Composti organostannici nell'ambiente marino e membrane biologiche: risposte molecolari e biochimiche nei molluschi bivalvi

Organotin compounds are worldwide diffused environmental contaminants, mainly as consequence of their extensive past use as biocides in antifouling paints. In spite of law restrictions, due to unwanted effects, organotin still persist in waters, being poorly degraded, easily resuspended from sediments and bioaccumulated in exposed organisms. The widespread toxicity and the possible threat to humans, likely to be organotin-exposed through contaminated seafood, make organotin interactions with biomolecules an intriguing biochemical topic, apart from a matter of ecotoxicological concern. Among organotins, tributyltin (TBT) is long known as the most dangerous and abundant chemical species in the Mediterranean Sea. Due to its amphiphilic nature, provided by three lipophilic arms and an electrophilic tin core, TBT can be easily incorporated in biomembranes and affect their functionality. Accordingly, it is known as a membrane-active toxicant and a mitochondrial poison. Up to now the molecular action modes of TBT are still partially unclear and poorly explored in bivalve mollusks, even if the latter play a not neglectable role in the marine trophic chain and efficiently accumulate organotins. The bivalve mollusk Mytilus galloprovincialis, selected for all experiments, is widely cultivated in the Mediterranean and currently used in ecotoxicological studies. Most work of this thesis was devoted to TBT effects on mussel mitochondria, but other possible targets of TBT were also considered. A great deal of literature points out TBT as endocrine disrupter and the masculinization of female marine gastropods, the so-called imposex, currently signals environmental organotin contamination. The hormonal status of TBT-exposed mussels and the possible interaction between hormones and contaminants in modulating microsomal hydroxilases, involved in steroid hormone and organotin detoxification, were the research topics in the period spent in Barcelona (Marco Polo fellowship). The variegated experimental approach, which consisted of two exposure experiments and in vitro tests, and the choice of selected tissues of M. galloprovincialis, the midgut gland for mitochondrial and microsomal preparations for subsequent laboratory assays and the gonads for the endocrine evaluations, aimed at drawing a clarifying pattern on the molecular mechanisms involved in organotin toxicity. TBT was promptly incorporated in midgut gland mitochondria of adult mussels exposed to 0.5 and 1.0 μg/L TBT, and partially degraded to DBT. TBT incorporation was accompanied by a decrease in the mitochondrial oligomycin-sensitive Mg-ATPase activity, while the coexistent oligomycin-insensitive fraction was unaffected. Mitochondrial fatty acids showed a clear rise in n-3 polyunsaturated fatty acids after 120 hr of TBT exposure, mainly referable to an increase in 22:6 level. TBT was also shown to inhibit the ATP hydrolytic activity of the mitochondrial F1FO complex in vitro and to promote an apparent loss of oligomycin sensitivity at higher than 1.0 μM concentration. The complex dose-dependent profile of the inhibition curve lead to the hypothesis of multiple TBT binding sites. At lower than 1.0 μM TBT concentrations the non competitive enzyme inhibition by TBT was ascribed to the non covalent binding of TBT to FO subunit. On the other hand the observed drop in oligomycin sensitivity at higher than 1.0 μM TBT could be related to the onset of covalent bonds involving thiolic groups on the enzyme structure, apparently reached only at high TBT levels. The mitochondrial respiratory complexes were in vitro affected by TBT, apart from the cytocrome c oxidase which was apparently refractory to the contaminant. The most striking inhibitory effect was shown on complex I, and ascribed to possible covalent bonds of TBT with –SH groups on the enzyme complexes. This mechanism, shouldered by the progressive decrease of free cystein residues in the presence of increasing TBT concentrations, suggests that the onset of covalent tin-sulphur bonds in distinct protein structures may constitute the molecular basis of widespread TBT effects on mitochondrial complexes. Energy production disturbances, in turn affecting energy consuming mechanisms, could be involved in other cellular changes. Mussels exposed to a wide range of TBT concentrations (20 - 200 and 2000 ng/L respectively) did not show any change in testosterone and estrogen levels in mature gonads. Most hormones were in the non-biologically active esterified form both in control and in TBT-treated mussels. Probably the endocrine status of sexually mature mussels could be refractory even to high TBT doses. In mussel digestive gland the high biological variability of microsomal 7-benzyloxy-4-trifluoromethylcoumarin-O-Debenzyloxylase (BFCOD) activity, taken as a measure of CYP3A-like efficiency, probably concealed any enzyme response to TBT exposure. On the other hand the TBT-driven enhancement of BFCOD activity in vitro was once again ascribed to covalent binding to thiol groups which, in this case, would stimulate the enzyme activity. In mussels from Barcelona harbour, a highly contaminated site, the enzyme showed a decreased affinity for the 7-benzyloxy-4-trifluoromethylcoumarin (BCF) substrate with respect to mussel sampled from Ebro Delta, a non-polluted marine site. Contaminant exposure may thus alter the kinetic features of enzymes involved in detoxification mechanisms. Contaminants and steroid hormones were clearly shown to mutually interact in the modulation of detoxification mechanisms. The xenoestrogen 17α-ethylenyl estradiol (EE2) displayed a non-competitive mixed inhibition of CYP3A-like activity by a preferential bond to the free enzyme both in Barcelona harbour and Ebro Delta mussels. The possible interaction with co-present contaminants in Barcelona harbour mussels apparently lessened the formation of the ternary complex enzyme-EE2-BCF. The whole of data confirms TBT as membrane toxicant in mussels as in other species and stresses TBT covalent binding to protein thiols as a widespread mechanism of membrane-bound-enzyme activity modulation by the contaminant.

