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Caratterizzazione cristallochimica e chimico-fisica delle fibre minerali finalizzata alla comprensione del loro potenziale tossicologico
No full textCon il termine "fibre minerali" si intende un gruppo di minerali naturali diffuso in tutta la Terra. Tra questi, i più rilevanti e certamente i più temuti sono i minerali dell’amianto e le zeoliti fibrose come l'erionite. Questi minerali rappresentano un interessante oggetto di studio in quanto i meccanismi con cui inducono danni a livello cito- e geno-tossico rimangono poco chiari e manca la comprensione del rapporto causa-effetto tra l'esposizione alle fibre e l'insorgenza delle malattie. Le difficoltà derivano dalla grande variabilità chimica, morfologica e strutturale di questi minerali, che influenza fortemente le reazioni biogeochimiche.
Per questi motivi, la presente tesi di dottorato si propone di contribuire alla valutazione dei meccanismi di interazione e di tossicità biologica del crisotilo, degli anfiboli e dell'erionite, partendo da una solida caratterizzazione sistematica delle loro proprietà.
Per lo studio, sono state selezionate 8 fibre di importanza sociale ed economico-industriale. Le impurità sono state individuate e quantitativamente stimate servendosi della diffrazione di raggi X da polveri (XRPD) cui è seguito lo studio della reattività di superficie, attraverso misure di potenziale Zeta e di area superficiale.
Successivamente l'attenzione si è focalizzata sull'ambiente chimico del ferro all'interno delle strutture cristalline, mediante spettroscopia di assorbimento di raggi X (XAS) e spettroscopia Mössbauer.
Una volta ottenuto un quadro soddisfacente dal punto di vista fisico-chimico e mineralogico, le indagini sono state indirizzate ai cambiamenti strutturali subiti dalle fibre dopo essere state in contatto con colture cellulari umane, tramite μXANES, μXRD e mappatura XRF del ferro in situ con luce di sincrotrone.
Sono stati inoltre condotti esperimenti di dissoluzione su fibre di crisotilo in contatto con una soluzione che simula i fluidi polmonari (S.L.F.) mentre gli esperimenti su anfiboli ed erionite sono tuttora in corso.
I principali risultati possono essere così sintetizzati:
1) Tutte le fibre a contatto con la soluzione S.L.F. mostrano valori di potenziale Zeta negativi e simili tra loro, cadendo nell'intervallo di valori in cui è favorita l'aggregazione delle fibre. Tale comportamento potrebbe virtualmente pregiudicare la risposta apoptotica attraverso il sequestro di ioni Ca2+.
2) In tutti i campioni il ferro è stato trovato in coordinazione ottaedrica, con gli ioni Fe2+ situati nelle posizioni della struttura meno influenzate dall'ossidazione. Considerando il tempo di dissoluzione più breve del crisotilo rispetto agli anfiboli (sebbene questi ultimi siano più ricchi in ferro) il rilascio di ferro potrebbe essere comparabile. rappresenta un caso particolare poiché il ferro è presente solo come Fe3+ in coordinazione ottaedrica all'interno di un rivestimento superficiale di nanoparticelle di ossido.
3) Il contatto delle fibre di crisotilo con le colture cellulari porta alla loro amorfizzazione, poi seguita dalla dissoluzione in senso stretto. La crocidolite mostra lievi segni precoci di amorfizzazione mentre l'erionite sembra essere la specie fibrosa più stabile a contatto con le cellule. La formazione di uno scheletro siliceo fibroso in seguito alla pseudo-amorfizzazione del crisotilo potrebbe indurre la produzione di radicali ossidrili in sinergia con le specie di ferro presenti in superficie; quindi il crisotilo potrebbe essere molto più reattivo e citotossico in vitro nel breve termine, mentre l'attività della crocidolite e dell'erionite sarebbe più lenta ma persistente nel lungo termine. Il lavoro qui descritto rappresenta un ulteriore passo verso lo sviluppo di un modello generale che descriva il complesso meccanismo di interazione tra fibre e ambiente cellulare.With the general term “mineral fibres” is intended a group of natural minerals widespread throughout the Earth. Among them, the most relevant and certainly the most feared ones are asbestos minerals and fibrous zeolites such as erionite. These minerals represent an interesting subject of study since the mechanisms by which they induces cyto- and geno-toxic damage remain unclear and there is a lack in understanding the cause-effect relationship between exposure to the fibres and the onset of the disease. The difficulties arise from the great chemical, morphological and structural variability of these minerals, which affect the biogeochemical reactions.
For these reasons, the present doctoral thesis aims to contribute to the assessment of the interaction mechanisms and biological toxicity of chrysotile, amphyboles and erionite, starting from a strong systematic characterization of their properties.
For the study, 8 mineral fibres of social and economic-industrial importance were selected. The impurities were detected and quantitatively estimated by using XRPD both from conventional and unconventional sources; the following step was the characterization of the surface reactivity, through Zeta potential and surface area measurements. Subsequently the focus has shifted on the chemical environment of iron within the crystal structures, using X-ray absorption and Mössbauer spectroscopy.
