Controlled Functionalization of Gold Nanoparticles with Mixtures of Calix[4]arenes Revealed by Infrared Spectroscopy

Abstract

Labile ligands such as thiols and carboxylates are commonly used to functionalize AuNPs, though little control over the composition is possible when mixtures of ligands are used. It was shown recently that robustly functionalized AuNPs can be obtained through the reductive grafting of calix[4]arenes bearing diazonium groups on the large rim. Here, we report a calix[4]arene-tetradiazonium decorated by four oligo(ethylene glycol) chains on the small rim, which upon grafting gave AuNPs with excellent stability thanks to the C-Au bonds. Mixtures of this calixarene and one with four carboxylate groups were grafted on AuNPs. The resulting particles were analyzed by infrared spectroscopy, which revealed that the composition of the ligand shell clearly reflected the ratio of calixarenes that was present in solution. This strategy opens the way to robustly protected AuNPs with well-defined numbers of functional or postfunctionalizable groups.

Synthesis of a Calix[4]arene‐Monodiazonium Salt for Surface Modification

“…1 H NMR spectra were recorded either at 300 or 400 MHz. 13 C NMR spectra were recorded at 100 MHz. Traces of residual solvents were used as internal standards for 1 H and 13 C chemical shift referencing.…”

“…Surface modification with calix[4]arene‐tetradiazonium salts X 4 N 4 a – c , . Inset: targeted calix[4]arene‐monodiazonium salt 1 .…”

“…[11] Furthermore, this method allows for controlling the composition of binary mixed monolayers, which is essential for sensing applications. [12,13] All in all, calix [4]arene-tetradiazonium salts represent nowadays an established class of compounds that can find various applications in the field of surface modification. [14] In order to enlarge this family of compounds as well as to gain insights into the factors that govern this calixarenebased coating methodology, we wanted to investigate the grafting of a calix [4]arene bearing a single diazonium group.…”

“…Indeed, such a calix [4]arene-monodiazonium salt would allow us to evaluate the influence of the number of anchoring points on the robustness and compactness of the grafted layer. Moreover, the number of anchoring points may also influence the 3D conformation of the calixarene once anchored onto the sur- [4]arene-tetradiazonium salts X 4 N 4 a-c. [7,[9][10][11][12][13] Inset: targeted calix [4]arene-monodiazonium salt 1. Note that the representation of the grafted calixarene does not necessarily imply that the four aryl units are linked to the surface.…”

“…CH 3 ) ppm 13. C NMR (100 MHz, CDCl 3 , 298 K): δ = 170.9, 169.5, 155.7, 154.2, 152.6, 135.8, 133.5, 132.3, 131.4, 130.9, 129.6, 128.9, 128.5, 124.2, 123.5, 110.6, 72.2, 70.4, 61.2, 60.5, 31.9, 31.0, 29.8, 14.3 ppm.…”