Publications by authors named "Francesco Turci"

72 Publications

Antioxidant Activity of Silica-Based Bioactive Glasses.

ACS Biomater Sci Eng 2021 Apr 27. Epub 2021 Apr 27.

Politecnico di Torino, Department of Applied Science and Technology, Institute of Materials Physics and Engineering, Torino 10129, Italy.

Bioactive glasses are the materials of choice in the field of bone regeneration. Antioxidant properties of interest to limit inflammation and foreign body reactions have been conferred to bioactive glasses by the addition of appropriate ions (such as Ce or Sr). On the other hand, the antioxidant activity of bioactive glasses without specific ion/molecular doping has been occasionally cited in the literature but never investigated in depth. In the present study, three silica-based bioactive glasses have been developed and characterized for their surface properties (wettability, zeta potential, chemical composition, and reactivity) and radical scavenging activity in the presence/absence of cells. For the first time, the antioxidant activity of simple silica-based (SiO-CaO-NaO) bioactive glasses has been demonstrated.
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http://dx.doi.org/10.1021/acsbiomaterials.1c00048DOI Listing
April 2021

Phase Separation and Multibody Effects in Three-Dimensional Active Brownian Particles.

Phys Rev Lett 2021 Jan;126(3):038002

H. H. Wills Physics Laboratory, Tyndall Avenue, Bristol, BS8 1TL, United Kingdom.

Simulation studies of the phase diagram of repulsive active Brownian particles in three dimensions reveal that the region of motility-induced phase separation between a high and low density phase is enclosed by a region of gas-crystal phase separation. Near-critical loci and structural crossovers can additionally be identified in analogy with simple fluids. Motivated by the striking similarity to the behavior of equilibrium fluids with short-ranged pairwise attractions, we show that a direct mapping to pair potentials in the dilute limit implies interactions that are insufficiently attractive to engender phase separation. Instead, this is driven by the emergence of multibody effects associated with particle caging that occurs at sufficiently high number density. We quantify these effects via information-theoretical measures of n-body effective interactions extracted from the configurational structure.
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http://dx.doi.org/10.1103/PhysRevLett.126.038002DOI Listing
January 2021

Short Preirradiation of TiO Nanoparticles Increases Cytotoxicity on Human Lung Coculture System.

Chem Res Toxicol 2021 Mar 17;34(3):733-742. Epub 2021 Jan 17.

Mines Saint-Etienne, Univ Lyon, Univ Jean Monnet, INSERM, U 1059 Sainbiose, Centre CIS, F-42023 Saint-Etienne, France.

Anatase titanium dioxide nanoparticles (TiO NPs) are used in a large range of industrial applications mainly due to their photocatalytic properties. Before entering the lung, virtually all TiO NPs are exposed to some UV light, and lung toxicity of TiO NPs might be influenced by photoexcitation that is known to alter TiO surface properties. Although the TiO NPs toxicity has been extensively investigated, limited data are available regarding the toxicity of TiO NPs that have been pre-exposed to UV light, and their impact on humans remains unknown. In this study, five types of TiONPs with tailored physicochemical features were characterized and irradiated by UV for 30 min. Following irradiation, cytotoxicity, pro-inflammatory response, and oxidative stress on a human lung coculture system (A549 epithelial cells and macrophages differentiated from THP-1 cells) were assessed. The surface charge of all samples was less negative after UV irradiation of TiO NPs, and the average aggregate size was slightly increased. A higher cytotoxic effect was observed for preirradiated TiO NPs compared to nonirradiated samples. Preirradiation of TiO NPs had no significant impact on the pro-inflammatory response and oxidative stress as shown by a similar production of IL-8, TNF-α, and reactive oxygen species.
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http://dx.doi.org/10.1021/acs.chemrestox.0c00354DOI Listing
March 2021

Nearly free surface silanols are the critical molecular moieties that initiate the toxicity of silica particles.

Proc Natl Acad Sci U S A 2020 11 23;117(45):27836-27846. Epub 2020 Oct 23.

Department of Chemistry, University of Turin, 10124 Turin, Italy.

Inhalation of silica particles can induce inflammatory lung reactions that lead to silicosis and/or lung cancer when the particles are biopersistent. This toxic activity of silica dusts is extremely variable depending on their source and preparation methods. The exact molecular moiety that explains and predicts this variable toxicity of silica remains elusive. Here, we have identified a unique subfamily of silanols as the major determinant of silica particle toxicity. This population of "nearly free silanols" (NFS) appears on the surface of quartz particles upon fracture and can be modulated by thermal treatments. Density functional theory calculations indicates that NFS locate at an intersilanol distance of 4.00 to 6.00 Å and form weak mutual interactions. Thus, NFS could act as an energetically favorable moiety at the surface of silica for establishing interactions with cell membrane components to initiate toxicity. With ad hoc prepared model quartz particles enriched or depleted in NFS, we demonstrate that NFS drive toxicity, including membranolysis, in vitro proinflammatory activity, and lung inflammation. The toxic activity of NFS is confirmed with pyrogenic and vitreous amorphous silica particles, and industrial quartz samples with noncontrolled surfaces. Our results identify the missing key molecular moieties of the silica surface that initiate interactions with cell membranes, leading to pathological outcomes. NFS may explain other important interfacial processes involving silica particles.
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http://dx.doi.org/10.1073/pnas.2008006117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7668052PMC
November 2020

Competing active and passive interactions drive amoebalike crystallites and ordered bands in active colloids.

