1,721,018 research outputs found
Applicazione della tecnologia sol-gel: sintesi di un materiale ibrido biocompatibile e studio delle proprietà spettroscopiche ed elettrochimiche del citocromo c incapsulato in un bio sol-gel
Full text linkAim of the study is the structural characterization of a new hybrid silica biomaterial and the spectroscopic amd electrochemical behaviour of cyt c encapsulated in a bio sol-gel.
In the first part of the project we investigated a new silica biomaterial synthesized through the sol-gel method. The inorganic/organic hybrids were synthesized combining an acid chitosan solution with an inorganic phase (TMOS), previously modified by the addition of calcium and phosphate ions.
The structural test of the hybrids, containing a different chitosan -to silica ratios (BK1, BK2, BK3) were performed by employing Fourier-transform infrared spectroscopy. Hybrids spectra were compared with the bioactive sol-gel.
In vivo, material bioactivity is associated to the ability to form an hydroxycarbonate apatite layer on its surface. To investigate the effect of chitosan amount on sol-gel biocompatibility, bioactivity essays were performed in vitro soaking the samples with static immersion for different time intervals (30 min, 6h e 24h) in a 0.01 M di Tris- HCl solution (pH 7.0). Ions release (Ca2+ e PO43- ) was determinated using couple induced emission spectroscopy (ICP). On BK3 surface, after sample immersion in a 0.01 M Tris-HCl for 48h, confocal microscopy has underlined the formation of crystalline aggregates. Although we can not state unequivocally that they are inequivocally composed by hydroxycarbonate apatite, we observed that the amounts of crystals increases with chitosan amount.
Matrix structural changes, induced by chitosan, were investigated by swelling and permeability measurements.
Swelling process was investigated to analyze hybrids stability in water environment.
Permeability study, tense to clarify chitosan effect on solvent diffusion across the silica matrix, was performed using a fluorescent probe, named RubPy.
Swelling measurements, demonstrate that samples weight increase, due to solvent diffusion across the matrix, is strongly correlated with chitosan concentration. Samples with high chitosan amount need longer times to reach an equilibrium state. More structural information are obtained comparing infrared spectrum of the bioactive gel with that of the hybrid material. An interesting result is the absorption band observed around 1400 cm-1, that can be ascribed to the organic modification of the silica matrix and, in particular, to the formation of Si-C bond.
The ternary system, CaO- SiO2-P2O5, even if shows interesting properties, cannot be used as support for protein encapsulation; the major impediment is represented by the low pH (< 2.5); we synthesized a binary CaO-SiO2 bioactive system (bio sol-gel) which, although missing the phosphates, contains calcium, an element considered fundamental for biocompatibility.
In the present work, we used the horse heart cytocrome c as a protein model. Structural properties of bio sol-gel encapsulated cyt c were investigated comparing the electronic absorption spectra and dicrioic spectra with those of the protein in solution (pH 7; 25° C) .We also investigated i) the acid-induced protein denaturation, (ii) the protein stability and (iii) the electrochemical behaviour of the embedded protein. Our data demonstrate that immobilization process do not alter protein functionality. System protein/ modified electrode show a quasi- reversible voltammetric behaviour in the Fe(III)/Fe(II) redox process, for all the scan rates investigated. The experimentally formal potential, E1/2 = 0.244 V vs NHE, is very close to the formal redox potential determined for soluble cyt c at the same pH (E1/2 = 0.255 V). To investigate system stability cyclic voltammogram of the samples was run for one week; surprisingly the protein preserves its redox activity.
The electronic absorption and CD spectra demonstrate that bio sol-gel encapsulated protein do not present structural changes.
The acid - induced denaturation process, achieved adding an HCl solution, was investigated by following the shift of the Soret absorption band from 408nm (native state) to 395nm (denaturated protein) as a function of time.
Biogel entrapped cyt c clearly requires longer time to unfold than the soluble protein.The protein undergoes denaturation more promptly when entrapped in the salt-doped sol gel (i.e., in the presence of calcium nitrate) with respect to the case it is in pure (i.e., salt missing) sol-gel. Probably, this may be ascribed to the salt that prevent a correct sol gel reticulation and induces formation of larger pores. Also, different samples unfolding kinetics can be correlated with the a different solvent diffusion
The refolding process, proved that unfolding-refolding process of cyt c entrapped in the bio sol-gel is fully reversible, under the conditions investigated
Spectroscopic and electrochemical characterization of cytochrome c encapsulated in a bio sol-gel matrix
No full textSol-gel technique represents a remarkably versatile method for protein encapsulation. To enhance sol-gel biocompatibility, systems envisaging the presence of calcium and phosphates in the sol-gel composition were recently prepared and investigated. Unfortunately, the low pH at which solutions were prepared (pH < 2.5) dramatically limited their application to proteins, because the acidic environment induces protein denaturation. In this paper we apply a new protocol based on the introduction of calcium nitrate to the inorganic phase, with formation of a binary bioactive system. In this case protein encapsulation results versatile and secure, being achieved at a pH close to neutrality (pH 6.0); also, the presence of calcium is expected to enhance system biocompatibility. To determine the properties of the salt-doped sol-gel and the influence exerted on entrapped biosystems, the structural and functional properties of embedded cytochrome c have been investigated. Data obtained indicate that the salt-doped sol-gel induces no significant change in the structure and the redox properties of the embedded protein; also, the matrix increases protein stability. Interestingly, the presence of calcium nitrate appears determinant for refolding of the acid-denatured protein. This is of interest in the perspective of future applications in biosensoristic area
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
Scleroglucan/borax gel based immobilization: a new tool for protein electron transfer characterization
No full textVariations 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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Travels in Architectural History
Full text linkTravel: Special collection 2016-2017 for the EAHN open access journal, Architectural Histories. 10 original essays stemming from an international call for papers; all double-blind peer reviewed following a pre-selection. This Special Collection explores how travel, as a collective and individual practice, has been implicated in diverse architectural cultures across a wide range of periods and geographies. It offers new perspectives on the architect's journey, examines representations of places by travellers, and considers the place of architecture within modern tourist itineraries and practices. Travel is a powerful force in shaping the perception of the modern world and plays an ever-growing role within architectural and urban cultures. Inextricably linked to political and ideological issues, travel redefines places and landscapes through new transport infrastructures and buildings. Architecture, in turn, is reconstructed through visual and textual narratives produced by scores of modern travellers - including writers and artists along with architects themselves. In the age of the camera, travel is bound up with new kinds of imaginaries; private records and recollections often mingle with official, stereotyped views, as the value of architectural heritage increasingly rests on the mechanical reproduction of its images. Whilst students often learn about architectural history through image collections, the place of the journey in the formation of the architect itself shifts. No longer a lone and passionate antiquarian or an itinerant designer, the modern architect eagerly hops on buses, trains and planes in pursuit of personal as well as professional interests. Increasingly built on a presumption of mobility, architectural culture integrates travel into cultural debates and design experiments. By addressing such issues from a variety of perspectives, this collection prompts us to rethink the mobile conditions in which architecture has historically been produced and received
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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