Mechanistic study of the nucleation and conformational changes of polyamines in presence of phosphate ions

Polyamine Phosphate Nanoparticles (PANs) have great potential for the delivery of large therapeutics, such as plasmids and/or siRNAs. The formation of PANs by complexation of Poly(allylamine hydrochloride) (PAH) and phosphate ions from Phosphate Buffer (PB) was studied here, and how it is affected by the presence of phosphate ions from PB and ionic strength. From Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) the critical PB concentration for PANs formation was determined. Below this critical point, Small Angle X-ray Scattering (SAXS) studies revealed that small PAH-phosphate aggregates coexist with not complexed or weakly complexed polymer chains in solution and that the presence of the phosphate ions increases the Kuhn length of the polymer chains until that only spherical aggregates are present in solution. TEM, DLS and SAXS showed the increase of PANs size with ionic strength up to 250 mM NaCl. At higher NaCl concentrations, PANs disassemble into smaller aggregates. Isothermal Titration Calorimetry (ITC) showed that PAN formation is an exothermic process and the association of phosphates below the critical PB concentration is entropically controlled.Fil: Andreozzi, Patrizia. Centro de Investigacion Cooperativa En Biomateriales.; EspañaFil: Ricci, Caterina. Università Politecnica Delle Marche; ItaliaFil: Martinez Porcel, Joaquin Emiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Moretti, Paolo. Università Politecnica Delle Marche; ItaliaFil: Di Silvio, Desirè. Centro de Investigacion Cooperativa En Biomateriales.; EspañaFil: Amenitsch, Heinz. Graz University Of Technology.; AustriaFil: Ortore, Maria Grazia. Università Politecnica Delle Marche; ItaliaFil: Moya, Sergio Enrique. Centro de Investigacion Cooperativa En Biomateriales.; Españ