Phys Rev E 2020 Sep;102(3-1):032609

H.H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, United Kingdom.

Swimmers and self-propelled particles are physical models for the collective behavior and motility of a wide variety of living systems, such as bacteria colonies, bird flocks, and fish schools. Such artificial active materials are amenable to physical models which reveal the microscopic mechanisms underlying the collective behavior. Here we study colloids in a dc electric field. Our quasi-two-dimensional system of electrically driven particles exhibits a rich and exotic phase behavior exhibiting passive crystallites, motile crystallites, an active gas, and banding. Amongst these are two mesophases, reminiscent of systems with competing interactions. At low field strengths activity suppresses demixing, leading to motile crystallites. Meanwhile, at high field strengths, activity drives partial demixing to traveling bands. We parametrize a particulate simulation model which reproduces the experimentally observed phases.
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http://dx.doi.org/10.1103/PhysRevE.102.032609DOI Listing
September 2020

Dynamical phase transitions and their relation to structural and thermodynamic aspects of glass physics.

J Chem Phys 2020 Sep;153(9):090901

Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128 Mainz, Germany.

We review recent developments in structural-dynamical phase transitions in trajectory space based on dynamic facilitation theory. An open question is how the dynamic facilitation perspective on the glass transition may be reconciled with thermodynamic theories that posit collective reorganization accompanied by a growing static length scale and, eventually, a vanishing configurational entropy. In contrast, dynamic facilitation theory invokes a dynamical phase transition between an active phase (close to the normal liquid) and an inactive phase, which is glassy and whose order parameter is either a time-averaged dynamic or structural quantity. In particular, the dynamical phase transition in systems with non-trivial thermodynamics manifests signatures of a lower critical point that lies between the mode-coupling crossover and the putative Kauzmann temperature, at which a thermodynamic phase transition to an ideal glass state would occur. We review these findings and discuss such criticality in the context of the low-temperature decrease in configurational entropy predicted by thermodynamic theories of the glass transition.
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http://dx.doi.org/10.1063/5.0006998DOI Listing
September 2020

Impact of the Physicochemical Features of TiO Nanoparticles on Their Toxicity.

Chem Res Toxicol 2020 Sep 24;33(9):2324-2337. Epub 2020 Aug 24.

Mines Saint-Etienne, Université Lyon, Université Jean Monnet, INSERM, U1059 Sainbiose, Centre CIS, F-42023 Saint-Etienne, France.

The concern about titanium dioxide nanoparticles (TiO-NPs) toxicity and their possible harmful effects on human health has increased. Their biological impact is related to some key physicochemical properties, that is, particle size, charge, crystallinity, shape, and agglomeration state. However, the understanding of the influence of such features on TiO-NP toxicity remains quite limited. In this study, cytotoxicity, proinflammatory response, and oxidative stress caused by five types of TiO-NPs with different physicochemical properties were investigated on A549 cells used either as monoculture or in co-culture with macrophages differentiated from the human monocytic THP-1 cells. We tailored bulk and surface TiO physicochemical properties and differentiated NPs for size/specific surface area, shape, agglomeration state, and surface functionalization/charge (aminopropyltriethoxysilane). An impact on the cytotoxicity and to a lesser extent on the proinflammatory responses depending on cell type was observed, namely, smaller, large-agglomerated TiO-NPs were shown to be less toxic than P25, whereas rod-shaped TiO-NPs were found to be more toxic. Besides, the positively charged particle was slightly more toxic than the negatively charged one. Contrarily, TiO-NPs, whatever their physicochemical properties, did not induce significant ROS production in both cell systems compared to nontreated control groups. These results may contribute to a better understanding of TiO-NPs toxicity in relation with their physicochemical features.
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http://dx.doi.org/10.1021/acs.chemrestox.0c00106DOI Listing
September 2020

Thermal inertization of amphibole asbestos modulates Fe topochemistry and surface reactivity.

J Hazard Mater 2020 Nov 10;398:123119. Epub 2020 Jun 10.

