Biomedical Engineering Reference
In-Depth Information
Figure 1.6
Projections of the crystal structure of chitosan in the anhydrous (annealed) polymorph on the ab (top) and bc
(bottom) planes. All hydrogen atoms are omitted, and hydrogen bonds are shown as dashed lines.
up chain, and the neighbor is down chain, that is, they are also packed in an antiparallel
fashion. However, there is no water molecule in this crystal, indicating that this is an anhy-
drous crystal. Different from the previous tendon polymorph, neighbor chains having
parallel direction are bonded by direct hydrogen bonds to make a sheet, and neighbor
sheets having antiparallel direction are stacked along the a -axis. Each chitosan chain takes
an extended twofold helix, zigzag structure, similar to the tendon polymorph. Thus, only
the zigzag structure has been found in chitosan crystals so far. This structure is also simi-
lar to those of chitin and cellulose.
1.4.2 infrared Spectroscopy and Nuclear Magnetic resonance
FTIR spectra of α- and β-chitin samples are shown in Figure 1.7. The C=O stretching region
of the amide moiety, between 1600 and 1500 cm −1 , is quite interesting because it yields dif-
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