Antonella Fontana

Disaggregation of single-walled carbon nanotubes (SWNTs) promoted by the ionic liquid-based surfactant 1-hexadecyl-3-vinyl-imidazolium bromide in aqueous solution

Stable homogeneous aqueous dispersions of pristine single-walled carbon nanotubes (SWNTs) are obtained by using a water-soluble long-chain imidazolium ionic liquid (hvimBr) above its critical micelle concentration. The amount of hivmBr and the sonication time are two essential factors to obtain a good dispersion. The effective concentration of exfoliated SWNTs in aqueous solution is determined by simple, convenient and rapid UV-visible spectrophotometric measurements.

Palladium nanoparticles on carbon nanotubes as catalysts of cross-coupling reactions

The macroscopic properties of composite nanotube–nanoparticle superstructures are determined by a complex interplay of structural parameters at the nanoscale. The catalytic performance of different carbon nanotube–palladium nanoparticle catalysts, where nanoparticles were formed either directly onto nanotubes or preformed prior to deposition on nanotubes using different types of surfactants, were tested in cross-coupling reactions. The decoration of multi-walled carbon nanotubes with preformed thiolate-stabilised palladium nanoparticles yielded the optimum catalyst, exhibiting high activity and stability towards carbon–carbon bond formation and excellent recyclability, retaining high activity from cycle to cycle. The type of carbon nanotube support has pronounced effects on the density of deposited nanoparticles, with more polarisable MWNT able to uptake the highest number of nanoparticles per unit surface area as compared to other carbon nanostructures (MWNT > DWNT > SWNT ∼ GNF). Microscopic investigation of the nanoscale morphology found that nanoparticles increase in size during catalysis. The extent of growth is dependent on the type of nanocarbon support, with wider MWNT possessing lower curvature and thus retarding the growth and coalescence of nanoparticles to a greater extent than other carbon nanostructures (SWNT ≫ DWNT > MWNT ∼ GNF). The type of halogen X in the C–X bond activated by palladium appears to influence the evolution of nanoparticles during catalysis, with X = Br having the greatest effect as compared to X = Cl or I. Overall, preformed thiolate-stabilised palladium nanoparticles deposited on MWNT from solution was found to possess the most functional catalytic properties, with optimum activity, stability and recyclability in a range of cross-coupling reactions.

Non-covalent and reversible functionalization of carbon nanotubes

Summary Carbon nanotubes (CNTs) have been proposed and actively explored as multipurpose innovative nanoscaffolds for applications in fields such as material science, drug delivery and diagnostic applications. Their versatile physicochemical features are nonetheless limited by their scarce solubilization in both aqueous and organic solvents. In order to overcome this drawback CNTs can be easily non-covalently functionalized with different dispersants. In the present review we focus on the peculiar hydrophobic character of pristine CNTs that prevent them to easily disperse in organic solvents. We report some interesting examples of CNTs dispersants with the aim to highlight the essential features a molecule should possess in order to act as a good carbon nanotube dispersant both in water and in organic solvents. The review pinpoints also a few examples of dispersant design. The last section is devoted to the exploitation of the major quality of non-covalent functionalization that is its reversibility and the possibility to obtain stimuli-responsive precipitation or dispersion of CNTs.

Aggregation Behavior of Poly(ethylene glycol-bl-propylene sulfide) Di- and Triblock Copolymers in Aqueous Solution

Block copolymers of poly(ethylene glycol)-bl-poly(propylene sulfide) (PEG-PPS) have recently emerged as a new macromolecular amphiphile capable of forming a wide range of morphologies when dispersed in water. To understand better the relationship between stability and morphology in terms of the relative and absolute block compositions, we have synthesized a collection of PEG-PPS block copolymers and quantified their critical aggregation concentration and observed their morphology using cryogenic transmission electron microscopy after thin film hydration with extrusion and after solvent dispersion from tetrahydrofuran, a solvent for both blocks. By understanding the relationship between aggregate character and block copolymer architecture, we have observed that whereas the relative block lengths control morphology, the stability of the aggregates upon dilution is determined by the absolute block length of the hydrophobic PPS block. We have compared results obtained with PEG-PPS to those obtained with poly(ethylene glycol)-bl-poly(propylene oxide)-bl-poly(ethylene glycol) block copolymers (Pluronics). The results reveal that the PEG-PPS aggregates are substantially more stable than Pluronic aggregates, by more than an order of magnitude. PEG-PPS can form a wide variety of stable or metastable morphologies in dilute solution within normal time and temperature ranges, whereas Pluronics can generally form only spherical micelles under the same conditions. On the basis of these results, block copolymers of PEG with poly(propylene sulfide) may present distinct advantages over those with poly(propylene glycol) for a number of applications.

