A novel thorium (IV) MOF, Th(2,6-naphtalenedicarboxylate)2, has been synthesized via solvothermal reaction of thorium nitrate and 2,6-naphtalendicarboxilyc acid. This compound shows a new structural arrangement with an interesting topology and an excellent thermal resistance, as the framework is stable in air up to 450 °C. Most notably this MOF, combining the radioactivity of its metal center and the scintillation property of the ligand, has been proven capable of spontaneous photon emission.

Spherical hybrid cyanine-silica nanoparticles, quite homogeneous in size (ca. 50 nm) were prepared by the reverse microemulsion method. Solvatochromism tests indicated that all fluorophore molecules were actually entrapped within the inorganic matrix. The combination of steady-state and time-resolved fluorescence measurements allowed us to conclude that almost all cyanine molecules exhibited the same photophysical behavior and this suggested they should be dispersed in a monomeric form. Such behavior resulted in a significant brightness enhancement per cubic nanometer of nanoparticle with respect to molecules in solution. The occurrence of the optical interparticle effect by progressively decreasing the distance among hybrid nanoparticles passing from suspension to a dry powder was also investigated.

As a continuation of our previous work on the kinetics of photocatalytic reduction of NO by CO on titanium dioxide, interaction of a Degussa P-25 TiO2 photocatalyst with NO, CO, and NO−CO mixtures at ambient temperature has been studied by FTIR and TPD. Only reversible weak adsorption of NO on surface Ti4+ ions is found to occur in the dark. UV−vis irradiation greatly enhances the NO adsorption on Ti4+ and yields N2O, NO−, NO2 −, and NO3 − surface species. After irradiation of TiO2 in a CO atmosphere, IR bands of surface CO2 − and CO3 − species appear in addition to a continuous IR absorption tail towards lower wavenumbers due to free carriers in the reduced semiconductor. When TiO2 is exposed to a equimolar NO−CO mixture, N2O and CO2 − are formed without irradiation supposedly by the reaction 2 NO + 2 CO + O2 − → 2 CO2 − + N2O. Subsequent light irradiation is accompanied by the accumulation of NO− and Ti4 +...NO complexes. No TiO2 reduction occurs in this case. FTIR spectra show that NO− produced by the photoinduced adsorption of NO can be eliminated by the following reaction: NO− + CO → italich normalν CO2 − + (1/2) N2. It is believed that this reaction is a key step in the nitrogen production by the photocatalytic process. The data obtained enable us to refine the earlier proposed reaction mechanism and to directly prove some of its key steps.

The adsorption of bovine serum albumin (BSA) on two types of silica nanoparticles (NPs), one pyrolytic (P−SiO 2 ; namely AOX50 by Evonik) and the other colloidal (lab-made by using inverse micelles microemulsion, M−SiO 2 ), is studied. Both materials are characterized in terms of size of primary particles (by transmission electron microscopy), amounts (by thermogravimetry) and distribution of silanols (IR spectroscopy in controlled atmosphere, augmented by H/D isotopic exchange and reaction with VOCl 3 , to distinguish silanols actually located at the surface of nanoparticles), water contact angle, ζ−potential and dispersion state in water, PBS buffer and BSA solutions in PBS (by dynamic light scattering, DLS). Proteins are found to act as dispersing agent toward the large aggregates formed by both types of NPs in PBS buffer, although monodispersion was not attained in the conditions investigated. The problem of the determination of the silica surface actually available in NPs agglomerates for protein adsorption is addressed, and a model based on the external area of the agglomerates determined by DLS is proposed, supported by the trend of ζ−potential in dependence on the amount of adsorbed BSA and by the UV circular dichroism spectra of adsorbed proteins. The spectra reveal the occurrence of protein-protein interactions for BSA on P−SiO 2 , where multilayers of irreversibly adsorbed BSA molecules (i.e. a so called protein hard corona) are proposed to be formed. Conversely, the model indicates the formation of a sub-monolayer protein hard corona on M−SiO 2 . The difference in protein coverage appears to be related to differences in the distribution of surface silanols, more than to differences in ζ−potential.

SiO 2 nanoparticles (NPs), in addition to their widespread utilization in consumer goods, are also being engineered for clinical use. They are considered to exert low toxicity both in vivo and in vitro, but the mechanisms involved in the cellular responses activated by these nanoobjects, even at non toxic doses, have not been characterized in detail.This is of particular relevance for their interaction with the nervous system: silica NPs are good candidates for nanoneuromedicine applications. Here, by using the GT1-7 neuronal cell line, derived from gonadotropin hormone releasing hormone (GnRH) neurons, we describe the mechanisms involved in the perturbation of calcium signaling, a key controller of neuronal function. At the non toxic dose of 20 µg mL -1 , 50nm SiO 2 NPs induce long lasting but reversible calcium signals, that in most cases show a complex oscillatory behavior. Using fluorescent NPs, we show that these signals do not depend on NPs internalization, are totally ascribable to calcium influx and are dependent in a complex way from size and surface charge. We provide evidence of the involvement of voltage-dependent and transient receptor potential-vanilloid 4 (TRPV4) TRPV4 channels.

Highly bright and photostable cyanine dye-doped silica nanoparticles, IRIS Dots, are developed, which can efficiently label human mesenchymal stem cells (hMSCs). The application procedure used to label hMSCs is fast (2 h), the concentration of IRIS Dots for efficient labeling is low (20 μg mL(-1) ), and the labeled cells can be visualized by flow cytometry, confocal microscopy, and transmission electron microscopy. Labeled hMSCs are unaffected in their viability and proliferation, as well as stemness surface marker expression and differentiation capability into osteocytes. Moreover, this is the first report that shows nonfunctionalized IRIS Dots can discriminate between live and early-stage apoptotic stem cells (both mesenchymal and embryonic) through a distinct external cell surface distribution. On the basis of biocompatibility, efficient labeling, and apoptotic discrimination potential, it is suggested that IRIS Dots can serve as a promising stem cell tracking agent.

A well-defined silica nanoparticle model system was developed to study the effect of the size and structure of aggregates on their membranolytic activity. The aggregates were stable and characterized using transmission electron microscopy, dynamic light scattering, nitrogen adsorption, small-angle X-ray scattering, infrared spectroscopy, and electron paramagnetic resonance. Human red blood cells were used for assessing the membranolytic activity of aggregates. We found a decreasing hemolytic activity for increasing hydrodynamic diameter of the nanoparticle aggregates, in contrast to trends observed for isolated particles. We propose here a qualitative model that considers the fractal structure of the aggregates and its influence on membrane deformation to explain these observations. The open structure of the aggregates means that only a limited number of primary particles, from which the aggregates are built up, are in contact with the cell membrane. The adhesion energy is thus expected to decrease resulting in an overall lowered driving force for membrane deformation. Hence, the hemolytic activity of aggregates, following an excessive deformation of the cell membrane, decreases as the aggregate size increases. Our results indicate that the aggregate size and structure determine the hemolytic activity of silica nanoparticle aggregates.

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