Ion complex formation between poly(amido amine) dendrimer HCl salt and poly(L-glutamic acid) sodium salt

Formation of ion complexes between poly(amido amine) (PAMAM) dendrimer HCl salt (1) (ethylenediamine core, generation G = 3.0 and 5.0) and poly(L-glut amic acid) sodium salt (2) (M-w, 1.3 x 10(4), 1.5 x 10(4), and 8.9 x 10(4)) in water and phosphate buffers (pH 6.0, 6.9, and 7.9) was investigated by pH, turbidity, and viscosity measurements and electrophoresis analysis. In pH and turbidity measurements in water, the highest turbidity and neutraliz ation were observed around a 1 : 1 charge ratio, demonstrating that not onl y primary amines on the surface but also internal tertiary amines of 1 part icipate in the ion complex formation. When lower molecular weight 2 (M-w, 1 .3 X 10(4) and 1.5 x 10(4)) were used for complexation in water and phospha te buffers, mixtures of 1 and 2 did not become turbid except around the poi nt of neutralization in water. In electrophoresis, the non-turbid mixtures of 1 (G = 5.0) and 2 (M-w, 1.5 x 10(4)) showed a characteristic broad band, meaning ion complex formation. Viscosity of the aqueous solutions of a mix ture of 1 and 2 (M-w, 1.5 X 10(4)) was lower than that of 2 (M-w, 1.5 x 10( 4)). The conformation of 2 in the complex was proved to be a random coil by circular dichroism (CD) analysis. These results were interpreted in terms of water-soluble ion complex formation due to the globular shape and molecu lar structure of 1.