Titanium dioxide (TiO2) is widely used as ingredient in several products in the nanoform. TiO2-nanoparticles (NPs) are also currently studied for different medical applications. A large debate exists on possible adverse health effects related to their exposure. While there is some evidence of TiO2-NP central nervous system toxicity, their effects on peripheral neurons have been poorly explored. In this study we investigated the effects of TiO2-NPs on dorsal root ganglion (DRG) sensory neurons and satellite glial cells that may be reached by nanoparticles from the bloodstream. We found that TiO2-NPs are internalized in DRG cells and induce apoptosis in a dose dependent manner in both types of cells, ROS production and changes in expression of proinflammatory cytokine IL-1 beta. Furthermore, we found that the axonal retrograde transport is altered in neurons upon exposure to TiO2-NPs. Overall, the results indicate a potential neurotoxic effect of TiO2-NPs on DRG cells. (C) 2015 Elsevier Inc. All rights reserved.

The advantage in coupling adsorption microcalorimetry with IR spectroscopy and/or ab initio modelling in surface studies is illustrated by a selection of examples dealing with metal oxides and silica-based (either non porous or microporous) materials. Correlations between thermodynamic and vibrational parameters are illustrated for the adsorption of CO and of NH3, employed as probe molecules for studying the Lewis/Bronsted acidity of the investigated materials. Surface reconstruction processes, responsible for endothermic effects, are invoked to interpret the unexpectedly low heat measured in the calorimetric cell for the high-coverage adsorption of CO on transition aluminas, the adsorption of NH3 on a defective all-silica zeolite and the adsorption of H2O on an amorphous alumino-silicate.

Some fundamental concepts about the features of a solid material surface and the adsorption at the gas-solid interface are illustrated. The basic tools dealing with the thermodynamics aspects of adsorption processes are also discussed. The stepwise adsorption microcalorimetry technique, which is a tool of greatest quantitative merit in surface chemistry studies, is described in detail through a selection of gas-solid interface systems, taken from different materials science fields. Criteria for discriminating physical and chemical adsorption are given, based on the nature of the forces involved in the process and the heat of adsorption values. The molecular interpretation of the volumetric-calorimetric data, favored by the joint use of adsorption microcalorimetry, spectroscopic and/or ab initio modeling techniques, is also stressed by illustrating a number of examples dealing with either physical or associative/dissociative chemical adsorption.

The membranolytic activity of silica particles toward red blood cells (RBCs) has been known for a long time and is sometimes associated with silica pathogenicity. However, the molecular mechanism and the reasons why hemolysis differs according to the silica form are still obscure. A panel of 15 crystalline (pure and commercial) and amorphous (pyrogenic, precipitated from aqueous solutions, vitreous) silica samples differing in size, origin, morphology, and surface chemical composition were selected and specifically prepared. Silica particles were grouped into six groups to compare their potential in disrupting RBC membranes so that one single property differed in each group, while other features were constant. Free radical production and crystallinity were not strict determinants of hemolytic activity. Particle curvature and morphology modulated the hemolytic effect, but silanols and siloxane bridges at the surface were the main actors. Hemolysis was unrelated to the overall concentration of silanols as fully rehydrated surfaces (such as those obtained from aqueous solution) were inert, and one pyrogenic silica also lost its membranolytic potential upon progressive dehydration. Overall results are consistent with a model whereby hemolysis is determined by a defined surface distribution of dissociated/undissociated silanols and siloxane groups strongly interacting with specific epitopes on the RBC membrane.