"G. Scansetti" Center for Studies on Asbestos and Other Toxic Particulates and Dipartimento di Chimica, Università di Torino, V. P. Giuria 7, I-10125, Turin, Italy. Electronic address:

This study discloses the morphological and chemical-structural modifications that occur during thermal degradation of amphibole asbestos. Low-iron tremolite and iron-rich crocidolite were heated at temperatures ranging from r.t. to 1200 °C. Heating promoted a complex sequence of iron oxidation, migration and/or clustering and, finally, the formation of brittle fibrous pseudomorphs consisting of newly formed minerals and amorphous nanophases. The effects of the thermal modifications on toxicologically relevant asbestos reactivity were evaluated by quantifying carbon- and oxygen-centred, namely hydroxyl (OH), radicals. Heating did not alter carbon radicals, but largely affected oxygen-centred radical yields. At low temperature, reactivity of both amphiboles decreased. At 1200 °C, tremolite structural breakdown was achieved and the reactivity was further reduced by migration of reactive iron ions into the more stable TO tetrahedra of the newly formed pyroxene(s). Differently, crocidolite breakdown at 1000 °C induced the formation of hematite, Fe-rich pyroxene, cristobalite, and abundant amorphous material and restored radical reactivity. Our finding suggests that thermally treated asbestos and its breakdown products still share some toxicologically relevant properties with pristine fibre. Asbestos inertization studies should consider morphology and surface reactivity, beyond crystallinity, when proving that a thermally inactivated asbestos-containing material is safe.
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http://dx.doi.org/10.1016/j.jhazmat.2020.123119DOI Listing
November 2020

Cytotoxicity of fractured quartz on THP-1 human macrophages: role of the membranolytic activity of quartz and phagolysosome destabilization.

Arch Toxicol 2020 09 26;94(9):2981-2995. Epub 2020 Jun 26.

"G. Scansetti" Interdepartmental Center for Studies On Asbestos and Other Toxic Particulates, Department of Chemistry, University of Torino, Via P. Giuria 7, 10125, Turin, Italy.

The pathogenicity of quartz involves lysosomal alteration in alveolar macrophages. This event triggers the inflammatory cascade that may lead to quartz-induced silicosis and eventually lung cancer. Experiments with synthetic quartz crystals recently showed that quartz dust is cytotoxic only when the atomic order of the crystal surfaces is upset by fracturing. Cytotoxicity was not observed when quartz had as-grown, unfractured surfaces. These findings raised questions on the potential impact of quartz surfaces on the phagolysosomal membrane upon internalization of the particles by macrophages. To gain insights on the surface-induced cytotoxicity of quartz, as-grown and fractured quartz particles in respirable size differing only in surface properties related to fracturing were prepared and physico-chemically characterized. Synthetic quartz particles were compared to a well-known toxic commercial quartz dust. Membranolysis was assessed on red blood cells, and quartz uptake, cell viability and effects on lysosomes were assessed on human PMA-differentiated THP-1 macrophages, upon exposing cells to increasing concentrations of quartz particles (10-250 µg/ml). All quartz samples were internalized, but only fractured quartz elicited cytotoxicity and phagolysosomal alterations. These effects were blunted when uptake was suppressed by incubating macrophages with particles at 4 °C. Membranolysis, but not cytotoxicity, was quenched when fractured quartz was incubated with cells in protein-supplemented medium. We propose that, upon internalization, the phagolysosome environment rapidly removes serum proteins from the quartz surface, restoring quartz membranolytic activity in the phagolysosomes. Our findings indicate that the cytotoxic activity of fractured quartz is elicited by promoting phagolysosomal membrane alteration.
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http://dx.doi.org/10.1007/s00204-020-02819-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7415752PMC
September 2020

Structural Ordering in Liquid Gallium under Extreme Conditions.

Phys Rev Lett 2020 Apr;124(14):145501

School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, United Kingdom.

The atomic-scale structure, melting curve, and equation of state of liquid gallium has been measured to high pressure (p) and high temperature (T) up to 26 GPa and 900 K by in situ synchrotron x-ray diffraction. Ab initio molecular dynamics simulations up to 33.4 GPa and 1000 K are in excellent agreement with the experimental measurements, providing detailed insight at the level of pair distribution functions. The results reveal an absence of dimeric bonding in the liquid state and a continuous increase in average coordination number n[over ¯]_{Ga}^{Ga} from 10.4(2) at 0.1 GPa approaching ∼12 by 25 GPa. Topological cluster analysis of the simulation trajectories finds increasing fractions of fivefold symmetric and crystalline motifs at high p-T. Although the liquid progressively resembles a hard-sphere structure towards the melting curve, the deviation from this simple description remains large (≥40%) across all p-T space, with specific motifs of different geometries strongly correlating with low local two-body excess entropy at high p-T.
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http://dx.doi.org/10.1103/PhysRevLett.124.145501DOI Listing
April 2020

LiCoO particles used in Li-ion batteries induce primary mutagenicity in lung cells via their capacity to generate hydroxyl radicals.

Part Fibre Toxicol 2020 01 29;17(1). Epub 2020 Jan 29.

Louvain centre for Toxicology and Applied Pharmacology, Institut de Recherche Expérimentale et Clinique, Université catholique de Louvain, Avenue Hippocrate 57, box B1.57.06, 1200, Brussels, Belgium.

Background: Li-ion batteries (LIB) are used in most portable electronics. Among a wide variety of materials, LiCoO (LCO) is one of the most used for the cathode of LIB. LCO particles induce oxidative stress in mouse lungs due to their Co content, and have a strong inflammatory potential. In this study, we assessed the mutagenic potential of LCO particles in lung cells in comparison to another particulate material used in LIB, LTO (LiTiO), which has a low inflammatory potential compared to LCO particles.

