1,720,972 research outputs found
Polyelectrolyte Hydrogels with Complexing Ability Towards Metal Ions
No full textStimuli-responsive hydrogels have been synthesized, that exhibit dramatic changes in their swelling behaviour, network structure and permeability in response to a number of external stimuli, including pH, ionic strength of the surrounding fluid, temperature and presence of specific solutes. Because of their nature, these materials can be used in a wide variety of applications, including separation, biosensors, drug delivery devices and tissue engineering.
The produced hydrogels are based on L-phenylalanine and L-histidine residues, the first being poly(anionic), while the second poly(ampholyte). Figure 1 shows the equilibrium degree of swelling (EDS) in relation to the temperature, at different pHs, for the hydrogel CP2, i.e., a gel containing the thermosensitive N-isopropylacrylamide (NIPAAm) and the pH-responsive N-acryloyl-L-phenylalanine (Phe) 1-2. Low pH values improve the protonation of the carboxyl group, thus reducing the Lower Critical Solution Temperature (LCST).
Figure 1: Effect of the temperature on the Equilibrium Degree of Swelling for the hydrogel CP2 at different pHs.
On the other hand, the ampholyte hydrogels 3-4 containing N-acryloyl-L-histidine (H5 and H10) show a greater swellability before and after their isoelectric point (Figure 2). The different cross-linking density (5 and 10 mol%) affects the swellability only at high pHs. The different basicity constants (logK) of the two basic groups in the monomer unit is in line with this behaviour.
Both the hydrogel systems are able to form complex species with Cu(II) and Ru(II) ions, showing a decreasing pattern of the EDS as a consequence of the charge neutralization and of the stoichiometric arrangement of the gel basic groups around the metal ion. The comparison with the free polymer analogues better elucidates the protonation and complex-formation mechanisms.
Figure 2: Effect of the pH on the Equilibrium Degree of Swelling (EDS) for the hydrogel H5 and H10 at 25°C.
All the synthetic hydrogels of the present study are not toxic, as shown by the leukemic monocyte (RAW264, from a mouse) cells. This result, in conjunction with the kinetic reversibility of their swelling, makes these kinds of material suitable candidates for biomedical and pharmaceutical applications.
REFERENCES
(1) A.Fini, M. Casolaro, Temperature and pH sensitive hydrogels based on N-acryloyl-L-histidine and N-acryloyl-L-phenylalanine. European Conference on Drug delivery and Pharmaceutical Technology, Sevilla (Spain) May 10-12, 2004
(2) M.Casolaro, E.Paccagnini, R.Mendichi, Y.Ito. Macromolecules 2005, 38, 2460-2468
(3) M.Casolaro, S.Bottari, A.Cappelli, R:Mendichi, Y.Ito. Vinyl polymers based on L-histidine residues. Part 1. The thermodynamics of poly(ampholyte)s in the free and in the cross-linked gel form. Biomacromolecules 2004, 5, 1325-133
(4) M. Casolaro, I. Carbonaro, A.Fini. Vinyl Polymers Based on L-Histidine Residues: The Thermodynamics of Soluble and Cross-linked Poly(ampholyte) Hydrogels. ISMEC 03, Capri 6-11 giugno 200
An ABC of Citizenship, vol. 2
No full textE' il primo di due fascicoli monografici che raccoglie i lavori e le intuizioni nate anche in sinergia con alcune associazioni del territorio pugliese: creare degli Abbecedari della cittadinanza, legati a grappoli di eventi, capaci di coinvolgere territori, scuole e in generale agenzie educative. L'esperienza ha a sua volta sollecitato docenti e ricercatori universitari italiani e stranieri, che hanno inviato i loro contributi. La molteplicità di materiale e l'interesse del percorso teorico-pratico ci ha appunto convinto a dividere quanto giunto in redazione in due fascicoli, che raccolgono saggi legati a 21 sezioni, una per ogni lettera dell'alfabeto di questo ideale abbecedario comunitario: dalla A di amicizia alla Z di Zero povertà. Con contributi anche di tipo internazionale: B. Weber, W. Kohan, E. Cejva
Community-based
No full textThis issue of Logoi has at least three roots and three reasons. The first one is to start a reflection on the so-called Community-based participatory research (CBPR). This dossier is opened by a paper of Meredith Minkler (University of Berkeley) who is one of the founders of the method CBPR and of reflection on it.
