117,939 research outputs found
Introduzione a: Reimpiego, rilavorazione, rifunzionalizzazione: la “lunga vita” della scultura medievale nei cantieri di Età moderna, a cura di Paola Vitolo, Clario Di Fabio, Laura Cavazzini, in «Mélanges de l’École française de Rome» 2021, 133/1, pp. 1-120.
No full textArte in facciata: le decorazioni pittoriche e scultoree nei processi di trasformazione urbana ed architettonica
No full textWithin the complex phenomena of reconstruction and restoration of buildings that accompany
the processes of urban transformation, the external pictorial and sculptural decorations play a
role of great importance.
The facades, as liminal surfaces, denounce both the intended uses and the political, social
and cultural implications that accompany the functions of the buildings, also communicating
the requests, claims, ambitions of the owners and users (individuals, groups, communities or
institutions). For these reasons, they are the witnesses of continuity of use and persistence of
values, or the expression of new meanings and life styles.
At the same time, the facades represent the scenic backgrounds of urban perspectives, but
also of religious, civic and cultural events, and as such they are called to adapt to more
general urban renewal plans: they are, therefore, often expected to support needs in a
certain sense ‘imposed’ by the use of the spaces outside them. Both in large cities and in
small towns, the transformations of the façades are conducted as a spontaneous enterprise
focused on the single monument or are planned on the wide urban scale, sometimes after
dramatic events (wars, earthquakes, etc.). Documented only by written sources or sometimes
also by material traces, changes and transformations represent an eloquent ‘manifesto’ of the
processes of the historical memory, of the dynamics that accompany them, of the social
instances and cultural impulses that determine them.
The essays of this session analyse a wide range of cases in different chronological and
geographical contexts, which reveal the role played by the façade decorations and related
transformations as an expression and representation of the human and material history of the
cities and of their spaces.
The theme of the session falls within the area of interest of the the project Memory and
identity. Reuse, reworking and rearrangement of the Medieval sculpture in the Modern Age
between historical research and new technologies, FISR 2019_05012
METODOLOGIE CROMATOGRAFICHE NELLO STUDIO DEI PROCESSI DI ADSORBIMENTO
No full textIn analytical chromatography, the sample we analyze is usually rather dilute and allows
the development of a rather straightforward method. Due to the minute concentrations we
deal with in analytical chromatography, we face a linear behavior. The retention time of
the analytes and the selectivity of a given separation can be forecast by simple rules that
tremendously help us to develop efficient and fast separations. However, when we increase
the sample size and a finite amount of sample is introduced in a chromatographic column,
we leave the shelter of linear chromatography and have to cope with more complex peak
shapes and phenomena.
When the amount of the sample is comparable to the adsorption capacity of the
zone of the column the migrating molecules occupy, the analyte molecules compete for
adsorption on the surface of the stationary phase. The molecules disturb the adsorption
of other molecules, and that phenomenon is normally taken into account by nonlinear
adsorption isotherms. The nonlinear adsorption isotherm arises from the fact that the
equilibrium concentrations of the solute molecules in the stationary and the mobile phases
are not directly proportional. The stationary phase has a finite adsorption capacity;
lateral interactions may arise between molecules in the adsorbed layer, and those lead
to nonlinear isotherms. If we work in the concentration range where the isotherms are
nonlinear, we arrive to the field of nonlinear chromatography where thermodynamics
controls the peak shapes. The retention time, selectivity, plate number, peak width,
and peak shape are no longer constant but depend on the sample size and several other
factors. In addition to be a fundamental piece of information to modeling and optimizing
preparative separations, adsorption isotherm determination is the key to study analytestationary
phase interactions. Besides they allow for the characterization in terms of
adsorption energy distribution of the surface heterogeneity. If biomolecules (peptides,
proteins, etc.) or molecules with biological activity (such as drugs, etc.) were chemically
bound to the stationary phase one speaks in terms of bioaffinity chromatography. In
these cases, adsorption isotherm measurements are a powerful tool to study molecular
recognition processes between the adsorbed biomolecules and any analyte injected into
the chromatographic column.
