Complexation of calix[4]arene protected gold nanoparticles with pyridinium and bipyridinium compounds

Calix[4]arene and calix[4]arene/alkanethiol protected gold nanoparticles with narrow size distributions were synthesised and characterized with NMR, thermogravimetric analysis (TGA) and a transmission electron microscope (TEM). NMR and light scattering (LS) were used to study the complexation of the nanoparticles with a pyridinium modified polyethylene oxide (Pyr-PEO2k-Pyr) complexant and a small 16 carbon pyridinium compound (Pyr-C16). Results give clear evidence of complexation induced aggregation of the nanoparticles as pyridinium proton signals shift upon changing the host: guest ratio and LS shows a change from a narrow size distribution into a broad one. The addition of alkanethiols with longer dimensions than that of the calixarene derivative and the type of the complexant can be used to tune the complexation. The studies also provide evidence of induced fit complexation into calix[4]arene cavities and solution phase interdigitation (secondary monolayer formation) when the nanoparticles are complexed with Pyr-C16.