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Surface dehydroxylation of amorphous and crystalline silicas (quartz dust) has been investigated from the standpoint of the development of hydrophobicity upon thermal treatment. Hydrophobicity occurs when only siloxane bridges and isolated silanols (IR band at ca. 3750 cm-') are present and is monitored by an enthalpy of adsorption of water lower than the latent heat of liquefaction (44 kJ mol-'). This calorimetric method allows the evaluation of the extent of hydrophilic and hydrophobic patches when both are present at the surface. All silicas develop hydrophobicity upon thermal treatment in vacuo, but quartz is much less easily dehydroxylated than amorphous materials. It is still mainly hydrophilic after outgassing at 1073 K, whereas pyrogenic silicas (Aerosil) become hydrophobic upon outgassing at T < 673 K. Quartz is also characterized by a few very reactive sites (q 9 90 kJ mol-'), absent on the amorphous specimens. Both these facts might be related to the specific quartz pathogenicity. Rehydroxylation at room temperature of dehydroxylated silicas occurs to a very limited extent. Hydrophilic patches exhibit a marked heterogeneity towards water with an enthalpy of adsorption decreasing from 90 to 44 kJ mol-'. The enthalpy of adsorption approaches 44 kJ mol-' corresponding to the addition of multilayers of adsorbed water.

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Experimental studies indicate that carbon nanotubes (CNTs) have the potential to induce adverse pulmonary effects, including alveolitis, fibrosis, and genotoxicity in epithelial cells. Here, we explored the physicochemical determinants of these toxic responses with progressively and selectively modified CNTs: ground multiwall CNTs modified by heating at 600 degrees C (loss of oxygenated carbon functionalities and reduction of oxidized metals) or at 2400 degrees C (annealing of structural defects and elimination of metals) and by grinding the material that had been heated at 2400 degrees C before (introduction of structural defects in a metal-deprived framework). The CNTs were administered intratracheally (2 mg/rat) to Wistar rats to evaluate the short-term response (3 days) in bronchoalveolar lavage fluid (LDH, proteins, cellular infiltration, IL-1beta, and TNF-alpha). The long-term (60 days) lung response was assessed biochemically by measuring the lung hydroxyproline content and histologically. In vitro experiments were also performed on rat lung epithelial cells to assess the genotoxic potential of the modified CNTs with the cytokinesis block micronucleus assay. The results show that the acute pulmonary toxicity and the genotoxicity of CNT were reduced upon heating but restored upon grinding, indicating that the intrinsic toxicity of CNT is mainly mediated by the presence of defective sites in their carbon framework.

The potential for free radical release has been measured by means of the spin trapping technique on three kinds of iron containing particulate: two asbestos fibers (chrysotile and crocidolite); an iron-exchanged zeolite and two iron oxides (magnetite and haematite). DMPO (5,5'-dimethyl-1-pirroline-N-oxide), used as spin trap in aqueous suspensions of the solids, reveals the presence of the hydroxyl and carboxylate radicals giving rise respectively to the two adducts [DMPO-OH] and [DMPO-CO2], each characterized by a well-defined EPR spectrum. Two target molecules have been considered: the formate ion to evidence potential for hydrogen abstraction in any biological compartment and hydrogen peroxide, always present in the phagosome during phagocytosis. The kinetics of decomposition of hydrogen peroxide has also been measured on all solids. Ferrozine and desferrioxamine, specific chelators of Fe(II) and Fe(III) respectively, have been used to remove selectively iron ions. Iron is implicated in free radical release but the amount of iron at the surface is unrelated to the amount of radicals formed. Only few surface ions in a particular redox and coordination state are active. Three different kinds of sites have been evidenced: one acting as H abstracter, the other as a heterogeneous catalyst for hydroxyl radical release, the third one related to catalysis of hydrogen peroxide disproportionation. In both mechanisms of free radical release, the Fe-exchanged zeolite mimics the behaviour of asbestos whereas the two oxides are mostly inert. Conversely magnetite turns out to be an excellent catalyst for hydrogen peroxide disproportionation while haematite is inactive also in this reaction. The results agree with the implication of a radicalic mechanism in the in vitro DNA damage and in the in vivo toxicity of asbestos.

Nanotoxicology studies require investigations of several physico-chemical aspects of the particle/body fluid interaction, here described by reviewing recent literature in the light of new experimental data. Current characterization mostly covers morphology and metric-related characteristics (form, chemical composition, specific surface area, primary particle size and size distribution), and is mandatory in any experimental study. To unveil toxicity mechanisms, several other physico-chemical properties relevant to (geno) toxicity need to be assessed, typically the release or quenching of radical/ROS (Reactive Oxygen Species), the presence of active metal ions, evidence of structural defects. Major tasks for physical chemists working on nanoparticles-induced genotoxicity are described with some examples: (i), Tailored preparation of the same material in different sizes; (ii) particle modification changing a single property at a time; and (iii) identification of appropriate reference materials. Phenomena occurring during the contact between nanoparticles and cellular media or biological fluids (dispersion, agglomeration/aggregation, protein adsorption) are discussed in relation to the surface properties of the nanoparticles considered.

The adsorption of carbon dioxide onto M-ZSM-5 zeolites (M = Li, Na, K, Cs) was studied by means of FTIR spectroscopy and adsorption microcalorimetry. Quantum chemical calculations, at the B3-LYP level, on the interaction of CO2 with the bare alkali-metal cations were performed to assist interpretation of the experimental results. With the likely exception of Li+, CO2 was found to undergo a two-step interaction with the metal ions. At a low equilibrium pressure linear 1:1 adducts of the type M+···OCO (M = Na+, K+, Cs+) are formed; upon increasing the CO2 equilibrium pressure, the metal cation coordinates a second CO2 molecule, forming a 2:1 adduct. Calculated (ab initio) bond lengths for the 1:1 adduct are given, as well as corresponding values of the binding energy and enthalpic term. Experimentally derived values of the main thermodynamic functions (ΔH°, ΔG°, and ΔS°) are discussed and correlated with detailed results from IR spectroscopy. The interaction cation/CO2 alone cannot account for the body of evidence, and the contribution of nearby O2- anions has to be invoked.