During this PhD thesis, different aspects of fundamentals of adsorption processes at
the liquid-solid interface have been considered. In parallel, we focused on the setup of
instrumental techniques for the automatic determination of adsorption isotherms.
For that which concerns the study of fundamentals of adsorption, stationary phases
traditionally employed in liquid chromatography (C18) have been characterized by investigating
the adsorption from binary mixtures of compounds with different chemico-physical
properties. This kind of study was essentially realized by measuring excess isotherms.
Through them, the preferential adsorption of one component with respect to the other
constituting the mixture can be determined. These studies are important to understand
the role of so-called organic modifiers in the chromatographic separation process. In fact,
in reversed phase chromatography the organic modifier is usually considered as a mean
to increase mobile phase analyte solubility, while its active role in the adsorption process
is often underestimated.
We then focused on bioaffiniy recognition studies by applying nonlinear concepts to
the characterization of adsorption of peptides and dipetides on a macrocyclic antibiotic
(Teicoplanin) chemically bounded to silica gel. It was demonstrated that nonlinear
chromatography can be considered a valid alternative to other techniques in use for the
determination of binding constants (such as ELISA, Surface Plasmon Resonance, etc.).
The fundamental advantage of nonlinear studies is that they permit to distinguish between
selective and non-selective interactions in the molecular recognition process, which
is not achievable by other investigation techniques.
Adsorption equilibria of insulin (a relatively small protein, about 5800 Da) in different
experimental conditions were studied with the purpose of understanding the mechanisms
responsible for the chromatographic behavior of this protein. In fact, insulin retention
is characterized by a very large sensitivity to the mobile phase composition. Nonlinear
adsorption data were coupled with circular dichroism and mass spectrometry measurements.
Our purpose was to understand if tertiary structure modifications or agglomerate
formation (dimers, trimers, etc.) could be at the origin of the observed phenomena.
Besides thermodynamic aspects, kinetic phenomena are fundamental to characterize
the chromatographic process. In chromatography, in particular, we refer to mass transfer
kinetics, that is the ensemble of the processes involved in the transfer of solute molecules
from the mobile to the stationary phase. In chromatography, these include axial dispersion
(molecular and eddy diffusion), external and internal mass transfer (pore diffusion
and surface diffusion), and adsorption-desorption kinetics. In this work, mass transfer
phenomena on a new kind of monolithic columns, obtained through gamma-ray polymerization,
were studied. The combined use of Van Deemter and kinetic plots allowed to
correlate column efficiency to the length of cross-linkers used in polymerization.
In addition to these fundamental studies, the other part of this work was about the
set-up of instrumentation for different kinds of purposes. A pseudo-bidimensional system
that allows for the deconvolution and online sampling of chromatographic peaks measured
under nonlinear and gradient conditions was developed. The importance of this system is
that it permits to achieve the information necessary for the determination of adsorption
isotherms in an optimized and automatic manner by exploiting numerical procedures,
known in literature as inverse methods. A second application was in the field of pharmaceutics.
By using a system which combines size exclusion and polar reversed-phase
columns, a method for the simultaneous purification and determination of iomeprol, a
radiopharmaceutical analyte, in human plasma was developed and validated
Metodo strumentale per l'analisi e la deconvoluzione on‐line di picchi cromatografici multicomponente in condizioni di overloading.
No full textUn sistema cromatografico bidimensionale, non ortogonale, è stato sviluppato per l'analisi on-line e la deconvoluzione di bande cromatografiche multicomponente in condizioni di overloading. Il set-up strumentale prevede l'uso di due pompe binarie, due colonne cromatografiche impaccate con fasi stazionarie simili, interfacciate tramite una valvola a due posizioni per il campionamento on-line, e un detector UV-Vis. Nella prima dimensione i componenti sono iniettati nel sistema in condizioni di overloading; ciò che viene eluito da questa prima colonna viene regolarmente campionato e iniettato nella seconda colonna in condizioni analitiche tramite la valvola multivie.
