Effects of different amino acids on the electrical characteristics of pharmaceutical polymers

The effect of variations in pH and in concentration of five different amino acids (alanine, glycine, lysine, threonine, and glutamic acid) on the electrical properties of the Aquacoat polymer/solution interface was investigated by means of electrophoretic mobility measurements. The results are explained on the basis of determinations of adsorption of the amino acids on the polymer particles. The pH appears to be a determining factor in the way amino acids interact with the negatively charged polymer particles. The net, pH-dependent charge on the amino acid molecules may significantly affect their interaction with Aquacoat; thus, electrostatic effects seem to be most important in the case of lysine and glutamic acid. However, specific effects related to the structure (polarizability, size, charge) of the side group of the amino acid species appear to play an important role in the interaction and adsorption phenomena involved.