Abstract
Two chitosan samples (fraction of acetylated units (F-A) 0.15 and
0.52) were fractionated by preparative size exclusion chromatography
(SEC). The molecular weights and molecular weight distributions of
the fractions were analyzed by analytical size exclusion chromatography
coupled to an on-line low angle laser light scattering detector and
a differential refractive index detector (SEC-LALLS-DRI), and their
intrinsic viscosities were determined. The exponent (a) of the Mark-Houwink-Kuhn-Sakurada
(MHKS) equation was found to be 0.92+/-0.07 and 1.1+/-0.1, respectively,
at I=0.1 and pH 4.5. No variation in F-A related to molecular weight
was found. Reversible interaction between chitosans and different
column packings strongly influenced the log M-V relationships. This
interaction was generally most pronounced for the low-F-A chitosan,
suggesting that the protonated amino groups are involved. Ammonium
acetate buffer reduced this effect and the use of a new type of SEC-packing
seemed to eliminate it. The more highly acetylated chitosan also
had a more pronounced tendency towards concentration dependent self-association,
which most probably involve intermolecular hydrophobic interactions
between the acetyl groups. (C) 1997 Elsevier Science Ltd.
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