Topic 4: Advanced materials based on carbon nanostructures.

Focusing on the CNTs-driven activities, our team has developed the first route based on H-bond driven reversible exohedral solubilization/functionalization of multi-walled MWCNTs in apolar organic solvents [J. Am. Chem. Soc., 2011, 133, 15412]. It has been demonstrated that efficient dispersion of CNTs could be obtained through a dynamic combination of self-assembly and self-organization processes involving first the formation of a supramolecular polymer, and subsequently its intertwinement around the outer wall of the MWCNTs (multiwalled carbon nanotubes).

Aiming at extending the concept to aqueous solutions for probing biochemical properties, we have also engineered supramolecular polymers efficiently dispersing CNTs in water and in biological media, in which the lateral alkyl substituents have been replaced by PEG-type chains. This is extremely useful to further increase the water solubility of our recently designed biocompatible, magnetically-active, Fe-filled CNTs [Adv. Funct. Mater., 2013, 23, 3173; Chem. Eur. J., 2015, 21, 9288; Nanoscale, 2015, 7, 20474]. Through a covalent linkage, we recently prepared exohedrally-functionalized Fe-filled CNTs with monoclonal antibody Cetuximab (in coll. with Prof. C. Michiels, University of Namur, Belgium), known to selectively bind the epidermal growth factor receptor (EGFR), a plasma membrane receptor over-expressed (EGFR+) in several cancer cells. In-vitro magnetic filtration experiments demonstrated that a selective removal of cancer cells (red: cancer cells, green: healthy cells) from a mixed population could be obtained with the hybrid material. Aiming at understanding the nature of the interactions between the tubular framework and the antibody, molecular dynamic and docking simulations of the Cetuximab-CNT bioconjugates were performed displaying the predominant role of the hydrophobic interactions [Chem. Eur. J., 2013, 19, 12281; Chem. Soc. Rev., 2015, 44, 6916]. Experiments to determine the bio-distribution profile of the CNT hybrids through magnetic resonance imaging (MRI) both in-vivo and after organ dissection are on going.

In another direction, following our seminal collaborative report with the group led by Prof. N. Armaroli (ISOF-CNR, Bologna, Italy) on luminescent CNTs [Adv. Funct. Mater., 2007, 17, 2975] in which we figured out that the low-lying electronic levels of CNTs do not quench lanthanide-centered emission, we have developed a series of protocols [Chem. Commun., 2011, 47, 1626; invited paper] for the covalent and non-covalent functionalization of MWCNTs with Eu(III) complexes. In order to further enhance the complex loading, MWCNTs were covalently functionalized with a second-generation positively-charged polycationic polyamidoamine (PAMAM) dendron presenting four ammonium groups per grafted aryl moiety [Chem. Eur. J., 2012, 18, 5889]. These newly-designed emissive CNTs hybrids are now being tested as active layers in electroluminescent devices (OLEDs, LECs) where the presence of the carbon material could provide substantial improvements of the conduction properties. In a parallel venue, we also developed an encapsulation protocol to prepare endohedral luminescent MWCNTs with a neutral and hydrophobic tris-hexafluoro acetylacetonate Eu(III) complex [Chem. Eur. J., 2011, 17, 8533]. Another encapsulated material, in which a fullerene-based carrier directed the encapsulation of a negatively-charged Eu(III) complex, has been also prepared showing an enhanced luminescent output suitable for bio-imaging applications [Nanoscale, 2014, 6, 2887].

Aiming at organizing carbon nanotubes in molecular materials, we have designed the first example of anisotropic fluorescent, thermoresponsive hydrogels containing Eu(III)-CNT hybrids, in which a water-soluble polycationic polyvinylpyridinium polymer is ion-paired with an anionic Eu(III) complex [Adv. Mater., 2013, 25, 2462]. Upon alignment of the CNT frameworks induced via a magnetic field, the emission properties of the hydrogel resulted anisotropically affected as compared to the non-magnetically treated materials. Based on these results, future directions with CNTs in our research group are focused on the design and engineering of hierarchically-structured CNTs-based materials in which organic or inorganic molecular guests are encapsulated inside the tubular hollow cavity [New J. Chem.201438, 22], exploiting in-situ and ex-situ protocols, and the external surface is exohedrally modified with covalent or non-covalent peripheral groups. While the electronic active features are dictated by the cavity-induced self-organized guest molecules, the final applications (i.e., catalysis, electrochromic or emitting devices) influence the choice of the external functionalization [Chem. Eur. J.201536, 12769]. Parts of the research objectives described in this section are supported by the European ‘SACS’ project (NMP-FP7 framework). Two main materials are targeted: a) CNT templates shaping hierarchical photosynthetic systems and b) functional platforms for magnetic-driven applications [Chem. Eur. J., 201521, 9288].

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