Page 309 - Advances in Textile Biotechnology

290 Advances in textile biotechnology

(a)
H COC OH H COC OH
3
3
NH O NH O
HO HO O
HO O HO O HO OH
O NH O NH
OH H COC OH H COC
3
3
n
(b)
OH H COC OH
3
N
NH 2 O O
HO HO O
O O HO O HO OH
O NH 2 O NH 2
OH OH
nX nY
(c)
OH OH
OH O OH O
HO O HO O
HO HO O HO OH
O O OH
OH
OH OH
n
12.1 Molecular structure of: (a) chitin, (b) chitosan (nX > nY) and (c)
cellulose.

cuticles of many invertebrates, and in the cell walls of green algae, some
fungi, and yeasts (Muzzarelli, 1994). Chitin exhibits structural similarity to
cellulose and differs from it with the replacement of C-2 hydroxyl residues
by acetamide groups. Depending on the polysaccharide source and isolation
conditions, chitin has a different degree of acetylation. The length of the
chitin molecule in nature varies widely. Although 5000–8000 N-acetyl-d-
glucosamine residues are found in crab chitin, the one from yeast contains
only up to 100 residues (Synowiecki and Al-Khateeb, 2003). Chitin mole-

cules, through hydrogen bonds, are assembled in fibrils occuring in antipar-
allel and parallel arrangement, named α- and β-chitin, respectively. The
chitinous microfibrils are arranged in sheets, which in the case of α-chitin

adhere strongly by hydrogen bonding. α-Chitin has very low hydrophilicity
and water permeability. β-Chitin, with a lower content of intersheet hydro-
gen bonds, swells readily and is more permeable. Chitin is insoluble in water,
diluted acidic or basic solutions and in most of the organic solvents. It is
usually dissolved in concentrated acids as well as in hexafl uoroisopropanole
or hexafl uoroacetone.

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