Silk degradation oxidation

Carbonyl formation due to oxidation results in an infrared band at 1735 cm in silk fibroin (33) but no evidence of this band was found in the Historic and Marine Silks. Degradation of fibroin both as a result of exposure to light (34,35,36) and chemical oxidants (37,38,39) has been shown to notably alter the tyrosine content of fibroin. However no evidence of alteration of the infrared band at 1515 cm attributed to the tyrosine moiety (30) was found in the Historic and Marine Silks in comparison to the Reference Silk. 

Silk deterioration takes place via two main mechanisms oxidation and hydrolysis. Harris (15) has shown that degradation by exposure to light results largely from oxidation and is accompanied by the formation of ammonia nitrogen. Degradation by hydrolysis, on the other hand, is accompanied by the formation of amino nitrogen. In this way, Harris has been able to separate the portions of fiber deterioration that can be attributed to oxidation and hydrolysis. 

Effect of Fiber Degradation on the Corrosion Solution. Hydrolysis and oxidation of protein and cellulose have been described in the literature primarily with the focus on degradation in industrial processing conditions. In alkaline conditions, amino acids are released from silk in a chain unzipping mechanism in acidic conditions, the scissions are random (8,9). As the polymer deteriorates, free carboxyl and amine end groups are formed. Tyrosine oxidizes to a quinone this reaction gives aged silk its yellow coloration. Amorphous areas of the fiber are attacked first. 

Silk fibrion is highly sensitive to oxidising agents like hypochlorite and chlorite solutions. Oxidation and substitution in the benzene ring of tyrosine is responsible for degradation of silk with the formation of chloro-amino acids, ketonic acids and chloramine in several stages [105]. 

As for linen and other natural fibres, silk is sensitive to a variety of environmentally driven degradative processes, though in most cases the actual damage is caused by hydrolysis and/or oxidation. Attack on the polymer chains is generally initiated in the amorphous zones as a consequence of their more open structure and the incidence of reactive amino-acids (specifically histidine, lysine, phenylalanine, proline, threonine, tryptophan, tyrosine and valine). 

Besides acids and alkalis, strong oxidants used to bleach silk also have the capacity to seriously degrade the fibres. The most significant reactions occur at tyrosine and threonine side-chains, resulting in their oxidation to acids and the breaking of surrounding peptide bonds cross-links are also generated, e.g. between lysine and tyrosine residues. 

Sericin is recovered during the various stages of producing raw silk. Sericin is oxidation-, bacterial-, and UV-resistant, and it absorbs and releases moisture rapidly. Sericin can be cross-linked, copolymerized, and blended with other macromolecular materials, especially artificial polymers. The materials modified with sericin and sericin composites are useful as degradable biomaterials, biomedical materials, polymers, functional membranes, fibers, and fabrics [26]. 

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