Microwave-Assisted Functionalization of Carbon Nanostructures in Ionic Liquids

The effect of microwave (MW) irradiation and ionic liquids (IL) on the cycloaddition of azomethine ylides to [60]fullerene has been investigated by screening the reaction protocol with regard to the IL medium composition, the applied MW power, and the simultaneous cooling of the system. [60]Fullerene conversion up to 98 % is achieved in 2-10 min, by using a 1:3 mixture of the IL 1-methyl-3-n-octyl imidazolium tetrafluoroborate ([omim]BF(4)) and o-dichlorobenzene, and an applied power as low as 12 W. The mono- versus poly-addition selectivity to [60]fullerene can be tuned as a function of fullerene concentration. The reaction scope includes aliphatic, aromatic, and fluorous-tagged (FT) derivatives. MW irradiation of IL-structured bucky gels is instrumental for the functionalization of single-walled carbon nanotubes (SWNTs), yielding group coverages of up to one functional group per 60 carbon atoms of the SWNT network. An improved performance is obtained in low viscosity bucky gels, in the order [bmim]BF(4)> [omim]BF(4)> [hvim]TF(2)N (bmim=1-methyl-3-n-butyl imidazolium; hvim=1-vinyl-3-n-hexadecyl imidazolium). With this protocol, the introduction of fluorous-tagged pyrrolidine moieties onto the SWNT surface (1/108 functional coverage) yields novel FT-CNS (carbon nanostructures) with high affinity for fluorinated phases.

TiCl4/Et3N-promoted three-component condensation between aromatic heterocycles, aldehydes, and active methylene compounds.

A one-pot methodology for the synthesis of polyfunctionalized indole derivatives by a TiCl4/Et3N-promoted trimolecular condensation of aldehydes, indole heterocycles, and various activated carbonyl compounds is reported. Rationalization of these reactions and extension to other heterocyclic systems is also described.

(R)‐α‐Lipoyl‐Glycyl‐L‐Prolyl‐L‐Glutamyl Dimethyl Ester Codrug as a Multifunctional Agent with Potential Neuroprotective Activities

The (R)‐α‐lipoyl‐glycyl‐L‐prolyl‐L‐glutamyl dimethyl ester codrug (LA‐GPE, 1) was synthesized as a new multifunctional drug candidate with antioxidant and neuroprotective properties for the treatment of neurodegenerative diseases. Physicochemical properties, chemical and enzymatic stabilities were evaluated, along with the capacity of LA‐GPE to penetrate the blood–brain barrier (BBB) according to an in vitro parallel artificial membrane permeability assay for the BBB. We also investigated the potential effectiveness of LA‐GPE against the cytotoxicity induced by 6‐hydroxydopamine (6‐OHDA) and H2O2 on the human neuroblastoma cell line SH‐SY5Y by using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) reduction assay. Our results show that codrug 1 is stable at both pH 1.3 and 7.4, exhibits good lipophilicity (log P=1.51) and a pH‐dependent permeability profile. Furthermore, LA‐GPE was demonstrated to be significantly neuroprotective and to act as an antioxidant against H2O2‐ and 6‐OHDA‐induced neurotoxicity in SH‐SY5Y cells.

Physicochemical properties of fluorescent probes: experimental and computational determination of the overlapping pKa values of carboxyfluorescein.

The overlapping pKa values of carboxyfluorescein have been measured by applying a UV-vis spectroscopic method that uses absorbance diagrams and chemometric analysis. Quantum chemical calculations have also been performed in order to analyze the experimental data.

Structural modifications of ionic liquid surfactants for improving the water dispersibility of carbon nanotubes: an experimental and theoretical study

The 1-hexadecyl-3-vinylimidazolium bromide (hvimBr), a water-soluble long-chain imidazolium ionic liquid (IL) with surfactant properties, showed the ability to produce stable homogeneous aqueous dispersions of pristine Single-Walled Carbon Nanotubes (SWNTs). The purpose of this study is the improvement of SWNT dispersing ability by assessing the effect of different groups in position 3 of the imidazole ring. In this regard structural analogues were synthesized and, after characterization, their capability to dissolve SWNTs in water was investigated. Molecular Dynamics (MD) simulations have been performed to provide a semi-quantitative indication of the affinity of each dispersing agent toward SWNT and to attempt an explanation of the experimental results.

Condensation of β‐Diester Titanium Enolates with Carbonyl Substrates: A Combined DFT and Experimental Investigation

The condensation of dialkyl beta-diesters with various aldehydes promoted by TiCl4 has been studied by DFT approaches and experimental methods, including NMR, IR and UV/Vis spectroscopy. Various possible reaction pathways have been investigated and their energy profiles evaluated to find out a plausible mechanism of the reaction. Theoretical results and experimental evidence point to a three-step mechanism: 1) Ti-induced formation of the enolate ion; 2) aldol reaction between the enolate ion and the aldehyde, both coordinated to titanium; and 3) intramolecular elimination that leads to a titanyl complex. The presented mechanistic hypothesis allows one to better understand the pivotal role of titanium(IV) in the reaction.