Questo approccio è stato validato sia in condizioni di eluizione isocratica, sia in gradiente. Esso rende agevolmente possibile, tramite una fase di calibrazione, la conversione on-line dell'intensità dei picchi in overloading da unità di assorbanza ad unità di concentrazione e la loro deconvoluzione nei singoli componenti [1, 2].
L'approccio proposto consente di analizzare in maniera automatica e veloce, sistemi multicomponente in condizioni nonlineari, laddove non sia possibile applicare comuni metodi per il modeling di separazioni cromatografiche (come ad esempio il metodo inverso). L'ottimizzazione di importanti parametri strumentali, come il tempo di campionamento tra la prima e la seconda dimensione in funzione della ritenzione nella seconda dimensione, consente una ricostruzione efficace dei profili di concentrazione dei singoli componenti.
Bibliografia
[1] A. Cavazzini, V. Costa, G. Nadalini, and F. Dondi. Instrumental method for automated on-line fraction analysis and peak deconvolution in multicomponentoverloaded high-performance liquid chromatography. Journal of Chromatography A, 1137 (2006) 36–41.
[2] V. Costa, L. Pasti, N. Marchetti, F. Dondi, A. Cavazzini. Automated instrumental method for on-line fraction analysis and peak deconvolution in gradient multicomponent overloaded high performance liquid chromatography. Journal of Chromatography A, 1217 (2010) 4919–4924
The complex processes of cellular vitamin A uptake and delivery: insights by NMR and other biophysical techniques
No full textVitamin A has diverse biological functions and is essential for human survival. It circulates in blood bound to serum retinol binding protein (RBP) and is transported into cells by a membrane receptor termed STRA6. The cellular trafficking and metabolism of vitamin A are regulated primarily by specific high-affinity carriers called CRBP-I and CRBP-II. Both proteins deliver retinol to membrane-bound enzymes, either for esterification with fatty acids or for oxidation to retinaldehyde. Until now it was not clear whether CRBPs may couple directly to STRA6 and to the enzymes, or the biomembranes modulate ligand uptake and delivery.
To gain insights into these complex processes, we have investigated the interactions of CRBPs (in the apo and holo forms) with biomembrane mimetic systems. NMR experiments were performed at different protein:vesicles molar ratios and by varying the composition of the phospholipid liposomes and the ionic strength. Chemical shifts perturbations and line shape analysis provided information on the interacting residues and proteins conformational dynamics. As the signals were broadened beyond detection at latest steps of the titrations, the NMR data have been complemented by other biophysical measurements.
The results revealed striking differences between CRBP-I and CRBP-II, despite they exhibit the same fold (a beta-barrel with two short alpha-helices) and identical retinol-binding motifs. Moreover, the interactions of the two homologs with the lipid bilayers depend upon the phospholipid composition and ionic strength.
The new evidences complement our previous studies which suggested that the two primary cellular retinol carriers adopt different mechanisms for ligand uptake [1, 2]. These differences may account for their distinct functional roles in the modulation of retinoid metabolism.
[1] T. Mittag, L. Franzoni, D. Cavazzini, B. Schaffhausen, G.L. Rossi, U.L. Günther J. Am. Chem. Soc. 128, 9844-9848 (2006).
[2] L. Franzoni, D. Cavazzini, G.L. Rossi, C. Lücke J. Lipid Res., 51, 1332-1343 (2010)
Biomolecular NMR, a versatile tool for the understanding of protein science: retinoid-binding proteins as an example
No full textProtein science stands at the heart of modern life sciences because it unravels fundamental biological mechanisms and forms the basis for rapid advances in biomedicine and biotechnology. NMR spectroscopy is uniquely suited to study various aspects of protein structure, dynamics, molecular interactions and function, because information for individual residues can be obtained; moreover, kinetic data, low-populated states and the possible formation of intermediates on the reaction pathway can be determined.
