Application of ferrocene-resorcinarene in silver nanoparticle synthesis

An amphiphilic resorcinarene with ferrocene groups at the lower rim has been applied as both reductant and stabilizer in the synthesis of colloidal silver nanoparticles.

Multidentate ionic surfactant mediated extraction and dispersion of gold nanoparticles in organic solvents

Resorcinarenes with three different quaternary ammonium headgroups were synthesized and evaluated for their ability to stabilize gold nanoparticles in organic and aqueous medium. Aqueous dispersions of citrate stabilized gold nanoparticles of dimensions up to 29 nm could be extracted into organic solvents by resorcinarenes functionalized with tetrapyridinium tetrabromide (1), tetratrimethylammonium tetrabromide (2), and tetratributylammonium tetrabromide (3). Such nanoparticles were characterized by TEM, EDS, UV-vis, and IR. Their long-term dispersion stability varied significantly and depended on the nature of the resorcinarene headgroup, and in particular nanoparticles extracted by resorcinarene 1 were stable for several weeks. Nanoparticles passivated by resorcinarenes 1 and 2 were also stable in the presence of thiourea for several hours in both aqueous and organic medium. This is notable as thiourea is known to result in the instantaneous aggregation of citrate stabilized nanoparticles. Remarkably nanoparticles stabilized by resorcinarenes 1 and 2 could be precipitated and redispersed in chloroform without any visible aggregation. The critical parameters controlling the extraction of the nanoparticles into the organic phase have also been evaluated. The resorcinarene surfactant mediated facile phase transfer of gold nanoparticles described here can be readily applied for the stabilization of other citrate stabilized mono- and bimetallic nanoparticles, thus providing opportunities to disperse and stabilize relatively larger nanoparticles in organic solvents using ionic surfactants opening up new applications.

Controlling the dynamics of a bidimensional gel above and below its percolation transition

The morphology and the microscopic internal dynamics of a bidimensional gel formed by spontaneous aggregation of gold nanoparticles confined at the water surface are investigated by a suite of techniques, including grazing-incidence x-ray photon correlation spectroscopy (GI-XPCS). The range of concentrations studied spans across the percolation transition for the formation of the gel. The dynamical features observed by GI-XPCS are interpreted in view of the results of microscopic imaging; an intrinsic link between the mechanical modulus and internal dynamics is demonstrated for all the concentrations. Our work presents an example of a transition from a stretched to a compressed correlation function actively controlled by quasistatically varying the relevant thermodynamic variable. Moreover, by applying a model proposed some time ago by Duri and Cipelletti [Europhys. Lett. 76, 972 (2006)] we are able to build a master curve for the shape parameter, whose scaling factor allows us to quantify a "long-time displacement length." This characteristic length is shown to converge, as the concentration is increased, to the "short-time localization length" determined by pseudo-Debye-Waller analysis of the initial contrast. Finally, the intrinsic dynamics of the system is then compared with that induced by means of a delicate mechanical perturbation applied to the interface.

Mixed-Monolayer-Protected Au25 Clusters with Bulky Calix[4]arene Functionalities

Although various complex, bulky ligands have been used to functionalize plasmonic gold nanoparticles, introducing them to small, atomically precise gold clusters is not trivial. Here, we demonstrate a simple one-pot procedure to synthesize fluorescent magic number Au25 clusters carrying controlled amounts of bulky calix[4]arene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calix[4]arene and 1-butanethiol. By systematic variation of the molar ratio of ligands, clusters carrying one to eight calixarene moieties were obtained. Structural characterization reveals unexpected binding of the calix[4]arenes to the Au25 cluster surface with two or four thiolates per moiety.