Evolution and Reversibility of Host/Guest Interactions with Temperature Changes in a Methyl Red@Palygorskite Polyfunctional Hybrid Nanocomposite

Palygorskite is a microporous clay mineral with several important applications, including use as a dye nanoscaffold, due to its ability to incorporate apt guest molecules and form exceptionally stable composites. Such a property covers widespread fields of interest, from pottery pigments to light harvesting. In all these applications, the stability of these composites at progressively increasing temperatures is an important parameter to determine their condition of usage. This work investigates the nature and strength of the stabilizing host/guest interactions at the basis of the exceptional stability of the methyl red@palygorskite composite system, which undergo a dynamic but reversible evolution depending on the level of heating. A multitechnique analytical protocol involving synchrotron X-ray powder diffraction (S-XRPD) and thermogravimetric analysis (TGA) coupled with infrared spectroscopy (FTIR) and gas chromatography (GC-MS) was followed, which allowed us to sharply identify the species evolved during heating. Moderate temperatures (140–300 °C) cause stabilization of H-bonds between the structural H₂O and the carboxyl group of the dye, whereas higher ones (>300 °C) trigger formation of direct COOH/octahedral Mg bonds favored by dehydration. Cooling below 300 °C implies gradual reversibility of the observed trend due to rehydration from environmental moisture; additional heating (>400 °C), conversely, causes methyl red decomposition, fragmentation, and further expulsion from the host tunnels (∼500 °C). The encapsulated dye in zwitterionic, trans, and/or protonated form affects the hosting system properties, preventing structural folding and strongly modifying the mechanism of water release for both structural and zeolitic H₂O. Experimental results were interpreted also with the help of structural models obtained by molecular mechanics simulations, offering atomistic insights on the mechanisms at the basis of the observed phenomena

Crystalline Phase Modulates the Potency of Nanometric TiO₂ to Adhere to and Perturb the Stratum Corneum of Porcine Skin under Indoor Light

Nanometric TiO₂ is largely employed in cosmetics, but in vitro toxic effects have been reported when nano-TiO₂ is exposed to UV light. The photoreactivity of TiO₂ largely depends on its crystal phase, namely, anatase and rutile. Surface acidity, which is also dependent on crystal structure, may impart a positive or negative charge to the nanomaterial surface and ultimately modulate particle adhesion to tissues. Three nanometric TiO₂ powders with a different crystal lattice and surface charge (anatase, rutile, and anatase/rutile) have been employed here to investigate their interaction with the skin and to examine the molecular mechanisms of the TiO₂-induced oxidative damage. The strength of the interaction of nano-TiO₂ with skin has been revealed by chemiometric mapping (μ-XRF and SEM–EDS) after tissue washing. Positively charged anatase and anatase/rutile, but not negatively charged rutile, were strongly held on the skin surface and were able to promote a structural rearrangement of the lipid bilayer in the stratum corneum (DSC and Raman) under controlled indoor illumination (UVA < 1 mW/m²). Under the same conditions, cell-free reactivity tests (ROS-mediated free-radical release and lipoperoxidation) indicated that anatase and anatase/rutile are more reactive than rutile, suggesting a ROS-mediated oxidative mechanism that may alter the structure of the stratum corneum. Both the higher oxidative potential and the stronger adhesion to skin of anatase and anatase/rutile TiO₂ may explain the stronger disorganization induced by these two samples and suggests the use of rutile to produce safer TiO₂-based cosmetic and pharmaceutical products

Markers of lipid oxidative damage in the exhaled breath condensate of nano TiO₂ production workers

<p>Nanoscale titanium dioxide (nanoTiO₂) is a commercially important nanomaterial. Animal studies have documented lung injury and inflammation, oxidative stress, cytotoxicity and genotoxicity. Yet, human health data are scarce and quantitative risk assessments and biomonitoring of exposure are lacking. NanoTiO₂ is classified by IARC as a group 2B, possible human carcinogen. In our earlier studies we documented an increase in markers of inflammation, as well as DNA and protein oxidative damage, in exhaled breath condensate (EBC) of workers exposed nanoTiO₂. This study focuses on biomarkers of lipid oxidation. Several established lipid oxidative markers (malondialdehyde, 4-hydroxy-trans-hexenal, 4-hydroxy-trans-nonenal, 8-isoProstaglandin F2α and aldehydes C₆–C₁₂) were studied in EBC and urine of 34 workers and 45 comparable controls. The median particle number concentration in the production line ranged from 1.98 × 10⁴ to 2.32 × 10⁴ particles/cm³ with ∼80% of the particles<i> </i><100 nm in diameter. Mass concentration varied between 0.40 and 0.65 mg/m³. All 11 markers of lipid oxidation were elevated in production workers relative to the controls (<i>p</i> < 0.001). A significant dose-dependent association was found between exposure to TiO₂ and markers of lipid oxidation in the EBC. These markers were not elevated in the urine samples. Lipid oxidation in the EBC of workers exposed to (nano)TiO₂ complements our earlier findings on DNA and protein damage. These results are consistent with the oxidative stress hypothesis and suggest lung injury at the molecular level. Further studies should focus on clinical markers of potential disease progression. EBC has reemerged as a sensitive technique for noninvasive monitoring of workers exposed to engineered nanoparticles.</p