Effect of aminoacids on the surface free energy of nitrofurantoin

Abstract

Changes in nitrofurantoin surface free energy components, Lifshitz-van der Waals, γ ^LW_s , electron donor, γ ⁻_s , and electron acceptor, γ ⁺_s , due to adsorption of the aminoacids: lysine, alanine and glutamic acid, were determined by means of the thin-layer wicking technique. It was found that the aminoacids slightly increase the γ ⁻_s component already at 10⁻⁴ M concentration. They reduce the γ ⁺_s component practically to zero, and a very sharp increase of γ ⁻_s was observed when the nitrofurantoin surface was precovered from the solutions at concentrations larger tan 10⁻⁴ M. It is concluded that the adsorption of the aminoacids takes place via hydrogen bonding and electrostatic interactions between nitrofurantoin surface and aminoacid molecules. The increase in the γ ⁻_s parameter is probably caused by the presence of carboxyl groups in the aminoacid molecules.