Amorphous silicas, opposite to crystalline polymorphs, have been regarded so far as nonpathogenic, but few studies have addressed the toxicity of the wide array of amorphous silica forms. With the advent of nanotoxicology, there has been a rising concern about the safety of silica nanoparticles to be used in nanomedicine. Here, we report a study on the toxicity of amorphous nanostructured silicas obtained with two different preparation procedures (pyrolysis vs. precipitation), the pyrogenic in two very different particle sizes, in order to assess the role of size and origin on surface properties and on the cell damage, oxidative stress, and inflammatory response elicited in murine alveolar macrophages. A quartz dust was employed as positive control and monodispersed silica spheres as negative control. Pyrogenic silicas were remarkably more active than the precipitated one as to cytotoxicity, reactive oxygen species production, lipid peroxidation, nitric oxide synthesis, and production of tumor necrosis factor-α, when compared both per mass and per unit surface. Between the two pyrogenic silicas, the larger one was the more active. Silanols density is the major difference in surface composition among the three silicas, being much larger than the precipitated one as indicated by joint calorimetric and infrared spectroscopy analysis. We assume here that full hydroxylation of a silica surface, with consequent stable coverage by water molecules, reduces/inhibits toxic behavior. The preparation route appears thus determinant in yielding potentially toxic materials, although the smallest size does not always correspond to an increased toxicity.

The affinity towards water of a selection of well-defined, nanostructured hydroxyapatite (HA) samples was investigated by H2O vapour adsorption microcalorimetry and infrared (IR) spectroscopy. A large hydrophilicity of all investigated materials was confirmed. The surface features of hydrated HA were investigated on the as-synthesized samples pre-treated in mild conditions atT=303 K, whereas dehydrated HA features were characterized on samples activated atT=573 K. The relatively large hydrophilicity of the hydrated surface (−ΔadsH∼100–50 kJ mol−1) was due to the interaction of water with the highly polarized H2O molecules strongly coordinated to the surface Ca2+cations. At the dehydrated surface, exposing coordinatively unsaturated (cus) Ca2+cations, H2O was still molecularly adsorbed but more strongly (−ΔadsH∼120–90 kJ mol−1). The use of CO adsorption to quantify the Lewis acidic strength of HA surface sites revealed only a moderate strength ofcusCa2+cations, as confirmed by both microcalorimetric and IR spectroscopic measurements andab initiocalculations. This result implies that the large HA/H2O interaction energy is due to the interplay betweencusCa2+sites and nearby hydrophilic PO4groups, not revealed by the CO probe. The lower density ofcusCa2+cations at the 573 K activated HA surface with respect to the pristine one did not affect the whole hydrophilicity of the surface, as the polarizing effect of Ca sites is so strong to extend up to the fourth hydrated layer, as confirmed by both high-coverage microcalorimetric and IR spectroscopic data. No specific effects due to the investigated specimen preparation method and/or different morphology were observed.

The hydrophilic/hydrophobic properties of a variety of commercial TiO(2) nanoparticles (NP), to be employed as inorganic filters in sunscreen lotions, were investigated both as such (dry powders) and dispersed in aqueous media. Water uptake and the related interaction energy have been determined by means of adsorption microcalorimetry of H(2)O vapor, whereas dispersion features in aqueous solutions were investigated by dynamic light scattering and electrokinetic measurements (zeta potential). The optimized dispersions in cell culture medium were employed to assess the possible in vitro neuro-toxicological effect on dorsal root ganglion (DRG) cells upon exposure to TiO(2)-NP, as a function of crystal phase, surface area and coating. All investigated materials, with the only exception of the uncoated rutile, were found to induce apoptosis on DRG cells; the inorganic/organic surface coating was found not to protect against the TiO(2)-induced apoptosis. The risk profile for DRG cells, which varies for the uncoated samples in the same sequence as the photo-catalytic activity of the different polymorphs: anatase-rutile>anatase>>rutile, was found not to be correlated with the surface hydrophilicity of the uncoated/coated specimens. Aggregates/agglomerates hydrodynamic diameter was comprised in the ~200-400 nm range, compatible with the internalization within DRG cells.