La rue Mallet-Stevens forma e linguaggi nell'architettura di Mallet-Stevens

La ricerca ha avuto come obiettivo l’analisi delle residenze lungo la rue Mallet-Stevens, a Parigi, realizzate da Robert Mallet-Stevens negli anni 1925-1930. Si tratta di un intervento pensato unitariamente, i cui dispositivi spaziali sono rivelatori tanto del concetto spazio-forma, quanto del processo d’ideazione dello stesso nell’ambito dei paradigmi gestaltici e compositivi della modernità. All’epoca la necessità di espressione e affermazione di un simile concetto si tradusse nell’interpretazione spaziale dalla scala dell’abitazione alla scala della città. Le residenze, realizzate nella zona di Auteuil (16 arrondissement), occupano l’area di una nuova lottizzazione, da cui il successivo nome dell’intervento: case su rue Mallet-Stevens. Il programma comprendeva cinque abitazioni, commissionate da artisti e ricchi borghesi, una piccola maison per il guardiano del confinante parco, e un progetto, mai realizzato che nella prima versione comprendeva due interventi: un hôtel particulier e un edificio per appartamenti. La rue Mallet-Stevens si costituì come frammento di città possibile, ove si manifestava un’idea di urbanità chiaramente ispirata al modello della città giardino e ai valori del vivere moderno. I volumi “stereometrici” sono la cifra dell’idea di spazio che, a quel punto della sua attività, Mallet-Stevens aveva maturato sia come architetto, sia come scenografo. La metodologia di analisi critica dell’oggetto architettonico adottata in questa ricerca, si è servita di una lettura incrociata del testo (l’oggetto architettonico), del paratesto (ciò che l’autore ha scritto di sé e della propria opera) e dell’intertesto, in altre parole l’insieme di quelle relazioni che possono ricondurre sia ad altre opere dello stesso autore, sia ai modelli cui l’architetto ha fatto riferimento. Il ridisegno bidimensionale e tridimensionale degli edifici della rue Mallet-Stevens ha costituito lo strumento fondamentale di analisi per la comprensione dei temi architettonici. Le conclusioni cui la ricerca è giunta mostrano come la posizione culturale di Mallet-Stevens si è arricchita di molteplici influenze creative, sulla scia di una consapevole e costante strategia di contaminazione. Mallet-Stevens, osservando i linguaggi a lui contemporanei, si appropriò della componente morfologica del progetto, privilegiandola rispetto a quella sintattica, per poi giungere ad una personalissima sintesi delle stesse.

Dall'involucro all'invaso. Lo spazio a pianta centrale nell'opera architettonica di Adalberto Libera

