Chitosans enzymatic modification

The enzymatic treatment of chitosan in the presence of tyrosinase and phenol derivatives produced new materials based on chitosan.91 During the reaction, unstable o-quinones were formed, followed by the reaction with the amino group of chitosan to give the modified chitosan. The tyrosinase-catalyzed modification of chitosan with phenols dramatically altered rheological and surface properties of chitosan. The modification with chlorogenic acid onto chitosan conferred the water solubility of chitosan under basic conditions.92 A new water-resistant adhesive was developed by the tyrosinase-catalyzed reaction of 3,4-dihydroxyphenethylamine and chitosan.93 Poly(4-hydroxystyrene) was modified with aniline by using tyrosinase catalyst.94 The incorporated ratio of aniline into the polymer was very low (1.3%). 

Chitosan is known to have many biological activities, which are affected by MW or chain length and DD. Therefore, desired properties of chitosan or its derivatives that are necessary to exhibit different biological activities can be obtained by chemical and enzymatic modification. In this chapter, antihypertensive actions of chitosan and its derivatives are discussed. 

This enzymatic modification of chitosan was applied for the synthesis of a chitosan-catechin conjugate. The formation of a Michael-type adduct and/or Schiff base was proposed during the PPO-catalyzed conjugation of catechin with chitosan [60]. Rheological measurement demonstrates that the resulting conjugate behaves as an associative thickener. 

It has been established that the process of enzymatic destmction of chitosan (CHT) film specimens obtained from acetic acid solution experiences the influence of the prehistory of film formation, including the concentration of acetic acid used for films preparation and the thermal film modification. 

Chitosan (N-deacetylated derivative of chitin), a naturally abundant mucopolysaccharide and its derivatives containing COSs were prepared by enzymatic and chemical modification. In addition, chitosan and its derivatives showed potent antioxidant activity. Moreover, chemical modification of chitosan can be easily provided with more powerful antioxidative compounds. Considering the above findings, it is expected that chitosan and its derivatives contained COSs wonld be promising candidates as potent antioxidative agents leading to their valuable use in neutracenticals and expand their applications in Biomedicine. 

Chitosan and its derivatives produced by enzymatic and chemical modification have become popular biomolecules during the past few decades because of their unique biological aspects. In addition, they also showed high potential antihypertensive activity. Moreover, the chemical modification of chitosan can easily provide more powerful antihypertensive compounds. Therefore, it is expected that these biomolecules would be promising candidates as antihypertensive agents. 

Major chitosan functionalization could be carried out by (1) substitution, introducing small functional groups to the chitosan backbone, and (2) depolymerization by chemical, physical or enzymatic treatments. Moreover, further chemical modifications of the functionalized chitosans can be performed in order to extend the range of their applications [47]. 

Along with physical modification, chitosan is most commonly modified by a number of chemical techniques including traditional chemical modification techniques such as photochemical, enzymatic, radiation, and plasma-induced graft copolymerization. Figure 1.6 summarizes some of the commercially used modification techniques for surface modification of chitosans. 

PPO was used as catalyst for modification of natural polymers. The enzymatic treatment of a chitosan film in fhe presence of PPO and phenol derivatives produced a new material of chitosan derivatives [ 55]. During the reaction, unstable o-quinones were formed, which then reacted with chitosan to yield modified chitosans. In the enzymatic treatment of p-cresol with a low concentration of chitosan (< 1%), the reaction solution was converted into a gel [56]. 

The present paper deals with enzymatic biodegradation of film chitosan coatings which can be used for protecting open wounds (burning, surgical ones) and the means of their modification for extending the service life. 

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