Results: We assessed the mutagenic potential of LCO and LTO particles in vitro by performing a cytokinesis-block micronucleus (MN) assay with rat lung epithelial cells (RLE), as well as in vivo in alveolar type II epithelial (AT-II) cells. LCO particles induced MN in vitro at non-cytotoxic concentrations and in vivo at non-inflammatory doses, indicating a primary genotoxic mechanism. LTO particles did not induce MN. Electron paramagnetic resonance and terephthalate assays showed that LCO particles produce hydroxyl radicals (•OH). Catalase inhibits this •OH production. In an alkaline comet assay with the oxidative DNA damage repair enzyme human 8-oxoguanine DNA glycosylase 1, LCO particles induced DNA strand breaks and oxidative lesions. The addition of catalase reduced the frequency of MN induced by LCO particles in vitro.

Conclusions: We report the mutagenic activity of LCO particles used in LIB in vitro and in vivo. Our data support the role of Co(II) ions released from these particles in their primary genotoxic activity which includes the formation of •OH by a Fenton-like reaction, oxidative DNA lesions and strand breaks, thus leading to chromosomal breaks and the formation of MN. Documenting the genotoxic potential of the other LIB particles, especially those containing Co and/or Ni, is therefore needed to guarantee a safe and sustainable development of LIB.
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http://dx.doi.org/10.1186/s12989-020-0338-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6990559PMC
January 2020

Many-body correlations from integral geometry.

Phys Rev E 2019 Dec;100(6-1):062126

H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, United Kingdom.

In a recent letter we presented a framework for predicting the concentrations of many-particle local structures inside the bulk liquid as a route to assessing changes in the liquid approaching dynamical arrest. Central to this framework was the morphometric approach, a synthesis of integral geometry and liquid-state theory, which has traditionally been derived from fundamental measure theory. We present the morphometric approach in a new context as a generalization of scaled-particle theory, and we derive several morphometric theories for hard spheres of fundamental and practical interest. Our central result is a new theory that is particularly suited to the treatment of many-body correlation functions in the hard-sphere liquid, which we demonstrate by numerical tests against simulation.
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http://dx.doi.org/10.1103/PhysRevE.100.062126DOI Listing
December 2019

The puzzling issue of silica toxicity: are silanols bridging the gaps between surface states and pathogenicity?

Part Fibre Toxicol 2019 08 16;16(1):32. Epub 2019 Aug 16.

Department of Chemistry, G. Scansetti Center, University of Torino, Turin, Italy.

Background: Silica continues to represent an intriguing topic of fundamental and applied research across various scientific fields, from geology to physics, chemistry, cell biology, and particle toxicology. The pathogenic activity of silica is variable, depending on the physico-chemical features of the particles. In the last 50 years, crystallinity and capacity to generate free radicals have been recognized as relevant features for silica toxicity. The 'surface' also plays an important role in silica toxicity, but this term has often been used in a very general way, without defining which properties of the surface are actually driving toxicity. How the chemical features (e.g., silanols and siloxanes) and configuration of the silica surface can trigger toxic responses remains incompletely understood.

Main Body: Recent developments in surface chemistry, cell biology and toxicology provide new avenues to improve our understanding of the molecular mechanisms of the adverse responses to silica particles. New physico-chemical methods can finely characterize and quantify silanols at the surface of silica particles. Advanced computational modelling and atomic force microscopy offer unique opportunities to explore the intimate interactions between silica surface and membrane models or cells. In recent years, interdisciplinary research, using these tools, has built increasing evidence that surface silanols are critical determinants of the interaction between silica particles and biomolecules, membranes, cell systems, or animal models. It also has become clear that silanol configuration, and eventually biological responses, can be affected by impurities within the crystal structure, or coatings covering the particle surface. The discovery of new molecular targets of crystalline as well as amorphous silica particles in the immune system and in epithelial lung cells represents new possible toxicity pathways. Cellular recognition systems that detect specific features of the surface of silica particles have been identified.

Conclusions: Interdisciplinary research bridging surface chemistry to toxicology is progressively solving the puzzling issue of the variable toxicity of silica. Further interdisciplinary research is ongoing to elucidate the intimate mechanisms of silica pathogenicity, to possibly mitigate or reduce surface reactivity.
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http://dx.doi.org/10.1186/s12989-019-0315-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6697921PMC
August 2019

Dynamical solid-liquid transition through oscillatory shear.

Soft Matter 2019 May;15(21):4371-4379

École Normale Supérieure de Lyon, 65 Allée d'Italie, 69007 Lyon, France.

