Lucia Pasquato

Decorating carbon nanotubes with metal or semiconductor nanoparticles

Due to their large chemically active surface and stability at high temperatures carbon nanotubes (CNTs) have been used as a support material for the dispersion and stabilization of metal and semiconductor nanoparticles (NPs). These hybrid materials have found several applications in catalysis, nanoelectronics, optics, nanobiotechnology, etc. Several ways have been described in the literature to immobilize NPs on CNTs and they can be divided into two main pathways: (a) the formation (and stabilization) of metal NPs directly on the carbon nanotube surface, and (b) the connection of chemically modified NPs to carbon nanotubes or to modified CNTs. A plethora of methods for the synthesis of different NPs have been very recently developed. This know-how is now available for the generation of a large variety of new hybrid products in combination with CNTs. A selection of representative examples of the synthesis, properties and applications of NP–CNTs is here reported and discussed.

Functional gold nanoparticles for recognition and catalysis

Gold nanoparticles passivated by a monolayer of functional thiolates represent a new promising tool in supramolecular chemistry since they allow the preparation of complex, self-organized, polyvalent structures with a very modest synthetic effort. These systems have sizes comparable to those of many biological molecules including proteins and nucleic acids, and to those of many cellular sub-structures. In this way they are good candidates to model recognition processes and to develop new biomimetic catalysts. Some interesting examples towards these goals are reviewed briefly.

The role of sulfur functionalities in activating and directing olefins in cycloaddition reactions

Revue sur les reactions de cycloadditions (2+2) et (4+2) de sulfures et sulfoxydes vinyliques, de sulfones vinyliques, alleniques et acetyleniques

Water-Soluble Gold Nanoparticles Protected by Fluorinated Amphiphilic Thiolates

The preparation and the properties of gold nanoparticles (Au NPs) protected by perfluorinated amphiphiles are described. The thiols were devised to form a perfluorinated region close to the gold surface and to have a hydrophilic portion in contact with the bulk solvent to impart solubility in water. The monolayer protected clusters were prepared, in an homogeneous phase using sodium thiolates because of the low nucleophilicity of the alpha-perfluorinated thiols, and fully characterized with (1)H, (19)F NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Au NPs with core diameters ranging from 1.6 to 2.9 nm, depending on the reaction conditions, were obtained. Water-soluble NPs (MPC-F8-PEGs) were obtained with the thiol HS-F8-PEG ending with a short poly(ethylene glycol) unit (PEG-OMe 550), whereas thiols with shorter PEG chains give rise to NPs insoluble in water. MPC-F8-PEGs undergo an exchange reaction with amphiphilic alkyl thiols. ESR investigations, using a hydrophobic radical probe, indicate that the MPC-F8-PEG monolayer shows a greater hydrophobicity compared to the analogous hydrogenated monolayer.

Synthesis, characterization and properties of water-soluble gold nanoparticles with tunable core size

Robust, water-soluble gold clusters protected by monolayers of ligands containing a short alkyl chain (C7) close to the gold surface and a triethylene glycol monomethylether unit (TEG) to impart solubility in water and other polar solvents were prepared and characterized. Thiol 7 (N1-{2-[2-(2-methoxyethoxy)ethoxy]ethyl}-8-sulfanyloctanamide) constitutes a good and versatile capping agent for the preparation of these nanoparticles. By tuning the Au/thiol ratio and sodium borohydride addition rate, nanoparticles with different core diameters ranging from 1.5 to 4.2 nm, as determined by TEM analysis, could be obtained. The size distribution of the gold cores appears to become broader as the Au/thiol ratio used to prepare the nanoparticles increases. Characterization of these nanoclusters also by NMR, UV-Vis and FTIR spectroscopies is reported. Solubility properties have been studied in a large variety of solvents and different solubility behaviors were observed for nanoparticles of different sizes. Exchange reactions were carried out successfully with small (1.9 nm) and large nanoparticles (4.2 nm) using dodecanethiol as the entering thiol. This demonstrates that these materials can be used for the preparation of nanoclusters with different functional groups soluble in polar solvents including water. The synthetic procedure described represents a facile route to tailoring the size and solubility properties of Au nanoparticles.

Morphology of mixed-monolayers protecting metal nanoparticles

Anisotropic nanoparticles with precisely controlled chemical functionality are attractive building blocks for the assembly of sophisticated new materials and devices. Metal nanoparticles protected by self-assembled organic monolayers (MPCs) have drawn increasing attention due to potential applications in biosensing, catalysis, electronics and nanotechnology. However, a significant challenge remaining in nanoscience research is the capability to break symmetry in the isotropic ligand shell passivating these metal particles. Here we present recent strategies exploited to control the topology of multi-component self-assembled monolayers on metal nanoparticles.

Nanozymes: Functional Nanoparticle-based Catalysts

This short review highlights recent results on the use of nanoclusters of gold protected by a monolayer of functional ligands in both molecular recognition and catalysis. Particular emphasis is given to the multivalent properties of these systems and, in the case of catalysis, to the cooperativity between functional groups present in the ligands of the monolayer. The outstanding catalytic efficiency of some of the functional nanoparticles synthesized led us to call them nanozymes by analogy with the activity of catalytic polymers (synzymes).

N-Methylimidazole-functionalized gold nanoparticles as catalysts for cleavage of a carboxylic acid ester

New N-methylimidazole-functionalized gold clusters 2 catalyze, in 6∶4 methanol–water solution, the cleavage of 2,4-dinitrophenyl acetate with more than an order of magnitude rate acceleration with respect to acetyl-N-methylhistamine 3; comparison with dodecanoyl-N-methylhistamine 4 comicellized with Brij 35 reveals that 2 is still a better catalyst than the comicellar system and highlights analogies and differences between the two systems.

Self-Organization of Mixtures of Fluorocarbon and Hydrocarbon Amphiphilic Thiolates on the Surface of Gold Nanoparticles

Self-assembled monolayers composed of a mixture of thiolate molecules, featuring hydrocarbon or perfluorocarbon chains (H- and F-chains) terminating with a short poly(oxoethylene) (PEG) moiety, are the most extreme example of surfactant immiscibility on gold nanoparticles reported so far. The phase segregation between H-chains and F-chains and the consequent, peculiar folding of PEG chains are responsible for the increased affinity of a selected radical probe for the fluorinated region, which increases as the size of the fluorinated domains decrease, independently of the shape of such domains. This feature has been revealed by ESR measurements and an in silico innovative multiscale molecular simulations approach in explicit water. Our results reveal an underlying mechanism of a transmission of the organization of the monolayer from the inner region close to the gold surface toward the external hydrophilic PEG region. Moreover, this study definitively proves that a mixed monolayer is a complex system with properties markedly different from those characterizing the parent homoligand monolayers.

Gold nanoparticles protected by fluorinated ligands for 19F MRI

Gold nanoparticles coated with fluorinated ligands (F-MPCs) present features suitable for (19)F MRI as observed from phantom experiments. Cellular uptake, by HeLa cells, and toxicity of fluorescent dye-decorated F-MPCs are presented together with their ability to bind hydrophobic molecules allowing for a potential combination of targeting, delivery and imaging features.