INTERACTION OF SOLUBLE CHITOSANS WITH DYES IN WATER .2. THERMODYNAMIC DATA

Three water-soluble chitosan derivatives, namely N-carboxymethyl chitosan (NCMCh), N-carboxybutyl chitosan (NCBCh), and the reduction product of the aldimine obtained from chitosan and 5-hydroxymethyl-2-furaldehyde (NHMFCh), were found to interact in dilute aqueous solution with anionic dyes. The binding was studied at 25 degrees C with optical and thermodynamic (i.e. isothermal microcalorimetry and dilatometry) techniques under weakly acidic conditions. By using the Scatchard and Hill methods, the values of the binding constants were obtained from the absorption spectra. They ranged from 6 x 10(4) to 7 x 10(8) litre mol(-1). The binding ability seems to decrease in the order NHMFCh > NCBCh > NCMCh and Orange II > Alizarin S = Congo Red > Alizarin GG, respectively. From the Delta G degrees and Delta H values of binding the variation of entropy with interaction was computed for the chitosan derivatives-dyes systems. The values of Delta S of interaction were very small or negative and the Delta V of binding were nil, indicating that no desolvation of the species occurs on binding.