Once obtained a satisfactory general picture from the physical-chemical and mineralogical point of view, investigations were addressed on aspects of biological interaction. Specifically, we have studied the structural changes undergone by the fibres after being in contact (for different times) with human cell cultures, using in situ synchrotron XRF iron mapping, μXANES, and μXRD. Moreover, in recent months, dissolution experiments on chrysotile fibres have been conducted in contact with simulated lung fluid solution (S.L.F.) at acidic pH; dissolution experiments on amphiboles and erionite are still in progress.
The main results can be summarized as follows:
1) All amphibole, chrysotile and erionite fibres, when in contact with S.L.F. solution, display negative Zeta potentials and minor differences, falling in the range of values where the agglomeration of fibres is favoured. Such behaviour may virtually impair apoptotic response via the sequestration of Ca2+ ions.
2) In all investigated fibres, iron has been found in octahedral cavities, with Fe2+ ions located in the innermost structure positions inside the crystal lattice less affected by oxidation. Taking into account the much shorter dissolution time of chrysotile with respect to amphiboles (although the latter are much more rich in iron) the release of iron could be comparable. Erionite turns out to be a special case since iron is present as octahedrally coordinated Fe3+ likely inside a surface coating of oxide nanoparticles.
3) The contact of the chrysotile fibres with the cell cultures leads to amorphization, interpreted as the first dissolution step, later followed by dissolution sensu stricto. Crocidolite shows minor early signs of amorphization whereas erionite seems to be the more stable fibre species in contact with the cells. The formation of a silica-rich fibre skeleton after pseudo-amorphization of chrysotile may prompt the production of hydroxyl radicals in synergy with surface iron species; this could indicate that chrysotile may be much more reactive and cytotoxic in vitro in the short term whereas the activity of crocidolite and erionite would be much more sluggish but persistent in the long term.
The work presented here could be helpful for the development of a general model describing the complex mechanism of interaction between fibres and cellular environment
Inorganic polymers from laterite using activation with phosphoric acid and alkaline sodium silicate solution: Mechanical and microstructural properties
No full textGeopolymers from laterite, an iron-rich soil available in developing countries, have great potential as building materials. In this work, laterite from Togo (Africa) was used to prepare geopolymers using both phosphoric acid and alkaline sodium silicate solution. Microstructural properties were investigated by scanning electron microscopy, X-ray powder diffraction and mercury porosimetry, whereas thermal properties were evaluated by thermal analyses. The local environment of iron was studied by X-ray Absorption Spectroscopy (XANES region). The mechanical properties were determined. Modulus of Rupture and Young's modulus fell in the ranges 3.3–4.5 MPa and 12–33 GPa, respectively, rendering the materials good candidates for construction purposes. Heating above 900 °C results in weight-gain, presumably due to iron redox reactions. X-ray Absorption Spectroscopy data evidence changes in the chemical and structural environments of iron following thermal treatment of geopolymers. These changes indicate interaction between the geopolymer structure and iron during heating, possibly leading to redox properties
Solubilization and coordination of the HgCl2 molecule in water, methanol, acetone, and acetonitrile: an X-ray absorption investigation
No full textX-ray absorption spectroscopy (XAS) has been employed to carry out structural characterization of the local environment around mercury after the dissolution of the HgCl2 molecule. A combined EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) data analysis has been performed on the Hg L3-edge absorption spectra recorded on 0.1 M HgCl2 solutions in water, methanol (MeOH), acetone and acetonitrile. The Hg-Cl distance determined by EXAFS (2.29(2)-2.31(2) Å) is always comparable to that found in the HgCl2 crystal (2.31(2) Å), demonstrating that the HgCl2 molecule dissolves in these solvents without dissociating. A small sensitivity of EXAFS to the solvent molecules interacting with HgCl2 has been detected and indicates a high degree of configurational disorder associated with this contribution. XANES data analysis, which is less affected by the disorder, was therefore carried out for the first time on these systems to shed light into the still elusive structural arrangement of the solvent molecules around HgCl2. The obtained results show that, in aqueous and MeOH solutions, the XANES data are compatible with three solvent molecules arranged around the HgCl2 unit to form a trigonal bipyramidal structure. The determination of the three-body Cl-Hg-Cl distribution shows a certain degree of uncertainty around the average 180° bond angle value, suggesting that the HgCl2 molecule probably vibrates in the solution around a linear configuration
Bulk spectroscopy of mineral fibres
No full textSpectroscopic methods are utilized widely for characterizing minerals and other geomaterials
in terms of electronic, vibrational and nuclear properties. The basics and
applications of spectroscopic methods in mineralogy were reported comprehensively by
Hawthorne (1988), and later discussed carefully and updated by Burns (1993) and Clark
(1999), by Beran and Libowitzky (2004) and more recently by Henderson et al. (2014).
