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Il Terzo Regno: la recezione di Gioacchino da Fiore nella filosofia politica del 1900.
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Industria tessile, competitività, sviluppo economico: insegnamenti dal caso indiano.
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Nonomuraea sp. ATCC 39727 a rare actinomycete producing the glycopeptide A40926: mechanism of self resistance.
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Materiali fotoattivi nanostrutturati: sintesi, caratterizzazioni e applicazioni.
No full textTitanium dioxide is suitable to answer some important needs of our society, particularly in the environmental field, as a photo catalyst, and in the energy field, for realization of devices for a rational use of solar energy. Thanks to nanotechnology, this material has found a renewed interest by the scientific community for innovative properties that occur as a result of its nanoscale.
The materials based on titanium dioxide produced in this work were obtained by sol-gel method, which is now one of the most studied techniques for the synthesis of nanostructured materials. The interest stimulated by this method is its extreme versatility and advantages of ease of control of process parameters. Specifically, samples were synthesized containing either only titanium dioxide, or inorganic hybrid silica / titania.
The reasons that led to the trial presented here lie in understanding the influence of experimental parameters (composition, temperature, time) that govern the synthesis process on nature and structural characteristics of the material isolated. Morphology, crystallinity and micro-structure, have been investigated by X-ray Powder Diffraction (XRPD), Nitrogen Physisorption, Atomic Force Microscope (AFM) and Debye Function Analysis (DFA). We also correlated the effect of experimental and structural aspects on the functional properties (photocatalytic activity) of the synthesized materials.
Another important aspect of this work concerns the investigation of the application of the materials produced for the surface modification of textile substrates (polyester) in order to obtain "smart textiles" that can effectively reduce environmental pollutants. In this area we investigated the effects of variation of process parameters on the performance exhibited by functionalized textiles
Obbligo politico e libertà. Francisco Suárez: precursore del giusnaturalismo moderno.
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Data infrastructures and spatial models for biodiversity assessment and analysis: applications to vertebrate communities.
No full textIn conservation biology the computation of biodiversity maps, based on statistical models is a central concern. These maps, produced with objective and repeatable methods are an essential tool for conservation and monitoring programs as well as for landuse planning.
Since the computation of biodiversity maps requires complex and time consuming procedures for data processing and analysis, it is necessary to design methods for homogeneous, scalable and repeatable data management and analysis.
Moreover, the huge volume of data used in ecological modelling requires suitable software architectures to store, analyze, retrieve and distribute information in order to support research and management actions in due time.
First of all we developed an analysis system (SOS - Species Open Spreader) providing statistical and mathematical models to predict species distribution in relation to a set of predictive environmental and geographical variables The system is composed of a module for data input/output toward and from the GIS and of a package of scripts for the application of different modelling techniques. At present, three statistical techniques are integrated in SOS: Logistic Regression Analysis (LRA), Environmental Niche Factor Analysis (ENFA) and flexible Discriminant Analysis with method BRUTO. Furthermore, two empirical spatial methods of analysis are available within SOS: Habitat Suitability Index (HSI) and Spatial Overlay.
The system is designed to work with the GIS (Geographical Information System) soft-ware GRASS and the statistical environment R, coupled together through the SPGRASS6 library. Three different outputs are expected: text and graphical outputs with statistical results and suitability maps.
Second, we tested the use of spatial Database Management Systems (Spatial DBMS) to handle wildlife and socio-economic data and we developed a web database application to provide facilities for database access. The information system was built for the Meru district (Tanzania) in the context of an Italian cooperation project of land use planning in Maasai rural areas.
We tested two di_erent solutions: SpatiaLite and PostgreSQL-PostGIS; they both offer advanced technical facilities and spatial extensions to analyze spatial data. SpatiaLite is a new solution and offers the main advantages to consist of a unique file and to present a user-friendly interface, which make it the best solution for many applications. in spite of this we used PostgreSQL-PostGIS since it represents a well-established information system supported by libraries for web applications development.
We applied SOS to three case studies at different spatial scale: Brescia plain (small scale), Mount Meru region - Tanzania (medium scale) and Lombardy region (big scale) in order to produce maps of species potential distribution and biodiversity maps for planning and management.
We applied logistic regression analyses to compute models and ROC analysis for classification performance evaluation. The automation of processes through SOS gave us the possibility to build models for a large number of vertebrate species. The analysis produced very reliable results at middle and big scale while regression methods did not converge at small scale. This is probably due to habitat homogeneity and to the use of environmental variables with an insufficient level of detail.
The potential distribution and biodiversity maps produced also had in all cases an applicative use in fact we used mammal species models computed for Mt. Meru region to produce a map of biodiversity within the area: this map represents an informative base for land use planning at village level within a cooperation project for Maasai economic development and environmental redemption.
