Metachromatic behavior: Influence of the molecular weights of chitosan in thionine-sodium dodecyl sulfate system

Chitosans having three molecular weights (4.0 × 104, 8.0 × 104, and 16.0 × 104 Da) were isolated by an ultrasonic degradation of chitin obtained from crab shell wastes and used to determine a metachromic behavior from the effect of aggregation characteristics. The metachromatic behaviors of thionine (Th)-sodium dodecyl sulfate (SDS), Th-SDS-chitosan system were investigated by the absorption and fluorescence spectroscopy.For SDS/Th < 40, the order of decrease of fluorescence intensity in Th-SDS-chitosan system was found to be 40k > 80k > 160k of molecular weight of chitosan. In spite of adding small amount of chitosan to Th-SDS system, a reversal of metachromatic behavior in the Th-SDS-chitosan system occurs. From the measurement of the solvent effect by adding ethanol to Th-SDS-chitosan system, the order of increase of the disaggregation was determined to be 40k < 80k < 160k of molecular weights of chitosan.