthesized. Nevertheless, during biopolymer extraction and purification processes they degrade in one way or another. For example, polygalactomannan, different types of cellulose (wood or cotton), chitosan and hyaluronan are isolated as a wide range of the relatively narrow dispersed macromolecule fractions. 

Pritchard, N. J., Hughes, D. E., Peacocke, A. R. The ultrasonic degradation of biological macromolecules under condition of stable cavitation. 1. Biopolymers 4,259 (1966). 

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