Amphibians and reptiles models, computed for Lombardy, represent a good informative base for planning management actions in the region
Combinatorial and supramolecular saproaches to monodentate phosphorus-ligands for transition metal catalyzed asymmetric reactions.
No full textIn recent years, monodentate phosphorus ligands (e.g. phosphites, phosphonites, phosphoramidites and phosphinamines) have held the stage in asymmetric catalysis.1 In addition to their outstanding activity and selectivity, comparable or even superior to those of bidentate ligands, the convenient, fast and practical preparation from commercially available materials underlines their potential for industrial applications. Furthermore, the modular nature of all these ligands allows the synthesis of a variety of representatives, thereby making a combinatorial approach possible.
My PhD research project deals with the synthesis of libraries of new chiral monodentate P-ligands and their screening in asymmetric transition metal-catalyzed reactions through two innovative approaches: combination of binaphthol-derived phosphites and C1-symmetric phosphinamines for the selective generation of heteroleptic catalysts in Rh- and Pd-mediated reactions (Ligand Combination Approach, Research line 1);
supramolecular ligand-ligand interactions for highly selective transition metal catalysis (Supramolecular Approach, Research line 2).
Research line 1
In 2002-3, the groups of Reetz and Feringa independently used a binary mixture of chiral monodentate Pligands in several asymmetric rhodium-catalyzed reactions. By mixing two different ligands (La and Lb) in the presence of a transition metal [M], three species can be formed: [M]LaLa, [M]LbLb (homocomplexes) and [M]LaLb (heterocomplex). The heterocomplex is often more reactive and more (regio-, diastereo-, enantio-) selective than either of the two homocomplexes. Moreover, under thermodynamic control the heterocomplex : homocomplexes ratios usually exceed the statistical value (2 :1 :1).
The ideal case would constitute an equilibrium completely in favor of the heterocomplex [M]LaLb, because a single well-defined catalyst would then exist in the reaction mixture and the undesired competition of the less selective homocomplexes would be avoided.
We were intrigued by the remarkable selectivities reported for the mixtures of chiral ligands (binolderived phosphites, phosphonites and phosphoramidites) with achiral phosphines.4 In particular, the 1:1 mixture of a chiral phosphite with an achiral phosphine was reported to induce reversal of the enantioselectivity in the Rh-catalysed hydrogenation of N-acetamido acrylate (compared to the chiral phosphite alone). The only possible explanation for this peculiar behaviour is the selective formation of the phosphite-phosphine Rh-heterocomplex, favoured by electronically matching one -donor ligand (phosphine) and one -acceptor ligand (phosphite). As enantiomerically pure chiral phosphines are not easy to synthesize, we were wondering whether the phosphine ligands could be substituted by other - donor phosphorus ligands still retaining the thermodynamic preference for the formation of the heterocomplex. For this reason, we turned our attention to chiral phosphinamines, which are easy to prepare enantiomerically pure, and have electronic properties similar to those of phosphines.5 DFT
calculations showed that the phosphite-phosphinamine rhodium heterocomplex is more stable than the two homocomplexes by 11.29 kcal/mol
We synthesized a library of monodentate chiral phosphites 1a-d by reacting enantiopure BINOL-PCl with different chiral and achiral alcohols. Monodentate chiral phosphinamines 2a-e were prepared by reaction of Ph2PCl with a number of C2-symmetric secondary amines and C1-symmetric secondary and primary amines. Complexation studies were performed by means of 31P-NMR, using Rh(acac)(C2H4)2 as the rhodium source. When C1-symmetric phosphinamine ligands were employed, the cis-heterocomplexes were formed with selectivity ranging from moderate (70%) to excellent (_ 99%).
The homo- and heterocombinations of phosphites and C1-symmetric phosphinamines were then screened in the rhodium-catalyzed hydrogenation of methyl 2-acetamidoacrylate. Remarkably, the 1:1 combination of a BINOL-derived phosphite and a phosphinamine induced reversal of the enantioselectivity, compared both to the phosphite and the phosphinamine alone. This heterocombination induced a peculiar stereochemical outcome also in the palladium-catalyzed asymmetric allylic substitution of rac-1,3-
The heterocomplexes formed in this way are expected to have reduced degrees of freedom7 compared to the complexes of normal monodentate ligands, and thus supramolecular ligands somehow resemble traditional bidentate ligands. According to this analogy, they are often referred to as supramolecular bidentate ligands or self-assembled ligands, thanks to their ability to spontaneously form bidentate systems in solution. These terms also apply to those supramolecular ligands that are only capable of noncomplementary interactions: indeed these systems are still capable of forming rigid and conformationally restricted complexes, although they cannot selectively form heterocomplexes when used in a mixture, which quite reduces their "combinatorial appeal".
