Abstract

The theory and mathematical treatment of the evaluation of the interactions of water-soluble polymers with low molecular-weight molecules is presented. The interaction of the water-soluble polymer poly(sodium 4-styrenesulfonate) with L-tryptophan (Try), L-phenylalanine (Phe), chlorpheniramine maleate (CPM), and 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) is studied by this technique. Ultrafiltration experiments at pH 7.5, and different ionic strength values show weak interactions of the low molecular weight molecules TTC and CPM with the polymer with apparent dissociation constants of 0.26 and 0.32 respectively in the absence of NaNO3, and 2.02 and 1.2 in the presence of 0.10 of NaNO3 and 0.13 M of NaCl respectively. Negligible interactions are found for Try or Phe at pHs ranging between 4 and 10 and NaNO3 concentrations ranging between 0.0 and 0.15 M. This suggests that the interactions are mainly due to both long-range electrostatic forces and short-range interactions that may include hydrophobic forces or charge transfer complexation. The interaction of TTC with PSS in the absence of NaNO3 is reflected in UV-Vis spectroscopic studies by a decrease on the intensity of the maximum at 248 nm