Antonello Di Crescenzo

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.

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.

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.

Modeling of Chemical Reactions in Micelle: Water-Mediated Keto-Enol Interconversion As a Case Study

The effect of a zwitterionic micelle environment on the efficiency of the keto-enol interconversion of 2-phenylacetylthiophene has been investigated by means of a joint application of experimental and theoretical/computational approaches. Results have revealed a reduction of the reaction rate constant if compared with bulk water essentially because of the different solvation conditions experienced by the reactant species, including water molecules, in the micelle environment. The slight inhibiting effect due to the application of a static electric field has also been theoretically investigated and presented.

Surfactant Hydrogels for the Dispersion of Carbon-Nanotube-Based Catalysts

Novel hydrogel phases based on positively charged and zwitterionic surfactants, namely, N-[p-(n-dodecyloxybenzyl)]-N,N,N-trimethylammonium bromide (pDOTABr) and p-dodecyloxybenzyldimethylamine oxide (pDOAO), which combine pristine carbon nanotubes (CNTs), were obtained, thus leading to stable dispersions and enhanced cross-linked networks. The composite hydrogel featuring a well-defined nanostructured morphology and an overall positively charged surface was shown to efficiently immobilise a polyanionic and redox-active tetraruthenium-substituted polyoxometalate (Ru4POM) by complementary charge interactions. The resulting hybrid gel has been characterised by electron microscopy techniques, whereas the electrostatic-directed assembly has been monitored by means of fluorescence spectroscopy and ζ-potential tests. This protocol offers a straightforward supramolecular strategy for the design of novel aqueous-based electrocatalytic soft materials, thereby improving the processability of CNTs while tuning their interfacial decoration with multiple catalytic domains. Electrochemical evidence confirms that the activity of the catalyst is preserved within the gel media.

Dispersion of SWCNTs with Imidazolium-Rich Surfactants

Starting from previous evidence on the crucial role of imidazolium ions, long alkyl chains, and aromatic rings in favoring the adsorption of surfactants onto carbon nanotube (CNT) walls, we have synthesized novel gemini surfactants with the aim to optimize and identify a reference structure for CNT dispersants. The efficiency of the novel surfactants has been evaluated, discussed, and compared with already well-investigated dispersants. The good affinity of the surfactants for the CNT sidewalls is highlighted by the presence of resonant van Hove absorption and highly resolved Raman and fluorescence spectra, while the strong hydrophobic interactions and favorable packing between the two alkyl chains of the investigated gemini surfactants and the CNT sidewalls ensure good CNT dispersion. Our results show no selectivity toward specific diameters/chiralities, confirming the twin heads of imidazolium surfactants are pointed toward the bulk water, while the alkyl chains are arranged on the CNT walls, improving water solubility at the expense of potential selectivity.

Optimizing the Interactions of Surfactants with Graphitic Surfaces and Clathrate Hydrates.

Surfactants are amphiphilic molecules active at the surface/interface and able to self-assemble. Because of these properties, surfactants have been extensively used as detergents, emulsifiers, foaming agents, and wetting agents. New perspectives have been opened by the exploitation of surfactants for their capacity to interact as well with simple molecules or surfaces. This feature article gives an overview of significant contributions in the panorama of the current research on surfactants, partly accomplished as well by our research group. We look at several recent applications (e.g., adsorption to graphitic surfaces and interactions with hydrate crystals) with the eye of physical organic chemists. We demonstrate that, from the detailed investigation of the forces involved in the interactions with hydrophobic surfaces, it is possible to optimize the design of the surfactant that is able to form a stable and unbundled carbon nanotube dispersion as well as the best exfoliating agent for graphitic surfaces. By studying the effect of different surfactants on the capacity to favor or disfavor the formation of a gas hydrate, it is possible to highlight the main features that a surfactant should possess in order to be devoted to that specific application.

Graphene oxide improves the biocompatibility of collagen membranes in an in vitro model of human primary gingival fibroblasts

Commercial collagen membranes are used in oral surgical procedures as scaffolds for bone deposition in guided bone regeneration. Here, we have enriched them with graphene oxide (GO) via a simple non-covalent functionalization, exploiting the capacity of oxygenated carbon functional moieties of GO to interact through hydrogen bonding with collagen. In the present paper, the GO-coated membranes have been characterized in terms of stability, nano-roughness, biocompatibility and induction of inflammatory response in human primary gingival fibroblast cells. The obtained coated membranes are demonstrated not to leak GO in the bulk solution, and to change some features of the membrane, such as stiffness and adhesion between the membrane and the atomic force microscopy (AFM) tip. Moreover, the presence of GO increases the roughness and the total surface exposed to the cells, as demonstrated by AFM analyses. The obtained material is biocompatible, and does not induce inflammation in the tested cells.

Diastereomer Interconversion via Enolization: A Case Study

The three-component reaction of indole, isobutyraldehyde, and methyl acetoacetate affords methyl 2-(acetyl)-3-(1H-indol-3-yl)-4-methylpentanoate as a single diastereomer. To investigate the origin of the observed diastereoselectivity, the thermodynamics and kinetics of interconversion of diastereomers 1 and 2 in solution were studied by a combination of (1)H nuclear magnetic resonance (NMR) spectroscopy, high-performance liquid chromatography (HPLC), mass spectrometry, and deuteration experiments. The results indicate that interconversion is both acid- and base-catalyzed, and that the alpha carbon is the only stereolabile center in the molecule. The evidence points to an enolization mechanism for the interconversion process. The selective precipitation of 1 in the presence of the equilibrium 1⇆2 eventually results in the exclusive formation of 1 (crystallization-induced asymmetric transformation).