ABSTRACT
Oligomers and polymers of chitin and chitosan are homo-polymers or hetero-polymers of two monosaccharides [β-(1-4)-2-acetamido-2-deoxy-d-glucose (GlcNAc); and β-(1-4)-2-amino-2-deoxy-dglucose (GlcN)], which are joined by glycosidic linkages. Oligosaccharides are generally dened as carbohydrate polymers containing a few monomer residues. The borderline between oligosaccharides and polysaccharides is not precise. The number of monomer units for oligosaccharides have
12.1 Introduction .......................................................................................................................... 149 12.2 Description of Different Techniques for Structural Characterization
and the DA Determination .................................................................................................... 150 12.2.1 1H NMR Spectroscopy ............................................................................................. 151 12.2.2 13C NMR Spectroscopy ............................................................................................ 151 12.2.3 15N NMR Spectroscopy ............................................................................................ 152 12.2.4 Infrared Spectroscopy .............................................................................................. 152 12.2.5 Near Infrared (NIR) Spectroscopy ........................................................................... 152
12.3 Discussion ............................................................................................................................. 152 12.3.1 General Aspects ........................................................................................................ 152 12.3.2 NMR Spectroscopy .................................................................................................. 154
12.3.2.1 General Considerations .............................................................................. 154 12.3.2.2 1H NMR ..................................................................................................... 155 12.3.2.3 13C NMR .................................................................................................... 158 12.3.2.4 15N NMR .................................................................................................... 158
12.3.3 IR and Near-IR Spectroscopy ................................................................................... 159 12.3.3.1 IR ............................................................................................................... 159 12.3.3.2 Near-IR ...................................................................................................... 161
12.3.4 Determination of Morphology and Structural Characterization of Chitin/Chitosan by NMR and IR Techniques ...................................................... 162
12.4 Comparison of Various Types of NMR and IR Spectroscopy for Structural Characterization and the Degree of N-Acetylation Determination ...................................... 163
12.5 Conclusions ........................................................................................................................... 165 12.6 Future Work and Perspectives .............................................................................................. 166 References ...................................................................................................................................... 166
been reported to be up to 10 or 20 monomer residues. The word “chitosan” is used for both partially and completely deacetylated chitosans. The chemical structure of chitin is similar to that of cellulose. The difference between the chemical structure of cellulose and that of chitin is that the 2-hydroxy groups of cellulose have been replaced with N-acetyl groups. The chemical structures of cellulose, fully N-acetylated chitin, and completely N-deacetylated chitosan are illustrated in Figure 12.1. However, fully N-acetylated chitin and completely N-deacetylated chitosan are not commercially available. The degree of N-acetylation (DA) has been employed to differentiate chitin from chitosan.