Prompted by the studies of Prof. Reek and co-workers on the synthesis of supramolecular bidentate heterocomplexes through complementary interactions (e.g. coordinative bondings)8 and by the efficient resolution strategy of racemic N-benzyl _-amino acids (N-Bn-AA) by liquid-liquid extraction using a chiral salen–cobalt(III) complex as enantioselective receptor, accomplished in our laboratories, we decided to use the salen-cobalt(III)-N-benzyl-L-serine complex as a chiral platform for the preparation of new families of supramolecular mono- and bi-dentate P-ligands (Scheme 4 A and B).
The salen-cobalt(III)-N-Bn-AA complexes, in fact, possess a rigid framework with the salen ligand in a cis-_-folded arrangement around the octahedral cobalt ion. The remaining two cis coordination sites are occupied by the N-benzyl _-amino acid, which is thus accommodated in the “binding pocket” of the chiral cobalt complex. 9b
Ligands 3 were synthesized in good yields starting from the symmetrical tetra-t-butyl-salen which was transformed into the corresponding cobalt(III) acetate complex, and the acetate ion was exchanged with Nbenzyl- L-serine. In the case of symmetric salen backbone, the complex was obtained pure in high yield and the phosphite moieties were then introduced by reaction with different diol-derived chlorophosphite.
In the case of the supramolecular bidentate ligands 4, the unsymmetrical hydroxymethyl-containing salen afforded the corresponding cobalt(III) acetate complex as a mixture of two inseparable diastereoisomers.
Complexation of monodentate ligands 3 to rhodium(I) was studied by 31P-NMR spectroscopy, which showed the formation of the desired Rh-complexes. The reactivity of supramolecular monodentate Pligands was investigated in two Pd-catalyzed-allylic alkylation on (E)-1,3-diphenylallyl acetate and Pdcatalized desymmetrization of meso-cyclopenten-2-ene-1,4-diol biscarbamate.
We are now exploring new synthetic pathways to obtain the unsymmetrical (S,S)-salen-ligand and the corresponding unsymmetrical (S,S)-salen-cobalt(III)-N-Bn-L-serine bidentate P-ligand in a pure diastereoisomeric fashion.
We have also investigated the design and synthesis of a novel class of chiral monodentate phosphite ligands, named PhthalaPhos, which contain a phthalic acid primary diamide moiety. Such phthalamidic group displays both donor and acceptor hydrogen bonding properties that, in principle, can give rise to supramolecular interactions both between the ligands and with the reaction substrate
The pre-catalytic Rh complex of one of these ligands was fully characterized and studied by NMR, IR and mass spectroscopy, which confirmed the presence of hydrogen bonds between the coordinated ligands, and the formation of a supramolecular bidentate ligand.
The catalytic properties of these new ligands were assessed in the rhodium-catalyzed hydrogenation of benchmark olefins (e.g. methyl 2-acetoamidoacrylate and N-(1-phenylvinyl)acetamide), taking the known phosphite 9 as a touchstone. Four ligands gave e.e. values higher than 97% with methyl 2-acetoamidoacrylate as substrate, and six reached the same level of performance with N-(1-phenylvinyl)acetamide. Remarkably, the reference ligand 9, featuring the same BINOL phosphite moiety, gave only 84% and 90% e.e. respectively for the same substrates, thus suggesting that the phthalimide residue significantly influences the catalytic properties of these ligands.
Evaluation of the catalytic properties of the Phthalaphos ligands were also extended to the Rh-catalyzed hydrogenation of more challenging substrates of potential industrial interest, such as N-(3,4-dihydronaphthalen-1-yl)acetamide and (E)-methyl 2-(acetamidomethyl)-3-phenylacrylate. The results of this screening were quite variegated both in terms of activity and enantioselectivity, but the employment of a Phthalaphos ligand gave the highest e.e. value ever obtained on N-(3,4-dihydronaphthalen-1-yl)acetamide with phosphite ligands and the highest e.e. value ever obtained with (E)-methyl 2-(acetamidomethyl)-3-phenylacrylate
Allostery in a monomeric protein: the case of human serum albumin.
No full textHuman serum albumin (HSA), the most prominent protein in plasma, binds different classes of ligands at multiple sites. HSA provides a depot for many compounds, affects pharmacokinetics of many drugs, holds some ligands in a strained orientation providing their metabolic modification, renders potential toxins harmless transporting them to disposal sites. Its modular domain organization provides a variety of ligand-binding sites and the flexible modular structure involves more than the immediate vicinity of the binding site(s), affecting the ligand-binding properties of the full protein. Ferric human serum heme–albumin (heme– HSA) shows a peculiar spectroscopic properties that allow to investigate structural and functional aspects of the protein.
Here, a characterization of the environment of the metal binding site and of its dynamics is reported. Moreover, the effect of different endogenous and exogenous ligands on the allosteric properties of HSA and link between binding sites are investigated.
As a whole, the complex mechanism modulating ligand binding to HAS represents one of the most important structure-function correlations ever reported for monomeric proteins in general