Preparation of nanostructures composed of dextran sulfate/ruthenium nanoparticles and their interaction with phospholipid monolayers at a liquid–liquid interface

Nanostructures composed of dextran sulfate (DS)/ruthenium (Ru) nanoparticles (NPs) adsorbed on phospholipid monolayers at a liquid–liquid interface were prepared and characterized electrochemically in relation to their potential use in drug delivery systems. First, positively charged Ru NPs were prepared, and then negatively charged DS was adsorbed on the surface of the NPs, thus forming well-defined and organized structures, as observed under the transmission electron microscope, which are referred to composite nanoclusters. The lipid monolayers were formed by depositing either 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine or 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-rac-(1-glycerol) at an air–liquid interface with an aqueous subphase containing calcium chloride and the composite nanoclusters. Using the Langmuir–Blodgett technique, the lipid monolayers were transferred onto an immobilized organic gel at different surface pressures (32, 40, and 47 mN/m) and their physicochemical properties were studied by compression π–A isotherms and capacitance–potential curves. All the relevant changes in these latter curves were successfully explained with a theoretical model and were ascribed to a reduced surface charge density at the interface after the adsorption of the composite nanoclusters. The transfer mechanism of two ionisable compounds of pharmaceutical interest, the Alzheimer drug tacrine (9-amino-1,2,3,4-tetrahydroacridine hydrochloride) and the therapeutic anti-infective dye aminacrine (9-aminoacridine hydrochloride), across these interfacial composite nanostructures was then studied by cyclic voltammetry. It was demonstrated that the lipid layer retards the rate of ion transfer.