Fabio Carniato

A Chemical Strategy for the Relaxivity Enhancement of GdIII Chelates Anchored on Mesoporous Silica Nanoparticles

Functionalised MCM-41 mesoporous silica nanoparticles were used as carriers of Gd(III) complexes for the development of nanosized magnetic resonance imaging contrast agents. Three Gd(III) complexes based on the 1,4,7,10-tetraazacyclododecane scaffold (DOTA; monoamide-, DOTA- and DO3A-like complexes) with distinct structural and magnetic properties were anchored on the silica nanoparticles functionalised with NH(2) groups. The interaction between Gd(III) chelates and surface functional groups markedly influenced the relaxometric properties of the hybrid materials, and were deeply modified passing from ionic -NH(3)(+) to neutral amides. A complete study of the structural, textural and surface properties together with a full (1)H relaxometric characterisation of these hybrid materials before and after surface modification was carried out. Particularly for the anionic complex 2 attached to MCM-41, an impressive increase in relaxivity (r(1p)) was observed (from 20.3 to 37.8 mM(-1) s(-1), 86.2% enhancement at 20 MHz and 310 K), mainly due to a threefold faster water exchange rate after acetylation of the surface -NH(3)(+) ions. This high r(1p) value, coupled with the large molar amount of grafted 2 onto the silica nanoparticles gives rise to a value of relaxivity per particle of 29,500 mM(-1) s(-1), which possibly allows it to be used in molecular imaging procedures. Smaller changes were observed for the hybrid materials based on neutral 1 and 3 complexes. In fact, whereas 1 shows a weak interaction with the surface and acetylation induced only some decrease of the local rotation, complex 3 appears to be involved in a strong interaction with surface silanols. This results in the displacement of a coordinated water molecule and in a decrease of the accessibility of the solvent to the metal centre, which is unaffected by the modification of ammonium ions to neutral amides.

Relaxivity modulation in Gd-functionalised mesoporous silicas.

Two hybrid materials based on mesoporous silicas SBA-15 and MCM-41 functionalized with stable and electrically neutral Gd(iii) macrocyclic complexes were prepared, and their (1)H NMR relaxometric properties investigated as a function of temperature and magnetic field strength.

Titanosilsesquioxane Anchored on Mesoporous Silicas: A Novel Approach for the Preparation of Heterogeneous Catalysts for Selective Oxidations

Polyhedral oligomeric silsesquioxanes (POSS) are a class of condensed three-dimensional organosiliceous compounds with cage frameworks that have different degrees of symmetry. These molecular materials have a general formula R8Si8O12 [1–3] and display silicon atoms bound to one-and-ahalf oxygen atoms (sesqui), the remaining valence being saturated by organic entities (R). Numerous metals have been incorporated successfully into POSS cages with the aim to obtain either specific homogeneous catalysts, or models for active sites of heterogeneous catalysts. For example, POSS cages with titanium(IV) complexes proved to be highly active in the epoxidation of olefins. Special attention was recently devoted to the heterogenisation of Ti–POSS compounds onto insoluble and easily recoverable supports. Interesting examples encompass the incorporation of Ti–POSS into mesoporous MCM-41, sol–gel matrices, polysiloxanes and the preparation of organic–inorganic hybrid materials and coatings based on polystyrene polymers containing Ti–POSS moieties. However, the literature on the direct anchoring, through covalent bonding of preformed Ti–POSS cages onto silica supports is very poor. The stabilisation of Ti–POSS compounds onto silica surfaces through covalent bonds is a relevant issue for obtaining heterogeneous catalysts with isolated active centres, because it may avoid metal leaching from the catalysts. This work is focused on the preparation of Ti–POSSbased heterogeneous catalysts, by anchoring of a functional titanium-containing silsesquioxane on the surface of an ordered mesoporous silica (SBA-15) and of a non-ordered silica (SiO2-Dav). An innovative bifunctional POSS, bearing in the structure both a Ti metal centre and a triethoxy group for grafting on the silica surfaces, was specifically synthesised for this purpose and named Ti–POSS–TSIPI (Scheme 1, 2). Ti–POSS–TSIPI was prepared by an equimolar reaction between Ti–NH2POSS (Scheme 1, 1), the synthesis of which was reported by some of us, and 3-isocyanatopropyl triethoxysilane (TSIPI) under basic conditions. The product of the reaction was monitored by both IR (Figure 1) and H NMR spectroscopy (see Experimental

Selective Anchoring of GdIII Chelates on the External Surface of Organo-Modified Mesoporous Silica Nanoparticles: A New Chemical Strategy To Enhance Relaxivity

The optimization of the physico-chemical properties of both Gd(III) chelates and nanocarriers is of great importance for the development of effective nanosystems for magnetic resonance imaging (MRI) applications. With this aim, macrocyclic Gd(III) chelates were selectively attached to the pendant amino groups exposed to the external surface of spheroidal mesoporous silica nanoparticles (MSNs). This was achieved by treating the metal complexes with MSNs that contained the templating surfactant molecules confined within the silica channels (hexadecyltrimethylammonium (CTA)/MSN), followed by extraction of the surfactant. The nanoparticles showed greatly improved (1)H relaxometric efficiency relative to corresponding systems that also feature Gd(III) chelates conjugated inside the pores. A further significant relaxivity enhancement was observed after chemical transformation of the free amino groups into amides. The ionic relaxivity of the final nanoparticles (r(1p) =79.1 mM(-1) s(-1); 0.5 T, 310 K) is one of the highest reported so far.

