A study of the effect of different amino acids on the electrical properties of nitrofurantoin suspensions

The effect of variations in pH and in concentration of four different amino acids (alanine, glycine, lysine, and threonine) on the electrical properties of the nitrofurantoin/aqueous solution interface is first investigated by the microelectrophoresis method. pH appears to be a determinant factor in the way amino acids interact with the negatively charged nitrofurantoin particles. The fact that alanine (with a non-polar R-group in its molecule) is the amino acid with the smallest effect on the zeta potential of the particles suggests that the polarity of the group is essential in accounting for such interaction. These data are used to interpret experimental results on the stability of the suspensions, as detected from the rate of change of their turbidity with time.