These esteemed books and reviews focused generally on topics of immediate
mineralogical interest, but nevertheless contain stimulating parallel excursions into the
fields of geology and materials sciences. This chapter is built on the shoulders of those
giants and is devoted specifically to exploring spectroscopic investigations of electronic
and nuclear properties of mineral fibres, a topic not reviewed previously. A number of
spectroscopies (though not all) will be mentioned without covering in detail their
physical bases (which can be found easily in the books and reviews mentioned above),
because this chapter is intended to serve as a review of their contribution to increasing
comprehension of the bulk properties of mineral fibres
Crystal chemistry of the high temperature product of transformation of cement-asbestos
No full textIn this work, the high-temperature inertization product of a representative batch of samples of cement-asbestos (CA) from different localities in Italy have been characterized with a multidisciplinary approach. All the raw CA samples were heated at 1200°C for 15 min. After firing, they underwent a series of solid state reactions leading to global structural changes of the matrix. Effects of annealing time and temperature on the crystallization kinetics were thoroughly investigated. Both factors acted in favour of equilibrium. Three classes of CA were identified with the aid of phase diagrams and of specific plots relating chemical and mineralogical parameters. This result was considered of importance in view of the potential use of transformed cement-asbestos as a secondary raw material. In principle, the content of CA packages removed from the environment and their corresponding heat-treated products can be classified simply using XRF. This method allows for the selection of appropriate fractions in function of the most suitable recycling solution adopted. Samples belonging to the class called larnite-rich, turned out to be of great interest as possible candidate for substituting a fraction of cement in many building materials and innovative green cement productions
Stability of mineral fibres in contact with human cell cultures. An in situ mXANES, mXRD and XRF iron mapping study
Full text linkRelevant mineral fibres of social and economic importance (chrysotile UICC, crocidolite UICC and a
fibrous erionite from Jersey, Nevada, USA) were put in contact with cultured diploid human nontumorigenic
bronchial epithelial (Beas2B) and pleural transformed mesothelial (MeT5A) cells to test
their cytotoxicity. Slides of each sample at different contact times up to 96 h were studied in situ using
synchrotron XRF, m-XRD and m-XAS (I18 beamline, Diamond Light Source, UK) and TEM investigations.
XRF maps of samples treated for 96 h evidenced that iron is still present within the chrysotile and
crocidolite fibres and retained at the surface of the erionite fibres, indicating its null to minor mobilization
in contact with cell media; this picture was confirmed by the results of XANES pre-edge analyses.
m-XRD and TEM data indicate greater morphological and crystallinity modifications occurring in
chrysotile, whereas crocidolite and erionite show to be resistant in the biological environment. The
contact of chrysotile with the cell cultures seems to lead to earlier amorphization, interpreted as the first
dissolution step of these fibres. The formation of such silica-rich fibre skeleton may prompt the production
of HO in synergy with surface iron species and could indicate that chrysotile may be much more
reactive and cytotoxic in vitro in the (very) short term whereas the activity of crocidolite and erionite
would be much more sluggish but persistent in the long term
The zeta potential of mineral fibres
No full textFor the first time, the zeta (ξ) potential of pathogenic mineral fibres (chrysotiles, amphiboles and erionite) was systematically investigated to shed light on the relationship between surface reactivity and fibre pathogenicity. A general model explaining the zeta potential of chrysotile, amphiboles and erionite has been postulated. In double distilled water, chrysotiles showed positive values while crocidolite and erionite showed negative values. In contact with organic solutions, all fibres exhibited negative values of zeta potential. The decrease of the surface potential is deemed to be a defensive chemical response of the macrophage cells to minimize hemolytic damage. Negatively charged surfaces favour the binding of collagen and redox activated Fe-rich proteins, to form the so-called asbestos bodies and prompt the formation of HO via the reaction with peroxide (H2O2+e(-)→HO+HO(-)). An additional mechanism accounting for higher carcinogenicity is possibly related to the Ca(2+) sequestration by the fibres with surface negative potential, impairing the mitochondrial apoptotic pathway. It was also found that with a negative zeta potential, the attractive forces prevailed over repulsions and favoured processes such as agglomeration responsible of a tumorigenic chronic inflammation.For the first time, the zeta (ξ) potential of pathogenic mineral fibres (chrysotiles, amphiboles and erionite) was systematically investigated to shed light on the relationship between surface reactivity and fibre pathogenicity. A general model explaining the zeta potential of chrysotile, amphiboles and erionite has been postulated. In double distilled water, chrysotiles showed positive values while crocidolite and erionite showed negative values. In contact with organic solutions, all fibres exhibited negative values of zeta potential. The decrease of the surface potential is deemed to be a defensive chemical response of the macrophage cells to minimize hemolytic damage. Negatively charged surfaces favour the binding of collagen and redox activated Fe-rich proteins, to form the so-called asbestos bodies and prompt the formation of HO via the reaction with peroxide (H2O2+e-→HO+HO-). An additional mechanism accounting for higher carcinogenicity is possibly related to the Ca2+ sequestration by the fibres with surface negative potential, impairing the mitochondrial apoptotic pathway. It was also found that with a negative zeta potential, the attractive forces prevailed over repulsions and favoured processes such as agglomeration responsible of a tumorigenic chronic inflammation. © 2014
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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