Starting from an ideal crystalline state, we numerically study a nonequilibrium dynamical order-disorder transition promoted by the application of a periodic shearing protocol at low temperatures in model systems in three dimensions. We observe a discontinuous dynamical transition from an ordered to a disordered steady state. Through the analysis of large-scale simulations, we show that the amorphization mechanism around the discontinuous transition is reminiscent of spinodal decomposition.
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http://dx.doi.org/10.1039/c8sm01950aDOI Listing
May 2019

Morphometric Approach to Many-Body Correlations in Hard Spheres.

Phys Rev Lett 2019 Feb;122(6):068004

H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, United Kingdom.

We model the thermodynamics of local structures within the hard sphere liquid at arbitrary volume fractions through the morphometric calculation of n-body correlations. We calculate absolute free energies of local geometric motifs in excellent quantitative agreement with molecular dynamics simulations across the liquid and supercooled liquid regimes. We find a bimodality in the density library of states where fivefold symmetric structures appear lower in free energy than fourfold symmetric structures and from a single reaction path predict a dynamical barrier which scales linearly in the compressibility factor. The method provides a new route to assess changes in the free energy landscape at volume fractions dynamically inaccessible to conventional techniques.
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http://dx.doi.org/10.1103/PhysRevLett.122.068004DOI Listing
February 2019

Coupling of sedimentation and liquid structure: Influence on hard sphere nucleation.

J Chem Phys 2018 Nov;149(20):204506

HH Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, United Kingdom.

The discrepancy in nucleation rate densities between simulated and experimental hard spheres remains staggering and unexplained. Suggestively, more strongly sedimenting colloidal suspensions of hard spheres nucleate much faster than weakly sedimenting systems. In this work, we consider first the effect of sedimentation on the structure of colloidal hard spheres by tuning the density mismatch between solvent and colloidal particles. In particular, we investigate the effect on the degree of the fivefold symmetry present. Second, we study the size of density fluctuations in these experimental systems in comparison to simulations. The density fluctuations are measured by assigning each particle a local density, which is related to the number of particles within a distance of 3.25 particle diameters. The standard deviation of these local densities gives an indication of the fluctuations present in the system. Fivefold symmetry is suppressed by a factor of two when sedimentation is induced in our system. Density fluctuations are increased by a factor of two in experiments compared to simulations. The change in fivefold symmetry makes a difference to the expected nucleation rates, but we demonstrate that it is ultimately too small to resolve the discrepancy between experiment and simulation, while the fluctuations are shown to be an artefact of 3d particle tracking.
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http://dx.doi.org/10.1063/1.5050397DOI Listing
November 2018

Innovative unattended SEM-EDS analysis for asbestos fiber quantification.

Talanta 2018 Dec 27;190:158-166. Epub 2018 Jul 27.

"G. Scansetti" Interdepartmental Center for Studies on Asbestos and Other Toxic Particulates, University of Torino, Torino, Italy; Department of Chemistry, University of Torino, Via P. Giuria, 7, I-10125 Torino, Italy. Electronic address:

Scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) is the only affordable analytical technique that can discriminate both morphology and elemental composition of inorganic fibers. SEM-EDS is indeed required to quantify asbestos in confounding natural matrixes (e.g. ophiolites), but is also time-consuming, operator dependent, and strongly relies on the stochastic distribution of the fibers on the filter surface. The balance between analytical time/cost and the method sensibility allows only about 0.5% of the filter to be analyzed, strongly affecting the statistical significance of results. To improve sensitivity and precision and enhance productivity, an unattended quantitative measurement of the asbestos fibers by SEM-EDS is proposed. The method identifies the particle shape first and determines their chemical composition later, saving EDS analytical time. Our approach was tested on four asbestos standards and the relative error on replicated measurements was < 10%. The proposed unattended method quantifies asbestos in natural confounding matrix, also with a very low asbestos content.
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http://dx.doi.org/10.1016/j.talanta.2018.07.083DOI Listing
December 2018

Local structure in deeply supercooled liquids exhibits growing lengthscales and dynamical correlations.

Nat Commun 2018 08 16;9(1):3272. Epub 2018 Aug 16.

H.H. Wills Physics Laboratory, Tyndall Avenue, Bristol, BS8 1TL, UK.

Glasses are among the most widely used of everyday materials, yet the process by which a liquid's viscosity increases by 14 decades to become a glass remains unclear, as often contradictory theories provide equally good descriptions of the available data. Knowledge of emergent lengthscales and higher-order structure could help resolve this, but this requires time-resolved measurements of dense particle coordinates-previously only obtained over a limited time interval. Here we present an experimental study of a model colloidal system over a dynamic window significantly larger than previous measurements, revealing structural ordering more strongly linked to dynamics than previously found. Furthermore we find that immobile regions and domains of local structure grow concurrently with density, and that these regions have low configurational entropy. We thus show that local structure plays an important role at deep supercooling, consistent with a thermodynamic interpretation of the glass transition rather than a principally dynamic description.
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http://dx.doi.org/10.1038/s41467-018-05371-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6095888PMC
August 2018

Iron from a geochemical viewpoint. Understanding toxicity/pathogenicity mechanisms in iron-bearing minerals with a special attention to mineral fibers.