The interaction of molecular ammonia with the highly dehydrated surface of a common nonporous amorphous silica (Aerosil 300 from Degussa) comprises two phenomena: (i) the widely studied H-bonding interaction with isolated surface silanols, with typical IR features, and (ii) an unspecific interaction that escaped detection so far, being not conspicuous in the IR spectra and only clearly revealed by quantitative measurements. These two adsorption processes occur simultaneously, notwithstanding a marked difference in their corresponding interaction energy. The former process is well described by a Langmuir model, the latter by a Henry-type adsorption isotherm. Coupling of adsorption microcalorimetry with IR spectroscopy at a controlled temperature showed that the silanol-related interaction has Delta H-0 = -58.4 kJ mol(-1) and Delta S-0 = -218 J mol(-1) K-1 (reference: 303 K, 1 mbar), whereas the unspecific interaction has Delta H-0 = -26.9 kJ mol(-1) and Delta S-0 = -135 J mol(-1) K-1. The perturbation induced on the IR modes of adsorbed ammonia molecules is small in both cases, and the corresponding frequencies close to those of the gaseous species. Experimentally determined energy values and vibrational features were compared with corresponding results of ab initio calculations (comprising dispersive contributions) on the interaction of ammonia molecules with a slab model of amorphous silica recently investigated by using large-scale periodic B3LYP calculations. All features, both energetic and vibrational, of the silanol-related ammonia adsorption process are accounted for very satisfactorily. Computational results suggest that unspecific adsorption takes place on dehydrated patches of the surface and that such adsorption is dominated by dispersion interactions, while no features of H-bonding are present. The calculated Delta H-0 value (-17.5 kJ mol(-1)) is remarkably smaller than the corresponding experimental value (-26.9 kJ mol(-1)), probably because of some inadequacy of the model to represent the actual structure of the dehydrated patches. The simultaneous occurrence of a weak and a relatively strong ammonia silica interaction, as well as the absence of other possible adsorption modes, is discussed.

Two Zn-doped sol-gel glasses with the same ZnO content (5 wt %; 4% mol) but different overall composition have been synthesized and characterized, in comparison with a bioactive Zn-free reference glass. The role of ZnO in modifying the bioactivity of sol-gel glasses was investigated by soaking the glasses in a simple tris(hydroxymethyl)amino-methane-buffered solution (TRIS-BS), so as to maximize the solubility and to minimize back-precipitation phenomena, which will depend only on the nature and concentration of dissolved glass components. Glass dissolution/ions release in TRIS-BS was monitored by ion coupled plasma emission spectroscopy, whereas modifications of surface composition upon reaction were checked by X-ray photoelectron spectroscopy (XPS). The deposition of a Ca-P layer and the consequent crystallization to hydroxy-apatite (HA) and/or hydroxy-carbonate-apatite (HCA) at the glass surface were investigated by X-ray diffraction and Raman, Fourier transform infrared (FTIR), and XPS spectroscopies. Glass dissolution rate, back-precipitation of silica gel, and formation/crystallization of an apatite-like layer on Zn-containing glasses were found to be either inhibited or delayed, according to the overall glass composition, in that the presence of the network former ZnO component enhances glass reticulation, with the consequent formation of Si-O-Zn units. The presence of a ZnO component has no effect per se, but its influence depends on the overall composition of the glass and, in particular, on the CaO/SiO2 and ZnO/CaO ratios, which determine the nature/structure of Zn and Ca surface species. Glass surface features were investigated by the combined use of in situ FTIR spectroscopy and adsorption microcalorimetry. The role played by surface Ca species, thought to be the most hydrophilic sites, was found to be a decisive factor in both glass dissolution mechanism and formation of an apatite-like surface layer: (i) the scarce dissolution in aqueous media of a (non bioactive) low-Ca and high-silica glass is due to the high reticulation caused by the scarce population of Ca2+ cations in the role of network modifiers; and (ii) the amount of the latter species is, instead, much larger in the corresponding (moderately bioactive) high-Ca and low-silica glass, which dissolves more, although exhibiting a larger durability in aqueous solution than the Zn-free glass.

