1,721,028 research outputs found
Contrast agents for magnetic resonance angiographic applications: 1H and 17O NMR relaxometric investigations of two gadulinium(III) DTPA-like chelates endowed with high binding affinity to human serum albumin
No full textThe relaxometric properties of two Gd(III)DTPA-like complexes (DTPA = diethylenetriamine-N,N,N,N--pentaacetic acid) bearing different substituents for binding to human serum albumin (HSA) are compared. In spite of the structural differences of the recognition synthon and of the residual electric charge, the two chelates display an analogous binding affinity for the serum protein. Upon formation of the adducts with HSA, the exchange rates of the coordinated water appear slowed down by an amount corresponding to ca. 50% of the rates found for the free complexes. The relaxivity of [Gd(BOM)3DTPA (H2O)]2 - is significantly higher than that of MS-325 either in the free complex or in the macromolecular adduct. Finally, the effect of pH on the stability of the HSA adducts and on the values of their relaxivities has been investigated
Peptide-based building blocks as structural elements for supramolecular Gd-containing MRI contrast agents
No full textMagnetic resonance imaging (MRI) is one of the most important clinic diagnostic tool
used to obtain high‐quality body images. The administration of low‐molecular‐weight
Gd complex–based MRI contrast agents (CAs) permits to increase the 1H relaxation
rate of nearby water molecules, thus modulating signal intensity and contrast
enhancement. Even if highly accurate, MRI modality suffers from its low sensitivity.
Moreover, low‐molecular‐weight CAs rapidly equilibrate between the intravascular
and extravascular spaces after their administration. In order to improve their sensitivity
and limit the extravasation phenomenon, several macromolecular and supramolecular
multimeric gadolinium complexes (dendrimers, polymers, carbon nanostructures,
micelles, and liposomes) have been designed until now. Because of their biocompatibility,
low immunogenicity, low cost, and easy synthetic modification, peptides are
attractive building blocks for the fabbrication of novel materials for biomedical
applications. We report on the state of the art of supramolecular CAs obtained by
self‐assembly of three different classes of building blocks containing a peptide
sequence, a gadolinium complex, and, if necessary, a third functional portion achieving
the organization process
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
Relaxometric and Modeling Studies of the Binding of a Lipophilic Gd-AAZTA Complex to Fatted and Defatted HSA
No full textA new lipophilic gadolinium chelate consisting of a long aliphatic chain bound to the AAZTA coordination cage (Gd-AAZTAC17) has been synthesised. It possesses two coordinated water molecules (q=2) in fast exchange with the solvent (equation image=67 ns), which yields a relaxivity of 10.2 mM−1 s−1. At concentrations greater than 0.1 mm, it forms micelles (average diameter 5.5 nm) characterised by a relaxivity of approximately 30 mM−1 s−1 at 20 MHz and 298 K. The latter value appears to be “quenched” by magnetic interactions among the GdIII ions on the surface of the micelle that cause a decrease in the electronic relaxation time. A relaxivity of 41 mM−1 s−1 was recorded for this micellar system when 98 % of the GdIII ions were replaced by diamagnetic YIII. Gd-AAZTAC17 exhibits a better affinity for fatted human serum albumin (HSA) than for defatted HSA, whereas the relaxivities of the supramolecular adducts are reversed. The relaxivity shown by Gd-AAZTAC17/defatted HSA (equation image(20 MHz, 298 K)=84 mm−1 s−1) is by far the highest relaxivity reported so far for non-covalent paramagnetic adducts with slow-moving substrates. As shown by molecular docking calculations, the gadolinium complex enters a hydrophobic pocket present in fatted HSA more extensively than the corresponding adduct with defatted HSA. Interestingly, no marked difference was observed in either the relaxation enhancement or the binding affinity between fatted and defatted HSA when the binding titrations were carried out at a Gd-AAZTAC17 concentration higher than its critical micellar concentration (cmc). This behaviour has been attributed to the formation of an association between the negatively charged micelle of the lipophilic metal complexes and the positive residues on the surface of the protein
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
Exofacial protein thiols as a route for the internalization of Gd(III)-based complexes for MRI cell labelling
No full textFour novel MRIGd(III)-based probes have been synthesized and evaluated for their labeling properties on cultured cell lines K562, C6, and B16. The labeling strategy relies upon the fact that cells display a large number of reactive exofacial protein thiols (EPTs) that can be exploited as anchorage points for suitably activated MRI probes. The probes are composed of a Gd(III) chelate (based on eitherDO3A or DTPA) connected through a flexible linker to the 2-pyridyldithio chemical function for binding to EPTs. GdDO3A-based chelates could efficiently label cells (up to a level of 1.2 1010 Gd(III) atoms/cell), whereas GdDTPA-based chelates showed poor or no cell labeling ability at all. Among the GdDO3A based compounds, that having the longest spacer (compound GdL1A) showed the best labeling efficacy. The mechanism of EPT mediated cell labeling by GdL1A involves probe internalization without sequestration of the Gd(III) chelate within subcellular structures such as endosomes
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