Free Radic Biol Med 2019 03 31;133:21-37. Epub 2018 Jul 31.

Department of Chemistry, University of Torino, via Pietro Giuria 7, I-10125 Torino, Italy; "G. Sca nsetti" Interdepartmen tal Centre for Studies on Asbestos and Other Toxic Particulates, University of Torino, via Pietro Giuria 9, I-10125 Torino, Italy.

Iron and its role as soul of life on Earth is addressed in this review as iron is one of the most abundant elements of our universe, forms the core of our planet and that of telluric (i.e., Earth-like) planets, is a major element of the Earth's crust and is hosted in an endless number of mineral phases, both crystalline and amorphous. To study iron at an atomic level inside the bulk of mineral phases or at its surface, where it is more reactive, both spectroscopy and diffraction experimental methods can be used, taking advantage of nearly the whole spectrum of electromagnetic waves. These methods can be successfully combined to microscopy to simultaneously provide chemical (e.g. iron mapping) and morphological information on mineral particles, and shed light on the interaction of mineral surfaces with organic matter. This review describes the crystal chemistry of iron-bearing minerals of importance for the environment and human health, with special attention to iron in toxic minerals, and the experimental methods used for their study. Special attention is devoted to the Fenton-like chain reaction involving Fe in the formation of highly reactive hydroxyl radicals. The final part of this review deals with release and adsorption of iron in biological fluids, coordinative and oxidative state of iron and in vitro reactivity. To disclose the very mechanisms of carcinogenesis induced by iron-bearing toxic mineral particles, crystal chemistry and surface chemistry are fundamental for a multidisciplinary approach which should involve geo-bio-scientists, toxicologists and medical doctors.
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http://dx.doi.org/10.1016/j.freeradbiomed.2018.07.023DOI Listing
March 2019

The race to the bottom: approaching the ideal glass?

J Phys Condens Matter 2018 Sep 4;30(36):363001. Epub 2018 Jul 4.

HH Wills Physics Laboratory, Tyndall Avenue, Bristol, BS8 1TL, United Kingdom. School of Chemistry, University of Bristol, Cantock Close, Bristol, BS8 1TS, United Kingdom. Centre for Nanoscience and Quantum Information, Tyndall Avenue, Bristol, BS8 1FD, United Kingdom.

Key to resolving the scientific challenge of the glass transition is to understand the origin of the massive increase in viscosity of liquids cooled below their melting temperature (avoiding crystallisation). A number of competing and often mutually exclusive theoretical approaches have been advanced to describe this phenomenon. Some posit a bona fide thermodynamic phase to an 'ideal glass', an amorphous state with exceptionally low entropy. Other approaches are built around the concept of the glass transition as a primarily dynamic phenomenon. These fundamentally different interpretations give equally good descriptions of the data available, so it is hard to determine which-if any-is correct. Recently however this situation has begun to change. A consensus has emerged that one powerful means to resolve this longstanding question is to approach the putative thermodynamic transition sufficiently closely, and a number of techniques have emerged to meet this challenge. Here we review the results of some of these new techniques and discuss the implications for the existence-or otherwise-of the thermodynamic transition to an ideal glass.
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http://dx.doi.org/10.1088/1361-648X/aad10aDOI Listing
September 2018

Structural covariance in the hard sphere fluid.

J Chem Phys 2018 May;148(20):204511

HH Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, United Kingdom.

We study the joint variability of structural information in a hard sphere fluid biased to avoid crystallisation and form five-fold symmetric geometric motifs. We show that the structural covariance matrix approach, originally proposed for on-lattice liquids [P. Ronceray and P. Harrowell, J. Stat. Mech.: Theory Exp. 2016(8), 084002], can be meaningfully employed to understand structural relationships between different motifs and can predict, within the linear-response regime, structural changes related to motifs distinct from that used to bias the system.
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http://dx.doi.org/10.1063/1.5024462DOI Listing
May 2018

Structural-dynamical transition in the Wahnström mixture.

Eur Phys J E Soft Matter 2018 Apr 26;41(4):54. Epub 2018 Apr 26.

H.H. Wills Physics Laboratory, University of Bristol, BS8 1TL, Bristol, UK.

In trajectory space, dynamical heterogeneities in glass-forming liquids correspond to the emergence of a dynamical phase transition between an active phase poor in local structure and an inactive phase which is rich in local structure. We support this scenario with the study of a model additive mixture of Lennard-Jones particles, quantifying how the choice of the relevant structural and dynamical observable affects the transition in trajectory space. We find that the low mobility, structure-rich phase is dominated by icosahedral order. Applying a non-equilibrium rheological protocol, we connect local order to the emergence of mechanical rigidity.
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http://dx.doi.org/10.1140/epje/i2018-11662-3DOI Listing
April 2018

Experimental determination of configurational entropy in a two-dimensional liquid under random pinning.