In vitro bioactivity features of a Ga-modified sol gel Si-Ca-P glass (SGGa) were investigated, in comparison with a plain ternary Si-Ca-P system (SG). Reaction/dissolution of the glass at increasing soaking times in simulated body fluids (SBF) and the consequent growth of an apatite-like layer, monitoring bioactivity, were studied by employing a variety of chemical and physical techniques. The growth of a crystalline apatitic layer at the Ga-modified-glass/SBF interface is severely delayed with respect to the Ga-free glass, and the reasons for it have been looked for in the dramatic changes induced, at the glass/SBF interface, by the presence of the Ga2O3 component. In situ Fourier transform infrared spectroscopy allowed to describe the nature/structure of surface terminations for the two glasses and to reveal/quantify the acidic strength of different Ga species exposed at the SGGa glass surface. 2,6-Dimethylpyridine and carbon monoxide were employed as molecular probes to reveal Bronsted and Lewis acidity. At the surface of the Ga-modified glass, both Bronsted and strong Lewis acidic sites are present. The enhanced surface acitiy of SGGa glass, with respect to the plain glass SG, has been proposed to be responsible for the slower glass dissolution in SBF and for the delayed deposition/crystallization of an apatite-like layer at the glass/SBF interface.

Hydroxyapatite is the mineral component of human bones and teeth enamel and is used as synthetic biomaterial. It also grows outside bioglasses as a response of their incorporation in body fluids. The focus is then on understanding the microscopic steps occurring at its surfaces as this allows researchers to understand the key features of biomolecular adhesion. This perspective article deals with in silico simulations of these processes by quantum-mechanical methods based on density functional theory using the hybrid B3LYP functional and Gaussian basis functions.

H2O adsorption on hexagonal hydroxyapatite (001) and (010) stoichiometric surfaces has been studied at B3LYP level with a localized Gaussian basis set of polarized double-zeta quality using the periodic CRYSTAL06 code. Because four Ca2+ cations are available at both surfaces, the considered H2O coverages span the 1/4<or=theta<or=5/4 range. The affinity of both HA surfaces for H2O is large: on the (001) surface, H2O adsorbs molecularly (binding energies BE approximately 80 kJ mol(-1) per adsorbed molecule), whereas it dissociates on the (010) surface, giving rise to new surface terminations (CaOwHw and POHw). The highly negative reaction energy for H2O dissociation (between -250 and -320 kJ mol(-1) per adsorbed H2O molecule) strongly suggests that the pristine (010) surface "as cut" from the hydroxyapatite bulk cannot survive in aqueous environment. Conversely, on the reacted surface, H2O adsorbs molecularly with BE similar to those computed for the (001) surface. The B3LYP BEs have been contrasted to the experimental water adsorption enthalpies measured by microcalorimetry on polycrystalline hydroxyapatite samples, showing a fairly good agreement and supporting the suggestion that H2O vapor adsorbs on the already reacted (010) crystalline faces. Harmonic B3LYP vibrational features of adsorbed H2O show, when compared to modes of the gas-phase H2O, a hypsochromic shift of the HOH bending mode (Deltadelta(HOH)=49 cm(-1)) and a bathochromic shift of the OH stretching modes larger than 1700 cm(-1) (Deltanu(OH)=427 cm(-1)), which are both in good agreement with literature experimental data.

The adsorption of CH3OH vapor at the surface of Ca-modified silica was studied by means of the combined use of an experimental and a theoretical approach. Parallel IR spectroscopic and microcalorimetric experiments were performed to describe quantitatively and energetically the surface features of nanosized Ca-modified specimens (A200/Cax, activated in mild conditions) as a function of Ca loading and in comparison with the unmodified parent silica (Aerosil 200). The presence of Ca species at the surface enhances the adsorption capacity with respect to the unmodified parent silica and creates a rather complex reactivity. Ab initio simulation provided microscopic information on the energetic of coordinated CH3OH adducts formed at the Ca sites (BE = 104 kJ/mol vs q(diff) similar to 100 kJ/mol) and on the possible reaction path toward products. The methoxylation of the surface, yielding Si-OCH3 and Ca-OH species (and not Ca-OCH3 and Si-OH) occurs only to a limited extent (30-40% of the total methanol uptake) and depends on both CH3OH pressure and time contact, according to the activated reaction pathway, as provided by ab initio simulation. Data from both volumetric-calorimetric and IR spectroscopic experiments indicated, in good agreement with ab initio simulation results, that the overall interaction involves both chemical and physical adsorption processes which, to a large extent, occur simultaneously, the relevant energy transfers being very similar.