The case of retinoid-binding proteins is discussed here, as an example. Vitamin A has diverse biological functions and is essential for human survival. It circulates in blood bound to serum retinol binding protein (RBP) and is transported into cells by a membrane receptor termed STRA6 (1). The cellular trafficking and metabolism of vitamin A are regulated primarily by specific high-affinity carriers called CRBP-I and CRBP-II. They represent an interesting case where structure determination as well as the study of fast dynamics (ps-ns time scale) (2) failed to elucidate the mode of retinol binding and thus to explain their diverse tissue distribution, functional roles and different ligand affinities.
The highly similar structure of the apo and holo forms (a beta-barrel with two short alpha-helices, see the cartoon) exhibits a closed conformation in both proteins, that seemingly offer no access for the ligand. Given the biological relevance of retinoids, the characterization of their protein interactions and targeted release is of special interest. To tackle this challenging subject we have employed a suite of NMR techniques: 15N relaxation dispersion experiments to investigate the proteins dynamics in the slower micros-ms timescale, line-shape analysis of 15N-HSQC spectra recorded during a retinol titration to get insights into the mechanism of ligand binding and H/D exchange experiments to investigate conformational stability. The results allowed to derive a model of retinol uptake, which is different for CRBP-I and CRBP-II (3, 4); moreover, a distinct local flexibility was found to modulate their binding properties (5).
The two proteins deliver retinol to microsomal membrane-bound enzymes, either for esterification with fatty acids (LRAT) (6, 7) or for oxidation to retinaldehyde (RDH) (8). Our current understanding of these processes remains incomplete, but there is evidence that the membrane microenvironment plays a role in the interactions of holo CRBPs with enzymes (8). To address this hypothesis, we have performed a series of NMR experiments with retinol-bound CRBP-I and CRBP-II in the presence of model membranes composed of either anionic or zwitterionic phospholipids, at varying protein:lipid molar ratios and ionic strength.
Both homologues interact with liposomes of anionic phospholipids, but in a significantly different way (9). A conformational rearrangement of the portal region, coupled to a change in protein dynamics, are required for retinol exchange; these processes seem to be triggered by a membrane-collision.
All the differences between CRBP-I and CRBP-II, when dissolved either in buffer or in the presence of biomembrane mimetic systems, may account for their distinct functional roles in the modulation of intracellular retinoid metabolism. Further experiments are in progress to better describe the ongoing processes in a biological context.
(1) Kawaguchi R., Yu J., Honda J., Hu J., Whitelegge J., Ping P., Wiita P., Bok D., Sun H. (2007) Science, 315, 820-825.
(2) Franzoni L., Lücke C., Pérez C., Cavazzini D., Rademacher M., Ludwig C., Spisni A., Rossi G.L., Rüterjans H. (2002) J. Biol. Chem., 277, 21983-21997.
(3) Mittag T., Franzoni L., Cavazzini D., Schaffhausen B., Rossi G.L., Günther U.L. (2006) J. Am. Chem. Soc., 128, 9844-9848.
(4) Franzoni L., Reed M., Cavazzini D., Rossi G.L., Günther U.L., in preparation.
(5) Franzoni L., Cavazzini D., Rossi G.L., Lücke C. (2010) J. Lipid Res., 51, 1332-1343.
(6) Amengual J., Golczak M., Palczewski K., von Lintig J. (2012) J. Biol. Chem., 287, 24216-24227.
(7) Jiang W., Napoli J.L. (2012) Biochim. Biophys. Acta, 1820, 859-869.
(8) Napoli J.L. (2012) Biochim. Biophys. Acta, 1821, 152-167.
(9) Franzoni L., Baroni F., Cavazzini D., Rossi G.L., Lücke C., in preparation
The complex process of cellular vitamin A uptake: first insights by NMR and other biophysical techniques
No full textVitamin A is essential for diverse aspects of life, ranging from embryogenesis to the proper functioning of most adult organs. It circulates in blood bound to serum retinol binding protein (RBP) and is transported into cells by a membrane receptor termed Stimulated by Retinoic Acid 6 (STRA6) [1]. The mechanism of the STRA6-mediated translocation of retinol from holo-RBP into target cells appears to be unique [2]. There are also evidences that a specific binding site for the intracellular carriers (CRBPs) might exist on the cytoplasmic side of the membrane [3] and that CRBP-I plays a key role other than simply to sustain retinol transport [4]. However, until now it is not clear whether the apo-CRBPs may bind STRA6 or they interact with the membrane for retinol uptake.
