Nanoparticles of a polyelectrolyte-fatty acid complex: carriers for Q10 and triiodothyronine

Poly(ethylene imine) (PEI) was used for the complexation of dodecanoic acid (C12) resulting in a poly(ethylene imine) dodecanoate complex (PEI-C12) with a lamellar nanostructure and a repeat unit of 2.9 nm. PEI-C12 was doped with coenzyme Q10 and the hormone triiodothyronine as typical hydrophobic and pharmacological active compounds, respectively. The PEI-C12 acts as a guest matrix that dissolves both molecules up to weight uptakes of about 20% (w/w) and 15% (w/w), respectively, both without crystallization. Agglomerate-free dispersions of core-shell type nanoparticles were developed. Ratios of PEI to C12 of 2:1 or higher were found to be suitable for this purpose. The particles exhibit hydrodynamic diameters in the range of 80-150 nm, which depend on the preparation conditions. Each particle consists of a relatively compact core surrounded by a diffuse corona. PEI-C12 forms the core, while non-complexed PEI acts as a cationic-active dispersing agent. It was found that the nanoparticles show high zeta potentials (approximately +40 mV) and are stable in NaCl solutions at concentrations of up to 0.3 mol x l(-1). The stabilization of the nanoparticles results from a combination of ionic and steric contributions. A variation of the pH value was used to activate the dissolution of the particles. The PEI-C12 nanoparticles may have potential as carriers for hydrophobic drugs.