Gold nanoparticles: calixarene complexation in a mixed calixarene–alkanethiol monolayer†

This paper describes a detailed study on the complexation of pyridinium derivatives with calixarenes bound to gold nanoparticles (AuNPs). The studied calixarene derivatives are mixed with alkanethiols to formmixed monolayers on AuNP surfaces. The key findings are: (i) even a small amount (less than 11 mol%) of calixarenes can retain their complexation abilities among a majority of alkanethiols in a mixed monolayer, showing that it is possible to dilute the active calixarene (and possibly other receptors) in gold surfaces, (ii) the chain length of the alkanethiol compared with the calixarene spacer length can be used to fine tune the complexation ability of the calixarene, and there exist calixarene–alkanethiol mixed monolayer compositions in which the particles become unstable due to mismatching ligand spacer lengths, (iii) calixarenes with very short spacers bound to the gold surface can experience an enhancement in the delocalized p-electron density available for cation complexation, likely due to the proximity of the gold-bound sulphur to the calixarene cavity.