Abstract
In this work specimens of chitosan which have been cross-linked covalently and ionically with different oxocarbon and pseudo-oxocarbon anions have been synthesised and characterized using infrared and Raman spectroscopic techniques, solid state 13C nuclear magnetic resonance (NMR) and by thermogravimetry. According to the spectroscopic and thermal results, ionically crosslinked chitosans are obtained with squarate, croconate and rhodizonate ions as crosslinking agents, whereas covalently crosslinked chitosan can be obtained when squaric acid is used as the crosslinking agent; the same products are not observed when the pseudo-oxocarbon anion croconate violet is used, which can be attributed to the low basic strength of the crosslinking species.
Highlights
Chitosan is a copolymer of β-(1→4)-linked 2-acetamido2-deoxy-D-glucopyranose and 2-amino-2-deoxy-Dglucopyranose.1 This polycationic biopolymer can be obtained by partial deacetylation of chitin extracted from crustaceans.2 The main parameters influencing the characteristics of chitosan are its molecular weight (MW) and degree of deacetylation (DD), representing the proportion of deacetylated units
These chemical modifications can sometimes only be achieved at the expense of a decreased thermal stability and the purpose of this study is to evaluate the potential improvements in the chemical behavior against any observed detrimental factors in the thermal properties of a range of crosslinked chitosan polymers
The formation of chitosan ionic cross-linked polymers can be observed by the increase in the turbidity in aqueous solutions of the appropriate oxocarbon upon the addition of an acidic solution of chitosan. This was observed for all experiments with the exception of the potassium croconate violet cross-linking agent. It seems that two different mechanisms could be acting: the cross-linking was initially effective by protonation at lower pH, whereas the chitosan-oxocarbon complex at higher pH was formed by the ionic interaction between the positively charged chitosan and the negatively charged oxocarbon ions
Summary
Chitosan is a copolymer of β-(1→4)-linked 2-acetamido2-deoxy-D-glucopyranose and 2-amino-2-deoxy-Dglucopyranose. This polycationic biopolymer can be obtained by partial deacetylation of chitin extracted from crustaceans. The main parameters influencing the characteristics of chitosan are its molecular weight (MW) and degree of deacetylation (DD), representing the proportion of deacetylated units. Chitosan has attracted much attention mainly due to its potential biological applications, which include a unique antichloristic effect, bio-compatibility, absorptivity, nonhypersensitivity, biodegradability and a significant wound healing ability.. Chitosan has attracted much attention mainly due to its potential biological applications, which include a unique antichloristic effect, bio-compatibility, absorptivity, nonhypersensitivity, biodegradability and a significant wound healing ability.6-9 Due to these properties this polymer has been used in several different applications, such as drug and gene delivery vehicles, tissue engineering scaffolds and in wound dressings.. In the search for novel applications for this versatile natural polymer, its chemical modification is desirable to enhance its stability in acidic media, to decrease its solubility in mineral and organic acids and to increase its resistance to biochemical and biological degradation These chemical modifications can sometimes only be achieved at the expense of a decreased thermal stability and the purpose of this study is to evaluate the potential improvements in the chemical behavior against any observed detrimental factors in the thermal properties of a range of crosslinked chitosan polymers
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