Flower-like silver nanoparticle superstructures are prepared by the reaction of silver nitrate and ascorbic acid in an acidic aqueous solution of a polynaphthalene system. The three-dimensional flower-like structure has a purely hierarchic arrangement, wherein each petal is composed of bundles of silver particle chains, each enclosed in a polymer sheath. The ordering arises from strong adsorption of silver ions onto the polymer and by the interplay of the redox properties of nitric and ascorbic acid. As a result, linear silver cyanide, formed on the polymer, probably due to intrinsic electric dipole fields, organizes the silver particle chains in dumbbell-like structures, resembling buds and flower-like structures. By dilution and heating of the mother liquors, it is also possible to obtain single petals, i.e. micrometer sized bundles of linearly aggregated silver nanoparticle chains, each enclosed in a polymer sheath. The comprehension of the hierarchic assembly of silver nanoparticles, paves the way to a facile general method to prepare polymer–metal nanoparticle chains and flower-like superstructures. The results of this study improve both the understanding of the formation mechanism of hierarchic structures at mild temperatures and our ability to tailor them to sizes and shapes appropriate for technological purposes.

A study aimed at the synthesis and structure optimization of new, efficient, optically active β-amino alcohol ligands with a structure suitable for immobilization on magnetite nanoparticles has been carried out. The optimized homogeneous amino alcohol catalysts 13a and 13b, the chirality of which arises from the Sharpless epoxidation of suitable allyl alcohols, were tested by employing the well-established enantioselective amino alcohol-promoted addition of diethylzinc to benzaldehyde, giving the corresponding benzyl alcohol with nearly quantitative yield and ee = 95%. Then, their broad applicability as chiral catalysts was evaluated by carrying out the same reaction on a family of aldehydes, including variously substituted aromatic ones as well as an aliphatic analogue. The results have confirmed the validity of the fine-tuning process performed on ligands 13a and 13b. In fact, both exhibited excellent catalytic activity as demonstrated by the chemical yields and ee obtained from all the tested aldehydes, almost independent of the position and type of substitution in the aromatic ring.

We show that using the same reaction procedure, by hindering or allowing the formation of a reaction intermediate, the Ag⁺dodecanethiolate polymeric complex, it is possible to selectively obtain Ag dodecanethiolate nanoparticles or Ag dodecanethiolate nanoclusters in the size range 4–2 nm. Moreover, the Ag dodecanethiolate nanoclusters display a lamellar superstructure templated from the precursor Ag⁺dodecanethiolate polymeric complex. A plausible formation mechanism is illustrated where, starting from the precursor and scaffold lamellar Ag⁺ thiolate polymeric complex, first the nanocluster Ag_n ⁰ core is formed by reduction of isoplanar Ag⁺ ions, followed by Ag⁺ thiolate units that build protection, the nanocluster shell, around the core. The nanoclusters are characterized by elemental analyses, XRD, ATR-FTIR, XPS, XAS, MALDI, ESI, UV-Vis and fluorescence measurements. The luminescent Ag₁₅(dodecanethiolate)₁₁·2H₂O nanocluster is achieved in good yield after 4 hours of reaction whereas after 2 hours, the luminescent Ag₃₅(dodecanethiolate)₁₆ is isolated. Both Ag nanoclusters present emission bands in the range 330–450 nm, the shifting depending on the excitation wavelength. This phenomenon is attributed to a possible dipolar state causing distribution in energies due to variability of dipole–dipole interactions. Moreover, both nanoclusters further present a NIR emission at about 700 nm independent from the excitation wavelength. Thanks to their optical and structural properties, the synthesized nanoclusters, perfect molecular/nanoparticle hybrids, have great potentiality for new applications in nanotechnologies.