Gold nanoparticles, capped by carboxy-calix[4]resorcinarenes: effect of structure and concentration of macrocycles on the nanoparticles size and aggregation

Small (d core ≈ 2–5 nm) well-dispersed gold nanoparticles (AuNPs) stabilized by amphiphilic octacarboxy-calix[4]resorcinarenes with different substituents on the lower rim—methyl ( С 1 –CR ), pentyl ( С 5 – CR ) and undecyl ( С 11 – CR )—in an aqueous solution were obtained. The nanoparticles were studied by spectrophotometry, transmission electron microscopy, FTIR-spectroscopy, dynamic light scattering, small angle X-ray scattering and X-ray powder diffraction. The influence of HAuCl 4 /macrocycle ratio during the synthesis on the nanoparticles size and aggregation only for weakly associated С 1 – CR and С 5 – CR was achieved. The self-association effect of С 11 – CR on the nanoparticles stabilization is found. The existence of gold in the form of crystallites and their average sizes were defined. The average nanoparticle sizes were determined and the structure of macrocyclic shells on the surface of nanoparticles in an aqueous solution was proposed. The formation of cooperative calix[4]resorcinarene associates on the AuNPs surface due to the multiple supramolecular interactions leads to the creation of functional gold nanoparticles.