To gain first insights into this complex process, we have investigated the interactions of CRBP-I and CRBP-II with biomembrane mimetic systems. NMR experiments were performed at different protein:vesicles molar ratios and by varying the composition of the phospholipid liposomes and the ionic strength. Chemical shifts perturbations and line shape analysis provided insights into the interacting residues and proteins conformational dynamics. As the signals were broadened beyond detection at latest steps of the titration, the NMR data have been complemented by other biophysical measurements.
The results revealed striking differences between CRBP-I and CRBP-II, despite they exhibit the same fold (a beta-barrel with two short alpha-helices) and identical retinol-binding motifs. Moreover, the interactions of the two homologs with the lipid bilayers depend upon the phospholipid composition and ionic strength.
These new evidences complement the lessons learned from our former studies which had suggested that the two primary cellular retinol carriers exhibit different mechanisms of ligand uptake [5, 6]. These differences may account for their distinct functional roles in the modulation of intracellular retinoid metabolism.
References
[1] R. Kawaguchi, J. Yu, J. Honda, J. Hu, J. Whitelegge, P. Ping, P. Wiita, D. Bok, and H. Sun Science 315, 820-825 (2007).
[2] R. Kawaguchi, J. Yu, M. Ter-Stepanian, M. Zhong, G. Cheng, Q. Yuan, M. Jin, G.H. Travis, D. Ong, and H. Sun ACS Chemical Biology 6, 1041-1051 (2011).
[3] C. Redondo, M. Vouropoulou, J. Evans, and J.B.C. Findlay The FASEB J. 22, 1043-1054 (2008).
[4] D.C. Berry, S.M. O'Byrne, A.C. Vreeland, W.S. Blaner, and N. Noy Mol. Cell. Biol. (2012) in press.
[5] T. Mittag, L. Franzoni, D. Cavazzini, B. Schaffhausen, G.L. Rossi, and U.L. Günther J. Am. Chem. Soc. 128, 9844-9848 (2006).
[6] L. Franzoni, D. Cavazzini, G.L. Rossi, and C. Lücke J. Lipid Res., 51, 1332-1343 (2010)
Adsorption of L-lysine on L and ZSM-5 zeolites
No full textZeolites are aluminosilicate minerals characterized by a regular crystalline structure with microporous cavities that confer a high superficial area. The physico-chemical properties of zeolites depend strongly on the composition of their framework, in particular, the hydrophilic/hydrophobic behaviour is affected by the SiO2/Al2O3 ratio (SAR). The ability of zeolites to adsorb amino acids is of particular relevance in industrial biotechnology due to the fact that these adsorbent materials could be used as solid solvents to stabilize the different charged forms of the amino acids. Moreover, these materials can also be employed in enrichment and separation of amino acids from complex mixtures.
In this work we evaluated the adsorption behaviour of zeolite L and ZSM-5 towards the amino acid L-lysine
Post-processing methods of PIV instantaneous flow fields for unsteady flows in turbomachines
No full textThe Particle Image Velocimetry is undoubtedly one of the most important technique in Fluid-dynamics since it allows to obtain a direct and instantaneous visualization of the flow field in a non-intrusive way. This innovative technique spreads in a wide number of research fields, from aerodynamics to medicine, from biology to turbulence researches, from aerodynamics to combustion processes. The book is aimed at presenting the PIV technique and its wide range of possible applications so as to provide a reference for researchers who intended to exploit this innovative technique in their research fields. Several aspects and possible problems in the analysis of large- and micro-scale turbulent phenomena, two-phase flows and polymer melts, combustion processes and turbo-machinery flow fields, internal waves and river/ocean flows were considered
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