In this work, we studied the surface/water interaction properties of a pure calcium hydroxyapatite (HA) and their modifications as a consequence of the partial Ca2+/Mg2+ (MHA) substitution by means of IR spectroscopy and microcalorimetry of adsorbed water. IR data indicated that water molecules in direct contact with the surface of HA are coordinated to surface cations and experience H-bond significantly stronger than in liquid water. The heats of adsorption associated to such interactions are very high, being twice-triple the heat of liquefaction of water. Interestingly, water experiences H-bond higher than in its bulk liquid state also in the second layer. Finally the entering in the material of Mg2+ ions was shown to significantly affect the affinity of the material toward water and the properties of its hydration layers.

A systematic investigation was carried out to elucidate several aspects of the gas/solid methylation of phenol over high Si/Al ratio beta-structured zeolite in protonated form, characterised by various techniques, including XRD, SEM, BET, ICP, FTIR, TGA, microcalorimetry, and modeling by ab initio calculations. Data on the characteristics and the kinetic and mechanistic features of the catalytic reaction, as well as on catalyst deactivation, show that these zeolites, besides being very active for the present reaction, lead to cresols and anisole as primary products. As catalyst deactivation proceeds, the selectivity to cresols and anisole increases substantially, accompanied by a rapid decrease in selectivity to polyalkylated species. Medium- to low-strength silanols are the main contributors to catalyst surface acidity. High-strength Lewis acid sites either are virtually absent (especially when metal cations partially substitute for protons) or play a role essentially in catalyst deactivation. Stacking faults in the zeolite framework, generated by the intergrowth of at least two beta polymorphs, lead to an increased concentration of silanol-based Brønsted acid sites. Deactivation is due to the interaction of phenol and oxygenated products with the silanol-based acid sites and of methanol only with the strong acid sites of both Lewis and Brønsted nature. Self-oligomerisation–cyclisation of methanol to olefins and aromatics, followed by further alkylation to aromatic C atoms, contributes to catalyst deactivation. At any conversion level and at any temperature, the anisole/cresol ratio is systematically lower for the larger-crystal size zeolite, because the secondary transformations of anisole to cresols by both intramolecular rearrangement and intermolecular alkylation of phenol is favoured by the longer residence time of anisole within the zeolite pores.

Lewis sites, in both proton-exchanged zeolites and silico-alumina systems, exhibit different coordination states, depending on the thermal and/or chemical treatments undergone by the material as well as on the experimental conditions. A new modulating effect of the Lewis acidity, similar to that reported for sulfated zirconia, vanadia, and tungstena materials, is addressed here for alumino-silicates, showing that the Lewis acidity of a formal Al(III) site may become "masked" when the local topology around the Al(III) ions allows the latter to expand their coordination by making an extra bond to the aluminosilicate-framework oxygen atoms. Their intrinsic Lewis acidic character is, however, not irreversibly lost because adsorbed molecules of sufficiently high basicity can unhook the Al atom from the framework. Although the "masking" effect has been discovered by ab initio modeling on the edingtonite framework, microcalorimetric data for the adsorption of N-2, CO, and NH3 on a Lewis-rich H-BEA zeolite provides experimental evidence that the "demasking" is an endothermic process occurring only with strong bases like NH3. The resulting enthalpy of adsorption is thus a compromise between the endothermic demasking process and the exothermic interaction with the restored Al(III) site.