No abstract

An electrochemical procedure, based on the dissolution of a metallic anode in an aprotic solvent, has been used to obtain silver nanoparticles ranging from 2 to 7 nm. By changing the current density, it is possible to obtain different silver particle sizes. The influence of the different electrochemical parameters on the final size was studied by using different kinds of counter electrodes. The effect of oxygen presence in the reaction medium as well as the type of particle stabilizer employed have also been investigated. In some conditions an oscillatory behavior is observed. Characterization of particles was carried out by TEM and UV-vis spectroscopy. The maximum and the bandwidth of the plasmon band are both strongly dependent on the size and interactions with the surrounding medium. The presence of different silver clusters was detected by UVvis spectroscopy. By using this technique, the existence of an autocatalytic step in the synthesis mechanism is proposed.

Small fluorescent atomic copper clusters, stabilized by tetrabutylammonium nitrate, have been synthesized by a simple electrochemical technique. These small clusters (Cu N , N < ≈14) show photoluminescence in the visible range with unusual high quantum yields (13%) and were characterized by UV−vis and fluorescence spectroscopies, LDI-TOF (laser desorption/ionization time-of-flight) mass spectroscopy, XPS (X-ray photoelectron spectroscopy), and TEM/HRTEM (high-resolution/transmission electron microscopy). Cu clusters are very stable and can be dispersed in both apolar and polar solvents, which makes them useful as very small building blocks, bringing new possibilities to construct novel nano/microstructures, with potential applications in fields such as biosensors, biomedicine, etc.

Products of an oxidative coupling were obtained in the gold(III)‐catalyzed cycloisomerization of tertiary allenyl carbinols. The absence of reduced organic products and an increase of these coupling products with the amount of gold(III) catalyst suggests that gold(III) is reduced in situ, possibly to gold(I) catalysts which were also shown to be active for these transformations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Nanoparticles of gold supported on nanocrystalline CeO 2 catalyse the isomerisation of w-alkynylfurans to phenols. Initial leaching of gold was observed, which could be minimised by calcining. Subsequent runs showed that once all soluble species had leached, the surface-bound, cationic gold species is still active and can reach turnover numbers of up to 391. This is the first time that a heterogeneous gold catalyst showed activity in the gold-catalysed phenol synthesis.