J Phys Condens Matter 2018 03;30(9):094003

School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom. H H Wills Physics Laboratory, Tyndall Avenue, Bristol, BS8 1TL, United Kingdom. Centre for Nanoscience and Quantum Information, Tyndall Avenue, Bristol, BS8 1FD, United Kingdom. Department of Chemical Engineering, University of California Santa Barbara, CA 93106-5080, United States of America.

A quasi two-dimensional colloidal suspension is studied under the influence of immobilisation (pinning) of a random fraction of its particles. We introduce a novel experimental method to perform random pinning and, with the support of numerical simulation, we find that increasing the pinning concentration smoothly arrests the system, with a cross-over from a regime of high mobility and high entropy to a regime of low mobility and low entropy. At the local level, we study fluctuations in area fraction and concentration of pins and map them to entropic structural signatures and local mobility, obtaining a measure for the local entropic fluctuations of the experimental system.
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http://dx.doi.org/10.1088/1361-648X/aaa869DOI Listing
March 2018

Surface reactivity of amphibole asbestos: a comparison between crocidolite and tremolite.

Sci Rep 2017 10 31;7(1):14696. Epub 2017 Oct 31.

Dipartimento di Chimica, Università di Torino, via Pietro Giuria 7, I-10125, Torino, Italy.

Among asbestos minerals, fibrous riebeckite (crocidolite) and tremolite share the amphibole structure but largely differ in terms of their iron content and oxidation state. In asbestos toxicology, iron-generated free radicals are largely held as one of the causes of asbestos malignant effect. With the aim of clarifying i) the relationship between Fe occurrence and asbestos surface reactivity, and ii) how free-radical generation is modulated by surface modifications of the minerals, UICC crocidolite and fibrous tremolite from Maryland were leached from 1 day to 1 month in an oxidative medium buffered at pH 7.4 to induce redox alterations and surface rearrangements that may occur in body fluids. Structural and chemical modifications and free radical generation were monitored by HR-TEM/EDS and spin trapping/EPR spectroscopy, respectively. Free radical yield resulted to be dependent on few specific Fe and Fe surface sites rather than total Fe content. The evolution of reactivity with time highlighted that low-coordinated Fe ions primarily contribute to the overall reactivity of the fibre. Current findings contribute to explain the causes of the severe asbestos-induced oxidative stress at molecular level also for iron-poor amphiboles, and demonstrate that asbestos have a sustained surface radical activity even when highly altered by oxidative leaching.
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http://dx.doi.org/10.1038/s41598-017-14480-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5665974PMC
October 2017

Long-lived non-equilibrium interstitial solid solutions in binary mixtures.

J Chem Phys 2017 Sep;147(12):124504

H.H. Wills Physics Laboratory, Tyndall Ave., Bristol BS8 1TL, United Kingdom.

We perform particle resolved experimental studies on the heterogeneous crystallisation process of two component mixtures of hard spheres. The components have a size ratio of 0.39. We compared these with molecular dynamics simulations of homogenous nucleation. We find for both experiments and simulations that the final assemblies are interstitial solid solutions, where the large particles form crystalline close-packed lattices, whereas the small particles occupy random interstitial sites. This interstitial solution resembles that found at equilibrium when the size ratios are 0.3 [L. Filion et al., Phys. Rev. Lett. 107, 168302 (2011)] and 0.4 [L. Filion, Ph.D. thesis, Utrecht University, 2011]. However, unlike these previous studies, for our system simulations showed that the small particles are trapped in the octahedral holes of the ordered structure formed by the large particles, leading to long-lived non-equilibrium structures in the time scales studied and not the equilibrium interstitial solutions found earlier. Interestingly, the percentage of small particles in the crystal formed by the large ones rapidly reaches a maximum of ∼14% for most of the packing fractions tested, unlike previous predictions where the occupancy of the interstitial sites increases with the system concentration. Finally, no further hopping of the small particles was observed.
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http://dx.doi.org/10.1063/1.4985917DOI Listing
September 2017

Weak temperature dependence of ageing of structural properties in atomistic model glassformers.

J Chem Phys 2017 Aug;147(5):054501

H. H. Wills Physics Laboratory, Tyndall Avenue, Bristol, United Kingdom.

Ageing phenomena are investigated from a structural perspective in two binary Lennard-Jones glassformers, the Kob-Andersen and Wahnström mixtures. In both, the geometric motif assumed by the glassformer upon supercooling, the locally favoured structure (LFS), has been established. The Kob-Andersen mixture forms bicapped square antiprisms; the Wahnström model forms icosahedra. Upon ageing, we find that the structural relaxation time has a time-dependence consistent with a power law. However, the LFS population and potential energy increase and decrease, respectively, in a logarithmic fashion. Remarkably, over the time scales investigated, which correspond to a factor of 10 change in relaxation times, the rate at which these quantities age appears almost independent of temperature. Only at temperatures far below the Vogel-Fulcher-Tamman temperature do the ageing dynamics slow.
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http://dx.doi.org/10.1063/1.4994836DOI Listing
August 2017

Experimental Evidence for a Structural-Dynamical Transition in Trajectory Space.

Phys Rev Lett 2017 Jul 13;119(2):028004. Epub 2017 Jul 13.