An archetype selected over the centuries Adalberto Libera wrote little, showing more inclination to use the project as the only means of verification. This study uses a survey of the project for purely compositional space in relation to the reason that most other returns with continuity and consistency throughout his work. "The fruit of a type selected over centuries", in the words of Libera, is one of the most widely used and repeated spatial archetypes present in the history of architecture, given its nature as defined by a few consolidated elements and precisely defined with characters of geometric precision and absoluteness, the central space is provided, over the course of evolution of architecture, and its construction aspects as well as symbolic, for various uses, from historical period in which it was to coincide with sacred space for excellence, to others in which it lends itself to many different expressive possibilities of a more "secular". The central space was created on assumptions of a constructive character, and the same exact reason has determined the structural changes over the centuries, calling from time to time with advances in technology, the maximum extent possible and the different applications, which almost always have coincided with the reason for the monumental space. But it’s in the Roman world that the reason for the central space is defined from the start of a series of achievements that fix the character in perpetuity. The Pantheon was seen maximum results and, simultaneously, the archetype indispensable, to the point that it becomes difficult to sustain a discussion of the central space that excludes. But the reason the space station has complied, in ancient Rome, just as exemplary, monuments, public spaces or buildings with very different implications. The same Renaissance, on which Wittkower's proving itself once and for all, the nature and interpretation of sacred space station, and thus the symbolic significance of that invaded underlying interpretations related to Humanism, fixing the space-themed drawing it with the study and direct observation by the four-sixteenth-century masters, the ruins that in those years of renewed interest in the classical world, the first big pieces of excavation of ancient Rome brought to light with great surprise of all. Not a case, the choice to investigate the architectural work of Libera through the grounds of the central space. Investigating its projects and achievements, it turns out as the reason invoked particularly evident from the earliest to latest work, crossing-free period of the war which for many authors in different ways, the distinction between one stage and another, or the final miss. The theme and the occasion for Libera always distinct, it is precisely the key through which to investigate her work, to come to discover that the first-in this case the central plan-is the constant underlying all his work, and the second reason that the quota with or at the same time, we will return different each time and always the same Libera, formed on the major works remained from ancient times, and on this building method, means consciously, that the characters of architectural works, if valid, pass the time, and survive the use and function contingent. As for the facts by which to formalize it, they themselves are purely contingent, and therefore available to be transferred from one work to another, from one project to another, using also the loan. Using the same two words-at-issue and it becomes clear now how the theme of this study is the method of Libera and opportunity to the study of the central space in his work. But there is one aspect that, with respect to space a central plan evolves with the progress of the work of Libera on the archetype, and it is the reason behind all the way, just because an area built entirely on reason centric. It 'just the "center" of space that, ultimately, tells us the real progression and the knowledge that over the years has matured and changed in Libera. In the first phase, heavily laden with symbolic superstructure, even if used in a "bribe" from Free-always ill-disposed to sacrifice the idea of architecture to a phantom-center space is just the figure that identifies the icon represents space itself: the cross, the flame or the statue are different representations of the same idea of center built around an icon. The second part of the work of clearing the space station, changed the size of the orders but the demands of patronage, grows and expands the image space centric, celebratory nature that takes and becomes, in a different way, this same symbol . You see, one in all, as the project of "Civiltà Italiana" or symbolic arch are examples of this different attitude. And at the same point of view, you will understand how the two projects formulated on the reuse of the Mausoleum of Augustus is the key to its passage from first to second phase: the Ara Pacis in the second project, making itself the center of the composition "breaks" the pattern of symbolic figure in the center, because it is itself an architecture. And, in doing so, the transition takes place where the building itself-the central space-to become the center of that space that itself creates and determines, by extending the potential and the expressiveness of the enclosure (or cover) that defines the basin centered. In this second series of projects, which will be the apex and the point of "crisis" in the Palazzo dei Congressi all'E42 received and is no longer so, the symbol at the very geometry of space, but space itself and 'action' will be determined within this; action leading a movement, in the case of the Arco simbolico and the "Civiltà Italiana" or, more frequently, or celebration, as in the great Sala dei Recevimenti all’E42, which, in the first project proposal, is represented as a large area populated by people in suits, at a reception, in fact. In other words, in this second phase, the architecture is no longer a mere container, but it represents the shape of space, representing that which "contains". In the next step-determining the knowledge from which mature in their transition to post-war-is one step that radically changes the way centric space, although formally and compositionally Libera continues the work on the same elements, compounds and relationships in a different way . In this last phase Freedom, center, puts the man in human beings, in the two previous phases, and in a latent, were already at the center of the composition, even if relegated to the role of spectators in the first period, or of supporting actors in the second, now the heart of space. And it’s, as we shall see, the very form of being together in the form of "assembly", in its different shades (up to that sacred) to determine the shape of space, and how to relate the parts that combine to form it. The reconstruction of the birth, evolution and development of the central space of the ground in Libera, was born on the study of the monuments of ancient Rome, intersected on fifty years of recent history, honed on the constancy of a method and practice of a lifetime, becomes itself, Therefore, a project, employing the same mechanisms adopted by Libera; the decomposition and recomposition, research synthesis and unity of form, are in fact the structure of this research work. The road taken by Libera is a lesson in clarity and rationality, above all, and this work would uncover at least a fragment.