Charge effects in water solution of a low generation sodium carboxylate terminated dendrimers

Abstract

Dendrimers, a class of novel nano-sized materials characterized by a highly ramified structure and a relevant number of functional surface groups, represent a versatile platform for a wide range of nanotechnology applications. The number and characteristic of their modifiable surface groups strongly influence the solution properties as well as some relevant processes involved in molecular recognition, signal processing as well as for binding various targeting or guest molecules. Owing to these properties dendrimers have attracted the interest of the researchers in the development of new prototypes implicated in many technological applications. However, despite of their recent extensive studies, their colloidal stability in solution environment have been relatively less investigated. With the aim to furnish useful insight about the inter-dendrimer interaction in solution, a Small Angle X-ray Scattering (SAXS) structural investigation on the sodium carboxylate terminated (-COO-Na) generations G1.5 of poly(amidoamine) dendrimers in water solution has been performed. The presence of a pronounced interference peak in the SAXS spectra in a wide range of concentrations gives evidence of a long range electrostatic interaction which has been ascribed to the ionisation of the surface carboxylate terminal end-groups. The experimental inter-dendrimer structure factor S(q) has been analysed in the framework of liquid integral equation theory. From that, we derived an effective inter-particle interaction composed of a screened Coulombic plus hard-sphere repulsion potential, which allows the estimation of the dendrimer effective surface charge Z_eff. The present analysis strongly supports the finding that colloidal stability and interaction of dendrimers in solution environment is strongly influenced by charge effects.