pH-sensitive nanoparticles of poly(amino acid) dodecanoate complexes

Nanoparticles were formed by the complexation of poly(-arginine) (PLA), poly(-histidine) (PLH) and poly(-lysine) (PLL) with dodecanoic acid (C12). Dynamic light scattering, ζ potential measurements, atomic force microscopy, fluorescence, and circular dichroism spectroscopy were used for their characterization. It was found that the diameters of the poly(-arginine) dodecanoate (PLA-C12), poly(-histidine) dodecanoate (PLH-C12), and poly(-lysine) dodecanoate (PLL-C12) complex nanoparticles were in the range 120–200 nm. Furthermore, the pH-sensitive dissolution and the surface charges can be adjusted by choosing PLA, PLH and PLL. The particle stability against basic pH values increases with increasing pK_a value of the poly(amino acid) in the series PLH-C12, PLL-C12 and PLA-C12. The particles as such show a core-shell morphology. Their cores are formed by stoichiometric poly(amino acid) dodecanoate complexes while the shells stabilizing the particles are formed by cationic poly(amino acid) chains in an uncomplexed state. The particles were tested as containers for hydrophobic molecules such as pyrene, which served as a fluorescence probe for measuring the polarity within the particles, and Q₁₀ which functioned as a model drug. The maximum uptake of Q₁₀ into the nanoparticles is about 13% (w/w), thereby making the complexes attractive as simple drug carriers for controlled release purposes. Circular dichroism measurements revealed that the poly(amino acid) chains of PLA-C12 and PLL-C12 adopt predominantly an -helix and that of PLH-C12 a β-sheet.