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-0.50) at pH 3.5 and 90% charged (
α
= -0.90) at pH 4.5. Hence, the
polyanionic character persists for pH values down to about 2.5-3.5, below
which alginate is no longer sufficiently charged.
Chitosan:
The amino group has a pK
A
of ca. 6.5. The charge is given by 1-
α
, since in
this case dissociation results in loss of a positive charge to form an uncharged
amine (-NH
3
+
→
NH
2
).
The figure below shows alginate and chitosan are oppositely charged roughly
between pH 3 and pH 7 (shaded area), and may form the PE complex. The
limits are not exact, but the rate of complexing and nature and stability of the
complexes depend on pH in the border regions.