This scenario is also linked to the two articles that we present in the section called Research Communities and ABCs, papers which on the one hand refer to the CBPR, but on the other side cross in particular another of our interests: the Abc method. In fact, Logoi is a partner of the research project called An ABC of Democratic Citizenship. “Community-Based Participatory Research” through Sciences & Humanities (University of Bari). The project is presented in this section. While another focus is on Latin America. You can read the contribution of Adriana Fresquet (Río
de Janeiro), Abecedarios audiovisuais comunitarios: de Perú para el mundo.
Let’s come to the third root/reason of this issue: the need to reflect, in many ways and with many languages, on the theme of community.
We therefore have some essays that either starting from some knowledge, disciplines, languages even extra-philosophical, or focusing on authors and specific themes, address the issue-community: Interdisciplinary issues (Simona Cohen - Tel-Aviv; et alii) and Particular issue
Synthesis, acid-base properties and preliminary cell compatibility evaluation of amphoteric poly(amido-hydrazine)s
No full textAmphoteric poly(amido-hydrazine)s (PAHYs) were obtained by
hydrogen-transfer polyaddition of hydrazine, 1,2-dimethylhydrazine and 1,1-
dimethylhydrazine to 2,2-bisacrylamidoacetic acid. These polymers were studied
for biomedical applications, such as degradability in water solution, acid–base
properties, and cell toxicity. They degraded rapidly in aqueous media under physiological
conditions, their molecular weight was reduced to about one-fourth, that
of the original polymer in less than two days. They exhibited a typical polyelectrolyte
behavior with isoelectric points between 4 and 5 and are prevailingly
anionic in the blood. In preliminary cell toxicity essays they proved to be remarkably
biocompatible, comparable in this respect to amphoteric poly(amido-amine)s
(PAAs), and much less toxic than poly-L-lysine and polyethylenimine
Temperature- and pH-sensitive Hydrogels Based on N-acryloyl-L-histidine and N-acryloyl-L-phenylalanine
No full textPurpose: To study new materials exhibiting reversible sensitivity to environmental conditions in view of their potential application in drug delivery technology.
Methods: The monomers N-acryloyl-L-histidine (Hist) and N-acryloyl-L-phenylalanine (Phe) were obtained by the acylation reaction of acryloyl chloride with the corresponding a-aminoacid in alkaline solution. Homopolymers and copolymers with N-isopropylacrylamide were obtained by radical polymerization in both soluble and cross-linked forms. All compounds were characterized by viscometry (h/C), potentiometry (basicity constants, logK) and solution calorimetry (enthalpy -DH° and entropy DS° changes). The equilibrium degree of swelling (EDS) for hydrogels was monitored at different temperature and pHs in buffers at the ionic strength of 0.15M NaCl.
Results: Thermodynamic data for the protonation of basic groups in polymers were similar for soluble and cross-linked closer-structured compounds. The EDS in relation to pH for cross-linked poly(Hist) showed the peculiar ampholyte character to be very similar to that showed by the soluble analogue, when the reduced viscosity (h/C) was considered. A linear relationship of EDS in relation to h/C was found. The EDS for cross-linked copolymers of poly(Phe) was strongly dependent on temperature and pH, showing greater EDS at higher pH than its logK, even at higher temperatures.
Conclusions: Both soluble and cross-linked polymers were not toxic against RAW 264 cell lines. This suggests the opportunity to use anionic or ampholyte polymers in the formulation of drug delivery products
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
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
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