On the hydrothermal stability of MCM-41 mesoporous silica nanoparticles and the preparation of luminescent materials

MCM-41 nanoparticles have recently attracted growing scientific interest for applications in biomedical and diagnostic fields, nevertheless their use is limited because of the low hydrothermal stability, rendering them not suitable for functionalisation (i.e. dye molecules loading, anchoring of luminescent guests, etc.) in aqueous media. In this work, nanosized MCM-41 was hydrothermally stabilised by properly adapting post-synthesis hydrothermal restructuring treatment already used for conventional MCM-41 material (particle size in the micron range). A significant improvement of the hydrothermal stability of nanosized MCM-41 was reached: the pore array of the stabilized MCM-41 was not significantly modified after hydrothermal treatment at 333 K, whereas under the same conditions the parent MCM-41 became partially amorphized. The hydrothermal stabilisation is due to pore wall restructuring occurring during post-synthesis modification, and an increase of hydrophobicity of the silica surface. The improved hydrothermal stability of nanosized MCM-41 rendered this solid suitable for dye impregnation in aqueous media and allowed the preparation of a luminescent fluorescein/MCM-41 nanocomposite material, which in aqueous suspension showed an emission efficiency 5 times higher than an equimolar fluorescein solution.

Niobium(V) Saponite Clay for the Catalytic Oxidative Abatement of Chemical Warfare Agents

A Nb(V)-containing saponite clay was designed to selectively transform toxic organosulfur chemical warfare agents (CWAs) under extremely mild conditions into nontoxic products with reduced environmental impact. Thanks to the insertion of Nb(V) sites within the saponite framework, a bifunctional catalyst with strong oxidizing and acid properties was obtained. Remarkable activity and high selectivity were observed for the oxidative abatement of (2-chloroethyl)ethyl sulfide (CEES), a simulant of sulfur mustard, at room temperature with aqueous hydrogen peroxide. This performance was significantly better compared to a conventional commercial decontamination powder.

A versatile route to bifunctionalized silsesquioxane (POSS): synthesis and characterisation of Ti-containing aminopropylisobutyl-POSS

A facile synthetic pathway leading to significant yields of bifunctional polyhedral oligomeric silsesquioxanes (POSS) with two different functionalities on the same cage structure, namely Ti-NH2POSS, is proposed in this manuscript.

Preparation of luminescent ZnO nanoparticles modified with aminopropyltriethoxy silane for optoelectronic applications

Highly luminescent ZnO nanoparticles have been synthesized through a co-precipitation method, starting from a solution of zinc acetate in methanol and precipitating the oxide phase in basic media in the presence of variable amounts of aminopropyltriethoxy silane (APTS). The adopted conditions led to the condensation between Zn-OH species and the alkoxy functionalities of the organosilane during the formation of nanoparticles (one-pot method) thus allowing covalent binding of organic functionalities on the ZnO surface. HR-TEM measurements indicated that samples synthesized with increasing concentration of APTS (from 1 to 10% of Si/Zn molar ratio) are made of ZnO nanoparticles of decreasing dimension, passing from ca. 6 nm for pure ZnO to ca. 3 nm for the ZnO functionalized with the highest organosilane loading. ZnO samples with reduced particle size showed a significant variation of the optical properties. In particular, the particle size reduction is associated with a significant modification of ZnO absorption properties, as studied by diffuse reflectance UV-Vis spectroscopy, and to an exceedingly high photoemission. The organo-modified ZnO nanopowder with the highest photoemission was successfully tested as a light-emitting layer in a new generation of LED devices thus proving that they also possess interesting electroluminescent properties.

Rational design of single-site heterogeneous catalysts: towards high chemo-, regio- and stereoselectivity

The main methods for the design and preparation of single-site heterogeneous catalysts on inorganic oxide supports are described and reviewed. Catalytically active metal sites can be either introduced into the framework of porous materials via direct synthesis or added to a pre-existing support by post-synthesis techniques. Particular attention is paid to selected examples where the geometry, the nature and the chemical surroundings of the active single site is a key factor to obtain catalytic systems with enhanced chemo-, regio- and stereoselectivity. The ever-increasing capabilities of ‘nanoarchitecture’ at molecular level enable chemists to build ideal catalysts for the sustainable transformation of bulky and high added-value molecules.

On a novel catalytic system based on electrospun nanofibers and M-POSS.

We report on a novel catalytic system based on electrospun polymer nanofibers, which were modified with a metal-containing polyhedral oligomeric silsesquioxanes (M-POSS). In particular, a titanium-based POSS, characterized by an amino group as reactive side, was contacted with poly(styrene-co-maleic anhydride) (PSMA) nanofibers, which were dispersed in a solvent capable of solubilizing the above metal silsesquioxane. FTIR measurements evidenced the occurrence of the reaction between the MA group of PSMA and the amino group of POSS molecule. The catalytic activity of the PSMA/Ti-POSS-NH(2) system was proved in the degradation of sulforhodamine B under UV light. The presence of metal center, directly attached to the nanofiber surface, renders the system catalytically active.