H.H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, United Kingdom.

Among the key insights into the glass transition has been the identification of a nonequilibrium phase transition in trajectory space which reveals phase coexistence between the normal supercooled liquid (active phase) and a glassy state (inactive phase). Here, we present evidence that such a transition occurs in experiments. In colloidal hard spheres, we find a non-Gaussian distribution of trajectories leaning towards those rich in locally favored structures (LFSs), associated with the emergence of slow dynamics. This we interpret as evidence for a nonequilibrium transition to an inactive LFS-rich phase. Reweighting trajectories reveals a first-order phase transition in trajectory space between a normal liquid and a LFS-rich phase. We also find evidence for a purely dynamical transition in trajectory space.
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http://dx.doi.org/10.1103/PhysRevLett.119.028004DOI Listing
July 2017

Ζ potential evidences silanol heterogeneity induced by metal contaminants at the quartz surface: Implications in membrane damage.

Colloids Surf B Biointerfaces 2017 Sep 13;157:449-455. Epub 2017 Jun 13.

Department of Chemistry, University of Torino, Via P. Giuria 7, 10125 Turin, Italy; "G. Scansetti" Interdepartmental Center for Studies on Asbestos and Other Toxic Particulates, University of Torino, Via P. Giuria 9, 10125 Turin, Italy. Electronic address:

Among the physico-chemical features responsible for the so-called "variability of quartz hazard", a key role has been assigned to the silica surface charge, evaluated by means of ζ potential measurement. The ζ potential of silica describes the protonation state of silanols which, in turn, determine interactions with cell membranes. To gain a molecular understanding of the role of silanols in silica pathogenicity, we conducted a systematic investigation of the variation of the ζ potential as a function of pH (ζ plot titration curve) on a large set of respirable quartz particles with different levels of metal contaminants. The membranolytic activity of the particles on red blood cells, used as a readout of pathogenic activity, was assessed in parallel. Pure quartz surfaces showed sigmoid-shaped ζ plots suggesting the presence of silanol families with similar acidity, whereas contaminated dusts exhibited convex-shaped ζ plots, indicating a higher silanol heterogeneity on contaminated surfaces with respect to the pure ones. The quartz particles with a higher surface heterogeneity related to metal contamination showed a higher membranolytic activity. By removing structural defects and chemical heterogeneity, the ζ plot shifted towards the typical shape of pure quartz and the membranolytic activity was reduced. We conclude that the ζ plot is a useful readout to measure the acid-base behavior of quartz surfaces and to describe the chemical heterogeneity of quartz silanols. Surface heterogeneity, here induced by metal contamination, is proposed as the main cause of quartz membranolytic activity, further supporting the hypothesis that surface silanol disorganization determines silica pathogenicity.
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http://dx.doi.org/10.1016/j.colsurfb.2017.06.012DOI Listing
September 2017

From Glass Formation to Icosahedral Ordering by Curving Three-Dimensional Space.

Phys Rev Lett 2017 May 26;118(21):215501. Epub 2017 May 26.

H.H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL, United Kingdom.

Geometric frustration describes the inability of a local molecular arrangement, such as icosahedra found in metallic glasses and in model atomic glass formers, to tile space. Local icosahedral order, however, is strongly frustrated in Euclidean space, which obscures any causal relationship with the observed dynamical slowdown. Here we relieve frustration in a model glass-forming liquid by curving three-dimensional space onto the surface of a 4-dimensional hypersphere. For sufficient curvature, frustration vanishes and the liquid "freezes" in a fully icosahedral structure via a sharp "transition." Frustration increases upon reducing the curvature, and the transition to the icosahedral state smoothens while glassy dynamics emerge. Decreasing the curvature leads to decoupling between dynamical and structural length scales and the decrease of kinetic fragility. This sheds light on the observed glass-forming behavior in Euclidean space.
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http://dx.doi.org/10.1103/PhysRevLett.118.215501DOI Listing
May 2017

Effects of vertical confinement on gelation and sedimentation of colloids.

Soft Matter 2017 May;13(17):3230-3239

H.H. Wills Physics Laboratory, University of Bristol, Bristol, BS8 1TL, UK.

We consider the sedimentation of a colloidal gel under confinement in the direction of gravity. The confinement allows us to compare directly experiments and computer simulations, for the same system size in the vertical direction. The confinement also leads to qualitatively different behaviour compared to bulk systems: in large systems gelation suppresses sedimentation, but for small systems sedimentation is enhanced relative to non-gelling suspensions, although the rate of sedimentation is reduced when the strength of the attraction between the colloids is strong. We map interaction parameters between a model experimental system (observed in real space) and computer simulations. Remarkably, we find that when simulating the system using Brownian dynamics in which hydrodynamic interactions between the particles are neglected, we find that sedimentation occurs on the same timescale as the experiments. An analysis of local structure in the simulations showed similar behaviour to gelation in the absence of gravity.
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http://dx.doi.org/10.1039/c6sm02221aDOI Listing
May 2017